Skylark: implemented 'break' and 'continue'
Fixes #233.
https://github.com/google/bazel/issues/233
--
MOS_MIGRATED_REVID=95632067
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/FlowStatement.java b/src/main/java/com/google/devtools/build/lib/syntax/FlowStatement.java
new file mode 100644
index 0000000..127b366
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/syntax/FlowStatement.java
@@ -0,0 +1,86 @@
+// Copyright 2014 Google Inc. 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;
+
+/**
+ * A class for flow statements (e.g. break and continue)
+ */
+public final class FlowStatement extends Statement {
+
+ public static final FlowStatement BREAK = new FlowStatement("break", true);
+ public static final FlowStatement CONTINUE = new FlowStatement("continue", false);
+
+ private final String name;
+ private final FlowException ex;
+
+ /**
+ *
+ * @param name The label of the statement (either break or continue)
+ * @param terminateLoop Determines whether the enclosing loop should be terminated completely
+ * (break)
+ */
+ protected FlowStatement(String name, boolean terminateLoop) {
+ this.name = name;
+ this.ex = new FlowException(terminateLoop);
+ }
+
+ @Override
+ void exec(Environment env) throws EvalException {
+ throw ex;
+ }
+
+ @Override
+ void validate(ValidationEnvironment env) throws EvalException {
+ if (!env.isInsideLoop()) {
+ throw new EvalException(getLocation(), name + " statement must be inside a for loop");
+ }
+ }
+
+ @Override
+ public String toString() {
+ return name;
+ }
+
+ @Override
+ public void accept(SyntaxTreeVisitor visitor) {
+ visitor.visit(this);
+ }
+
+ /**
+ * An exception that signals changes in the control flow (e.g. break or continue)
+ */
+ class FlowException extends EvalException {
+ private final boolean terminateLoop;
+
+ /**
+ *
+ * @param terminateLoop Determines whether the enclosing loop should be terminated completely
+ * (break)
+ */
+ public FlowException(boolean terminateLoop) {
+ super(FlowStatement.this.getLocation(), "FlowException with terminateLoop = "
+ + terminateLoop);
+ this.terminateLoop = terminateLoop;
+ }
+
+ /**
+ * Returns whether the enclosing loop should be terminated completely (break)
+ *
+ * @return {@code True} for 'break', {@code false} for 'continue'
+ */
+ public boolean mustTerminateLoop() {
+ return terminateLoop;
+ }
+ }
+}
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/ForStatement.java b/src/main/java/com/google/devtools/build/lib/syntax/ForStatement.java
index 054b21f..1660ce1 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/ForStatement.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/ForStatement.java
@@ -15,6 +15,7 @@
import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableList;
+import com.google.devtools.build.lib.syntax.FlowStatement.FlowException;
import java.util.List;
@@ -63,11 +64,20 @@
int i = 0;
for (Object it : ImmutableList.copyOf(col)) {
variable.assign(env, getLocation(), it);
- for (Statement stmt : block) {
- stmt.exec(env);
+
+ try {
+ for (Statement stmt : block) {
+ stmt.exec(env);
+ }
+ } catch (FlowException ex) {
+ if (ex.mustTerminateLoop()) {
+ return;
+ }
}
+
i++;
}
+
// TODO(bazel-team): This should not happen if every collection is immutable.
if (i != EvalUtils.size(col)) {
throw new EvalException(getLocation(),
@@ -83,14 +93,20 @@
@Override
void validate(ValidationEnvironment env) throws EvalException {
if (env.isTopLevel()) {
- throw new EvalException(getLocation(),
- "'For' is not allowed as a top level statement");
+ throw new EvalException(getLocation(), "'For' is not allowed as a top level statement");
}
- // TODO(bazel-team): validate variable. Maybe make it temporarily readonly.
