src/main/java/com/google/devtools/build/lib/syntax/SyntaxTreeVisitor.java

// 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.syntax.DictionaryLiteral.DictionaryEntryLiteral;
import com.google.devtools.build.lib.syntax.IfStatement.ConditionalStatements;
import java.util.List;

/**
 * A visitor for visiting the nodes in the syntax tree left to right, top to
 * bottom.
 */
public class SyntaxTreeVisitor {

  public void visit(ASTNode node) {
    // dispatch to the node specific method
    node.accept(this);
  }

  // methods dealing with sequences of nodes
  public void visitAll(List<? extends ASTNode> nodes) {
    for (ASTNode node : nodes) {
      visit(node);
    }
  }

  /**
   * Visit a sequence ("block") of statements (e.g. an if branch, for block, function block etc.)
   *
   * This method allows subclasses to handle statement blocks more easily, like doing an action
   * after every statement in a block without having to override visit(...) for all statements.
   *
   * @param statements list of statements in the block
   */
  public void visitBlock(List<Statement> statements) {
    visitAll(statements);
  }

  // node specific visit methods
  public void visit(Argument.Passed node) {
    visit(node.getValue());
  }

  public void visit(Parameter<Expression, Expression> node) {
    if (node.getDefaultValue() != null) {
      visit(node.getDefaultValue());
    }
  }

  public void visit(BuildFileAST node) {
    visitBlock(node.getStatements());
    visitAll(node.getComments());
  }

  public void visit(BinaryOperatorExpression node) {
    visit(node.getLhs());
    visit(node.getRhs());
  }

  public void visit(FuncallExpression node) {
    visit(node.getFunction());
    visitAll(node.getArguments());
  }

  public void visit(@SuppressWarnings("unused") Identifier node) {}

  public void visit(AbstractComprehension node) {
    for (ListComprehension.Clause clause : node.getClauses()) {
      visit(clause.getExpression());
      if (clause.getLValue() != null) {
        visit(clause.getLValue());
      }
    }
    visitAll(node.getOutputExpressions());
  }

  public void visit(ForStatement node) {
    visit(node.getCollection());
    visit(node.getVariable());
    visitBlock(node.getBlock());
  }

  public void visit(LoadStatement node) {
    for (LoadStatement.Binding binding : node.getBindings()) {
      visit(binding.getLocalName());
    }
  }

  public void visit(ListLiteral node) {
    visitAll(node.getElements());
  }

  public void visit(@SuppressWarnings("unused") IntegerLiteral node) {}

  public void visit(@SuppressWarnings("unused") StringLiteral node) {}

  public void visit(LValue node) {
    visit(node.getExpression());
  }

  public void visit(AssignmentStatement node) {
    visit(node.getExpression());
    visit(node.getLValue());
  }

  public void visit(AugmentedAssignmentStatement node) {
    visit(node.getExpression());
    visit(node.getLValue());
  }

  public void visit(ExpressionStatement node) {
    visit(node.getExpression());
  }

  public void visit(IfStatement node) {
    visitAll(node.getThenBlocks());
    visitBlock(node.getElseBlock());
  }

  public void visit(ConditionalStatements node) {
    visit(node.getCondition());
    visitBlock(node.getStatements());
  }

  public void visit(FunctionDefStatement node) {
    visit(node.getIdentifier());
    // Do not use visitAll for the parameters, because we would lose the type information.
    // Inside the AST, we know that Parameters are using Expressions.
    for (Parameter<Expression, Expression> param : node.getParameters()) {
      visit(param);
    }
    visitBlock(node.getStatements());
  }

  public void visit(PassStatement node) {}

  public void visit(ReturnStatement node) {
    if (node.getReturnExpression() != null) {
      visit(node.getReturnExpression());
    }
  }

  public void visit(FlowStatement node) {
  }

  public void visit(DictionaryLiteral node) {
    visitAll(node.getEntries());
  }

  public void visit(DictionaryEntryLiteral node) {
    visit(node.getKey());
    visit(node.getValue());
  }

  public void visit(UnaryOperatorExpression node) {
    visit(node.getOperand());
  }

  public void visit(DotExpression node) {
    visit(node.getObject());
    visit(node.getField());
  }

  public void visit(IndexExpression node) {
    visit(node.getObject());
    visit(node.getKey());
  }

  public void visit(SliceExpression node) {
    visit(node.getObject());
    if (node.getStart() != null) {
      visit(node.getStart());
    }
    if (node.getEnd() != null) {
      visit(node.getEnd());
    }
    if (node.getStep() != null) {
      visit(node.getStep());
    }
  }

  public void visit(@SuppressWarnings("unused") Comment node) {}

  public void visit(ConditionalExpression node) {
    visit(node.getCondition());
    visit(node.getThenCase());
    if (node.getElseCase() != null) {
      visit(node.getElseCase());
    }
  }
}