src/main/java/com/google/devtools/build/lib/syntax/ValidationEnvironment.java - bazel - Git at Google

 // 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.Event;
 import com.google.devtools.build.lib.events.EventHandler;
 import com.google.devtools.build.lib.events.Location;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 import javax.annotation.Nullable;

 /**
  * A class for doing static checks on files, before evaluating them.
  *
  * <p>We implement the semantics discussed in
  * https://github.com/bazelbuild/proposals/blob/master/docs/2018-06-18-name-resolution.md
  *
  * <p>When a variable is defined, it is visible in the entire block. For example, a global variable
  * is visible in the entire file; a variable in a function is visible in the entire function block
  * (even on the lines before its first assignment).
  */
 // TODO(adonovan): make this class private. Call it through the EvalUtils facade.
 public final class ValidationEnvironment extends NodeVisitor {

   enum Scope {
     /** Symbols defined inside a function or a comprehension. */
     Local("local"),
     /** Symbols defined at a module top-level, e.g. functions, loaded symbols. */
     Module("global"),
     /** Predefined symbols (builtins) */
     Universe("builtin");

     private final String qualifier;

     private Scope(String qualifier) {
       this.qualifier = qualifier;
     }

     String getQualifier() {
       return qualifier;
     }
   }

   private static class Block {
     private final Set<String> variables = new HashSet<>();
     private final Scope scope;
     @Nullable private final Block parent;

     Block(Scope scope, @Nullable Block parent) {
       this.scope = scope;
       this.parent = parent;
     }
   }

   /**
    * We use an unchecked exception around EvalException because the NodeVisitor doesn't let visit
    * methods throw checked exceptions. We might change that later.
    */
   private static class ValidationException extends RuntimeException {
     EvalException exception;

     ValidationException(EvalException e) {
       exception = e;
     }

     ValidationException(Location location, String message, String url) {
       exception = new EvalException(location, message, url);
     }

     ValidationException(Location location, String message) {
       exception = new EvalException(location, message);
     }
   }

   private final Environment env;
   private Block block;
   private int loopCount;
   /** In BUILD files, we have a slightly different behavior for legacy reasons. */
   private final boolean isBuildFile;

   /** Create a ValidationEnvironment for a given global Environment (containing builtins). */
   private ValidationEnvironment(Environment env, boolean isBuildFile) {
     Preconditions.checkArgument(env.isGlobal());
     this.env = env;
     this.isBuildFile = isBuildFile;
     block = new Block(Scope.Universe, null);
     Set<String> builtinVariables = env.getVariableNames();
     block.variables.addAll(builtinVariables);
   }

   /**
    * First pass: add all definitions to the current block. This is done because symbols are
    * sometimes used before their definition point (e.g. a functions are not necessarily declared in
    * order).
    */
   private void collectDefinitions(Iterable<Statement> stmts) {
     for (Statement stmt : stmts) {
       collectDefinitions(stmt);
     }
   }

   private void collectDefinitions(Statement stmt) {
     switch (stmt.kind()) {
       case ASSIGNMENT:
         collectDefinitions(((AssignmentStatement) stmt).getLHS());
         break;
       case AUGMENTED_ASSIGNMENT:
         collectDefinitions(((AugmentedAssignmentStatement) stmt).getLHS());
         break;
       case IF:
         IfStatement ifStmt = (IfStatement) stmt;
         for (IfStatement.ConditionalStatements cond : ifStmt.getThenBlocks()) {
           collectDefinitions(cond.getStatements());
         }
         collectDefinitions(ifStmt.getElseBlock());
         break;
       case FOR:
         ForStatement forStmt = (ForStatement) stmt;
         collectDefinitions(forStmt.getLHS());
         collectDefinitions(forStmt.getBlock());
         break;
       case FUNCTION_DEF:
         Identifier fctName = ((DefStatement) stmt).getIdentifier();
         declare(fctName.getName(), fctName.getLocation());
         break;
       case LOAD:
         for (LoadStatement.Binding binding : ((LoadStatement) stmt).getBindings()) {
           declare(binding.getLocalName().getName(), binding.getLocalName().getLocation());
         }
         break;
       case CONDITIONAL:
       case EXPRESSION:
       case FLOW:
       case RETURN:
         // nothing to declare
     }
   }

