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

// Copyright 2014 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.common.truth.Truth.assertWithMessage;
import static org.junit.Assert.assertThrows;
import static org.junit.Assert.fail;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
import com.google.common.collect.Sets;
import java.util.ArrayList;
import java.util.List;
import java.util.Set;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;

/** Tests of parser. */
@RunWith(JUnit4.class)
public final class ParserTest {

  private final List<SyntaxError> events = new ArrayList<>();
  private boolean failFast = true;

  private SyntaxError assertContainsError(String expectedMessage) {
    return LexerTest.assertContainsError(events, expectedMessage);
  }

  private void setFailFast(boolean failFast) {
    this.failFast = failFast;
  }

  // Joins the lines, parse, and returns an expression.
  private static Expression parseExpression(String... lines) throws SyntaxError.Exception {
    ParserInput input = ParserInput.fromLines(lines);
    return Expression.parse(input);
  }

  // Parses the expression, asserts that parsing fails,
  // and returns the first error message.
  private static String parseExpressionError(String src) {
    ParserInput input = ParserInput.fromLines(src);
    try {
      Expression.parse(input);
      throw new AssertionError("parseExpression(%s) succeeded unexpectedly: " + src);
    } catch (SyntaxError.Exception ex) {
      return ex.errors().get(0).message();
    }
  }

  // Joins the lines, parses, and returns a file.
  // Errors are added to this.events, or thrown if this.failFast;
  private StarlarkFile parseFile(String... lines) throws SyntaxError.Exception {
    ParserInput input = ParserInput.fromLines(lines);
    StarlarkFile file = StarlarkFile.parse(input);
    if (!file.ok()) {
      if (failFast) {
        throw new SyntaxError.Exception(file.errors());
      }
      // TODO(adonovan): return these, and eliminate a stateful field.
      events.addAll(file.errors());
    }
    return file;
  }

  // Joins the lines, parses, and returns the sole statement.
  private Statement parseStatement(String... lines) throws SyntaxError.Exception {
    return Iterables.getOnlyElement(parseStatements(lines));
  }

  // Joins the lines, parses, and returns the statements.
  private ImmutableList<Statement> parseStatements(String... lines) throws SyntaxError.Exception {
    return parseFile(lines).getStatements();
  }

  private static String getText(String text, Node node) {
    return text.substring(node.getStartOffset(), node.getEndOffset());
  }

  private static void assertLocation(int start, int end, Node node) throws Exception {
    int actualStart = node.getStartOffset();
    int actualEnd = node.getEndOffset();

    if (actualStart != start || actualEnd != end) {
      fail("Expected location = [" + start + ", " + end + "), found ["
          + actualStart + ", " + actualEnd + ")");
    }
  }

  // helper func for testListExpressions:
  private static int getIntElem(DictExpression.Entry entry, boolean key) {
    return ((IntegerLiteral) (key ? entry.getKey() : entry.getValue())).getValue();
  }

  // helper func for testListExpressions:
  private static int getIntElem(ListExpression list, int index) {
    return ((IntegerLiteral) list.getElements().get(index)).getValue();
  }

  // helper func for testListExpressions:
  private static DictExpression.Entry getElem(DictExpression list, int index) {
    return list.getEntries().get(index);
  }

  // helper func for testListExpressions:
  private static Expression getElem(ListExpression list, int index) {
    return list.getElements().get(index);
  }

  // helper func for testing arguments:
  private static Expression getArg(CallExpression f, int index) {
    return f.getArguments().get(index).getValue();
  }

  @Test
  public void testPrecedence1() throws Exception {
    BinaryOperatorExpression e =
      (BinaryOperatorExpression) parseExpression("'%sx' % 'foo' + 'bar'");

    assertThat(e.getOperator()).isEqualTo(TokenKind.PLUS);
  }

  @Test
  public void testPrecedence2() throws Exception {
    BinaryOperatorExpression e =
      (BinaryOperatorExpression) parseExpression("('%sx' % 'foo') + 'bar'");
    assertThat(e.getOperator()).isEqualTo(TokenKind.PLUS);
  }

  @Test
  public void testPrecedence3() throws Exception {
    BinaryOperatorExpression e =
      (BinaryOperatorExpression) parseExpression("'%sx' % ('foo' + 'bar')");
    assertThat(e.getOperator()).isEqualTo(TokenKind.PERCENT);
  }

  @Test
  public void testPrecedence4() throws Exception {
    BinaryOperatorExpression e =
        (BinaryOperatorExpression) parseExpression("1 + - (2 - 3)");
    assertThat(e.getOperator()).isEqualTo(TokenKind.PLUS);
  }

  @Test
  public void testPrecedence5() throws Exception {
    BinaryOperatorExpression e =
        (BinaryOperatorExpression) parseExpression("2 * x | y + 1");
    assertThat(e.getOperator()).isEqualTo(TokenKind.PIPE);
  }

  @Test
  public void testNonAssociativeOperators() throws Exception {
    assertThat(parseExpressionError("0 < 2 < 4"))
        .contains("Operator '<' is not associative with operator '<'");
    assertThat(parseExpressionError("0 == 2 < 4"))
        .contains("Operator '==' is not associative with operator '<'");
    assertThat(parseExpressionError("1 in [1, 2] == True"))
        .contains("Operator 'in' is not associative with operator '=='");
    assertThat(parseExpressionError("1 >= 2 <= 3"))
        .contains("Operator '>=' is not associative with operator '<='");
  }

  @Test
  public void testNonAssociativeOperatorsWithParens() throws Exception {
    parseExpression("(0 < 2) < 4");
    parseExpression("(0 == 2) < 4");
    parseExpression("(1 in [1, 2]) == True");
    parseExpression("1 >= (2 <= 3)");
  }

  @Test
  public void testUnaryMinusExpr() throws Exception {
    UnaryOperatorExpression e = (UnaryOperatorExpression) parseExpression("-5");
    UnaryOperatorExpression e2 = (UnaryOperatorExpression) parseExpression("- 5");

    IntegerLiteral i = (IntegerLiteral) e.getX();
    assertThat(i.getValue()).isEqualTo(5);
    IntegerLiteral i2 = (IntegerLiteral) e2.getX();
    assertThat(i2.getValue()).isEqualTo(5);
    assertLocation(0, 2, e);
    assertLocation(0, 3, e2);
  }

