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/*
* 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 static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import com.google.common.base.Preconditions;
import com.google.common.collect.HashMultimap;
import com.google.common.collect.SetMultimap;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.javascript.jscomp.ControlFlowGraph.Branch;
import com.google.javascript.jscomp.graph.DiGraph.DiGraphNode;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import java.util.ArrayDeque;
import java.util.Comparator;
import java.util.Deque;
import java.util.IdentityHashMap;
import java.util.List;
import java.util.PriorityQueue;
import org.jspecify.nullness.Nullable;
/**
* This class computes a {@link ControlFlowGraph} for a given AST
*
* Example usage:
*
*
{@code
* ControlFlowGraph cfg = ControlFlowAnalysis.builder()
* .setCompiler(compiler)
* .setCfgRoot(functionRoot)
* .setShouldIncludeEdgeAnnotations(true)
* .computeCfg())
* }
*/
public final class ControlFlowAnalysis implements NodeTraversal.Callback {
/**
* Based roughly on the first few pages of
*
* "Declarative Intraprocedural Flow Analysis of Java Source Code by Nilsson-Nyman, Hedin,
* Magnusson & Ekman",
*
*
This pass computes the control flow graph from the AST. However, a full attribute grammar is
* not necessary. We will compute the flow edges with a single post order traversal. The
* "follow()" of a given node will be computed recursively in a demand driven fashion.
*
*
At the moment, we are not performing any inter-procedural analysis.
*/
private final AbstractCompiler compiler;
private ControlFlowGraph cfg;
private @Nullable IdentityHashMap astPosition;
// We order CFG nodes by by looking at the AST positions.
// CFG nodes that come first lexically should be visited first, because
// they will often be executed first in the source program.
private final Comparator> priorityComparator =
Comparator.comparingInt(
digraphNode ->
checkNotNull(astPosition.get(digraphNode.getValue()), digraphNode.getValue()));
private int astPositionCounter;
private int priorityCounter;
private final boolean shouldTraverseFunctions;
private final boolean edgeAnnotations;
// We need to store where we started, in case we aren't doing a flow analysis
// for the whole scope. This happens, for example, when running type inference
// on only the externs.
private Node root;
/*
* This stack captures the structure of nested TRY blocks. The top of the
* stack is the inner most TRY block. A FUNCTION node in this stack implies
* that the handler is determined by the caller of the function at runtime.
*/
private final Deque exceptionHandler = new ArrayDeque<>();
/*
* This map is used to handle the follow of FINALLY. For example:
*
* while(x) {
* try {
* try {
* break;
* } catch (a) {
* } finally {
* foo();
* }
* fooFollow();
* } catch (b) {
* } finally {
* bar();
* }
* barFollow();
* }
* END();
*
* In this case finallyMap will contain a map from:
* first FINALLY -> bar()
* second FINALLY -> END()
*
* When we are connecting foo() and bar() to to their respective follow, we
* must also look up this map and connect:
* foo() -> bar()
* bar() -> END
*/
private final SetMultimap finallyMap = HashMultimap.create();
/**
* Constructor. Should only be called from within the {@link Builder}
*
* @param compiler Compiler instance.
* @param shouldTraverseFunctions Whether functions should be traversed
* @param edgeAnnotations Whether to allow edge annotations.