   private void collectDefinitions(Expression lhs) {
     for (Identifier id : Identifier.boundIdentifiers(lhs)) {
       declare(id.getName(), id.getLocation());
     }
   }

   private void assign(Expression lhs) {
     if (lhs instanceof Identifier) {
       if (!isBuildFile) {
         ((Identifier) lhs).setScope(block.scope);
       }
       // no-op
     } else if (lhs instanceof IndexExpression) {
       visit(lhs);
     } else if (lhs instanceof ListExpression) {
       for (Expression elem : ((ListExpression) lhs).getElements()) {
         assign(elem);
       }
     } else {
       throw new ValidationException(lhs.getLocation(), "cannot assign to '" + lhs + "'");
     }
   }

   @Override
   public void visit(Identifier node) {
     @Nullable Block b = blockThatDefines(node.getName());
     if (b == null) {
       // The identifier might not exist because it was restricted (hidden) by the current semantics.
       // If this is the case, output a more helpful error message than 'not found'.
       FlagGuardedValue result = env.getRestrictedBindings().get(node.getName());
       if (result != null) {
         throw new ValidationException(
             result.getEvalExceptionFromAttemptingAccess(
                 node.getLocation(), env.getSemantics(), node.getName()));
       }
       throw new ValidationException(Eval.createInvalidIdentifierException(node, getAllSymbols()));
     }
     // TODO(laurentlb): In BUILD files, calling setScope will throw an exception. This happens
     // because some AST nodes are shared across multipe ASTs (due to the prelude file).
     if (!isBuildFile) {
       node.setScope(b.scope);
     }
   }

   @Override
   public void visit(ReturnStatement node) {
     if (block.scope != Scope.Local) {
       throw new ValidationException(
           node.getLocation(), "return statements must be inside a function");
     }
     super.visit(node);
   }

   @Override
   public void visit(ForStatement node) {
     if (block.scope != Scope.Local) {
       throw new ValidationException(
           node.getLocation(),
           "for loops are not allowed at the top level. You may move it inside a function "
               + "or use a comprehension, [f(x) for x in sequence]");
     }
     loopCount++;
     visit(node.getCollection());
     assign(node.getLHS());
     visitBlock(node.getBlock());
     Preconditions.checkState(loopCount > 0);
     loopCount--;
   }

   @Override
   public void visit(LoadStatement node) {
     if (block.scope == Scope.Local) {
       throw new ValidationException(node.getLocation(), "load statement not at top level");
     }
     super.visit(node);
   }

   @Override
   public void visit(FlowStatement node) {
     if (node.getKind() != TokenKind.PASS && loopCount <= 0) {
       throw new ValidationException(
           node.getLocation(),
           node.getKind().toString() + " statement must be inside a for loop");
     }
     super.visit(node);
   }

   @Override
   public void visit(DotExpression node) {
     visit(node.getObject());
     // Do not visit the field.
   }

   @Override
   public void visit(Comprehension node) {
     openBlock(Scope.Local);
     for (Comprehension.Clause clause : node.getClauses()) {
       if (clause instanceof Comprehension.For) {
         Comprehension.For forClause = (Comprehension.For) clause;
         collectDefinitions(forClause.getVars());
       }
     }
     // TODO(adonovan): opt: combine loops
     for (Comprehension.Clause clause : node.getClauses()) {
       if (clause instanceof Comprehension.For) {
         Comprehension.For forClause = (Comprehension.For) clause;
         visit(forClause.getIterable());
         assign(forClause.getVars());
       } else {
         Comprehension.If ifClause = (Comprehension.If) clause;
         visit(ifClause.getCondition());
       }
     }
     visit(node.getBody());
     closeBlock();
   }

