src/test/java/com/google/devtools/build/lib/syntax/SkylarkEvaluationTest.java

// Copyright 2015 The Bazel Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package com.google.devtools.build.lib.syntax;

import static com.google.common.truth.Truth.assertThat;
import static com.google.devtools.build.lib.testutil.MoreAsserts.assertThrows;
import static java.util.stream.Collectors.joining;

import com.google.common.collect.ImmutableCollection;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.devtools.build.lib.analysis.test.AnalysisFailure;
import com.google.devtools.build.lib.analysis.test.AnalysisFailureInfo;
import com.google.devtools.build.lib.cmdline.Label;
import com.google.devtools.build.lib.collect.nestedset.NestedSetBuilder;
import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
import com.google.devtools.build.lib.events.Location;
import com.google.devtools.build.lib.packages.NativeInfo;
import com.google.devtools.build.lib.packages.NativeProvider;
import com.google.devtools.build.lib.packages.StructProvider;
import com.google.devtools.build.lib.skylarkinterface.Param;
import com.google.devtools.build.lib.skylarkinterface.ParamType;
import com.google.devtools.build.lib.skylarkinterface.SkylarkCallable;
import com.google.devtools.build.lib.skylarkinterface.SkylarkGlobalLibrary;
import com.google.devtools.build.lib.skylarkinterface.SkylarkModule;
import com.google.devtools.build.lib.syntax.StarlarkSemantics.FlagIdentifier;
import com.google.devtools.build.lib.testutil.TestMode;
import java.util.List;
import java.util.Map;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;

/** Tests of Starlark evaluation. */
// This test uses 'extends' to make a copy of EvaluationTest whose
// mode is overridden to SKYLARK, changing various environmental parameters.
@SkylarkGlobalLibrary // required for @SkylarkCallable-annotated methods
@RunWith(JUnit4.class)
public final class SkylarkEvaluationTest extends EvaluationTest {

  @Before
  public final void setup() throws Exception {
    setMode(TestMode.SKYLARK);
  }

  /**
   * Creates an instance of {@code SkylarkTest} in order to run the tests from the base class in a
   * Skylark context
   */
  @Override
  protected ModalTestCase newTest(String... skylarkOptions) {
    return new SkylarkTest(skylarkOptions);
  }

  @Immutable
  static class Bad {
    Bad () {
    }
  }

  @SkylarkCallable(name = "foobar", documented = false)
  public String foobar() {
    return "foobar";
  }

  @SkylarkCallable(name = "interrupted_function", documented = false)
  public NoneType interruptedFunction() throws InterruptedException {
    throw new InterruptedException();
  }

  private static final NativeProvider<NativeInfoMock> CONSTRUCTOR =
      new NativeProvider<NativeInfoMock>(NativeInfoMock.class, "native_info_mock") {};

  @SkylarkModule(name = "Mock", doc = "")
  class NativeInfoMock extends NativeInfo {

    public NativeInfoMock() {
      super(CONSTRUCTOR);
    }

    @SkylarkCallable(name = "callable_string", documented = false, structField = false)
    public String callableString() {
      return "a";
    }

    @SkylarkCallable(name = "struct_field_string", documented = false, structField = true)
    public String structFieldString() {
      return "a";
    }

    @SkylarkCallable(name = "struct_field_callable", documented = false, structField = true)
    public BuiltinCallable structFieldCallable() {
      return new BuiltinCallable(SkylarkEvaluationTest.this, "foobar");
    }

    @SkylarkCallable(
      name = "struct_field_none",
      documented = false,
      structField = true,
      allowReturnNones = true
    )
    public String structFieldNone() {
      return null;
    }
  }

  @SkylarkModule(name = "Mock", doc = "")
  class Mock implements StarlarkValue {
    @SkylarkCallable(
        name = "MockFn",
        selfCall = true,
        documented = false,
        parameters = {
          @Param(name = "pos", positional = true, type = String.class),
        })
    public String selfCall(String myName) {
      return "I'm a mock named " + myName;
    }

    @SkylarkCallable(
        name = "value_of",
        parameters = {@Param(name = "str", type = String.class)},
        documented = false)
    public Integer valueOf(String str) {
      return Integer.valueOf(str);
    }
    @SkylarkCallable(name = "is_empty",
        parameters = { @Param(name = "str", type = String.class) },
        documented = false)
    public Boolean isEmpty(String str) {
      return str.isEmpty();
    }
    public void value() {}
    @SkylarkCallable(name = "return_bad", documented = false)
    public Bad returnBad() {
      return new Bad(); // not a legal Starlark value
    }
    @SkylarkCallable(name = "struct_field", documented = false, structField = true)
    public String structField() {
      return "a";
    }

    @SkylarkCallable(
        name = "struct_field_with_extra",
        documented = false,
        structField = true,
        useStarlarkSemantics = true)
    public String structFieldWithExtra(StarlarkSemantics sem) {
      return "struct_field_with_extra("
        + (sem != null)
        + ")";
    }

    @SkylarkCallable(name = "struct_field_callable", documented = false, structField = true)
    public Object structFieldCallable() {
      return new BuiltinCallable(SkylarkEvaluationTest.this, "foobar");
    }

    @SkylarkCallable(name = "interrupted_struct_field", documented = false, structField = true)
    public BuiltinFunction structFieldInterruptedCallable() throws InterruptedException {
      throw new InterruptedException();
    }

    @SkylarkCallable(name = "function", documented = false, structField = false)
    public String function() {
      return "a";
    }

    @SuppressWarnings("unused")
    @SkylarkCallable(
        name = "nullfunc_failing",
        parameters = {
          @Param(name = "p1", type = String.class),
          @Param(name = "p2", type = Integer.class),
        },
        documented = false,
        allowReturnNones = false)
    public StarlarkValue nullfuncFailing(String p1, Integer p2) {
      return null;
    }

    @SkylarkCallable(name = "nullfunc_working", documented = false, allowReturnNones = true)
    public StarlarkValue nullfuncWorking() {
      return null;
    }
    @SkylarkCallable(name = "voidfunc", documented = false)
    public void voidfunc() {}
    @SkylarkCallable(name = "string_list", documented = false)
    public ImmutableList<String> stringList() {
      return ImmutableList.<String>of("a", "b");
    }
    @SkylarkCallable(name = "string", documented = false)
    public String string() {
      return "a";
    }
    @SkylarkCallable(name = "string_list_dict", documented = false)
    public Map<String, List<String>> stringListDict() {
      return ImmutableMap.of("a", ImmutableList.of("b", "c"));
    }

    @SkylarkCallable(
      name = "legacy_method",
      documented = false,
      parameters = {
        @Param(name = "pos", positional = true, type = Boolean.class),
        @Param(name = "legacyNamed", type = Boolean.class, positional = true, named = false,
            legacyNamed = true),
        @Param(name = "named", type = Boolean.class, positional = false, named = true),
      })
    public String legacyMethod(Boolean pos, Boolean legacyNamed, Boolean named) {
      return "legacy_method("
          + pos
          + ", "
          + legacyNamed
          + ", "
          + named
          + ")";
    }

    @SkylarkCallable(
        name = "with_params",
        documented = false,
        parameters = {
          @Param(name = "pos1"),
          @Param(name = "pos2", defaultValue = "False", type = Boolean.class),
          @Param(
              name = "posOrNamed",
              defaultValue = "False",
              type = Boolean.class,
              positional = true,
              named = true),
          @Param(name = "named", type = Boolean.class, positional = false, named = true),
          @Param(
              name = "optionalNamed",
              type = Boolean.class,
              defaultValue = "False",
              positional = false,
              named = true),
          @Param(
              name = "nonNoneable",
              type = Object.class,
              defaultValue = "\"a\"",
              positional = false,
              named = true),
          @Param(
              name = "noneable",
              type = Integer.class,
              defaultValue = "None",
              noneable = true,
              positional = false,
              named = true),
          @Param(
              name = "multi",
              allowedTypes = {
                @ParamType(type = String.class),
                @ParamType(type = Integer.class),
                @ParamType(type = Sequence.class, generic1 = Integer.class),
              },
              defaultValue = "None",
              noneable = true,
              positional = false,
              named = true)
        })
    public String withParams(
        Integer pos1,
        boolean pos2,
        boolean posOrNamed,
        boolean named,
        boolean optionalNamed,
        Object nonNoneable,
        Object noneable,
        Object multi) {
      return "with_params("
          + pos1
          + ", "
          + pos2
          + ", "
          + posOrNamed
          + ", "
          + named
          + ", "
          + optionalNamed
          + ", "
          + nonNoneable
          + (noneable != Starlark.NONE ? ", " + noneable : "")
          + (multi != Starlark.NONE ? ", " + multi : "")
          + ")";
    }

    @SkylarkCallable(
        name = "with_extra",
        documented = false,
        useLocation = true,
        useAst = true,
        useStarlarkThread = true,
        useStarlarkSemantics = true)
    public String withExtraInterpreterParams(
        Location location, FuncallExpression func, StarlarkThread thread, StarlarkSemantics sem) {
      return "with_extra("
          + location.getStartLine()
          + ", "
          + func.getArguments().size()
          + ", "
          + thread.isGlobal()
          + ", "
          + (sem != null)
          + ")";
    }