*/
private ControlFlowAnalysis(
AbstractCompiler compiler, boolean shouldTraverseFunctions, boolean edgeAnnotations) {
this.compiler = compiler;
this.shouldTraverseFunctions = shouldTraverseFunctions;
this.edgeAnnotations = edgeAnnotations;
}
/**
* Configures a {@link ControlFlowAnalysis} instance then computes the {@link ControlFlowGraph}
*/
public static final class Builder {
private AbstractCompiler compiler;
private Node cfgRoot;
private boolean shouldTraverseFunctions = false;
private boolean edgeAnnotations = false;
private Builder() {}
@CanIgnoreReturnValue
public Builder setCompiler(AbstractCompiler compiler) {
this.compiler = compiler;
return this;
}
@CanIgnoreReturnValue
public Builder setCfgRoot(Node cfgRoot) {
this.cfgRoot = cfgRoot;
return this;
}
@CanIgnoreReturnValue
public Builder setTraverseFunctions(boolean shouldTraverseFunctions) {
this.shouldTraverseFunctions = shouldTraverseFunctions;
return this;
}
@CanIgnoreReturnValue
public Builder setIncludeEdgeAnnotations(boolean includeEdgeAnnotations) {
this.edgeAnnotations = includeEdgeAnnotations;
return this;
}
public ControlFlowGraph computeCfg() {
Preconditions.checkNotNull(compiler, "Need to call setCompiler()");
Preconditions.checkNotNull(cfgRoot, "Need to call setCfgRoot()");
ControlFlowAnalysis cfa =
new ControlFlowAnalysis(compiler, shouldTraverseFunctions, edgeAnnotations);
cfa.computeCfg(this.cfgRoot);
return cfa.cfg;
}
}
public static Builder builder() {
return new Builder();
}
ControlFlowGraph getCfg() {
return cfg;
}
private void computeCfg(Node root) {
Preconditions.checkArgument(
NodeUtil.isValidCfgRoot(root), "Unexpected control flow graph root %s", root);
this.root = root;
astPosition = new IdentityHashMap<>();
astPositionCounter = 0;
cfg = new AstControlFlowGraph(computeFallThrough(root), edgeAnnotations);
// Traverse the graph.
NodeTraversal.traverse(compiler, root, this);
// Insert an implicit return last.
astPosition.put(null, ++astPositionCounter);
// Now, generate the priority of nodes by doing a depth-first
// search on the CFG.
priorityCounter = 0;
DiGraphNode entry = cfg.getEntry();
prioritizeFromEntryNode(entry);
if (shouldTraverseFunctions) {
// If we're traversing inner functions, we need to rank the
// priority of them too.
for (DiGraphNode candidate : cfg.getNodes()) {
Node value = candidate.getValue();
if (value != null && value.isFunction()) {
prioritizeFromEntryNode(candidate);
}
}
}
// Free our large table now that it is no longer needed
astPosition = null;
// At this point, all reachable nodes have been given a priority, but
// unreachable nodes have not been given a priority. Put them last.
// Presumably, it doesn't really matter what priority they get, since
// this shouldn't happen in real code.
for (DiGraphNode candidate : cfg.getNodes()) {
if (!candidate.hasPriority()) {
candidate.setPriority(++priorityCounter);
}
}
// Again, the implicit return node is always last.
cfg.getImplicitReturn().setPriority(++priorityCounter);
}
/** Given an entry node, find all the nodes reachable from that node and prioritize them. */
private void prioritizeFromEntryNode(DiGraphNode entry) {
PriorityQueue> worklist = new PriorityQueue<>(10, priorityComparator);
worklist.add(entry);
while (!worklist.isEmpty()) {
DiGraphNode current = worklist.remove();
if (current.hasPriority()) {
continue;
}
current.setPriority(++priorityCounter);
List> successors = cfg.getDirectedSuccNodes(current);
worklist.addAll(successors);
}
}
@Override
public boolean shouldTraverse(NodeTraversal nodeTraversal, Node n, Node parent) {
if (shouldTraverseIntoChildren(n, parent)) {
// Any AST node that will later have a corresponding CFG node must be in astPosition.
// To avoid having astPosition grow too large, we exclude AST nodes that are not traversed
// further, as they usually are not put in the CFG.
astPosition.put(n, astPositionCounter++);
return true;
}
return false;
}
/**
* Returns whether the children of this node should be traversed as part of this control-flow
* analysis, i.e. whether the control-flow graph being built may require any edges into children
* of this node.
*/
private boolean shouldTraverseIntoChildren(Node n, Node parent) {
switch (n.getToken()) {
case FUNCTION:
if (shouldTraverseFunctions || n == cfg.getEntry().getValue()) {
exceptionHandler.push(n);
return true;
}
return false;
case TRY:
exceptionHandler.push(n);
return true;
default:
break;
}
/*
* We are going to stop the traversal depending on what the node's parent
* is.
*
* We are only interested in adding edges between nodes that change control
* flow. The most obvious ones are loops and IF-ELSE's. A statement
* transfers control to its next sibling.
*
* In case of an expression tree, there is no control flow within the tree
* even when there are short circuited operators and conditionals. When we
* are doing data flow analysis, we will simply synthesize lattices up the
* expression tree by finding the meet at each expression node.