   @Override
   public void visit(DefStatement node) {
     if (block.scope == Scope.Local) {
       throw new ValidationException(
           node.getLocation(),
           "nested functions are not allowed. Move the function to the top level.");
     }
     for (Parameter<Expression, Expression> param : node.getParameters()) {
       if (param.isOptional()) {
         visit(param.getDefaultValue());
       }
     }
     openBlock(Scope.Local);
     for (Parameter<Expression, Expression> param : node.getParameters()) {
       if (param.hasName()) {
         declare(param.getName(), param.getLocation());
       }
     }
     collectDefinitions(node.getStatements());
     visitAll(node.getStatements());
     closeBlock();
   }

   @Override
   public void visit(IfStatement node) {
     if (block.scope != Scope.Local) {
       throw new ValidationException(
           node.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).");
     }
     super.visit(node);
   }

   @Override
   public void visit(AssignmentStatement node) {
     visit(node.getRHS());
     assign(node.getLHS());
   }

   @Override
   public void visit(AugmentedAssignmentStatement node) {
     if (node.getLHS() instanceof ListExpression) {
       throw new ValidationException(
           node.getLocation(), "cannot perform augmented assignment on a list or tuple expression");
     }
     // Other bad cases are handled in assign.
     visit(node.getRHS());
     assign(node.getLHS());
   }

   /** Declare a variable and add it to the environment. */
   private void declare(String varname, Location location) {
     // TODO(laurentlb): Forbid reassignment in BUILD files.
     if (!isBuildFile && block.scope == Scope.Module && block.variables.contains(varname)) {
       // Symbols defined in the module scope cannot be reassigned.
       throw new ValidationException(
           location,
           String.format("Variable %s is read only", varname),
           "https://bazel.build/versions/master/docs/skylark/errors/read-only-variable.html");
     }
     block.variables.add(varname);
   }

   /** Returns the nearest Block that defines a symbol. */
   private Block blockThatDefines(String varname) {
     for (Block b = block; b != null; b = b.parent) {
       if (b.variables.contains(varname)) {
         return b;
       }
     }
     return null;
   }

   /** Returns the set of all accessible symbols (both local and global) */
   private Set<String> getAllSymbols() {
     Set<String> all = new HashSet<>();
     for (Block b = block; b != null; b = b.parent) {
       all.addAll(b.variables);
     }
     return all;
   }

   /** Throws ValidationException if a load() appears after another kind of statement. */
   private static void checkLoadAfterStatement(List<Statement> statements) {
     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 ValidationException(
             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();
       }
     }
   }

   private void validateToplevelStatements(List<Statement> statements) {
     // Check that load() statements are on top.
     if (!isBuildFile && env.getSemantics().incompatibleBzlDisallowLoadAfterStatement()) {
       checkLoadAfterStatement(statements);
     }

     openBlock(Scope.Module);

     // Add each variable defined by statements, not including definitions that appear in
     // sub-scopes of the given statements (function bodies and comprehensions).
     collectDefinitions(statements);

     // Second pass: ensure that all symbols have been defined.
     visitAll(statements);
     closeBlock();
   }

   // Public entry point, throwing variant.
   // TODO(adonovan): combine with variant below.
   public static void validateFile(BuildFileAST file, Environment env, boolean isBuildFile)
       throws EvalException {
     try {
       ValidationEnvironment venv = new ValidationEnvironment(env, isBuildFile);
       venv.validateToplevelStatements(file.getStatements());
       // Check that no closeBlock was forgotten.
       Preconditions.checkState(venv.block.parent == null);
     } catch (ValidationException e) {
       throw e.exception;
     }
   }

   // Public entry point, error handling variant.
   public static boolean validateFile(
       BuildFileAST file, Environment env, boolean isBuildFile, EventHandler eventHandler) {
     try {
       validateFile(file, env, isBuildFile);
       return true;
     } catch (EvalException e) {
       if (!e.isDueToIncompleteAST()) {
         eventHandler.handle(Event.error(e.getLocation(), e.getMessage()));
       }
       return false;
     }
   }

   /** Open a new lexical block that will contain the future declarations. */
   private void openBlock(Scope scope) {
     block = new Block(scope, block);
   }

   /** Close a lexical block (and lose all declarations it contained). */
   private void closeBlock() {
     block = Preconditions.checkNotNull(block.parent);
   }