    @SkylarkCallable(
        name = "with_params_and_extra",
        documented = false,
        parameters = {
          @Param(name = "pos1"),
          @Param(name = "pos2", defaultValue = "False", type = Boolean.class),
          @Param(
              name = "posOrNamed",
              defaultValue = "False",
              type = Boolean.class,
              positional = true,
              named = true),
          @Param(name = "named", type = Boolean.class, positional = false, named = true),
          @Param(
              name = "optionalNamed",
              type = Boolean.class,
              defaultValue = "False",
              positional = false,
              named = true),
          @Param(
              name = "nonNoneable",
              type = Object.class,
              defaultValue = "\"a\"",
              positional = false,
              named = true),
          @Param(
              name = "noneable",
              type = Integer.class,
              defaultValue = "None",
              noneable = true,
              positional = false,
              named = true),
          @Param(
              name = "multi",
              allowedTypes = {
                @ParamType(type = String.class),
                @ParamType(type = Integer.class),
                @ParamType(type = Sequence.class, generic1 = Integer.class),
              },
              defaultValue = "None",
              noneable = true,
              positional = false,
              named = true)
        },
        useAst = true,
        useLocation = true,
        useStarlarkThread = true,
        useStarlarkSemantics = true)
    public String withParamsAndExtraInterpreterParams(
        Integer pos1,
        boolean pos2,
        boolean posOrNamed,
        boolean named,
        boolean optionalNamed,
        Object nonNoneable,
        Object noneable,
        Object multi,
        Location location,
        FuncallExpression func,
        StarlarkThread thread,
        StarlarkSemantics sem) {
      return "with_params_and_extra("
          + pos1
          + ", "
          + pos2
          + ", "
          + posOrNamed
          + ", "
          + named
          + ", "
          + optionalNamed
          + ", "
          + nonNoneable
          + (noneable != Starlark.NONE ? ", " + noneable : "")
          + (multi != Starlark.NONE ? ", " + multi : "")
          + ", "
          + location.getStartLine()
          + ", "
          + func.getArguments().size()
          + ", "
          + thread.isGlobal()
          + ", "
          + (sem != null)
          + ")";
    }

    @SkylarkCallable(name = "proxy_methods_object",
        doc = "Returns a struct containing all callable method objects of this mock",
        allowReturnNones = true)
    public ClassObject proxyMethodsObject() {
      ImmutableMap.Builder<String, Object> builder = new ImmutableMap.Builder<>();
      Starlark.addMethods(builder, this);
      return StructProvider.STRUCT.create(builder.build(), "no native callable '%s'");
    }

    @SkylarkCallable(
        name = "with_args_and_thread",
        documented = false,
        parameters = {
          @Param(name = "pos1", type = Integer.class),
          @Param(name = "pos2", defaultValue = "False", type = Boolean.class),
          @Param(name = "named", type = Boolean.class, positional = false, named = true),
        },
        extraPositionals = @Param(name = "args"),
        useStarlarkThread = true)
    public String withArgsAndThread(
        Integer pos1, boolean pos2, boolean named, Sequence<?> args, StarlarkThread thread) {
      String argsString = debugPrintArgs(args);
      return "with_args_and_thread("
          + pos1
          + ", "
          + pos2
          + ", "
          + named
          + ", "
          + argsString
          + ", "
          + thread.isGlobal()
          + ")";
    }

    @SkylarkCallable(
        name = "with_kwargs",
        documented = false,
        parameters = {
          @Param(name = "pos", defaultValue = "False", type = Boolean.class),
          @Param(name = "named", type = Boolean.class, positional = false, named = true),
        },
        extraKeywords = @Param(name = "kwargs"))
    public String withKwargs(boolean pos, boolean named, Dict<?, ?> kwargs) throws EvalException {
      String kwargsString =
          "kwargs("
              + kwargs
                  .getContents(String.class, Object.class, "kwargs")
                  .entrySet()
                  .stream()
                  .map(entry -> entry.getKey() + "=" + entry.getValue())
                  .collect(joining(", "))
              + ")";
      return "with_kwargs(" + pos + ", " + named + ", " + kwargsString + ")";
    }

    @SkylarkCallable(
        name = "with_args_and_kwargs",
        documented = false,
        parameters = {
          @Param(name = "foo", named = true, positional = true, type = String.class),
        },
        extraPositionals = @Param(name = "args"),
        extraKeywords = @Param(name = "kwargs"))
    public String withArgsAndKwargs(String foo, Sequence<?> args, Dict<?, ?> kwargs)
        throws EvalException {
      String argsString = debugPrintArgs(args);
      String kwargsString =
          "kwargs("
              + kwargs
                  .getContents(String.class, Object.class, "kwargs")
                  .entrySet()
                  .stream()
                  .map(entry -> entry.getKey() + "=" + entry.getValue())
                  .collect(joining(", "))
              + ")";
      return "with_args_and_kwargs(" + foo + ", " + argsString + ", " + kwargsString + ")";
    }

    @SkylarkCallable(name = "raise_unchecked_exception", documented = false)
    public void raiseUncheckedException() {
      throw new InternalError("buggy code");
    }

    @Override
    public String toString() {
      return "<mock>";
    }
  }

  private static String debugPrintArgs(Iterable<?> args) {
    Printer p = Printer.getPrinter();
    p.append("args(");
    String sep = "";
    for (Object arg : args) {
      p.append(sep).debugPrint(arg);
      sep = ", ";
    }
    return p.append(")").toString();
  }

  @SkylarkModule(name = "MockInterface", doc = "")
  static interface MockInterface extends StarlarkValue {
    @SkylarkCallable(name = "is_empty_interface",
        parameters = { @Param(name = "str", type = String.class) },
        documented = false)
    public Boolean isEmptyInterface(String str);
  }

  @SkylarkModule(name = "MockSubClass", doc = "")
  final class MockSubClass extends Mock implements MockInterface {
    @Override
    public Boolean isEmpty(String str) {
      return str.isEmpty();
    }
    @Override
    public Boolean isEmptyInterface(String str) {
      return str.isEmpty();
    }
  }

  @SkylarkModule(name = "MockClassObject", documented = false, doc = "")
  static final class MockClassObject implements ClassObject, StarlarkValue {
    @Override
    public Object getValue(String name) {
      switch (name) {
        case "field": return "a";
        case "nset":
          return NestedSetBuilder.stableOrder().build(); // not a legal Starlark value
        default: return null;
      }
    }

    @Override
    public ImmutableCollection<String> getFieldNames() {
      return ImmutableList.of("field", "nset");
    }

    @Override
    public String getErrorMessageForUnknownField(String name) {
      return null;
    }
  }

  @SkylarkModule(name = "ParamterizedMock", doc = "")
  static interface ParameterizedApi<ObjectT> extends StarlarkValue {
    @SkylarkCallable(
        name = "method",
        documented = false,
        parameters = {
            @Param(name = "foo", named = true, positional = true, type = Object.class),
        }
    )
    public ObjectT method(ObjectT o);
  }

  static final class ParameterizedMock implements ParameterizedApi<String> {
    @Override
    public String method(String o) {
      return o;
    }
  }

  // Verifies that a method implementation overriding a parameterized annotated interface method
  // is still treated as skylark-callable. Concretely, method() below should be treated as
  // callable even though its method signature isn't an *exact* match of the annotated method
  // declaration, due to the interface's method declaration being generic.
  @Test
  public void testParameterizedMock() throws Exception {
    new SkylarkTest()
        .update("mock", new ParameterizedMock())
        .setUp("result = mock.method('bar')")
        .testLookup("result", "bar");
  }

  @Test
  public void testSimpleIf() throws Exception {
    new SkylarkTest().setUp("def foo():",
        "  a = 0",
        "  x = 0",
        "  if x: a = 5",
        "  return a",
        "a = foo()").testLookup("a", 0);
  }

  @Test
  public void testIfPass() throws Exception {
    new SkylarkTest().setUp("def foo():",
        "  a = 1",
        "  x = True",
        "  if x: pass",
        "  return a",
        "a = foo()").testLookup("a", 1);
  }

  @Test
  public void testNestedIf() throws Exception {
    executeNestedIf(0, 0, 0);
    executeNestedIf(1, 0, 3);
    executeNestedIf(1, 1, 5);
  }

  private void executeNestedIf(int x, int y, int expected) throws Exception {
    String fun = String.format("foo%s%s", x, y);
    new SkylarkTest().setUp("def " + fun + "():",
        "  x = " + x,
        "  y = " + y,
        "  a = 0",
        "  b = 0",
        "  if x:",
        "    if y:",
        "      a = 2",
        "    b = 3",
        "  return a + b",
        "x = " + fun + "()").testLookup("x", expected);
  }

  @Test
  public void testIfElse() throws Exception {
    executeIfElse("foo", "something", 2);
    executeIfElse("bar", "", 3);
  }

  private void executeIfElse(String fun, String y, int expected) throws Exception {
    new SkylarkTest().setUp("def " + fun + "():",
        "  y = '" + y + "'",
        "  x = 5",
        "  if x:",
        "    if y: a = 2",
        "    else: a = 3",
        "  return a",
        "z = " + fun + "()").testLookup("z", expected);
  }