  @Test
  public void testFuncallExpr() throws Exception {
    CallExpression e = (CallExpression) parseExpression("foo[0](1, 2, bar=wiz)");

    IndexExpression function = (IndexExpression) e.getFunction();
    Identifier functionList = (Identifier) function.getObject();
    assertThat(functionList.getName()).isEqualTo("foo");
    IntegerLiteral listIndex = (IntegerLiteral) function.getKey();
    assertThat(listIndex.getValue()).isEqualTo(0);

    assertThat(e.getArguments()).hasSize(3);
    assertThat(e.getNumPositionalArguments()).isEqualTo(2);

    IntegerLiteral arg0 = (IntegerLiteral) e.getArguments().get(0).getValue();
    assertThat((int) arg0.getValue()).isEqualTo(1);

    IntegerLiteral arg1 = (IntegerLiteral) e.getArguments().get(1).getValue();
    assertThat((int) arg1.getValue()).isEqualTo(2);

    Argument arg2 = e.getArguments().get(2);
    assertThat(arg2.getName()).isEqualTo("bar");
    Identifier arg2val = (Identifier) arg2.getValue();
    assertThat(arg2val.getName()).isEqualTo("wiz");
  }

  @Test
  public void testMethCallExpr() throws Exception {
    CallExpression e = (CallExpression) parseExpression("foo.foo(1, 2, bar=wiz)");

    DotExpression dotExpression = (DotExpression) e.getFunction();
    assertThat(dotExpression.getField().getName()).isEqualTo("foo");

    assertThat(e.getArguments()).hasSize(3);
    assertThat(e.getNumPositionalArguments()).isEqualTo(2);

    IntegerLiteral arg0 = (IntegerLiteral) e.getArguments().get(0).getValue();
    assertThat((int) arg0.getValue()).isEqualTo(1);

    IntegerLiteral arg1 = (IntegerLiteral) e.getArguments().get(1).getValue();
    assertThat((int) arg1.getValue()).isEqualTo(2);

    Argument arg2 = e.getArguments().get(2);
    assertThat(arg2.getName()).isEqualTo("bar");
    Identifier arg2val = (Identifier) arg2.getValue();
    assertThat(arg2val.getName()).isEqualTo("wiz");
  }

  @Test
  public void testChainedMethCallExpr() throws Exception {
    CallExpression e = (CallExpression) parseExpression("foo.replace().split(1)");

    DotExpression dotExpr = (DotExpression) e.getFunction();
    assertThat(dotExpr.getField().getName()).isEqualTo("split");

    assertThat(e.getArguments()).hasSize(1);
    assertThat(e.getNumPositionalArguments()).isEqualTo(1);

    IntegerLiteral arg0 = (IntegerLiteral) e.getArguments().get(0).getValue();
    assertThat((int) arg0.getValue()).isEqualTo(1);
  }

  @Test
  public void testPropRefExpr() throws Exception {
    DotExpression e = (DotExpression) parseExpression("foo.foo");

    Identifier ident = e.getField();
    assertThat(ident.getName()).isEqualTo("foo");
  }

  @Test
  public void testStringMethExpr() throws Exception {
    CallExpression e = (CallExpression) parseExpression("'foo'.foo()");

    DotExpression dotExpression = (DotExpression) e.getFunction();
    assertThat(dotExpression.getField().getName()).isEqualTo("foo");

    assertThat(e.getArguments()).isEmpty();
  }

  @Test
  public void testStringLiteralOptimizationValue() throws Exception {
    StringLiteral l = (StringLiteral) parseExpression("'abc' + 'def'");
    assertThat(l.getValue()).isEqualTo("abcdef");
  }

  @Test
  public void testStringLiteralOptimizationToString() throws Exception {
    StringLiteral l = (StringLiteral) parseExpression("'abc' + 'def'");
    assertThat(l.toString()).isEqualTo("\"abcdef\"");
  }

  @Test
  public void testStringLiteralOptimizationLocation() throws Exception {
    StringLiteral l = (StringLiteral) parseExpression("'abc' + 'def'");
    assertThat(l.getStartOffset()).isEqualTo(0);
    assertThat(l.getEndOffset()).isEqualTo(13);
  }

  @Test
  public void testStringLiteralOptimizationDifferentQuote() throws Exception {
    StringLiteral l = (StringLiteral) parseExpression("'abc' + \"def\"");
    assertThat(l.getStartOffset()).isEqualTo(0);
    assertThat(l.getEndOffset()).isEqualTo(13);
  }

  @Test
  public void testIndex() throws Exception {
    IndexExpression e = (IndexExpression) parseExpression("a[i]");
    assertThat(e.getObject().toString()).isEqualTo("a");
    assertThat(e.getKey().toString()).isEqualTo("i");
    assertLocation(0, 4, e);
  }

  @Test
  public void testSubstring() throws Exception {
    SliceExpression s = (SliceExpression) parseExpression("'FOO.CC'[:].lower()[1:]");
    assertThat(((IntegerLiteral) s.getStart()).getValue()).isEqualTo(1);

    CallExpression e = (CallExpression) parseExpression("'FOO.CC'.lower()[1:].startswith('oo')");
    DotExpression dotExpression = (DotExpression) e.getFunction();
    assertThat(dotExpression.getField().getName()).isEqualTo("startswith");
    assertThat(e.getArguments()).hasSize(1);

    s = (SliceExpression) parseExpression("'FOO.CC'[1:][:2]");
    assertThat(((IntegerLiteral) s.getStop()).getValue()).isEqualTo(2);
  }

  @Test
  public void testSlice() throws Exception {
    evalSlice("'0123'[:]", "", "", "");
    evalSlice("'0123'[1:]", 1, "", "");
    evalSlice("'0123'[:3]", "", 3, "");
    evalSlice("'0123'[::]", "", "", "");
    evalSlice("'0123'[1::]", 1, "", "");
    evalSlice("'0123'[:3:]", "", 3, "");
    evalSlice("'0123'[::-1]", "", "", -1);
    evalSlice("'0123'[1:3:]", 1, 3, "");
    evalSlice("'0123'[1::-1]", 1, "", -1);
    evalSlice("'0123'[:3:-1]", "", 3, -1);
    evalSlice("'0123'[1:3:-1]", 1, 3, -1);