 }
	// 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.Event;
	import com.google.devtools.build.lib.events.EventHandler;
	import com.google.devtools.build.lib.events.Location;
	import java.util.HashSet;
	import java.util.List;
	import java.util.Set;
	import javax.annotation.Nullable;

	/**
	* A class for doing static checks on files, before evaluating them.
	*
	* <p>We implement the semantics discussed in
	* https://github.com/bazelbuild/proposals/blob/master/docs/2018-06-18-name-resolution.md
	*
	* <p>When a variable is defined, it is visible in the entire block. For example, a global variable
	* is visible in the entire file; a variable in a function is visible in the entire function block
	* (even on the lines before its first assignment).
	*/
	// TODO(adonovan): make this class private. Call it through the EvalUtils facade.
	public final class ValidationEnvironment extends NodeVisitor {

	enum Scope {
	/** Symbols defined inside a function or a comprehension. */
	Local("local"),
	/** Symbols defined at a module top-level, e.g. functions, loaded symbols. */
	Module("global"),
	/** Predefined symbols (builtins) */
	Universe("builtin");

	private final String qualifier;

	private Scope(String qualifier) {
	this.qualifier = qualifier;
	}

	String getQualifier() {
	return qualifier;
	}
	}

	private static class Block {
	private final Set<String> variables = new HashSet<>();
	private final Scope scope;
	@Nullable private final Block parent;

	Block(Scope scope, @Nullable Block parent) {
	this.scope = scope;
	this.parent = parent;
	}
	}

	/**
	* We use an unchecked exception around EvalException because the NodeVisitor doesn't let visit
	* methods throw checked exceptions. We might change that later.
	*/
	private static class ValidationException extends RuntimeException {
	EvalException exception;

	ValidationException(EvalException e) {
	exception = e;
	}

	ValidationException(Location location, String message, String url) {
	exception = new EvalException(location, message, url);
	}

	ValidationException(Location location, String message) {
	exception = new EvalException(location, message);
	}
	}

	private final Environment env;
	private Block block;
	private int loopCount;
	/** In BUILD files, we have a slightly different behavior for legacy reasons. */
	private final boolean isBuildFile;

	/** Create a ValidationEnvironment for a given global Environment (containing builtins). */
	private ValidationEnvironment(Environment env, boolean isBuildFile) {
	Preconditions.checkArgument(env.isGlobal());
	this.env = env;
	this.isBuildFile = isBuildFile;
	block = new Block(Scope.Universe, null);
	Set<String> builtinVariables = env.getVariableNames();
	block.variables.addAll(builtinVariables);
	}

	/**
	* First pass: add all definitions to the current block. This is done because symbols are
	* sometimes used before their definition point (e.g. a functions are not necessarily declared in
	* order).
	*/
	private void collectDefinitions(Iterable<Statement> stmts) {
	for (Statement stmt : stmts) {
	collectDefinitions(stmt);
	}
	}

	private void collectDefinitions(Statement stmt) {
	switch (stmt.kind()) {
	case ASSIGNMENT:
	collectDefinitions(((AssignmentStatement) stmt).getLHS());
	break;
	case AUGMENTED_ASSIGNMENT:
	collectDefinitions(((AugmentedAssignmentStatement) stmt).getLHS());
	break;
	case IF:
	IfStatement ifStmt = (IfStatement) stmt;
	for (IfStatement.ConditionalStatements cond : ifStmt.getThenBlocks()) {
	collectDefinitions(cond.getStatements());
	}
	collectDefinitions(ifStmt.getElseBlock());
	break;
	case FOR:
	ForStatement forStmt = (ForStatement) stmt;
	collectDefinitions(forStmt.getLHS());
	collectDefinitions(forStmt.getBlock());
	break;
	case FUNCTION_DEF:
	Identifier fctName = ((DefStatement) stmt).getIdentifier();
	declare(fctName.getName(), fctName.getLocation());
	break;
	case LOAD:
	for (LoadStatement.Binding binding : ((LoadStatement) stmt).getBindings()) {
	declare(binding.getLocalName().getName(), binding.getLocalName().getLocation());
	}
	break;
	case CONDITIONAL:
	case EXPRESSION:
	case FLOW:
	case RETURN:
	// nothing to declare
	}
	}