  @Test
  public void testIfElifElse_IfExecutes() throws Exception {
    execIfElifElse(1, 0, 1);
  }

  @Test
  public void testIfElifElse_ElifExecutes() throws Exception {
    execIfElifElse(0, 1, 2);
  }

  @Test
  public void testIfElifElse_ElseExecutes() throws Exception {
    execIfElifElse(0, 0, 3);
  }

  private void execIfElifElse(int x, int y, int v) throws Exception {
    new SkylarkTest().setUp("def foo():",
        "  x = " + x + "",
        "  y = " + y + "",
        "  if x:",
        "    return 1",
        "  elif y:",
        "    return 2",
        "  else:",
        "    return 3",
        "v = foo()").testLookup("v", v);
  }

  @Test
  public void testForOnList() throws Exception {
    new SkylarkTest().setUp("def foo():",
        "  s = ''",
        "  for i in ['hello', ' ', 'world']:",
        "    s = s + i",
        "  return s",
        "s = foo()").testLookup("s", "hello world");
  }

  @Test
  public void testForAssignmentList() throws Exception {
    new SkylarkTest().setUp("def foo():",
        "  d = ['a', 'b', 'c']",
        "  s = ''",
        "  for i in d:",
        "    s = s + i",
        "    d = ['d', 'e', 'f']", // check that we use the old list
        "  return s",
        "s = foo()").testLookup("s", "abc");
  }

  @Test
  public void testForAssignmentDict() throws Exception {
    new SkylarkTest().setUp("def func():",
        "  d = {'a' : 1, 'b' : 2, 'c' : 3}",
        "  s = ''",
        "  for i in d:",
        "    s = s + i",
        "    d = {'d' : 1, 'e' : 2, 'f' : 3}",
        "  return s",
        "s = func()").testLookup("s", "abc");
  }

  @Test
  public void testForUpdateList() throws Exception {
    new SkylarkTest().setUp("def foo():",
        "  xs = [1, 2, 3]",
        "  for x in xs:",
        "    if x == 1:",
        "      xs.append(10)"
        ).testIfErrorContains("trying to mutate a locked object", "foo()");
  }

  @Test
  public void testForUpdateDict() throws Exception {
    new SkylarkTest().setUp("def foo():",
        "  d = {'a': 1, 'b': 2, 'c': 3}",
        "  for k in d:",
        "    d[k] *= 2"
        ).testIfErrorContains("trying to mutate a locked object", "foo()");
  }

  @Test
  public void testForUnlockedAfterBreak() throws Exception {
    new SkylarkTest().setUp("def foo():",
        "  xs = [1, 2]",
        "  for x in xs:",
        "    break",
        "  xs.append(3)",
        "  return xs"
        ).testEval("foo()", "[1, 2, 3]");
  }

  @Test
  public void testForNestedOnSameListStillLocked() throws Exception {
    new SkylarkTest().setUp("def foo():",
        "  xs = [1, 2]",
        "  ys = []",
        "  for x1 in xs:",
        "    for x2 in xs:",
        "      ys.append(x1 * x2)",
        "    xs.append(4)",
        "  return ys"
        ).testIfErrorContains("trying to mutate a locked object", "foo()");
  }

  @Test
  public void testForNestedOnSameListErrorMessage() throws Exception {
    new SkylarkTest().setUp("def foo():",
        "  xs = [1, 2]",
        "  ys = []",
        "  for x1 in xs:",
        "    for x2 in xs:",
        "      ys.append(x1 * x2)",
        "      xs.append(4)",
        "  return ys"
        // No file name in message, due to how test is set up.
        ).testIfErrorContains("Object locked at the following location(s): :4:3, :5:5", "foo()");
  }

  @Test
  public void testForNestedOnSameListUnlockedAtEnd() throws Exception {
    new SkylarkTest().setUp("def foo():",
        "  xs = [1, 2]",
        "  ys = []",
        "  for x1 in xs:",
        "    for x2 in xs:",
        "      ys.append(x1 * x2)",
        "  xs.append(4)",
        "  return ys"
        ).testEval("foo()", "[1, 2, 2, 4]");
  }

  @Test
  public void testForNestedWithListCompGood() throws Exception {
    new SkylarkTest().setUp("def foo():",
        "  xs = [1, 2]",
        "  ys = []",
        "  for x in xs:",
        "    zs = [None for x in xs for y in (ys.append(x) or ys)]",
        "  return ys"
        ).testEval("foo()", "[1, 2, 1, 2]");
  }
  @Test
  public void testForNestedWithListCompBad() throws Exception {
    new SkylarkTest().setUp("def foo():",
        "  xs = [1, 2, 3]",
        "  ys = []",
        "  for x in xs:",
        "    zs = [None for x in xs for y in (xs.append(x) or ys)]",
        "  return ys"
        ).testIfErrorContains("trying to mutate a locked object", "foo()");
  }

  @Test
  public void testForDeepUpdate() throws Exception {
    // Check that indirectly reachable values can still be manipulated as normal.
    new SkylarkTest()
        .setUp(
            "def foo():",
            "  xs = [['a'], ['b'], ['c']]",
            "  ys = []",
            "  for x in xs:",
            "    for y in x:",
            "      ys.append(y)",
            "    xs[2].append(x[0])",
            "  return ys",
            "ys = foo()")
        .testLookup("ys", StarlarkList.of(null, "a", "b", "c", "a", "b"));
  }

  @Test
  public void testForNotIterable() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .testIfErrorContains(
            "type 'int' is not iterable",
            "def func():",
            "  for i in mock.value_of('1'): a = i",
            "func()\n");
  }

  @Test
  public void testForStringNotIterable() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .testIfErrorContains(
            "type 'string' is not iterable", "def func():", "  for i in 'abc': a = i", "func()\n");
  }

  @Test
  public void testForOnDictionary() throws Exception {
    new SkylarkTest().setUp("def foo():",
        "  d = {1: 'a', 2: 'b', 3: 'c'}",
        "  s = ''",
        "  for i in d: s = s + d[i]",
        "  return s",
        "s = foo()").testLookup("s", "abc");
  }

  @Test
  public void testBadDictKey() throws Exception {
    new SkylarkTest().testIfErrorContains(
        "unhashable type: 'list'",
        "{ [1, 2]: [3, 4] }");
  }

  @Test
  public void testForLoopReuseVariable() throws Exception {
    new SkylarkTest().setUp("def foo():",
        "  s = ''",
        "  for i in ['a', 'b']:",
        "    for i in ['c', 'd']: s = s + i",
        "  return s",
        "s = foo()").testLookup("s", "cdcd");
  }

  @Test
  public void testForLoopMultipleVariables() throws Exception {
    new SkylarkTest().setUp("def foo():",
        "  s = ''",
        "  for [i, j] in [[1, 2], [3, 4]]:",
        "    s = s + str(i) + str(j) + '.'",
        "  return s",
        "s = foo()").testLookup("s", "12.34.");
  }

  @Test
  public void testForLoopBreak() throws Exception {
    simpleFlowTest("break", 1);
  }

  @Test
  public void testForLoopContinue() throws Exception {
    simpleFlowTest("continue", 10);
  }

  @SuppressWarnings("unchecked")
  private void simpleFlowTest(String statement, int expected) throws Exception {
    exec(
        "def foo():",
        "  s = 0",
        "  hit = 0",
        "  for i in range(0, 10):",
        "    s = s + 1",
        "    " + statement + "",
        "    hit = 1",
        "  return [s, hit]",
        "x = foo()");
    assertThat((Iterable<Object>) lookup("x")).containsExactly(expected, 0).inOrder();
  }

  @Test
  public void testForLoopBreakFromDeeperBlock() throws Exception {
    flowFromDeeperBlock("break", 1);
    flowFromNestedBlocks("break", 29);
  }

  @Test
  public void testForLoopContinueFromDeeperBlock() throws Exception {
    flowFromDeeperBlock("continue", 5);
    flowFromNestedBlocks("continue", 39);
  }

  private void flowFromDeeperBlock(String statement, int expected) throws Exception {
    exec(
        "def foo():",
        "   s = 0",
        "   for i in range(0, 10):",
        "       if i % 2 != 0:",
        "           " + statement + "",
        "       s = s + 1",
        "   return s",
        "x = foo()");
    assertThat(lookup("x")).isEqualTo(expected);
  }

  private void flowFromNestedBlocks(String statement, int expected) throws Exception {
    exec(
        "def foo2():",
        "   s = 0",
        "   for i in range(1, 41):",
        "       if i % 2 == 0:",
        "           if i % 3 == 0:",
        "               if i % 5 == 0:",
        "                   " + statement + "",
        "       s = s + 1",
        "   return s",
        "y = foo2()");
    assertThat(lookup("y")).isEqualTo(expected);
  }

  @Test
  public void testNestedForLoopsMultipleBreaks() throws Exception {
    nestedLoopsTest("break", 2, 6, 6);
  }

  @Test
  public void testNestedForLoopsMultipleContinues() throws Exception {
    nestedLoopsTest("continue", 4, 20, 20);
  }

