/*
* Copyright 2008 The Closure Compiler Authors.
*
* 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.javascript.jscomp;
import com.google.common.base.Predicate;
import com.google.javascript.jscomp.ControlFlowGraph.Branch;
import com.google.javascript.jscomp.NodeTraversal.ScopedCallback;
import com.google.javascript.jscomp.graph.GraphNode;
import com.google.javascript.jscomp.graph.GraphReachability;
import com.google.javascript.jscomp.graph.GraphReachability.EdgeTuple;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.jstype.TernaryValue;
/**
* Use {@link ControlFlowGraph} and {@link GraphReachability} to inform user
* about unreachable code.
*
*/
class CheckUnreachableCode implements ScopedCallback {
static final DiagnosticType UNREACHABLE_CODE = DiagnosticType.warning(
"JSC_UNREACHABLE_CODE", "unreachable code");
private final AbstractCompiler compiler;
CheckUnreachableCode(AbstractCompiler compiler) {
this.compiler = compiler;
}
@Override
public void enterScope(NodeTraversal t) {
initScope(t.getControlFlowGraph());
}
@Override
public boolean shouldTraverse(NodeTraversal t, Node n, Node parent) {
GraphNode<Node, Branch> gNode = t.getControlFlowGraph().getNode(n);
if (gNode != null && gNode.getAnnotation() != GraphReachability.REACHABLE) {
// Only report error when there are some line number informations.
// There are synthetic nodes with no line number informations, nodes
// introduce by other passes (although not likely since this pass should
// be executed early) or some rhino bug.
if (n.getLineno() != -1 &&
// Allow spurious semi-colons and spurious breaks.
!n.isEmpty() && !n.isBreak()) {
compiler.report(t.makeError(n, UNREACHABLE_CODE));
// From now on, we are going to assume the user fixed the error and not
// give more warning related to code section reachable from this node.
new GraphReachability<>(
t.getControlFlowGraph()).recompute(n);
// Saves time by not traversing children.
return false;
}
}
return true;
}
private void initScope(ControlFlowGraph<Node> controlFlowGraph) {
new GraphReachability<>(
controlFlowGraph, new ReachablePredicate()).compute(
controlFlowGraph.getEntry().getValue());
}
@Override
public void exitScope(NodeTraversal t) {
}
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
}
private static final class ReachablePredicate implements
Predicate<EdgeTuple<Node, ControlFlowGraph.Branch>> {
@Override
public boolean apply(EdgeTuple<Node, Branch> input) {
Branch branch = input.edge;
if (!branch.isConditional()) {
return true;
}
Node predecessor = input.sourceNode;
Node condition = NodeUtil.getConditionExpression(predecessor);
// TODO(user): Handle more complicated expression like true == true,
// etc....
if (condition != null) {
TernaryValue val = NodeUtil.getImpureBooleanValue(condition);
if (val != TernaryValue.UNKNOWN) {
return val.toBoolean(true) == (branch == Branch.ON_TRUE);
}
}
return true;
}
}
}