    Expression slice = parseExpression("'0123'[1:3:-1]");
    assertLocation(0, 14, slice);
  }

  private static void evalSlice(String statement, Object... expectedArgs)
      throws SyntaxError.Exception {
    SliceExpression e = (SliceExpression) parseExpression(statement);

    // There is no way to evaluate the expression here, so we rely on string comparison.
    String start = e.getStart() == null ? "" : e.getStart().toString();
    String stop = e.getStop() == null ? "" : e.getStop().toString();
    String step = e.getStep() == null ? "" : e.getStep().toString();

    assertThat(start).isEqualTo(expectedArgs[0].toString());
    assertThat(stop).isEqualTo(expectedArgs[1].toString());
    assertThat(step).isEqualTo(expectedArgs[2].toString());
  }

  @Test
  public void testErrorRecovery() throws Exception {
    setFailFast(false);

    // We call parseFile, not parseExpression, as the latter is all-or-nothing.
    String src = "f(1, [x for foo foo foo foo], 3)";
    CallExpression e = (CallExpression) ((ExpressionStatement) parseStatement(src)).getExpression();

    assertContainsError("syntax error at 'foo'");

    // Test that the arguments are (1, '[x for foo foo foo foo]', 3),
    // where the second, errant one is represented as an Identifier.

    Identifier ident = (Identifier) e.getFunction();
    assertThat(ident.getName()).isEqualTo("f");

    assertThat(e.getArguments()).hasSize(3);
    assertThat(e.getNumPositionalArguments()).isEqualTo(3);

    IntegerLiteral arg0 = (IntegerLiteral) e.getArguments().get(0).getValue();
    assertThat((int) arg0.getValue()).isEqualTo(1);

    Argument arg1 = e.getArguments().get(1);
    Identifier arg1val = ((Identifier) arg1.getValue());
    assertThat(arg1val.getName()).isEqualTo("[x for foo foo foo foo]");

    assertLocation(5, 28, arg1val);
    assertThat(src.substring(5, 28)).isEqualTo("[x for foo foo foo foo]");
    assertThat(arg1val.getEndLocation().column()).isEqualTo(29);

    IntegerLiteral arg2 = (IntegerLiteral) e.getArguments().get(2).getValue();
    assertThat((int) arg2.getValue()).isEqualTo(3);
  }

  @Test
  public void testDoesntGetStuck() throws Exception {
    // Make sure the parser does not get stuck when trying
    // to parse an expression containing a syntax error.
    // This usually results in OutOfMemoryError because the
    // parser keeps filling up the error log.
    // We need to make sure that we will always advance
    // in the token stream.
    parseExpressionError("f(1, ], 3)");
    parseExpressionError("f(1, ), 3)");
    parseExpressionError("[ ) for v in 3)");
  }

  @Test
  public void testPrimaryLocation() throws SyntaxError.Exception {
    String expr = "f(1 + 2)";
    CallExpression call = (CallExpression) parseExpression(expr);
    Argument arg = call.getArguments().get(0);
    assertThat(arg.getEndLocation()).isLessThan(call.getEndLocation());
  }

  @Test
  public void testAssignLocation() throws Exception {
    List<Statement> statements = parseStatements("a = b;c = d\n");
    Statement statement = statements.get(0);
    assertThat(statement.getEndOffset()).isEqualTo(5);
  }

  @Test
  public void testAssignKeyword() throws Exception {
    assertThat(parseExpressionError("with = 4")).contains("keyword 'with' not supported");
  }

  @Test
  public void testBreak() throws Exception {
    assertThat(parseExpressionError("break"))
        .contains("syntax error at 'break': expected expression");
  }

  @Test
  public void testTry() throws Exception {
    assertThat(parseExpressionError("try: 1 + 1"))
        .contains("'try' not supported, all exceptions are fatal");
  }

  @Test
  public void testDel() throws Exception {
    assertThat(parseExpressionError("del d['a']"))
        .contains("'del' not supported, use '.pop()' to delete");
  }

  @Test
  public void testTupleAssign() throws Exception {
    List<Statement> statements = parseStatements("list[0] = 5; dict['key'] = value\n");
    assertThat(statements).hasSize(2);
    assertThat(statements.get(0)).isInstanceOf(AssignmentStatement.class);
    assertThat(statements.get(1)).isInstanceOf(AssignmentStatement.class);
  }

  @Test
  public void testAssign() throws Exception {
    List<Statement> statements = parseStatements("a, b = 5\n");
    assertThat(statements).hasSize(1);
    assertThat(statements.get(0)).isInstanceOf(AssignmentStatement.class);
    AssignmentStatement assign = (AssignmentStatement) statements.get(0);
    assertThat(assign.getLHS()).isInstanceOf(ListExpression.class);
  }

  @Test
  public void testInvalidAssign() throws Exception {
    assertThat(parseExpressionError("1 + (b = c)")).contains("syntax error");
  }

  @Test
  public void testAugmentedAssign() throws Exception {
    assertThat(parseStatements("x += 1").toString()).isEqualTo("[x += 1\n]");
    assertThat(parseStatements("x -= 1").toString()).isEqualTo("[x -= 1\n]");
    assertThat(parseStatements("x *= 1").toString()).isEqualTo("[x *= 1\n]");
    assertThat(parseStatements("x /= 1").toString()).isEqualTo("[x /= 1\n]");
    assertThat(parseStatements("x %= 1").toString()).isEqualTo("[x %= 1\n]");
    assertThat(parseStatements("x |= 1").toString()).isEqualTo("[x |= 1\n]");
    assertThat(parseStatements("x &= 1").toString()).isEqualTo("[x &= 1\n]");
    assertThat(parseStatements("x <<= 1").toString()).isEqualTo("[x <<= 1\n]");
    assertThat(parseStatements("x >>= 1").toString()).isEqualTo("[x >>= 1\n]");
  }

  @Test
  public void testPrettyPrintFunctions() throws Exception {
    assertThat(parseStatements("x[1:3]").toString()).isEqualTo("[x[1:3]\n]");
    assertThat(parseStatements("x[1:3:1]").toString()).isEqualTo("[x[1:3:1]\n]");
    assertThat(parseStatements("x[1:3:2]").toString()).isEqualTo("[x[1:3:2]\n]");
    assertThat(parseStatements("x[1::2]").toString()).isEqualTo("[x[1::2]\n]");
    assertThat(parseStatements("x[1:]").toString()).isEqualTo("[x[1:]\n]");
    assertThat(parseStatements("str[42]").toString()).isEqualTo("[str[42]\n]");
    assertThat(parseStatements("ctx.actions.declare_file('hello')").toString())
        .isEqualTo("[ctx.actions.declare_file(\"hello\")\n]");
    assertThat(parseStatements("new_file(\"hello\")").toString())
        .isEqualTo("[new_file(\"hello\")\n]");
  }