  @SuppressWarnings("unchecked")
  private void nestedLoopsTest(String statement, Integer outerExpected, int firstExpected,
      int secondExpected) throws Exception {
    exec(
        "def foo():",
        "   outer = 0",
        "   first = 0",
        "   second = 0",
        "   for i in range(0, 5):",
        "       for j in range(0, 5):",
        "           if j == 2:",
        "               " + statement + "",
        "           first = first + 1",
        "       for k in range(0, 5):",
        "           if k == 2:",
        "               " + statement + "",
        "           second = second + 1",
        "       if i == 2:",
        "           " + statement + "",
        "       outer = outer + 1",
        "   return [outer, first, second]",
        "x = foo()");
    assertThat((Iterable<Object>) lookup("x"))
        .containsExactly(outerExpected, firstExpected, secondExpected).inOrder();
  }

  @Test
  public void testForLoopBreakError() throws Exception {
    flowStatementInsideFunction("break");
    flowStatementAfterLoop("break");
  }

  @Test
  public void testForLoopContinueError() throws Exception {
    flowStatementInsideFunction("continue");
    flowStatementAfterLoop("continue");
  }

  // TODO(adonovan): move this and all tests that use it to Validation tests.
  private void assertValidationError(String expectedError, final String... lines) throws Exception {
    SyntaxError error = assertThrows(SyntaxError.class, () -> exec(lines));
    assertThat(error).hasMessageThat().contains(expectedError);
  }

  private void flowStatementInsideFunction(String statement) throws Exception {
    assertValidationError(
        statement + " statement must be inside a for loop",
        //
        "def foo():",
        "  " + statement,
        "x = foo()");
  }

  private void flowStatementAfterLoop(String statement) throws Exception {
    assertValidationError(
        statement + " statement must be inside a for loop",
        //
        "def foo2():",
        "   for i in range(0, 3):",
        "      pass",
        "   " + statement,
        "y = foo2()");
  }

  @Test
  public void testStructMembersAreImmutable() throws Exception {
    assertValidationError("cannot assign to 's.x'", "s = struct(x = 'a')", "s.x = 'b'\n");
  }

  @Test
  public void testNoneAssignment() throws Exception {
    new SkylarkTest()
        .setUp("def foo(x=None):", "  x = 1", "  x = None", "  return 2", "s = foo()")
        .testLookup("s", 2);
  }

  @Test
  public void testReassignment() throws Exception {
    exec(
        "def foo(x=None):", //
        "  x = 1",
        "  x = [1, 2]",
        "  x = 'str'",
        "  return x",
        "s = foo()");
    assertThat(lookup("s")).isEqualTo("str");
  }

  @Test
  public void testJavaCalls() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("b = mock.is_empty('a')")
        .testLookup("b", Boolean.FALSE);
  }

  @Test
  public void testJavaCallsOnSubClass() throws Exception {
    new SkylarkTest()
        .update("mock", new MockSubClass())
        .setUp("b = mock.is_empty('a')")
        .testLookup("b", Boolean.FALSE);
  }

  @Test
  public void testJavaCallsOnInterface() throws Exception {
    new SkylarkTest()
        .update("mock", new MockSubClass())
        .setUp("b = mock.is_empty_interface('a')")
        .testLookup("b", Boolean.FALSE);
  }

  @Test
  public void testJavaCallsNotSkylarkCallable() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .testIfExactError("'Mock' value has no field or method 'value'", "mock.value()");
  }

  @Test
  public void testNoOperatorIndex() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .testIfExactError("type 'Mock' has no operator [](int)", "mock[2]");
  }

  @Test
  public void testJavaCallsNoMethod() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .testIfExactError("'Mock' value has no field or method 'bad'", "mock.bad()");
  }

  @Test
  public void testJavaCallsNoMethodErrorMsg() throws Exception {
    new SkylarkTest()
        .testIfExactError("'int' value has no field or method 'bad'", "s = 3.bad('a', 'b', 'c')");
  }

  @Test
  public void testJavaCallWithKwargs() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .testIfExactError(
            "'Mock' value has no field or method 'isEmpty'", "mock.isEmpty(str='abc')");
  }

  @Test
  public void testStringListDictValues() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp(
            "def func(mock):",
            "  for i, v in mock.string_list_dict().items():",
            "    modified_list = v + ['extra_string']",
            "  return modified_list",
            "m = func(mock)")
        .testLookup("m", StarlarkList.of(thread.mutability(), "b", "c", "extra_string"));
  }

  @Test
  public void testProxyMethodsObject() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp(
            "m = mock.proxy_methods_object()",
            "b = m.with_params(1, True, named=True)")
        .testLookup("b", "with_params(1, true, false, true, false, a)");
  }

  @Test
  public void testLegacyNamed() throws Exception {
    new SkylarkTest("--incompatible_restrict_named_params=false")
        .update("mock", new Mock())
        .setUp("b = mock.legacy_method(True, legacyNamed=True, named=True)")
        .testLookup("b", "legacy_method(true, true, true)");

    new SkylarkTest("--incompatible_restrict_named_params=false")
        .update("mock", new Mock())
        .setUp("b = mock.legacy_method(True, True, named=True)")
        .testLookup("b", "legacy_method(true, true, true)");

    // Verify legacyNamed also works with proxy method objects.
    new SkylarkTest("--incompatible_restrict_named_params=false")
        .update("mock", new Mock())
        .setUp(
            "m = mock.proxy_methods_object()",
            "b = m.legacy_method(True, legacyNamed=True, named=True)")
        .testLookup("b", "legacy_method(true, true, true)");

    new SkylarkTest("--incompatible_restrict_named_params=false")
        .update("mock", new Mock())
        .setUp("m = mock.proxy_methods_object()", "b = m.legacy_method(True, True, named=True)")
        .testLookup("b", "legacy_method(true, true, true)");
  }

  /**
   * This test verifies an error is raised when a method parameter is set both positionally and
   * by name.
   */
  @Test
  public void testArgSpecifiedBothByNameAndPosition() throws Exception {
    // in with_params, 'posOrNamed' is positional parameter index 2. So by specifying both
    // posOrNamed by name and three positional parameters, there is a conflict.
    new SkylarkTest()
        .update("mock", new Mock())
        .testIfErrorContains("got multiple values for keyword argument 'posOrNamed'",
            "mock.with_params(1, True, True, posOrNamed=True, named=True)");
  }

  @Test
  public void testTooManyPositionalArgs() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .testIfErrorContains("expected no more than 3 positional arguments, but got 4",
            "mock.with_params(1, True, True, 'toomany', named=True)");

    new SkylarkTest()
        .update("mock", new Mock())
        .testIfErrorContains("expected no more than 3 positional arguments, but got 5",
            "mock.with_params(1, True, True, 'toomany', 'alsotoomany', named=True)");

    new SkylarkTest()
        .update("mock", new Mock())
        .testIfErrorContains("expected no more than 1 positional arguments, but got 2",
            "mock.is_empty('a', 'b')");
  }

  @Test
  public void testJavaCallWithPositionalAndKwargs() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("b = mock.with_params(1, True, named=True)")
        .testLookup("b", "with_params(1, true, false, true, false, a)");
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("b = mock.with_params(1, True, named=True, multi=1)")
        .testLookup("b", "with_params(1, true, false, true, false, a, 1)");
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("b = mock.with_params(1, True, named=True, multi='abc')")
        .testLookup("b", "with_params(1, true, false, true, false, a, abc)");

    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("b = mock.with_params(1, True, named=True, multi=[1,2,3])")
        .testLookup("b", "with_params(1, true, false, true, false, a, [1, 2, 3])");

    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("")
        .testIfExactError(
            "parameter 'named' has no default value, for call to "
                + "method with_params(pos1, pos2 = False, posOrNamed = False, named, "
                + "optionalNamed = False, nonNoneable = \"a\", noneable = None, multi = None) "
                + "of 'Mock'",
            "mock.with_params(1, True)");
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("")
        .testIfExactError(
            "parameter 'named' has no default value, for call to "
                + "method with_params(pos1, pos2 = False, posOrNamed = False, named, "
                + "optionalNamed = False, nonNoneable = \"a\", noneable = None, multi = None) "
                + "of 'Mock'",
            "mock.with_params(1, True, True)");
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("b = mock.with_params(1, True, True, named=True)")
        .testLookup("b", "with_params(1, true, true, true, false, a)");
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("b = mock.with_params(1, True, named=True, posOrNamed=True)")
        .testLookup("b", "with_params(1, true, true, true, false, a)");
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("b = mock.with_params(1, True, named=True, posOrNamed=True, optionalNamed=True)")
        .testLookup("b", "with_params(1, true, true, true, true, a)");
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("")
        .testIfExactError(
            "unexpected keyword 'n', for call to "
                + "method with_params(pos1, pos2 = False, posOrNamed = False, named, "
                + "optionalNamed = False, nonNoneable = \"a\", noneable = None, multi = None) "
                + "of 'Mock'",
            "mock.with_params(1, True, named=True, posOrNamed=True, n=2)");
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("")
        .testIfExactError(
            "parameter 'nonNoneable' cannot be None, for call to method "
                + "with_params(pos1, pos2 = False, posOrNamed = False, named, "
                + "optionalNamed = False, nonNoneable = \"a\", noneable = None, multi = None) "
                + "of 'Mock'",
            "mock.with_params(1, True, True, named=True, optionalNamed=False, nonNoneable=None)");