	private void collectDefinitions(Expression lhs) {
	for (Identifier id : Identifier.boundIdentifiers(lhs)) {
	declare(id.getName(), id.getLocation());
	}
	}

	private void assign(Expression lhs) {
	if (lhs instanceof Identifier) {
	if (!isBuildFile) {
	((Identifier) lhs).setScope(block.scope);
	}
	// no-op
	} else if (lhs instanceof IndexExpression) {
	visit(lhs);
	} else if (lhs instanceof ListExpression) {
	for (Expression elem : ((ListExpression) lhs).getElements()) {
	assign(elem);
	}
	} else {
	throw new ValidationException(lhs.getLocation(), "cannot assign to '" + lhs + "'");
	}
	}

	@Override
	public void visit(Identifier node) {
	@Nullable Block b = blockThatDefines(node.getName());
	if (b == null) {
	// The identifier might not exist because it was restricted (hidden) by the current semantics.
	// If this is the case, output a more helpful error message than 'not found'.
	FlagGuardedValue result = env.getRestrictedBindings().get(node.getName());
	if (result != null) {
	throw new ValidationException(
	result.getEvalExceptionFromAttemptingAccess(
	node.getLocation(), env.getSemantics(), node.getName()));
	}
	throw new ValidationException(Eval.createInvalidIdentifierException(node, getAllSymbols()));
	}
	// TODO(laurentlb): In BUILD files, calling setScope will throw an exception. This happens
	// because some AST nodes are shared across multipe ASTs (due to the prelude file).
	if (!isBuildFile) {
	node.setScope(b.scope);
	}
	}

	@Override
	public void visit(ReturnStatement node) {
	if (block.scope != Scope.Local) {
	throw new ValidationException(
	node.getLocation(), "return statements must be inside a function");
	}
	super.visit(node);
	}

	@Override
	public void visit(ForStatement node) {
	if (block.scope != Scope.Local) {
	throw new ValidationException(
	node.getLocation(),
	"for loops are not allowed at the top level. You may move it inside a function "
	+ "or use a comprehension, [f(x) for x in sequence]");
	}
	loopCount++;
	visit(node.getCollection());
	assign(node.getLHS());
	visitBlock(node.getBlock());
	Preconditions.checkState(loopCount > 0);
	loopCount--;
	}

	@Override
	public void visit(LoadStatement node) {
	if (block.scope == Scope.Local) {
	throw new ValidationException(node.getLocation(), "load statement not at top level");
	}
	super.visit(node);
	}

	@Override
	public void visit(FlowStatement node) {
	if (node.getKind() != TokenKind.PASS && loopCount <= 0) {
	throw new ValidationException(
	node.getLocation(),
	node.getKind().toString() + " statement must be inside a for loop");
	}
	super.visit(node);
	}

	@Override
	public void visit(DotExpression node) {
	visit(node.getObject());
	// Do not visit the field.
	}

	@Override
	public void visit(Comprehension node) {
	openBlock(Scope.Local);
	for (Comprehension.Clause clause : node.getClauses()) {
	if (clause instanceof Comprehension.For) {
	Comprehension.For forClause = (Comprehension.For) clause;
	collectDefinitions(forClause.getVars());
	}
	}
	// TODO(adonovan): opt: combine loops
	for (Comprehension.Clause clause : node.getClauses()) {
	if (clause instanceof Comprehension.For) {
	Comprehension.For forClause = (Comprehension.For) clause;
	visit(forClause.getIterable());
	assign(forClause.getVars());
	} else {
	Comprehension.If ifClause = (Comprehension.If) clause;
	visit(ifClause.getCondition());
	}
	}
	visit(node.getBody());
	closeBlock();
	}