  @Test
  public void testEndLineAndColumnIsExclusive() throws Exception {
    // The behavior was 'inclusive' for a couple of years (see CL 170723732),
    // but this was a mistake. Arithmetic on half-open intervals is much simpler.
    AssignmentStatement stmt = (AssignmentStatement) parseStatement("a = b");
    assertThat(stmt.getLHS().getEndLocation().toString()).isEqualTo(":1:2");
  }

  @Test
  public void testFuncallLocation() throws Exception {
    List<Statement> statements = parseStatements("a(b);c = d\n");
    Statement statement = statements.get(0);
    assertThat(statement.getEndOffset()).isEqualTo(4);
  }

  @Test
  public void testListPositions() throws Exception {
    String expr = "[0,f(1),2]";
    assertExpressionLocationCorrect(expr);
    ListExpression list = (ListExpression) parseExpression(expr);
    assertThat(getText(expr, getElem(list, 0))).isEqualTo("0");
    assertThat(getText(expr, getElem(list, 1))).isEqualTo("f(1)");
    assertThat(getText(expr, getElem(list, 2))).isEqualTo("2");
  }

  @Test
  public void testDictPositions() throws Exception {
    String expr = "{1:2,2:f(1),3:4}";
    assertExpressionLocationCorrect(expr);
    DictExpression list = (DictExpression) parseExpression(expr);
    assertThat(getText(expr, getElem(list, 0))).isEqualTo("1:2");
    assertThat(getText(expr, getElem(list, 1))).isEqualTo("2:f(1)");
    assertThat(getText(expr, getElem(list, 2))).isEqualTo("3:4");
  }

  @Test
  public void testArgumentPositions() throws Exception {
    String expr = "f(0,g(1,2),2)";
    assertExpressionLocationCorrect(expr);
    CallExpression f = (CallExpression) parseExpression(expr);
    assertThat(getText(expr, getArg(f, 0))).isEqualTo("0");
    assertThat(getText(expr, getArg(f, 1))).isEqualTo("g(1,2)");
    assertThat(getText(expr, getArg(f, 2))).isEqualTo("2");
  }

  @Test
  public void testSuffixPosition() throws Exception {
    assertExpressionLocationCorrect("'a'.len");
    assertExpressionLocationCorrect("'a'[0]");
    assertExpressionLocationCorrect("'a'[0:1]");
  }

  @Test
  public void testTuplePosition() throws Exception {
    String input = "for a,b in []: pass";
    ForStatement stmt = (ForStatement) parseStatement(input);
    assertThat(getText(input, stmt.getVars())).isEqualTo("a,b");

    input = "for (a,b) in []: pass";
    stmt = (ForStatement) parseStatement(input);
    assertThat(getText(input, stmt.getVars())).isEqualTo("(a,b)");

    assertExpressionLocationCorrect("a, b");
    assertExpressionLocationCorrect("(a, b)");
  }

  @Test
  public void testComprehensionPosition() throws Exception {
    assertExpressionLocationCorrect("[[] for x in []]");
    assertExpressionLocationCorrect("{1: [] for x in []}");
  }

  @Test
  public void testUnaryOperationPosition() throws Exception {
    assertExpressionLocationCorrect("not True");
  }

  @Test
  public void testLoadStatementPosition() throws Exception {
    String input = "load(':foo.bzl', 'bar')";
    LoadStatement stmt = (LoadStatement) parseStatement(input);
    assertThat(getText(input, stmt)).isEqualTo(input);
    // Also try it with another token at the end (newline), which broke the location in the past.
    stmt = (LoadStatement) parseStatement(input + "\n");
    assertThat(getText(input, stmt)).isEqualTo(input);
  }

  @Test
  public void testElif() throws Exception {
    IfStatement ifA =
        (IfStatement)
            parseStatement(
                "if a:", //
                "  pass", "elif b:", "  pass", "else:", "  pass", "");
    IfStatement ifB = (IfStatement) Iterables.getOnlyElement(ifA.getElseBlock());
    assertThat(ifB.isElif()).isTrue();

    ifA =
        (IfStatement)
            parseStatement(
                "if a:", //
                "  pass",
                "else:",
                "  if b:",
                "    pass",
                "  else:",
                "    pass",
                "");
    ifB = (IfStatement) Iterables.getOnlyElement(ifA.getElseBlock());
    assertThat(ifB.isElif()).isFalse();
  }

  @Test
  public void testIfStatementPosition() throws Exception {
    assertStatementLocationCorrect("if True:\n  pass");
    assertStatementLocationCorrect("if True:\n  pass\nelif True:\n  pass");
    assertStatementLocationCorrect("if True:\n  pass\nelse:\n  pass");
  }

  @Test
  public void testForStatementPosition() throws Exception {
    assertStatementLocationCorrect("for x in []:\n  pass");
  }

  @Test
  public void testDefStatementPosition() throws Exception {
    assertStatementLocationCorrect("def foo():\n  pass");
  }

  private void assertStatementLocationCorrect(String stmtStr) throws SyntaxError.Exception {
    Statement stmt = parseStatement(stmtStr);
    assertThat(getText(stmtStr, stmt)).isEqualTo(stmtStr);
    // Also try it with another token at the end (newline), which broke the location in the past.
    stmt = parseStatement(stmtStr + "\n");
    assertThat(getText(stmtStr, stmt)).isEqualTo(stmtStr);
  }

  private static void assertExpressionLocationCorrect(String exprStr) throws SyntaxError.Exception {
    Expression expr = parseExpression(exprStr);
    assertThat(getText(exprStr, expr)).isEqualTo(exprStr);
    // Also try it with another token at the end (newline), which broke the location in the past.
    expr = parseExpression(exprStr + "\n");
    assertThat(getText(exprStr, expr)).isEqualTo(exprStr);
  }

