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// 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.devtools.build.lib.syntax.compiler.ByteCodeUtils.append;
import com.google.common.base.Optional;
import com.google.common.collect.ImmutableList;
import com.google.devtools.build.lib.syntax.FlowStatement.FlowException;
import com.google.devtools.build.lib.syntax.compiler.ByteCodeMethodCalls;
import com.google.devtools.build.lib.syntax.compiler.ByteCodeUtils;
import com.google.devtools.build.lib.syntax.compiler.DebugInfo;
import com.google.devtools.build.lib.syntax.compiler.DebugInfo.AstAccessors;
import com.google.devtools.build.lib.syntax.compiler.IntegerVariableIncrease;
import com.google.devtools.build.lib.syntax.compiler.Jump;
import com.google.devtools.build.lib.syntax.compiler.Jump.PrimitiveComparison;
import com.google.devtools.build.lib.syntax.compiler.LabelAdder;
import com.google.devtools.build.lib.syntax.compiler.LoopLabels;
import com.google.devtools.build.lib.syntax.compiler.Variable.InternalVariable;
import com.google.devtools.build.lib.syntax.compiler.VariableScope;
import com.google.devtools.build.lib.util.Preconditions;
import net.bytebuddy.description.type.TypeDescription;
import net.bytebuddy.implementation.bytecode.ByteCodeAppender;
import net.bytebuddy.implementation.bytecode.Duplication;
import net.bytebuddy.implementation.bytecode.constant.IntegerConstant;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
/**
* Syntax node for a for loop statement.
*/
public final class ForStatement extends Statement {
private final LValue variable;
private final Expression collection;
private final ImmutableList<Statement> block;
/**
* Constructs a for loop statement.
*/
ForStatement(Expression variable, Expression collection, List<Statement> block) {
this.variable = new LValue(Preconditions.checkNotNull(variable));
this.collection = Preconditions.checkNotNull(collection);
this.block = ImmutableList.copyOf(block);
}
public LValue getVariable() {
return variable;
}
/**
* @return The collection we iterate on, e.g. `col` in `for x in col:`
*/
public Expression getCollection() {
return collection;
}
public ImmutableList<Statement> block() {
return block;
}
@Override
public String toString() {
// TODO(bazel-team): if we want to print the complete statement, the function
// needs an extra argument to specify indentation level.
return "for " + variable + " in " + collection + ": ...\n";
}
@Override
void doExec(Environment env) throws EvalException, InterruptedException {
Object o = collection.eval(env);
Iterable<?> col = EvalUtils.toIterable(o, getLocation());
EvalUtils.lock(o, getLocation());
try {
for (Object it : col) {
variable.assign(env, getLocation(), it);
try {
for (Statement stmt : block) {
stmt.exec(env);
}
} catch (FlowException ex) {
if (ex.mustTerminateLoop()) {
return;
}
}
}
} finally {
EvalUtils.unlock(o, getLocation());
}
}
@Override
public void accept(SyntaxTreeVisitor visitor) {
visitor.visit(this);
}
@Override
void validate(ValidationEnvironment env) throws EvalException {
if (env.isTopLevel()) {
throw new EvalException(getLocation(), "'For' is not allowed as a top level statement");
}
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());
}
}
@Override
ByteCodeAppender compile(
VariableScope scope, Optional<LoopLabels> outerLoopLabels, DebugInfo debugInfo)
throws EvalException {
// TODO(bazel-team): Remove obsolete logic for counting size of iterated collection.
AstAccessors debugAccessors = debugInfo.add(this);
List<ByteCodeAppender> code = new ArrayList<>();
InternalVariable originalIterable =
scope.freshVariable(new TypeDescription.ForLoadedType(Iterable.class));
InternalVariable iterator =
scope.freshVariable(new TypeDescription.ForLoadedType(Iterator.class));
// compute the collection and get it on the stack and transform it to the right type
code.add(collection.compile(scope, debugInfo));
append(code, debugAccessors.loadLocation, EvalUtils.toIterable, Duplication.SINGLE);
// save it for later concurrent modification check
code.add(originalIterable.store());
append(
code,
ByteCodeMethodCalls.BCImmutableList.copyOf,
ByteCodeMethodCalls.BCImmutableList.iterator);
code.add(iterator.store());
// for counting the size during the loop
InternalVariable sizeCounterVariable =
scope.freshVariable(new TypeDescription.ForLoadedType(int.class));
LabelAdder loopHeader = new LabelAdder();
LabelAdder loopBody = new LabelAdder();
LabelAdder breakLoop = new LabelAdder();
// for passing on the labels for continue/break statements
Optional<LoopLabels> loopLabels = LoopLabels.of(loopHeader.getLabel(), breakLoop.getLabel());
append(
code,
// initialize loop counter
IntegerConstant.ZERO);
code.add(sizeCounterVariable.store());
append(code, Jump.to(loopHeader), loopBody, iterator.load());
append(code, ByteCodeMethodCalls.BCIterator.next);
// store current element into l-value
code.add(variable.compileAssignment(this, debugAccessors, scope));
// compile code for the body
for (Statement statement : block) {
append(code, new IntegerVariableIncrease(sizeCounterVariable, 1));
code.add(statement.compile(scope, loopLabels, debugInfo));
}
// compile code for the loop header
append(
code,
loopHeader,
iterator.load(),
ByteCodeMethodCalls.BCIterator.hasNext,
// falls through to end of loop if hasNext() was false, otherwise jumps back
Jump.ifIntOperandToZero(PrimitiveComparison.NOT_EQUAL).to(loopBody),
breakLoop);
return ByteCodeUtils.compoundAppender(code);
}
}
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