*
* For example: within a Token.SWITCH, the expression in question does not
* change the control flow and need not to be considered.
*/
if (parent != null) {
switch (parent.getToken()) {
case FOR:
case FOR_IN:
case FOR_OF:
case FOR_AWAIT_OF:
// Only traverse the body of the for loop.
boolean shouldTraverseForChild = n == parent.getLastChild();
if (!shouldTraverseForChild) {
// The control-flow graph contains edges from a FOR node to all its children, even
// though only the body is actually traversed. So put the other children in astPosition.
astPosition.put(n, astPositionCounter++);
}
return shouldTraverseForChild;
case DO:
// Only traverse the body of the do-while.
return n != parent.getSecondChild();
// Skip conditions, and only traverse the body of the cases
case IF:
case WHILE:
case WITH:
case SWITCH:
case CASE:
case CATCH:
case LABEL:
return n != parent.getFirstChild();
case FUNCTION:
return n == parent.getLastChild();
case CLASS:
return shouldTraverseFunctions && n == parent.getLastChild();
case COMPUTED_PROP:
case CONTINUE:
case BREAK:
case EXPR_RESULT:
case VAR:
case LET:
case CONST:
case EXPORT:
case IMPORT:
case RETURN:
case THROW:
case MEMBER_FUNCTION_DEF:
case MEMBER_FIELD_DEF:
case COMPUTED_FIELD_DEF:
return false;
case TRY:
/* When we are done with the TRY block and there is no FINALLY block,
* or done with both the TRY and CATCH block, then no more exceptions
* can be handled at this TRY statement, so it can be taken out of the
* stack.
*/
if ((!NodeUtil.hasFinally(parent) && n == NodeUtil.getCatchBlock(parent))
|| NodeUtil.isTryFinallyNode(parent, n)) {
checkState(exceptionHandler.peek() == parent);
exceptionHandler.pop();
}
break;
default:
break;
}
// Don't traverse further in an arrow function expression
if (parent.hasParent() && parent.getParent().isArrowFunction() && !parent.isBlock()) {
return false;
}
}
return true;
}
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
switch (n.getToken()) {
case IF:
handleIf(n);
return;
case WHILE:
handleWhile(n);
return;
case DO:
handleDo(n);
return;
case FOR:
handleFor(n);
return;
case FOR_OF:
case FOR_IN:
case FOR_AWAIT_OF:
handleEnhancedFor(n);
return;
case SWITCH:
handleSwitch(n);
return;
case CASE:
handleCase(n);
return;
case DEFAULT_CASE:
handleDefault(n);
return;
case BLOCK:
case ROOT:
case SCRIPT:
case MODULE_BODY:
handleStmtList(n);
return;
case FUNCTION:
handleFunction(n);
return;
case EXPR_RESULT:
handleExpr(n);
return;
case THROW:
handleThrow(n);
return;
case TRY:
handleTry(n);
return;
case CATCH:
handleCatch(n);
return;
case BREAK:
handleBreak(n);
return;
case CONTINUE:
handleContinue(n);
return;
case RETURN:
handleReturn(n);
return;
case WITH:
handleWith(n);
return;
case LABEL:
case CLASS_MEMBERS:
case MEMBER_FUNCTION_DEF:
case MEMBER_FIELD_DEF:
case COMPUTED_FIELD_DEF:
return;
default:
handleStmt(n);
return;
}
}
private void handleIf(Node node) {
Node thenBlock = node.getSecondChild();
Node elseBlock = thenBlock.getNext();
createEdge(node, Branch.ON_TRUE, computeFallThrough(thenBlock));
if (elseBlock == null) {
createEdge(node, Branch.ON_FALSE, computeFollowNode(node, this)); // not taken branch
} else {
createEdge(node, Branch.ON_FALSE, computeFallThrough(elseBlock));
}
connectToPossibleExceptionHandler(node, NodeUtil.getConditionExpression(node));
}
private void handleWhile(Node node) {
Node cond = node.getFirstChild();
// Control goes to the first statement if the condition evaluates to true.
createEdge(node, Branch.ON_TRUE, computeFallThrough(cond.getNext()));
if (!cond.isTrue()) {
// Control goes to the follow() if the condition evaluates to false.