  @Test
  public void testForBreakContinuePass() throws Exception {
    List<Statement> file =
        parseStatements(
            "def foo():", //
            "  for i in [1, 2]:",
            "    break",
            "    continue",
            "    pass",
            "    break");
    assertThat(file).hasSize(1);
    List<Statement> body = ((DefStatement) file.get(0)).getBody();
    assertThat(body).hasSize(1);

    List<Statement> loop = ((ForStatement) body.get(0)).getBody();
    assertThat(loop).hasSize(4);

    assertThat(((FlowStatement) loop.get(0)).getKind()).isEqualTo(TokenKind.BREAK);
    assertLocation(34, 39, loop.get(0));

    assertThat(((FlowStatement) loop.get(1)).getKind()).isEqualTo(TokenKind.CONTINUE);
    assertLocation(44, 52, loop.get(1));

    assertThat(((FlowStatement) loop.get(2)).getKind()).isEqualTo(TokenKind.PASS);
    assertLocation(57, 61, loop.get(2));

    assertThat(((FlowStatement) loop.get(3)).getKind()).isEqualTo(TokenKind.BREAK);
    assertLocation(66, 71, loop.get(3));
  }

  @Test
  public void testListExpressions1() throws Exception {
    ListExpression list = (ListExpression) parseExpression("[0,1,2]");
    assertThat(list.isTuple()).isFalse();
    assertThat(list.getElements()).hasSize(3);
    assertThat(list.isTuple()).isFalse();
    for (int i = 0; i < 3; ++i) {
      assertThat(getIntElem(list, i)).isEqualTo(i);
    }
  }

  @Test
  public void testTupleLiterals2() throws Exception {
    ListExpression tuple = (ListExpression) parseExpression("(0,1,2)");
    assertThat(tuple.isTuple()).isTrue();
    assertThat(tuple.getElements()).hasSize(3);
    assertThat(tuple.isTuple()).isTrue();
    for (int i = 0; i < 3; ++i) {
      assertThat(getIntElem(tuple, i)).isEqualTo(i);
    }
  }

  @Test
  public void testTupleWithoutParens() throws Exception {
    ListExpression tuple = (ListExpression) parseExpression("0, 1, 2");
    assertThat(tuple.isTuple()).isTrue();
    assertThat(tuple.getElements()).hasSize(3);
    assertThat(tuple.isTuple()).isTrue();
    for (int i = 0; i < 3; ++i) {
      assertThat(getIntElem(tuple, i)).isEqualTo(i);
    }
  }

  @Test
  public void testTupleWithTrailingComma() throws Exception {
    // Unlike Python, we require parens here.
    assertThat(parseExpressionError("0, 1, 2, 3,")).contains("Trailing comma");
    assertThat(parseExpressionError("1 + 2,")).contains("Trailing comma");

    ListExpression tuple = (ListExpression) parseExpression("(0, 1, 2, 3,)");
    assertThat(tuple.isTuple()).isTrue();
    assertThat(tuple.getElements()).hasSize(4);
    assertThat(tuple.isTuple()).isTrue();
    for (int i = 0; i < 4; ++i) {
      assertThat(getIntElem(tuple, i)).isEqualTo(i);
    }
  }

  @Test
  public void testTupleLiterals3() throws Exception {
    ListExpression emptyTuple = (ListExpression) parseExpression("()");
    assertThat(emptyTuple.isTuple()).isTrue();
    assertThat(emptyTuple.getElements()).isEmpty();
  }

  @Test
  public void testTupleLiterals4() throws Exception {
    ListExpression singletonTuple = (ListExpression) parseExpression("(42,)");
    assertThat(singletonTuple.isTuple()).isTrue();
    assertThat(singletonTuple.getElements()).hasSize(1);
    assertThat(getIntElem(singletonTuple, 0)).isEqualTo(42);
  }

  @Test
  public void testTupleLiterals5() throws Exception {
    IntegerLiteral intLit = (IntegerLiteral) parseExpression("(42)"); // not a tuple!
    assertThat((int) intLit.getValue()).isEqualTo(42);
  }

  @Test
  public void testListExpressions6() throws Exception {
    ListExpression emptyList = (ListExpression) parseExpression("[]");
    assertThat(emptyList.isTuple()).isFalse();
    assertThat(emptyList.getElements()).isEmpty();
  }

  @Test
  public void testListExpressions7() throws Exception {
    ListExpression singletonList = (ListExpression) parseExpression("[42,]");
    assertThat(singletonList.isTuple()).isFalse();
    assertThat(singletonList.getElements()).hasSize(1);
    assertThat(getIntElem(singletonList, 0)).isEqualTo(42);
  }

  @Test
  public void testListExpressions8() throws Exception {
    ListExpression singletonList = (ListExpression) parseExpression("[42]"); // a singleton
    assertThat(singletonList.isTuple()).isFalse();
    assertThat(singletonList.getElements()).hasSize(1);
    assertThat(getIntElem(singletonList, 0)).isEqualTo(42);
  }

  @Test
  public void testDictExpressions() throws Exception {
    DictExpression dictionaryList =
        (DictExpression) parseExpression("{1:42}"); // a singleton dictionary
    assertThat(dictionaryList.getEntries()).hasSize(1);
    DictExpression.Entry tuple = getElem(dictionaryList, 0);
    assertThat(getIntElem(tuple, true)).isEqualTo(1);
    assertThat(getIntElem(tuple, false)).isEqualTo(42);
  }

  @Test
  public void testDictExpressions1() throws Exception {
    DictExpression dictionaryList = (DictExpression) parseExpression("{}"); // an empty dictionary
    assertThat(dictionaryList.getEntries()).isEmpty();
  }

  @Test
  public void testDictExpressions2() throws Exception {
    DictExpression dictionaryList =
        (DictExpression) parseExpression("{1:42,}"); // a singleton dictionary
    assertThat(dictionaryList.getEntries()).hasSize(1);
    DictExpression.Entry tuple = getElem(dictionaryList, 0);
    assertThat(getIntElem(tuple, true)).isEqualTo(1);
    assertThat(getIntElem(tuple, false)).isEqualTo(42);
  }

  @Test
  public void testDictExpressions3() throws Exception {
    DictExpression dictionaryList = (DictExpression) parseExpression("{1:42,2:43,3:44}");
    assertThat(dictionaryList.getEntries()).hasSize(3);
    for (int i = 0; i < 3; i++) {
      DictExpression.Entry tuple = getElem(dictionaryList, i);
      assertThat(getIntElem(tuple, true)).isEqualTo(i + 1);
      assertThat(getIntElem(tuple, false)).isEqualTo(i + 42);
    }
  }

