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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 com.google.common.base.Preconditions;
import com.google.devtools.build.lib.events.Location;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.Stack;
/**
* An Environment for the semantic checking of Skylark files.
*
* @see Statement#validate
* @see Expression#validate
*/
public final class ValidationEnvironment {
private final ValidationEnvironment parent;
private Set<String> variables = new HashSet<>();
private Map<String, Location> variableLocations = new HashMap<>();
private Set<String> readOnlyVariables = new HashSet<>();
// A stack of variable-sets which are read only but can be assigned in different
// branches of if-else statements.
private Stack<Set<String>> futureReadOnlyVariables = new Stack<>();
/**
* Tracks the number of nested for loops that contain the statement that is currently being
* validated
*/
private int loopCount = 0;
/**
* Create a ValidationEnvironment for a given global Environment.
*/
public ValidationEnvironment(Environment env) {
Preconditions.checkArgument(env.isGlobal());
parent = null;
Set<String> builtinVariables = env.getVariableNames();
variables.addAll(builtinVariables);
readOnlyVariables.addAll(builtinVariables);
}
/**
* Creates a local ValidationEnvironment to validate user defined function bodies.
*/
public ValidationEnvironment(ValidationEnvironment parent) {
// Don't copy readOnlyVariables: Variables may shadow global values.
this.parent = parent;
}
/**
* Returns true if this ValidationEnvironment is top level i.e. has no parent.
*/
public boolean isTopLevel() {
return parent == null;
}
/**
* Declare a variable and add it to the environment.
*/
public void declare(String varname, Location location)
throws EvalException {
checkReadonly(varname, location);
if (parent == null) { // top-level values are immutable
readOnlyVariables.add(varname);
if (!futureReadOnlyVariables.isEmpty()) {
// Currently validating an if-else statement
futureReadOnlyVariables.peek().add(varname);
}
}
variables.add(varname);
variableLocations.put(varname, location);
}
private void checkReadonly(String varname, Location location) throws EvalException {
if (readOnlyVariables.contains(varname)) {
throw new EvalException(location, String.format("Variable %s is read only", varname));
}
}
/**
* Returns true if the symbol exists in the validation environment.
*/
public boolean hasSymbolInEnvironment(String varname) {
return variables.contains(varname)
|| (parent != null && topLevel().variables.contains(varname));
}
private ValidationEnvironment topLevel() {
return Preconditions.checkNotNull(parent == null ? this : parent);
}
/**
* Starts a session with temporarily disabled readonly checking for variables between branches.
* This is useful to validate control flows like if-else when we know that certain parts of the
* code cannot both be executed.
*/
public void startTemporarilyDisableReadonlyCheckSession() {
futureReadOnlyVariables.add(new HashSet<String>());
}
/**
* Finishes the session with temporarily disabled readonly checking.
*/
public void finishTemporarilyDisableReadonlyCheckSession() {
Set<String> variables = futureReadOnlyVariables.pop();
readOnlyVariables.addAll(variables);
if (!futureReadOnlyVariables.isEmpty()) {
futureReadOnlyVariables.peek().addAll(variables);
}
}
/**
* Finishes a branch of temporarily disabled readonly checking.
*/
public void finishTemporarilyDisableReadonlyCheckBranch() {
readOnlyVariables.removeAll(futureReadOnlyVariables.peek());
}
/**
* Validates the AST and runs static checks.
*/
public void validateAst(List<Statement> statements) throws EvalException {
// Add every function in the environment before validating. This is
// necessary because functions may call other functions defined
// later in the file.
for (Statement statement : statements) {
if (statement instanceof FunctionDefStatement) {
FunctionDefStatement fct = (FunctionDefStatement) statement;
declare(fct.getIdent().getName(), fct.getLocation());
}
}
for (Statement statement : statements) {
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;
}
}
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