    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("")
        .testIfExactError(
            "expected value of type 'string or int or sequence of ints or NoneType' for parameter"
                + " 'multi', for call to method "
                + "with_params(pos1, pos2 = False, posOrNamed = False, named, "
                + "optionalNamed = False, nonNoneable = \"a\", noneable = None, multi = None) "
                + "of 'Mock'",
            "mock.with_params(1, True, named=True, multi=False)");

    // We do not enforce list item parameter type constraints.
    // Test for this behavior.
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("b = mock.with_params(1, True, named=True, multi=['a', 'b'])")
        .testLookup("b", "with_params(1, true, false, true, false, a, [\"a\", \"b\"])");
  }

  @Test
  public void testNoJavaCallsWithoutSkylark() throws Exception {
    new SkylarkTest()
        .testIfExactError("'int' value has no field or method 'to_string'", "s = 3.to_string()");
  }

  @Test
  public void testStructAccess() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("v = mock.struct_field")
        .testLookup("v", "a");
  }

  @Test
  public void testStructAccessAsFuncallNonCallable() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .testIfExactError("'string' object is not callable", "v = mock.struct_field()");
  }

  @Test
  public void testSelfCall() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("v = mock('bestmock')")
        .testLookup("v", "I'm a mock named bestmock");

    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("mockfunction = mock", "v = mockfunction('bestmock')")
        .testLookup("v", "I'm a mock named bestmock");

    new SkylarkTest()
        .update("mock", new Mock())
        .testIfErrorContains(
            "expected value of type 'string' for parameter 'pos', for call to function MockFn(pos)",
            "v = mock(1)");
  }

  @Test
  public void testStructAccessAsFuncall() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("v = mock.struct_field_callable()")
        .testLookup("v", "foobar");
  }

  @Test
  public void testCallingInterruptedStructField() throws Exception {
    update("mock", new Mock());
    assertThrows(InterruptedException.class, () -> eval("mock.interrupted_struct_field()"));
  }

  @Test
  public void testCallingInterruptedFunction() throws Exception {
    update("interrupted_function", new BuiltinCallable(this, "interrupted_function"));
    assertThrows(InterruptedException.class, () -> eval("interrupted_function()"));
  }

  @Test
  public void testCallingMethodThatRaisesUncheckedException() throws Exception {
    update("mock", new Mock());
    assertThrows(InternalError.class, () -> eval("mock.raise_unchecked_exception()"));
  }

  @Test
  public void testJavaFunctionWithExtraInterpreterParams() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("v = mock.with_extra()")
        .testLookup("v", "with_extra(1, 0, true, true)");
  }

  @Test
  public void testStructFieldWithExtraInterpreterParams() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("v = mock.struct_field_with_extra")
        .testLookup("v", "struct_field_with_extra(true)");
  }

  @Test
  public void testJavaFunctionWithParamsAndExtraInterpreterParams() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("b = mock.with_params_and_extra(1, True, named=True)")
        .testLookup("b", "with_params_and_extra(1, true, false, true, false, a, 1, 3, true, true)");
  }

  @Test
  public void testJavaFunctionWithExtraArgsAndThread() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("b = mock.with_args_and_thread(1, True, 'extraArg1', 'extraArg2', named=True)")
        .testLookup("b", "with_args_and_thread(1, true, true, args(extraArg1, extraArg2), true)");

    // Use an args list.
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp(
            "myargs = ['extraArg2']",
            "b = mock.with_args_and_thread(1, True, 'extraArg1', named=True, *myargs)")
        .testLookup("b", "with_args_and_thread(1, true, true, args(extraArg1, extraArg2), true)");
  }

  @Test
  public void testJavaFunctionWithExtraKwargs() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("b = mock.with_kwargs(True, extraKey1=True, named=True, extraKey2='x')")
        .testLookup("b", "with_kwargs(true, true, kwargs(extraKey1=true, extraKey2=x))");

    // Use a kwargs dict.
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp(
            "mykwargs = {'extraKey2':'x', 'named':True}",
            "b = mock.with_kwargs(True, extraKey1=True, **mykwargs)")
        .testLookup("b", "with_kwargs(true, true, kwargs(extraKey1=true, extraKey2=x))");
  }

  @Test
  public void testJavaFunctionWithArgsAndKwargs() throws Exception {
    // Foo is used positionally
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("b = mock.with_args_and_kwargs('foo', 'bar', 'baz', extraKey1=True, extraKey2='x')")
        .testLookup(
            "b", "with_args_and_kwargs(foo, args(bar, baz), kwargs(extraKey1=true, extraKey2=x))");

    // Use an args list and a kwargs dict
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp(
            "mykwargs = {'extraKey1':True}",
            "myargs = ['baz']",
            "b = mock.with_args_and_kwargs('foo', 'bar', extraKey2='x', *myargs, **mykwargs)")
        .testLookup(
            "b", "with_args_and_kwargs(foo, args(bar, baz), kwargs(extraKey2=x, extraKey1=true))");

    // Foo is used by name
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("b = mock.with_args_and_kwargs(foo='foo', extraKey1=True)")
        .testLookup("b", "with_args_and_kwargs(foo, args(), kwargs(extraKey1=true))");

    // Empty args and kwargs.
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("b = mock.with_args_and_kwargs('foo')")
        .testLookup("b", "with_args_and_kwargs(foo, args(), kwargs())");
  }

  @Test
  public void testProxyMethodsObjectWithArgsAndKwargs() throws Exception {
    // Foo is used positionally
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp(
            "m = mock.proxy_methods_object()",
            "b = m.with_args_and_kwargs('foo', 'bar', 'baz', extraKey1=True, extraKey2='x')")
        .testLookup(
            "b", "with_args_and_kwargs(foo, args(bar, baz), kwargs(extraKey1=true, extraKey2=x))");

    // Use an args list and a kwargs dict
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp(
            "mykwargs = {'extraKey1':True}",
            "myargs = ['baz']",
            "m = mock.proxy_methods_object()",
            "b = m.with_args_and_kwargs('foo', 'bar', extraKey2='x', *myargs, **mykwargs)")
        .testLookup(
            "b", "with_args_and_kwargs(foo, args(bar, baz), kwargs(extraKey2=x, extraKey1=true))");

    // Foo is used by name
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp(
            "m = mock.proxy_methods_object()",
            "b = m.with_args_and_kwargs(foo='foo', extraKey1=True)")
        .testLookup("b", "with_args_and_kwargs(foo, args(), kwargs(extraKey1=true))");

    // Empty args and kwargs.
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("m = mock.proxy_methods_object()", "b = m.with_args_and_kwargs('foo')")
        .testLookup("b", "with_args_and_kwargs(foo, args(), kwargs())");
  }

  @Test
  public void testStructAccessOfMethod() throws Exception {
    new SkylarkTest().update("mock", new Mock()).testExpression("type(mock.function)", "function");
    new SkylarkTest().update("mock", new Mock()).testExpression("mock.function()", "a");
  }

  @Test
  public void testStructAccessTypo() throws Exception {
    new SkylarkTest()
        .update("mock", new MockClassObject())
        .testIfExactError(
            "'MockClassObject' value has no field or method 'fild' (did you mean 'field'?)",
            "mock.fild");
  }

  @Test
  public void testStructAccessType_nonClassObject() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .testIfExactError(
            "'Mock' value has no field or method 'sturct_field' (did you mean 'struct_field'?)",
            "v = mock.sturct_field");
  }

  @Test
  public void testJavaFunctionReturnsIllegalValue() throws Exception {
    update("mock", new Mock());
    IllegalArgumentException e =
        assertThrows(IllegalArgumentException.class, () -> eval("mock.return_bad()"));
    assertThat(e)
        .hasMessageThat()
        .contains(
            "cannot expose internal type to Starlark: class"
                + " com.google.devtools.build.lib.syntax.SkylarkEvaluationTest$Bad");
  }

  @Test
  public void testJavaFunctionReturnsNullFails() throws Exception {
    update("mock", new Mock());
    IllegalStateException e =
        assertThrows(IllegalStateException.class, () -> eval("mock.nullfunc_failing('abc', 1)"));
    assertThat(e).hasMessageThat().contains("method invocation returned None");
  }

  @Test
  public void testClassObjectAccess() throws Exception {
    new SkylarkTest()
        .update("mock", new MockClassObject())
        .setUp("v = mock.field")
        .testLookup("v", "a");
  }

  @Test
  public void testUnionSet() throws Exception {
    new SkylarkTest("--incompatible_depset_union=false")
        .testExpression("str(depset([1, 3]) | depset([1, 2]))", "depset([1, 2, 3])")
        .testExpression("str(depset([1, 2]) | [1, 3])", "depset([1, 2, 3])")
        .testIfExactError("unsupported operand type(s) for |: 'int' and 'bool'", "2 | False");
  }