createEdge(node, Branch.ON_FALSE, computeFollowNode(node, this));
}
connectToPossibleExceptionHandler(node, NodeUtil.getConditionExpression(node));
}
private void handleDo(Node node) {
Node body = node.getFirstChild();
// The first edge can be the initial iteration as well as the iterations
// after.
createEdge(node, Branch.ON_TRUE, computeFallThrough(body));
Node cond = body.getNext();
if (!cond.isTrue()) {
// The edge that leaves the do loop if the condition fails.
createEdge(node, Branch.ON_FALSE, computeFollowNode(node, this));
}
connectToPossibleExceptionHandler(node, NodeUtil.getConditionExpression(node));
}
private void handleEnhancedFor(Node forNode) {
// We have: for (index in collection) { body }
// or: for (item of collection) { body }
// or: for await (item of collection) { body }
Node item = forNode.getFirstChild();
Node collection = item.getNext();
Node body = collection.getNext();
// The collection behaves like init.
createEdge(collection, Branch.UNCOND, forNode);
// The edge that transfer control to the beginning of the loop body.
createEdge(forNode, Branch.ON_TRUE, computeFallThrough(body));
// The edge to end of the loop.
createEdge(forNode, Branch.ON_FALSE, computeFollowNode(forNode, this));
connectToPossibleExceptionHandler(forNode, collection);
}
private void handleFor(Node forNode) {
// We have for (init; cond; iter) { body }
Node init = forNode.getFirstChild();
Node cond = init.getNext();
Node iter = cond.getNext();
Node body = iter.getNext();
// After initialization, we transfer to the FOR which is in charge of
// checking the condition (for the first time).
createEdge(init, Branch.UNCOND, forNode);
// The edge that transfer control to the beginning of the loop body.
createEdge(forNode, Branch.ON_TRUE, computeFallThrough(body));
// The edge to end of the loop.
if (!cond.isEmpty() && !cond.isTrue()) {
createEdge(forNode, Branch.ON_FALSE, computeFollowNode(forNode, this));
}
// The end of the body will have a unconditional branch to our iter
// (handled by calling computeFollowNode of the last instruction of the
// body. Our iter will jump to the forNode again to another condition
// check.
createEdge(iter, Branch.UNCOND, forNode);
connectToPossibleExceptionHandler(init, init);
connectToPossibleExceptionHandler(forNode, cond);
connectToPossibleExceptionHandler(iter, iter);
}
private void handleSwitch(Node node) {
// Transfer to the first non-DEFAULT CASE. if there are none, transfer
// to the DEFAULT or the EMPTY node.
Node next = getNextSiblingOfType(node.getSecondChild(), Token.CASE, Token.EMPTY);
if (next != null) { // Has at least one CASE or EMPTY
createEdge(node, Branch.UNCOND, next);
} else { // Has no CASE but possibly a DEFAULT
if (node.getSecondChild() != null) {
createEdge(node, Branch.UNCOND, node.getSecondChild());
} else { // No CASE, no DEFAULT
createEdge(node, Branch.UNCOND, computeFollowNode(node, this));
}
}
connectToPossibleExceptionHandler(node, node.getFirstChild());
}
private void handleCase(Node node) {
// Case is a bit tricky....First it goes into the body if condition is true.
createEdge(node, Branch.ON_TRUE, node.getSecondChild());
// Look for the next CASE, skipping over DEFAULT.
Node next = getNextSiblingOfType(node.getNext(), Token.CASE);
if (next != null) { // Found a CASE
checkState(next.isCase());
createEdge(node, Branch.ON_FALSE, next);
} else { // No more CASE found, go back and search for a DEFAULT.
Node parent = node.getParent();
Node deflt = getNextSiblingOfType(parent.getSecondChild(), Token.DEFAULT_CASE);
if (deflt != null) { // Has a DEFAULT
createEdge(node, Branch.ON_FALSE, deflt);
} else { // No DEFAULT found, go to the follow of the SWITCH.
createEdge(node, Branch.ON_FALSE, computeFollowNode(node, this));
}
}
connectToPossibleExceptionHandler(node, node.getFirstChild());
}
private void handleDefault(Node node) {
// Directly goes to the body. It should not transfer to the next case.
createEdge(node, Branch.UNCOND, node.getFirstChild());
}
private void handleWith(Node node) {
// Directly goes to the body. It should not transfer to the next case.
createEdge(node, Branch.UNCOND, node.getLastChild());
connectToPossibleExceptionHandler(node, node.getFirstChild());
}
private void handleStmtList(Node node) {
Node parent = node.getParent();
// Special case, don't add a block of empty CATCH block to the graph.
if (node.isBlock()
&& parent.isTry()
&& NodeUtil.getCatchBlock(parent) == node
&& !NodeUtil.hasCatchHandler(node)) {
return;
}
// A block transfer control to its first child if it is not empty.