- collection.validate(env);
- variable.validate(env, getLocation());
- for (Statement stmt : block) {
- stmt.validate(env);
+ env.enterLoop();
+
+ try {
+ // TODO(bazel-team): validate variable. Maybe make it temporarily readonly.
+ collection.validate(env);
+ variable.validate(env, getLocation());
+
+ for (Statement stmt : block) {
+ stmt.validate(env);
+ }
+ } finally {
+ env.exitLoop(getLocation());
}
}
}
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Parser.java b/src/main/java/com/google/devtools/build/lib/syntax/Parser.java
index c264259..71277a0 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/Parser.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/Parser.java
@@ -336,7 +336,7 @@
// Keywords that exist in Python and that we don't parse.
private static final EnumSet<TokenKind> FORBIDDEN_KEYWORDS =
- EnumSet.of(TokenKind.AS, TokenKind.ASSERT, TokenKind.BREAK, TokenKind.CONTINUE,
+ EnumSet.of(TokenKind.AS, TokenKind.ASSERT,
TokenKind.DEL, TokenKind.EXCEPT, TokenKind.FINALLY, TokenKind.FROM, TokenKind.GLOBAL,
TokenKind.IMPORT, TokenKind.IS, TokenKind.LAMBDA, TokenKind.NONLOCAL, TokenKind.RAISE,
TokenKind.TRY, TokenKind.WITH, TokenKind.WHILE, TokenKind.YIELD);
@@ -1154,6 +1154,7 @@
// small_stmt ::= assign_stmt
// | expr
// | RETURN expr
+ // | flow_stmt
// assign_stmt ::= expr ('=' | augassign) expr
// augassign ::= ('+=' )
// Note that these are in Python, but not implemented here (at least for now):
@@ -1171,6 +1172,8 @@
int start = token.left;
if (token.kind == TokenKind.RETURN) {
return parseReturnStatement();
+ } else if (token.kind == TokenKind.BREAK || token.kind == TokenKind.CONTINUE) {
+ return parseFlowStatement(token.kind);
}
Expression expression = parseExpression();
if (token.kind == TokenKind.EQUALS) {
@@ -1408,6 +1411,12 @@
}
}
+ // flow_stmt ::= break_stmt | continue_stmt
+ private FlowStatement parseFlowStatement(TokenKind kind) {
+ expect(kind);
+ return (kind == TokenKind.BREAK) ? FlowStatement.BREAK : FlowStatement.CONTINUE;
+ }
+
// return_stmt ::= RETURN expr
private ReturnStatement parseReturnStatement() {
int start = token.left;
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/ValidationEnvironment.java b/src/main/java/com/google/devtools/build/lib/syntax/ValidationEnvironment.java
index a615d67..7aedca2 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/ValidationEnvironment.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/ValidationEnvironment.java
@@ -47,6 +47,12 @@
// Whether this validation environment is not modified therefore clonable or not.
private boolean clonable;
+
+ /**
+ * Tracks the number of nested for loops that contain the statement that is currently being
+ * validated
+ */
+ private int loopCount = 0;
public ValidationEnvironment(Set<String> builtinVariables) {
parent = null;
@@ -174,4 +180,33 @@
statement.validate(this);
}
}
+
+ /**
+ * Returns whether the current statement is inside a for loop (either in this environment or one
+ * of its parents)
+ *
+ * @return True if the current statement is inside a for loop
+ */
+ public boolean isInsideLoop() {
+ return (loopCount > 0);
+ }
+
+ /**
+ * Signals that the block of a for loop was entered
+ */
+ public void enterLoop() {
+ ++loopCount;
+ }
+
+ /**
+ * Signals that the block of a for loop was left
+ *
+ * @param location The current location
+ * @throws EvalException If there was no corresponding call to
+ * {@code ValidationEnvironment#enterLoop}
+ */
+ public void exitLoop(Location location) throws EvalException {
+ Preconditions.checkState(loopCount > 0);
+ --loopCount;
+ }
}