  @Test
  public void testSetIsNotIterable() throws Exception {
    new SkylarkTest()
        .testIfErrorContains("not iterable", "list(depset(['a', 'b']))")
        .testIfErrorContains("not iterable", "max(depset([1, 2, 3]))")
        .testIfErrorContains("not iterable", "1 in depset([1, 2, 3])")
        .testIfErrorContains("not iterable", "sorted(depset(['a', 'b']))")
        .testIfErrorContains("not iterable", "tuple(depset(['a', 'b']))")
        .testIfErrorContains("not iterable", "[x for x in depset()]")
        .testIfErrorContains("not iterable", "len(depset(['a']))");
  }

  @Test
  public void testFieldReturnsNestedSet() throws Exception {
    update("mock", new MockClassObject());
    IllegalArgumentException e =
        assertThrows(IllegalArgumentException.class, () -> eval("mock.nset"));
    assertThat(e)
        .hasMessageThat()
        .contains(
            "invalid Starlark value: class"
                + " com.google.devtools.build.lib.collect.nestedset.NestedSet");
  }

  @Test
  public void testJavaFunctionReturnsNone() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("v = mock.nullfunc_working()")
        .testLookup("v", Starlark.NONE);
  }

  @Test
  public void testVoidJavaFunctionReturnsNone() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("v = mock.voidfunc()")
        .testLookup("v", Starlark.NONE);
  }

  @Test
  public void testAugmentedAssignment() throws Exception {
    new SkylarkTest().setUp("def f1(x):",
        "  x += 1",
        "  return x",
        "",
        "foo = f1(41)").testLookup("foo", 42);
  }

  @Test
  public void testAugmentedAssignmentHasNoSideEffects() throws Exception {
    // Check object position.
    new SkylarkTest()
        .setUp(
            "counter = [0]",
            "value = [1, 2]",
            "",
            "def f():",
            "  counter[0] = counter[0] + 1",
            "  return value",
            "",
            "f()[1] += 1") // `f()` should be called only once here
        .testLookup("counter", StarlarkList.of(thread.mutability(), 1));

    // Check key position.
    new SkylarkTest()
        .setUp(
            "counter = [0]",
            "value = [1, 2]",
            "",
            "def f():",
            "  counter[0] = counter[0] + 1",
            "  return 1",
            "",
            "value[f()] += 1") // `f()` should be called only once here
        .testLookup("counter", StarlarkList.of(thread.mutability(), 1));
  }

  @Test
  public void testInvalidAugmentedAssignment_ListExpression() throws Exception {
    assertValidationError(
        "cannot perform augmented assignment on a list or tuple expression",
        //
        "def f(a, b):",
        "  [a, b] += []",
        "f(1, 2)");
  }


  @Test
  public void testInvalidAugmentedAssignment_NotAnLValue() throws Exception {
    assertValidationError(
        "cannot assign to 'x + 1'",
        //
        "x + 1 += 2");
  }

  @Test
  public void testAssignmentEvaluationOrder() throws Exception {
    new SkylarkTest()
        .setUp(
            "ordinary = []",
            "augmented = []",
            "value = [1, 2]",
            "",
            "def f(record):",
            "  record.append('f')",
            "  return value",
            "",
            "def g(record):",
            "  record.append('g')",
            "  return value",
            "",
            "f(ordinary)[0] = g(ordinary)[1]",
            "f(augmented)[0] += g(augmented)[1]")
        .testLookup(
            "ordinary", StarlarkList.of(thread.mutability(), "g", "f")) // This order is consistent
        .testLookup("augmented", StarlarkList.of(thread.mutability(), "f", "g")); // with Python
  }

  @Test
  public void testDictComprehensions_IterationOrder() throws Exception {
    new SkylarkTest().setUp("def foo():",
        "  d = {x : x for x in ['c', 'a', 'b']}",
        "  s = ''",
        "  for a in d:",
        "    s += a",
        "  return s",
        "s = foo()").testLookup("s", "cab");
  }

  @Test
  public void testDotExpressionOnNonStructObject() throws Exception {
    new SkylarkTest()
        .testIfExactError("'string' value has no field or method 'field'", "x = 'a'.field");
  }

  @Test
  public void testPlusEqualsOnListMutating() throws Exception {
    new SkylarkTest()
        .setUp(
            "def func():",
            "  l1 = [1, 2]",
            "  l2 = l1",
            "  l2 += [3, 4]",
            "  return l1, l2",
            "lists = str(func())")
        .testLookup("lists", "([1, 2, 3, 4], [1, 2, 3, 4])");

    // The same but with += after an IndexExpression
    new SkylarkTest()
        .setUp(
            "def func():",
            "  l = [1, 2]",
            "  d = {0: l}",
            "  d[0] += [3, 4]",
            "  return l, d[0]",
            "lists = str(func())")
        .testLookup("lists", "([1, 2, 3, 4], [1, 2, 3, 4])");
  }

  @Test
  public void testPlusEqualsOnTuple() throws Exception {
    new SkylarkTest()
        .setUp(
            "def func():",
            "  t1 = (1, 2)",
            "  t2 = t1",
            "  t2 += (3, 4)",
            "  return t1, t2",
            "tuples = func()")
        .testLookup("tuples", Tuple.of(Tuple.of(1, 2), Tuple.of(1, 2, 3, 4)));
  }

  @Test
  public void testPlusOnDictDeprecated() throws Exception {
    new SkylarkTest()
        .testIfErrorContains(
            "unsupported operand type(s) for +: 'dict' and 'dict'", "{1: 2} + {3: 4}");
    new SkylarkTest()
        .testIfErrorContains(
            "unsupported operand type(s) for +: 'dict' and 'dict'",
            "def func():",
            "  d = {1: 2}",
            "  d += {3: 4}",
            "func()");
  }

  @Test
  public void testDictAssignmentAsLValue() throws Exception {
    new SkylarkTest().setUp("def func():",
        "  d = {'a' : 1}",
        "  d['b'] = 2",
        "  return d",
        "d = func()").testLookup("d", ImmutableMap.of("a", 1, "b", 2));
  }

  @Test
  public void testNestedDictAssignmentAsLValue() throws Exception {
    new SkylarkTest().setUp("def func():",
        "  d = {'a' : 1}",
        "  e = {'d': d}",
        "  e['d']['b'] = 2",
        "  return e",
        "e = func()").testLookup("e", ImmutableMap.of("d", ImmutableMap.of("a", 1, "b", 2)));
  }

  @Test
  public void testListAssignmentAsLValue() throws Exception {
    new SkylarkTest().setUp("def func():",
        "  a = [1, 2]",
        "  a[1] = 3",
        "  a[-2] = 4",
        "  return a",
        "a = str(func())").testLookup("a", "[4, 3]");
  }

  @Test
  public void testNestedListAssignmentAsLValue() throws Exception {
    new SkylarkTest().setUp("def func():",
        "  d = [1, 2]",
        "  e = [3, d]",
        "  e[1][1] = 4",
        "  return e",
        "e = str(func())").testLookup("e", "[3, [1, 4]]");
  }

  @Test
  public void testDictTupleAssignmentAsLValue() throws Exception {
    new SkylarkTest().setUp("def func():",
        "  d = {'a' : 1}",
        "  d['b'], d['c'] = 2, 3",
        "  return d",
        "d = func()").testLookup("d", ImmutableMap.of("a", 1, "b", 2, "c", 3));
  }

  @Test
  public void testDictItemPlusEqual() throws Exception {
    new SkylarkTest().setUp("def func():",
        "  d = {'a' : 2}",
        "  d['a'] += 3",
        "  return d",
        "d = func()").testLookup("d", ImmutableMap.of("a", 5));
  }

  @Test
  public void testDictAssignmentAsLValueSideEffects() throws Exception {
    new SkylarkTest()
        .setUp("def func(d):", "  d['b'] = 2", "d = {'a' : 1}", "func(d)")
        .testLookup("d", Dict.of((Mutability) null, "a", 1, "b", 2));
  }

  @Test
  public void testAssignmentToListInDictSideEffect() throws Exception {
    new SkylarkTest()
        .setUp("l = [1, 2]", "d = {0: l}", "d[0].append(3)")
        .testLookup("l", StarlarkList.of(null, 1, 2, 3));
  }

  @Test
  public void testUserFunctionKeywordArgs() throws Exception {
    new SkylarkTest().setUp("def foo(a, b, c):",
        "  return a + b + c", "s = foo(1, c=2, b=3)")
        .testLookup("s", 6);
  }

  @Test
  public void testFunctionCallOrdering() throws Exception {
    new SkylarkTest().setUp("def func(): return foo() * 2",
         "def foo(): return 2",
         "x = func()")
         .testLookup("x", 4);
  }

  @Test
  public void testFunctionCallBadOrdering() throws Exception {
    new SkylarkTest()
        .testIfErrorContains(
            "global variable 'foo' is referenced before assignment.",
            "def func(): return foo() * 2",
            "x = func()",
            "def foo(): return 2");
  }

  @Test
  public void testLocalVariableDefinedBelow() throws Exception {
    new SkylarkTest()
        .setUp(
            "def beforeEven(li):", // returns the value before the first even number
            "    for i in li:",
            "        if i % 2 == 0:",
            "            return a",
            "        else:",
            "            a = i",
            "res = beforeEven([1, 3, 4, 5])")
        .testLookup("res", 3);
  }