  @Test
  public void testListExpressions9() throws Exception {
    ListExpression singletonList =
        (ListExpression) parseExpression("[ abi + opt_level + \'/include\' ]");
    assertThat(singletonList.isTuple()).isFalse();
    assertThat(singletonList.getElements()).hasSize(1);
  }

  @Test
  public void testListComprehensionSyntax() throws Exception {
    assertThat(parseExpressionError("[x for")).contains("syntax error at 'newline'");
    assertThat(parseExpressionError("[x for x")).contains("syntax error at 'newline'");
    assertThat(parseExpressionError("[x for x in")).contains("syntax error at 'newline'");
    assertThat(parseExpressionError("[x for x in []")).contains("syntax error at 'newline'");
    assertThat(parseExpressionError("[x for x for y in ['a']]")).contains("syntax error at 'for'");
    assertThat(parseExpressionError("[x for x for y in 1, 2]")).contains("syntax error at 'for'");
  }

  @Test
  public void testListComprehensionEmptyList() throws Exception {
    List<Comprehension.Clause> clauses =
        ((Comprehension) parseExpression("['foo/%s.java' % x for x in []]")).getClauses();
    assertThat(clauses).hasSize(1);
    Comprehension.For for0 = (Comprehension.For) clauses.get(0);
    assertThat(for0.getIterable().toString()).isEqualTo("[]");
    assertThat(for0.getVars().toString()).isEqualTo("x");
  }

  @Test
  public void testListComprehension() throws Exception {
    List<Comprehension.Clause> clauses =
        ((Comprehension) parseExpression("['foo/%s.java' % x for x in ['bar', 'wiz', 'quux']]"))
            .getClauses();
    assertThat(clauses).hasSize(1);
    Comprehension.For for0 = (Comprehension.For) clauses.get(0);
    assertThat(for0.getVars().toString()).isEqualTo("x");
    assertThat(for0.getIterable()).isInstanceOf(ListExpression.class);
  }

  @Test
  public void testForForListComprehension() throws Exception {
    List<Comprehension.Clause> clauses =
        ((Comprehension)
                parseExpression("['%s/%s.java' % (x, y) for x in ['foo', 'bar'] for y in list]"))
            .getClauses();
    assertThat(clauses).hasSize(2);
    Comprehension.For for0 = (Comprehension.For) clauses.get(0);
    assertThat(for0.getVars().toString()).isEqualTo("x");
    assertThat(for0.getIterable()).isInstanceOf(ListExpression.class);
    Comprehension.For for1 = (Comprehension.For) clauses.get(1);
    assertThat(for1.getVars().toString()).isEqualTo("y");
    assertThat(for1.getIterable()).isInstanceOf(Identifier.class);
  }

  @Test
  public void testParserRecovery() throws Exception {
    setFailFast(false);
    List<Statement> statements =
        parseStatements(
            "def foo():",
            "  a = 2 for 4", // parse error
            "  b = [3, 4]",
            "",
            "d = 4 ada", // parse error
            "",
            "def bar():",
            "  a = [3, 4]",
            "  b = 2 * * 5", // parse error
            "");

    assertContainsError("syntax error at 'for': expected newline");
    assertContainsError("syntax error at 'ada': expected newline");
    assertContainsError("syntax error at '*': expected expression");
    assertThat(events).hasSize(3);
    assertThat(statements).hasSize(3);
  }

  @Test
  public void testParserContainsErrors() throws Exception {
    setFailFast(false);
    parseFile("*");
    assertContainsError("syntax error at '*'");
  }

  @Test
  public void testSemicolonAndNewline() throws Exception {
    List<Statement> stmts =
        parseStatements(
            "foo='bar'; foo(bar)", //
            "",
            "foo='bar'; foo(bar)");
    assertThat(stmts).hasSize(4);
  }

  @Test
  public void testSemicolonAndNewline2() throws Exception {
    setFailFast(false);
    List<Statement> stmts = parseStatements("foo='foo' error(bar)", "", "");
    assertContainsError("syntax error at 'error'");
    assertThat(stmts).hasSize(1);
  }

  @Test
  public void testExprAsStatement() throws Exception {
    List<Statement> stmts =
        parseStatements(
            "li = []", //
            "li.append('a.c')",
            "\"\"\" string comment \"\"\"",
            "foo(bar)");
    assertThat(stmts).hasSize(4);
  }

  @Test
  public void testParseBuildFileWithSingleRule() throws Exception {
    List<Statement> stmts =
        parseStatements(
            "genrule(name = 'foo',", //
            "   srcs = ['input.csv'],",
            "   outs = [ 'result.txt',",
            "           'result.log'],",
            "   cmd = 'touch result.txt result.log')",
            "");
    assertThat(stmts).hasSize(1);
  }

  @Test
  public void testParseBuildFileWithMultipleRules() throws Exception {
    List<Statement> stmts =
        parseStatements(
            "genrule(name = 'foo',", //
            "   srcs = ['input.csv'],",
            "   outs = [ 'result.txt',",
            "           'result.log'],",
            "   cmd = 'touch result.txt result.log')",
            "",
            "genrule(name = 'bar',",
            "   srcs = ['input.csv'],",
            "   outs = [ 'graph.svg'],",
            "   cmd = 'touch graph.svg')");
    assertThat(stmts).hasSize(2);
  }

  @Test
  public void testParseBuildFileWithComments() throws Exception {
    StarlarkFile result =
        parseFile(
            "# Test BUILD file", //
            "# with multi-line comment",
            "",
            "genrule(name = 'foo',",
            "   srcs = ['input.csv'],",
            "   outs = [ 'result.txt',",
            "           'result.log'],",
            "   cmd = 'touch result.txt result.log')");
    assertThat(result.getStatements()).hasSize(1);
    assertThat(result.getComments()).hasSize(2);
  }