	@Override
	public void visit(DefStatement node) {
	if (block.scope == Scope.Local) {
	throw new ValidationException(
	node.getLocation(),
	"nested functions are not allowed. Move the function to the top level.");
	}
	for (Parameter<Expression, Expression> param : node.getParameters()) {
	if (param.isOptional()) {
	visit(param.getDefaultValue());
	}
	}
	openBlock(Scope.Local);
	for (Parameter<Expression, Expression> param : node.getParameters()) {
	if (param.hasName()) {
	declare(param.getName(), param.getLocation());
	}
	}
	collectDefinitions(node.getStatements());
	visitAll(node.getStatements());
	closeBlock();
	}

	@Override
	public void visit(IfStatement node) {
	if (block.scope != Scope.Local) {
	throw new ValidationException(
	node.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).");
	}
	super.visit(node);
	}

	@Override
	public void visit(AssignmentStatement node) {
	visit(node.getRHS());
	assign(node.getLHS());
	}

	@Override
	public void visit(AugmentedAssignmentStatement node) {
	if (node.getLHS() instanceof ListExpression) {
	throw new ValidationException(
	node.getLocation(), "cannot perform augmented assignment on a list or tuple expression");
	}
	// Other bad cases are handled in assign.
	visit(node.getRHS());
	assign(node.getLHS());
	}

	/** Declare a variable and add it to the environment. */
	private void declare(String varname, Location location) {
	// TODO(laurentlb): Forbid reassignment in BUILD files.
	if (!isBuildFile && block.scope == Scope.Module && block.variables.contains(varname)) {
	// Symbols defined in the module scope cannot be reassigned.
	throw new ValidationException(
	location,
	String.format("Variable %s is read only", varname),
	"https://bazel.build/versions/master/docs/skylark/errors/read-only-variable.html");
	}
	block.variables.add(varname);
	}

	/** Returns the nearest Block that defines a symbol. */
	private Block blockThatDefines(String varname) {
	for (Block b = block; b != null; b = b.parent) {
	if (b.variables.contains(varname)) {
	return b;
	}
	}
	return null;
	}

	/** Returns the set of all accessible symbols (both local and global) */
	private Set<String> getAllSymbols() {
	Set<String> all = new HashSet<>();
	for (Block b = block; b != null; b = b.parent) {
	all.addAll(b.variables);
	}
	return all;
	}

	/** Throws ValidationException if a load() appears after another kind of statement. */
	private static void checkLoadAfterStatement(List<Statement> statements) {
	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 ValidationException(
	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();
	}
	}
	}

	private void validateToplevelStatements(List<Statement> statements) {
	// Check that load() statements are on top.
	if (!isBuildFile && env.getSemantics().incompatibleBzlDisallowLoadAfterStatement()) {
	checkLoadAfterStatement(statements);
	}

	openBlock(Scope.Module);

	// Add each variable defined by statements, not including definitions that appear in
	// sub-scopes of the given statements (function bodies and comprehensions).
	collectDefinitions(statements);

	// Second pass: ensure that all symbols have been defined.
	visitAll(statements);
	closeBlock();
	}

	// Public entry point, throwing variant.
	// TODO(adonovan): combine with variant below.
	public static void validateFile(BuildFileAST file, Environment env, boolean isBuildFile)
	throws EvalException {
	try {
	ValidationEnvironment venv = new ValidationEnvironment(env, isBuildFile);
	venv.validateToplevelStatements(file.getStatements());
	// Check that no closeBlock was forgotten.
	Preconditions.checkState(venv.block.parent == null);
	} catch (ValidationException e) {
	throw e.exception;
	}
	}

	// Public entry point, error handling variant.
	public static boolean validateFile(
	BuildFileAST file, Environment env, boolean isBuildFile, EventHandler eventHandler) {
	try {
	validateFile(file, env, isBuildFile);
	return true;
	} catch (EvalException e) {
	if (!e.isDueToIncompleteAST()) {
	eventHandler.handle(Event.error(e.getLocation(), e.getMessage()));
	}
	return false;
	}
	}

	/** Open a new lexical block that will contain the future declarations. */
	private void openBlock(Scope scope) {
	block = new Block(scope, block);
	}

	/** Close a lexical block (and lose all declarations it contained). */
	private void closeBlock() {
	block = Preconditions.checkNotNull(block.parent);
	}

	}