  @Test
  public void testShadowisNotInitialized() throws Exception {
    new SkylarkTest()
        .testIfErrorContains(
            /* error message */ "local variable 'gl' is referenced before assignment",
            "gl = 5",
            "def foo():",
            "    if False: gl = 2",
            "    return gl",
            "res = foo()");
  }

  @Test
  public void testShadowBuiltin() throws Exception {
    new SkylarkTest()
        .testIfErrorContains(
            "global variable 'len' is referenced before assignment",
            "x = len('abc')",
            "len = 2",
            "y = x + len");
  }

  @Test
  public void testFunctionCallRecursion() throws Exception {
    new SkylarkTest().testIfErrorContains("Recursion was detected when calling 'f' from 'g'",
        "def main():",
        "  f(5)",
        "def f(n):",
        "  if n > 0: g(n - 1)",
        "def g(n):",
        "  if n > 0: f(n - 1)",
        "main()");
  }

  @Test
  // TODO(adonovan): move to Validation tests.
  public void testTypo() throws Exception {
    assertValidationError(
        "name 'my_variable' is not defined (did you mean 'myVariable'?)",
        //
        "myVariable = 2",
        "x = my_variable + 1");
  }

  @Test
  public void testNoneTrueFalseInSkylark() throws Exception {
    new SkylarkTest()
        .setUp("a = None", "b = True", "c = False")
        .testLookup("a", Starlark.NONE)
        .testLookup("b", Boolean.TRUE)
        .testLookup("c", Boolean.FALSE);
  }

  @Test
  public void testHasattrMethods() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp("a = hasattr(mock, 'struct_field')", "b = hasattr(mock, 'function')",
            "c = hasattr(mock, 'is_empty')", "d = hasattr('str', 'replace')",
            "e = hasattr(mock, 'other')\n")
        .testLookup("a", Boolean.TRUE)
        .testLookup("b", Boolean.TRUE)
        .testLookup("c", Boolean.TRUE)
        .testLookup("d", Boolean.TRUE)
        .testLookup("e", Boolean.FALSE);
  }

  @Test
  public void testGetattrMethods() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .setUp(
            "a = str(getattr(mock, 'struct_field', 'no'))",
            "b = str(getattr(mock, 'function', 'no'))",
            "c = str(getattr(mock, 'is_empty', 'no'))",
            "d = str(getattr('str', 'replace', 'no'))",
            "e = str(getattr(mock, 'other', 'no'))\n")
        .testLookup("a", "a")
        .testLookup("b", "<built-in function function>")
        .testLookup("c", "<built-in function is_empty>")
        .testLookup("d", "<built-in function replace>")
        .testLookup("e", "no");
  }

  @Test
  public void testListAnTupleConcatenationDoesNotWorkInSkylark() throws Exception {
    new SkylarkTest().testIfExactError("unsupported operand type(s) for +: 'list' and 'tuple'",
        "[1, 2] + (3, 4)");
  }

  @Test
  public void testCannotCreateMixedListInSkylark() throws Exception {
    new SkylarkTest().testExactOrder("['a', 'b', 1, 2]", "a", "b", 1, 2);
  }

  @Test
  public void testCannotConcatListInSkylarkWithDifferentGenericTypes() throws Exception {
    new SkylarkTest().testExactOrder("[1, 2] + ['a', 'b']", 1, 2, "a", "b");
  }

  @Test
  public void testConcatEmptyListWithNonEmptyWorks() throws Exception {
    new SkylarkTest().testExactOrder("[] + ['a', 'b']", "a", "b");
  }

  @Test
  public void testFormatStringWithTuple() throws Exception {
    new SkylarkTest().setUp("v = '%s%s' % ('a', 1)").testLookup("v", "a1");
  }

  @Test
  public void testSingletonTuple() throws Exception {
    new SkylarkTest().testExactOrder("(1,)", 1);
  }

  @Test
  public void testDirFindsClassObjectFields() throws Exception {
    new SkylarkTest().update("mock", new MockClassObject())
        .testExactOrder("dir(mock)", "field", "nset");
  }

  @Test
  public void testDirFindsJavaObjectStructFieldsAndMethods() throws Exception {
    new SkylarkTest()
        .update("mock", new Mock())
        .testExactOrder(
            "dir(mock)",
            "function",
            "interrupted_struct_field",
            "is_empty",
            "legacy_method",
            "nullfunc_failing",
            "nullfunc_working",
            "proxy_methods_object",
            "raise_unchecked_exception",
            "return_bad",
            "string",
            "string_list",
            "string_list_dict",
            "struct_field",
            "struct_field_callable",
            "struct_field_with_extra",
            "value_of",
            "voidfunc",
            "with_args_and_kwargs",
            "with_args_and_thread",
            "with_extra",
            "with_kwargs",
            "with_params",
            "with_params_and_extra");
  }

  @Test
  public void testStrNativeInfo() throws Exception {
    new SkylarkTest()
        .update("mock", new NativeInfoMock())
        .testEval(
            "str(mock)",
            "'struct(struct_field_callable = <built-in function foobar>, struct_field_none = None, "
                + "struct_field_string = \"a\")'");
  }

  @Test
  public void testDirNativeInfo() throws Exception {
    new SkylarkTest()
        .update("mock", new NativeInfoMock())
        .testEval(
            "dir(mock)",
            "['callable_string', 'struct_field_callable', 'struct_field_none', "
                + "'struct_field_string', 'to_json', 'to_proto']")
        .testExpression("str(mock.to_json)", "<built-in function to_json>")
        .testExpression("str(getattr(mock, 'to_json'))", "<built-in function to_json>");
  }

  @Test
  public void testPrint() throws Exception {
    // TODO(fwe): cannot be handled by current testing suite
    setFailFast(false);
    exec("print('hello')");
    assertContainsDebug("hello");
    exec("print('a', 'b')");
    assertContainsDebug("a b");
    exec("print('a', 'b', sep='x')");
    assertContainsDebug("axb");
  }

  @Test
  public void testPrintBadKwargs() throws Exception {
    new SkylarkTest()
        .testIfErrorContains(
            "unexpected keywords 'end', 'other', for call to function print(sep = \" \", *args)",
            "print(end='x', other='y')");
  }

  // Override tests in EvaluationTest incompatible with Skylark

  @SuppressWarnings("unchecked")
  @Override
  @Test
  public void testConcatLists() throws Exception {
    new SkylarkTest().testExactOrder("[1,2] + [3,4]", 1, 2, 3, 4).testExactOrder("(1,2)", 1, 2)
        .testExactOrder("(1,2) + (3,4)", 1, 2, 3, 4);

    // TODO(fwe): cannot be handled by current testing suite
    // list
    Object x = eval("[1,2] + [3,4]");
    assertThat((Iterable<Object>) x).containsExactly(1, 2, 3, 4).inOrder();

    // tuple
    x = eval("(1,2)");
    assertThat((Iterable<Object>) x).containsExactly(1, 2).inOrder();
    assertThat(x).isInstanceOf(Tuple.class);

    x = eval("(1,2) + (3,4)");
    assertThat((Iterable<Object>) x).containsExactly(1, 2, 3, 4).inOrder();
    assertThat(x).isInstanceOf(Tuple.class);
  }

  @Override
  @Test
  public void testListConcatenation() throws Exception {}

  @Override
  @Test
  public void testListComprehensionsMultipleVariablesFail() throws Exception {
    new SkylarkTest()
        .testIfErrorContains(
            "assignment length mismatch: left-hand side has length 3, but right-hand side "
                + "evaluates to value of length 2",
            "def foo (): return [x + y for x, y, z in [(1, 2), (3, 4)]]",
            "foo()");

    new SkylarkTest()
        .testIfErrorContains(
            "type 'int' is not iterable", "def bar (): return [x + y for x, y in (1, 2)]", "bar()");

    new SkylarkTest()
        .testIfErrorContains(
            "assignment length mismatch: left-hand side has length 3, but right-hand side "
                + "evaluates to value of length 2",
            "[x + y for x, y, z in [(1, 2), (3, 4)]]");

    new SkylarkTest()
        .testIfErrorContains("type 'int' is not iterable", "[x2 + y2 for x2, y2 in (1, 2)]");

    new SkylarkTest()
        // returns [2] in Python, it's an error in Skylark
        .testIfErrorContains("must have at least one item", "[2 for [] in [()]]");
  }

  @Override
  @Test
  public void testNotCallInt() throws Exception {
    new SkylarkTest()
        .setUp("sum = 123456")
        .testLookup("sum", 123456)
        .testIfExactError("'int' object is not callable", "sum(1, 2, 3, 4, 5, 6)")
        .testExpression("sum", 123456);
  }

  @Test
  public void testConditionalExpressionAtToplevel() throws Exception {
    new SkylarkTest().setUp("x = 1 if 2 else 3").testLookup("x", 1);
  }

  @Test
  public void testConditionalExpressionInFunction() throws Exception {
    new SkylarkTest()
        .setUp("def foo(a, b, c): return a+b if c else a-b\n")
        .testExpression("foo(23, 5, 0)", 18);
  }

