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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.devtools.build.lib.events.Event;
import com.google.devtools.build.lib.events.EventHandler;
import com.google.devtools.build.lib.events.Location;
import com.google.devtools.build.lib.util.Preconditions;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import javax.annotation.Nullable;
/**
* An Environment for the semantic checking of Skylark files.
*
* @see Statement#validate
* @see Expression#validate
*/
public final class ValidationEnvironment {
private class Scope {
private final Set<String> variables = new HashSet<>();
private final Set<String> readOnlyVariables = new HashSet<>();
@Nullable private final Scope parent;
Scope(@Nullable Scope parent) {
this.parent = parent;
}
}
private final SkylarkSemanticsOptions semantics;
private Scope scope;
/** Create a ValidationEnvironment for a given global Environment. */
ValidationEnvironment(Environment env) {
Preconditions.checkArgument(env.isGlobal());
scope = new Scope(null);
Set<String> builtinVariables = env.getVariableNames();
scope.variables.addAll(builtinVariables);
scope.readOnlyVariables.addAll(builtinVariables);
semantics = env.getSemantics();
}
/** Returns true if this ValidationEnvironment is top level i.e. has no parent. */
boolean isTopLevel() {
return scope.parent == null;
}
SkylarkSemanticsOptions getSemantics() {
return semantics;
}
/** Declare a variable and add it to the environment. */
void declare(String varname, Location location) throws EvalException {
checkReadonly(varname, location);
if (scope.parent == null) { // top-level values are immutable
scope.readOnlyVariables.add(varname);
}
scope.variables.add(varname);
}
private void checkReadonly(String varname, Location location) throws EvalException {
if (scope.readOnlyVariables.contains(varname)) {
throw new EvalException(
location,
String.format("Variable %s is read only", varname),
"https://bazel.build/versions/master/docs/skylark/errors/read-only-variable.html");
}
}
/** Returns true if the symbol exists in the validation environment (or a parent). */
boolean hasSymbolInEnvironment(String varname) {
for (Scope s = scope; s != null; s = s.parent) {
if (s.variables.contains(varname)) {
return true;
}
}
return false;
}
/** Returns the set of all accessible symbols (both local and global) */
Set<String> getAllSymbols() {
Set<String> all = new HashSet<>();
for (Scope s = scope; s != null; s = s.parent) {
all.addAll(s.variables);
}
return all;
}
/** Throws EvalException if a load() appears after another kind of statement. */
private static void checkLoadAfterStatement(List<Statement> statements) throws EvalException {
Location firstStatement = null;
for (Statement statement : statements) {
// Ignore string literals (e.g. docstrings).
if (statement instanceof ExpressionStatement
&& ((ExpressionStatement) statement).getExpression() instanceof StringLiteral) {
continue;
}
if (statement instanceof LoadStatement) {
if (firstStatement == null) {
continue;
}
throw new EvalException(
statement.getLocation(),
"load() statements must be called before any other statement. "
+ "First non-load() statement appears at "
+ firstStatement
+ ". Use --incompatible_bzl_disallow_load_after_statement=false to temporarily "
+ "disable this check.");
}
if (firstStatement == null) {
firstStatement = statement.getLocation();
}
}
}
/** Throws EvalException if a `if` statement appears at the top level. */
private static void checkToplevelIfStatement(List<Statement> statements) throws EvalException {
for (Statement statement : statements) {
if (statement instanceof IfStatement) {
throw new EvalException(
statement.getLocation(),
"if statements are not allowed at the top level. You may move it inside a function "
+ "or use an if expression (x if condition else y). "
+ "Use --incompatible_disallow_toplevel_if_statement=false to temporarily disable "
+ "this check.");
}
}
}
/** Validates the AST and runs static checks. */
void validateAst(List<Statement> statements) throws EvalException {
// Check that load() statements are on top.
if (semantics.incompatibleBzlDisallowLoadAfterStatement) {
checkLoadAfterStatement(statements);
}
// Check that load() statements are on top.
if (semantics.incompatibleDisallowToplevelIfStatement) {
checkToplevelIfStatement(statements);
}
// 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.getIdentifier().getName(), fct.getLocation());
}
}
for (Statement statement : statements) {
statement.validate(this);
}
}
public static void validateAst(Environment env, List<Statement> statements) throws EvalException {
ValidationEnvironment venv = new ValidationEnvironment(env);
venv.validateAst(statements);
// Check that no closeScope was forgotten.
Preconditions.checkState(venv.scope.parent == null);
}
public static boolean validateAst(
Environment env, List<Statement> statements, EventHandler eventHandler) {
try {
validateAst(env, statements);
return true;
} catch (EvalException e) {
if (!e.isDueToIncompleteAST()) {
eventHandler.handle(Event.error(e.getLocation(), e.getMessage()));
}
return false;
}
}
/** Open a new scope that will contain the future declarations. */
public void openScope() {
this.scope = new Scope(this.scope);
}
/** Close a scope (and lose all declarations it contained). */
public void closeScope() {
this.scope = Preconditions.checkNotNull(this.scope.parent);
}
}
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