  @Test
  public void testParseBuildFileWithManyComments() throws Exception {
    StarlarkFile result =
        parseFile(
            "# 1", //
            "# 2",
            "",
            "# 4 ",
            "# 5",
            "#", // 6 - find empty comment for syntax highlighting
            "# 7 ",
            "# 8",
            "genrule(name = 'foo',",
            "   srcs = ['input.csv'],",
            "   # 11",
            "   outs = [ 'result.txt',",
            "           'result.log'], # 13",
            "   cmd = 'touch result.txt result.log')",
            "# 15");
    assertThat(result.getStatements()).hasSize(1); // Single genrule
    StringBuilder commentLines = new StringBuilder();
    for (Comment comment : result.getComments()) {
      // Comments start and end on the same line
      Location start = comment.getStartLocation();
      Location end = comment.getEndLocation();
      assertWithMessage(start.line() + " ends on " + end.line())
          .that(end.line())
          .isEqualTo(start.line());
      commentLines.append('(');
      commentLines.append(start.line());
      commentLines.append(',');
      commentLines.append(start.column());
      commentLines.append(") ");
    }
    assertWithMessage("Found: " + commentLines)
        .that(result.getComments().size()).isEqualTo(10); // One per '#'
  }

  @Test
  public void testMissingComma() throws Exception {
    setFailFast(false);
    // Regression test.
    // Note: missing comma after name='foo'
    parseFile("genrule(name = 'foo'\n"
              + "      srcs = ['in'])");
    assertContainsError("syntax error at 'srcs'");
  }

  @Test
  public void testDoubleSemicolon() throws Exception {
    setFailFast(false);
    // Regression test.
    parseFile("x = 1; ; x = 2;");
    assertContainsError("syntax error at ';'");
  }

  @Test
  public void testDefSingleLine() throws Exception {
    List<Statement> statements = parseStatements("def foo(): x = 1; y = 2\n");
    DefStatement stmt = (DefStatement) statements.get(0);
    assertThat(stmt.getBody()).hasSize(2);
  }

  @Test
  public void testForPass() throws Exception {
    List<Statement> statements = parseStatements("def foo():", "  pass\n");

    assertThat(statements).hasSize(1);
    DefStatement stmt = (DefStatement) statements.get(0);
    assertThat(stmt.getBody().get(0)).isInstanceOf(FlowStatement.class);
  }

  @Test
  public void testForLoopMultipleVariables() throws Exception {
    List<Statement> stmts1 = parseStatements("[ i for i, j, k in [(1, 2, 3)] ]\n");
    assertThat(stmts1).hasSize(1);

    List<Statement> stmts2 = parseStatements("[ i for i, j in [(1, 2, 3)] ]\n");
    assertThat(stmts2).hasSize(1);

    List<Statement> stmts3 = parseStatements("[ i for (i, j, k) in [(1, 2, 3)] ]\n");
    assertThat(stmts3).hasSize(1);
  }

  @Test
  public void testReturnNone() throws Exception {
    List<Statement> defNone = parseStatements("def foo():", "  return None\n");
    assertThat(defNone).hasSize(1);

    List<Statement> bodyNone = ((DefStatement) defNone.get(0)).getBody();
    assertThat(bodyNone).hasSize(1);

    ReturnStatement returnNone = (ReturnStatement) bodyNone.get(0);
    assertThat(((Identifier) returnNone.getResult()).getName()).isEqualTo("None");

    int i = 0;
    for (String end : new String[]{";", "\n"}) {
      List<Statement> defNoExpr = parseStatements("def bar" + i + "():", "  return" + end);
      i++;
      assertThat(defNoExpr).hasSize(1);

      List<Statement> bodyNoExpr = ((DefStatement) defNoExpr.get(0)).getBody();
      assertThat(bodyNoExpr).hasSize(1);

      ReturnStatement returnNoExpr = (ReturnStatement) bodyNoExpr.get(0);
      assertThat(returnNoExpr.getResult()).isNull();
    }
  }

  @Test
  public void testForLoopBadSyntax() throws Exception {
    setFailFast(false);
    parseFile("[1 for (a, b, c in var]\n");
    assertContainsError("syntax error");
  }

  @Test
  public void testForLoopBadSyntax2() throws Exception {
    setFailFast(false);
    parseFile("[1 for in var]\n");
    assertContainsError("syntax error");
  }

  @Test
  public void testFunCallBadSyntax() throws Exception {
    setFailFast(false);
    parseFile("f(1,\n");
    assertContainsError("syntax error");
  }

  @Test
  public void testFunCallBadSyntax2() throws Exception {
    setFailFast(false);
    parseFile("f(1, 5, ,)\n");
    assertContainsError("syntax error");
  }

  @Test
  public void testLoadNoSymbol() throws Exception {
    setFailFast(false);
    parseFile("load('//foo/bar:file.bzl')\n");
    assertContainsError("expected at least one symbol to load");
  }

  @Test
  public void testLoadOneSymbol() throws Exception {
    String text = "load('//foo/bar:file.bzl', 'fun_test')\n";
    List<Statement> statements = parseStatements(text);
    LoadStatement stmt = (LoadStatement) statements.get(0);
    assertThat(stmt.getImport().getValue()).isEqualTo("//foo/bar:file.bzl");
    assertThat(stmt.getBindings()).hasSize(1);
    Identifier sym = stmt.getBindings().get(0).getLocalName();
    assertThat(getText(text, sym)).isEqualTo("fun_test"); // apparent location within string literal
  }

  @Test
  public void testLoadOneSymbolWithTrailingComma() throws Exception {
    List<Statement> statements = parseStatements("load('//foo/bar:file.bzl', 'fun_test',)\n");
    LoadStatement stmt = (LoadStatement) statements.get(0);
    assertThat(stmt.getImport().getValue()).isEqualTo("//foo/bar:file.bzl");
    assertThat(stmt.getBindings()).hasSize(1);
  }

  @Test
  public void testLoadMultipleSymbols() throws Exception {
    List<Statement> statements = parseStatements("load(':file.bzl', 'foo', 'bar')\n");
    LoadStatement stmt = (LoadStatement) statements.get(0);
    assertThat(stmt.getImport().getValue()).isEqualTo(":file.bzl");
    assertThat(stmt.getBindings()).hasSize(2);
  }

  @Test
  public void testLoadLabelQuoteError() throws Exception {
    setFailFast(false);
    parseFile("load(non_quoted, 'a')\n");
    assertContainsError("syntax error");
  }

  @Test
  public void testLoadSymbolQuoteError() throws Exception {
    setFailFast(false);
    parseFile("load('label', non_quoted)\n");
    assertContainsError("syntax error");
  }