  // This class extends NativeInfo (which provides @SkylarkCallable-annotated fields)
  // with additional fields from a map. The only production code that currently
  // does that is ToolchainInfo and its subclasses.
  @SkylarkModule(name = "SkylarkClassObjectWithSkylarkCallables", doc = "")
  private static final class SkylarkClassObjectWithSkylarkCallables extends NativeInfo {

    static final NativeProvider<SkylarkClassObjectWithSkylarkCallables> CONSTRUCTOR =
        new NativeProvider<SkylarkClassObjectWithSkylarkCallables>(
            SkylarkClassObjectWithSkylarkCallables.class, "struct_with_skylark_callables") {};

    // A function that returns "fromValues".
    Object returnFromValues =
        new StarlarkCallable() {
          @Override
          public String getName() {
            return "returnFromValues";
          }

          @Override
          public Object callImpl(
              StarlarkThread thread,
              FuncallExpression call,
              List<Object> args,
              Map<String, Object> kwargs) {
            return "fromValues";
          }
        };

    final Map<String, Object> fields =
        ImmutableMap.of(
            "values_only_field",
            "fromValues",
            "values_only_method",
            returnFromValues,
            "collision_field",
            "fromValues",
            "collision_method",
            returnFromValues);

    SkylarkClassObjectWithSkylarkCallables() {
      super(CONSTRUCTOR, Location.BUILTIN);
    }

    @Override
    public Object getValue(String name) throws EvalException {
      Object x = fields.get(name);
      return x != null ? x : super.getValue(name);
    }

    @Override
    public ImmutableCollection<String> getFieldNames() {
      return ImmutableSet.<String>builder()
          .addAll(fields.keySet())
          .addAll(super.getFieldNames())
          .build();
    }

    @SkylarkCallable(name = "callable_only_field", documented = false, structField = true)
    public String getCallableOnlyField() {
      return "fromSkylarkCallable";
    }

    @SkylarkCallable(name = "callable_only_method", documented = false, structField = false)
    public String getCallableOnlyMethod() {
      return "fromSkylarkCallable";
    }

    @SkylarkCallable(name = "collision_field", documented = false, structField = true)
    public String getCollisionField() {
      return "fromSkylarkCallable";
    }

    @SkylarkCallable(name = "collision_method", documented = false, structField = false)
    public String getCollisionMethod() {
      return "fromSkylarkCallable";
    }
  }

  @Test
  public void testStructFieldDefinedOnlyInValues() throws Exception {
    new SkylarkTest()
        .update("val", new SkylarkClassObjectWithSkylarkCallables())
        .setUp("v = val.values_only_field")
        .testLookup("v", "fromValues");
  }

  @Test
  public void testStructMethodDefinedOnlyInValues() throws Exception {
    new SkylarkTest()
        .update("val", new SkylarkClassObjectWithSkylarkCallables())
        .setUp("v = val.values_only_method()")
        .testLookup("v", "fromValues");
  }

  @Test
  public void testStructFieldDefinedOnlyInSkylarkCallable() throws Exception {
    new SkylarkTest()
        .update("val", new SkylarkClassObjectWithSkylarkCallables())
        .setUp("v = val.callable_only_field")
        .testLookup("v", "fromSkylarkCallable");
  }

  @Test
  public void testStructMethodDefinedOnlyInSkylarkCallable() throws Exception {
    new SkylarkTest()
        .update("val", new SkylarkClassObjectWithSkylarkCallables())
        .setUp("v = val.callable_only_method()")
        .testLookup("v", "fromSkylarkCallable");
  }


  @Test
  public void testStructMethodDefinedInValuesAndSkylarkCallable() throws Exception {
    // This test exercises the resolution of ambiguity between @SkylarkCallable-annotated
    // fields and those reported by ClassObject.getValue.
    new SkylarkTest()
        .update("val", new SkylarkClassObjectWithSkylarkCallables())
        .setUp("v = val.collision_method()")
        .testLookup("v", "fromSkylarkCallable");
  }

  @Test
  public void testStructFieldNotDefined() throws Exception {
    new SkylarkTest()
        .update("val", new SkylarkClassObjectWithSkylarkCallables())
        .testIfExactError(
            // TODO(bazel-team): This should probably list callable_only_method as well.
            "'struct_with_skylark_callables' value has no field or method 'nonexistent_field'\n"
                + "Available attributes: callable_only_field, collision_field, collision_method, "
                + "values_only_field, values_only_method",
            "v = val.nonexistent_field");
  }

  @Test
  public void testStructMethodNotDefined() throws Exception {
    new SkylarkTest()
        .update("val", new SkylarkClassObjectWithSkylarkCallables())
        .testIfExactError(
            "'struct_with_skylark_callables' value has no field or method 'nonexistent_method'\n"
                + "Available attributes: callable_only_field, collision_field, collision_method, "
                + "values_only_field, values_only_method",
            "v = val.nonexistent_method()");
  }

  @Test
  public void testListComprehensionsShadowGlobalVariable() throws Exception {
    exec(
        "a = 18", //
        "def foo():",
        "  b = [a for a in range(3)]",
        "  return a",
        "x = foo()");
    assertThat(lookup("x")).isEqualTo(18);
  }

  @Test
  public void testAnalysisFailureInfo() throws Exception {
    AnalysisFailure cause = new AnalysisFailure(Label.create("test", "test"), "ErrorMessage");

    AnalysisFailureInfo info = AnalysisFailureInfo.forAnalysisFailures(ImmutableList.of(cause));

    new SkylarkTest()
        .update("val", info)
        .setUp(
            "causes = val.causes",
            "label = causes.to_list()[0].label",
            "message = causes.to_list()[0].message")
        .testLookup("label", Label.create("test", "test"))
        .testLookup("message", "ErrorMessage");
  }

  @Test
  // TODO(adonovan): move to Validation tests.
  public void testExperimentalFlagGuardedValue() throws Exception {
    // This test uses an arbitrary experimental flag to verify this functionality. If this
    // experimental flag were to go away, this test may be updated to use any experimental flag.
    // The flag itself is unimportant to the test.
    FlagGuardedValue val =
        FlagGuardedValue.onlyWhenExperimentalFlagIsTrue(
            FlagIdentifier.EXPERIMENTAL_BUILD_SETTING_API, "foo");
    String errorMessage =
        "GlobalSymbol is experimental and thus unavailable with the current "
            + "flags. It may be enabled by setting --experimental_build_setting_api";


    new SkylarkTest(ImmutableMap.of("GlobalSymbol", val), "--experimental_build_setting_api=true")
        .setUp("var = GlobalSymbol")
        .testLookup("var", "foo");

    new SkylarkTest(ImmutableMap.of("GlobalSymbol", val), "--experimental_build_setting_api=false")
        .testIfErrorContains(errorMessage, "var = GlobalSymbol");

    new SkylarkTest(ImmutableMap.of("GlobalSymbol", val), "--experimental_build_setting_api=false")
        .testIfErrorContains(errorMessage, "def my_function():", "  var = GlobalSymbol");

    new SkylarkTest(ImmutableMap.of("GlobalSymbol", val), "--experimental_build_setting_api=false")
        .setUp("GlobalSymbol = 'other'", "var = GlobalSymbol")
        .testLookup("var", "other");
  }

  @Test
  public void testIncompatibleFlagGuardedValue() throws Exception {
    // This test uses an arbitrary incompatible flag to verify this functionality. If this
    // incompatible flag were to go away, this test may be updated to use any incompatible flag.
    // The flag itself is unimportant to the test.
    FlagGuardedValue val = FlagGuardedValue.onlyWhenIncompatibleFlagIsFalse(
        FlagIdentifier.INCOMPATIBLE_NO_TARGET_OUTPUT_GROUP,
        "foo");
    String errorMessage = "GlobalSymbol is deprecated and will be removed soon. It may be "
        + "temporarily re-enabled by setting --incompatible_no_target_output_group=false";

    new SkylarkTest(
            ImmutableMap.of("GlobalSymbol", val),
            "--incompatible_no_target_output_group=false")
        .setUp("var = GlobalSymbol")
        .testLookup("var", "foo");

    new SkylarkTest(
            ImmutableMap.of("GlobalSymbol", val),
            "--incompatible_no_target_output_group=true")
        .testIfErrorContains(errorMessage,
            "var = GlobalSymbol");

    new SkylarkTest(
            ImmutableMap.of("GlobalSymbol", val),
            "--incompatible_no_target_output_group=true")
        .testIfErrorContains(errorMessage,
            "def my_function():",
            "  var = GlobalSymbol");

    new SkylarkTest(
            ImmutableMap.of("GlobalSymbol", val),
            "--incompatible_no_target_output_group=true")
        .setUp("GlobalSymbol = 'other'",
            "var = GlobalSymbol")
        .testLookup("var", "other");
  }

  @Test
  public void testFunctionEvaluatedBeforeArguments() throws Exception {
    // ''.nonesuch must be evaluated (and fail) before f().
    new SkylarkTest()
        .testIfErrorContains(
            "'string' value has no field or method 'nonesuch'",
            "def f(): x = 1//0",
            "''.nonesuch(f())");
  }
}