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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.devtools.build.lib.syntax.compiler.ByteCodeUtils;
import com.google.devtools.build.lib.syntax.compiler.DebugInfo;
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.VariableScope;
import net.bytebuddy.implementation.bytecode.ByteCodeAppender;
import java.util.ArrayList;
import java.util.List;
/**
* Syntax node for an if/else expression.
*/
public final class ConditionalExpression extends Expression {
// Python conditional expressions: $thenCase if $condition else $elseCase
// https://docs.python.org/3.5/reference/expressions.html#conditional-expressions
private final Expression thenCase;
private final Expression condition;
private final Expression elseCase;
public Expression getThenCase() { return thenCase; }
public Expression getCondition() { return condition; }
public Expression getElseCase() { return elseCase; }
/**
* Constructor for a conditional expression
*/
public ConditionalExpression(
Expression thenCase, Expression condition, Expression elseCase) {
this.thenCase = thenCase;
this.condition = condition;
this.elseCase = elseCase;
}
/**
* Constructs a string representation of the if expression
*/
@Override
public String toString() {
return thenCase + " if " + condition + " else " + elseCase;
}
@Override
Object doEval(Environment env) throws EvalException, InterruptedException {
if (EvalUtils.toBoolean(condition.eval(env))) {
return thenCase.eval(env);
} else {
return elseCase.eval(env);
}
}
@Override
public void accept(SyntaxTreeVisitor visitor) {
visitor.visit(this);
}
@Override
void validate(ValidationEnvironment env) throws EvalException {
condition.validate(env);
thenCase.validate(env);
elseCase.validate(env);
}
@Override
ByteCodeAppender compile(VariableScope scope, DebugInfo debugInfo) throws EvalException {
List<ByteCodeAppender> code = new ArrayList<>();
LabelAdder afterLabel = new LabelAdder();
LabelAdder elseLabel = new LabelAdder();
// compile condition and convert to boolean
code.add(condition.compile(scope, debugInfo));
append(
code,
EvalUtils.toBoolean,
// jump to else block if false
Jump.ifIntOperandToZero(PrimitiveComparison.EQUAL).to(elseLabel));
// otherwise evaluate the expression for "then" and jump to end
code.add(thenCase.compile(scope, debugInfo));
append(
code,
Jump.to(afterLabel),
// add label for "else" and evaluate the expression
elseLabel);
code.add(elseCase.compile(scope, debugInfo));
append(code, afterLabel);
return ByteCodeUtils.compoundAppender(code);
}
}
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