  @Test
  public void testLoadDisallowSameLine() throws Exception {
    setFailFast(false);
    parseFile("load('foo.bzl', 'foo') load('bar.bzl', 'bar')");
    assertContainsError("syntax error");
  }

  @Test
  public void testLoadNotAtTopLevel() throws Exception {
    // "This is not a parse error." --Magritte
    parseFile("if 1: load('', 'x')\n");
  }

  @Test
  public void testLoadModuleNotStringLiteral() throws Exception {
    setFailFast(false);
    parseFile("load(123, 'x')");
    assertContainsError("syntax error at '123': expected string literal");
  }

  @Test
  public void testLoadAlias() throws Exception {
    List<Statement> statements = parseStatements("load('//foo/bar:file.bzl', my_alias = 'lawl')\n");
    LoadStatement stmt = (LoadStatement) statements.get(0);
    ImmutableList<LoadStatement.Binding> actualSymbols = stmt.getBindings();

    assertThat(actualSymbols).hasSize(1);
    Identifier sym = actualSymbols.get(0).getLocalName();
    assertThat(sym.getName()).isEqualTo("my_alias");
    int startOffset = sym.getStartOffset();
    assertWithMessage("getStartOffset()").that(startOffset).isEqualTo(27);
    assertWithMessage("getEndOffset()").that(sym.getEndOffset()).isEqualTo(startOffset + 8);
  }

  @Test
  public void testLoadAliasMultiple() throws Exception {
    runLoadAliasTestForSymbols(
        "my_alias = 'lawl', 'lol', next_alias = 'rofl'", "my_alias", "lol", "next_alias");
  }

  private void runLoadAliasTestForSymbols(String loadSymbolString, String... expectedSymbols)
      throws SyntaxError.Exception {
    List<Statement> statements =
        parseStatements(String.format("load('//foo/bar:file.bzl', %s)\n", loadSymbolString));
    LoadStatement stmt = (LoadStatement) statements.get(0);

    List<String> actualSymbolNames = new ArrayList<>();
    for (LoadStatement.Binding binding : stmt.getBindings()) {
      actualSymbolNames.add(binding.getLocalName().getName());
    }
    assertThat(actualSymbolNames).containsExactly((Object[]) expectedSymbols);
  }

  @Test
  public void testLoadAliasSyntaxError() throws Exception {
    setFailFast(false);
    parseFile("load('//foo:bzl', test1 = )\n");
    assertContainsError("syntax error at ')': expected string");

    parseFile("load(':foo.bzl', test2 = 1)\n");
    assertContainsError("syntax error at '1': expected string");

    parseFile("load(':foo.bzl', test3 = old)\n");
    assertContainsError("syntax error at 'old': expected string");
  }

  @Test
  public void testLoadIsASmallStatement() throws Exception {
    // Regression test for b/148802200.
    parseFile("a=1; load('file', 'b'); c=3");
  }

  @Test
  public void testParseErrorNotComparison() throws Exception {
    setFailFast(false);
    parseFile("2 < not 3");
    assertContainsError("syntax error at 'not'");
  }

  @Test
  public void testNotWithArithmeticOperatorsBadSyntax() throws Exception {
    setFailFast(false);
    parseFile("0 + not 0");
    assertContainsError("syntax error at 'not'");
  }

  @Test
  public void testElseWithoutIf() throws Exception {
    setFailFast(false);
    parseFile(
        "def func(a):",
        // no if
        "  else: return a");
    assertContainsError("syntax error at 'else': expected expression");
  }

  @Test
  public void testForElse() throws Exception {
    setFailFast(false);
    parseFile(
        "def func(a):", //
        "  for i in range(a):",
        "    print(i)",
        "  else: return a");
    assertContainsError("syntax error at 'else': expected expression");
  }

  @Test
  public void testTryStatementInBuild() throws Exception {
    setFailFast(false);
    parseFile("try: pass");
    assertContainsError("'try' not supported, all exceptions are fatal");
  }

  @Test
  public void testClassDefinitionInBuild() throws Exception {
    setFailFast(false);
    parseFile("class test(object): pass");
    assertContainsError("keyword 'class' not supported");
  }

  @Test
  public void testClassDefinitionInStarlark() throws Exception {
    setFailFast(false);
    parseFile("class test(object): pass");
    assertContainsError("keyword 'class' not supported");
  }


  @Test
  public void testStringsAreDeduped() throws Exception {
    StarlarkFile file = parseFile("L1 = ['cat', 'dog', 'fish']", "L2 = ['dog', 'fish', 'cat']");
    Set<String> uniqueStringInstances = Sets.newIdentityHashSet();
    NodeVisitor collectAllStringsInStringLiteralsVisitor =
        new NodeVisitor() {
          @Override
          public void visit(StringLiteral stringLiteral) {
            uniqueStringInstances.add(stringLiteral.getValue());
          }
        };
    collectAllStringsInStringLiteralsVisitor.visit(file);
    assertThat(uniqueStringInstances).containsExactly("cat", "dog", "fish");
  }

  @Test
  public void testConditionalExpressions() throws Exception {
    assertThat(parseExpressionError("1 if 2"))
        .contains("missing else clause in conditional expression or semicolon before if");
  }

  @Test
  public void testParseFileStackOverflow() throws Exception {
    StarlarkFile file = StarlarkFile.parse(veryDeepExpression());
    SyntaxError ex = LexerTest.assertContainsError(file.errors(), "internal error: stack overflow");
    assertThat(ex.message()).contains("parseDictEntry"); // includes stack
    assertThat(ex.message()).contains("Please report the bug");
    assertThat(ex.message()).contains("include the text of foo.star"); // includes file name
  }

  @Test
  public void testParseExpressionStackOverflow() throws Exception {
    SyntaxError.Exception ex =
        assertThrows(SyntaxError.Exception.class, () -> Expression.parse(veryDeepExpression()));
    SyntaxError err = LexerTest.assertContainsError(ex.errors(), "internal error: stack overflow");
    assertThat(err.message()).contains("parseDictEntry"); // includes stack
    assertThat(err.message())
        .contains("while parsing Starlark expression <<{{{{"); // includes expression
    assertThat(err.message()).contains("Please report the bug");
  }

  private static ParserInput veryDeepExpression() {
    StringBuilder s = new StringBuilder();
    for (int i = 0; i < 1000; i++) {
      s.append("{");
    }
    return ParserInput.fromString(s.toString(), "foo.star");
  }
}