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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.query2.engine;
import java.util.Collection;
import java.util.Set;
import java.util.regex.Pattern;
/**
* A let expression.
*
* <pre>expr ::= LET WORD = expr IN expr</pre>
*/
class LetExpression extends QueryExpression {
private static final String VAR_NAME_PATTERN = "[a-zA-Z_][a-zA-Z0-9_]*$";
// Variables names may be any legal identifier in the C programming language
private static final Pattern NAME_PATTERN = Pattern.compile("^" + VAR_NAME_PATTERN);
// Variable references are prepended with the "$" character.
// A variable named "x" is referenced as "$x".
private static final Pattern REF_PATTERN = Pattern.compile("^\\$" + VAR_NAME_PATTERN);
static boolean isValidVarReference(String varName) {
return REF_PATTERN.matcher(varName).matches();
}
static String getNameFromReference(String reference) {
return reference.substring(1);
}
private final String varName;
private final QueryExpression varExpr;
private final QueryExpression bodyExpr;
LetExpression(String varName, QueryExpression varExpr, QueryExpression bodyExpr) {
this.varName = varName;
this.varExpr = varExpr;
this.bodyExpr = bodyExpr;
}
@Override
public <T> Set<T> eval(QueryEnvironment<T> env) throws QueryException, InterruptedException {
if (!NAME_PATTERN.matcher(varName).matches()) {
throw new QueryException(this, "invalid variable name '" + varName + "' in let expression");
}
Set<T> varValue = varExpr.eval(env);
Set<T> prevValue = env.setVariable(varName, varValue);
try {
return bodyExpr.eval(env);
} finally {
env.setVariable(varName, prevValue); // restore
}
}
@Override
public void collectTargetPatterns(Collection<String> literals) {
varExpr.collectTargetPatterns(literals);
bodyExpr.collectTargetPatterns(literals);
}
@Override
public String toString() {
return "let " + varName + " = " + varExpr + " in " + bodyExpr;
}
}
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