Node child = node.getFirstChild();
// Function declarations are skipped since control doesn't go into that
// function (unless it is called)
while (child != null && child.isFunction()) {
child = child.getNext();
}
if (child != null) {
createEdge(node, Branch.UNCOND, computeFallThrough(child));
} else {
createEdge(node, Branch.UNCOND, computeFollowNode(node, this));
}
// Synthetic blocks
if (parent != null) {
switch (parent.getToken()) {
case DEFAULT_CASE:
case CASE:
case TRY:
break;
case ROOT:
// TODO(b/71873602): why is this path necessary?
if (node.isRoot() && node.getNext() != null) {
createEdge(node, Branch.UNCOND, node.getNext());
}
break;
default:
if (node.isBlock() && node.isSyntheticBlock()) {
createEdge(node, Branch.SYN_BLOCK, computeFollowNode(node, this));
}
break;
}
}
}
private void handleFunction(Node node) {
// A block transfer control to its first child if it is not empty.
checkState(node.isFunction());
checkState(node.hasXChildren(3));
createEdge(node, Branch.UNCOND, computeFallThrough(node.getLastChild()));
checkState(exceptionHandler.peek() == node);
exceptionHandler.pop();
}
private void handleExpr(Node node) {
createEdge(node, Branch.UNCOND, computeFollowNode(node, this));
connectToPossibleExceptionHandler(node, node);
}
private void handleThrow(Node node) {
connectToPossibleExceptionHandler(node, node);
}
private void handleTry(Node node) {
createEdge(node, Branch.UNCOND, node.getFirstChild());
}
private void handleCatch(Node node) {
createEdge(node, Branch.UNCOND, node.getLastChild());
}
private void handleBreak(Node node) {
String label = null;
// See if it is a break with label.
if (node.hasChildren()) {
label = node.getFirstChild().getString();
}
Node cur;
Node previous = null;
Node lastJump;
Node parent = node.getParent();
/*
* Continuously look up the ancestor tree for the BREAK target or the target
* with the corresponding label and connect to it. If along the path we
* discover a FINALLY, we will connect the BREAK to that FINALLY. From then
* on, we will just record the control flow changes in the finallyMap. This
* is due to the fact that we need to connect any node that leaves its own
* FINALLY block to the outer FINALLY or the BREAK's target but those nodes
* are not known yet due to the way we traverse the nodes.
*/
for (cur = node, lastJump = node;
!isBreakTarget(cur, label);
cur = parent, parent = parent.getParent()) {
if (cur.isTry() && NodeUtil.hasFinally(cur) && cur.getLastChild() != previous) {
if (lastJump == node) {
createEdge(lastJump, Branch.UNCOND, computeFallThrough(cur.getLastChild()));
} else {
finallyMap.put(lastJump, computeFallThrough(cur.getLastChild()));
}
lastJump = cur;
}
if (parent == null) {
if (compiler.getOptions().canContinueAfterErrors()) {
// In IDE mode, we expect that the data flow graph may
// not be well-formed.
return;
} else {
throw new IllegalStateException("Cannot find break target.");
}
}
previous = cur;
}
if (lastJump == node) {
createEdge(lastJump, Branch.UNCOND, computeFollowNode(cur, this));
} else {
finallyMap.put(lastJump, computeFollowNode(cur, this));
}
}
private void handleContinue(Node node) {
String label = null;
if (node.hasChildren()) {
label = node.getFirstChild().getString();
}
Node cur;
Node previous = null;
Node lastJump;
// Similar to handBreak's logic with a few minor variation.
for (cur = node, lastJump = node; !isContinueTarget(cur, label); cur = cur.getParent()) {
if (cur.isTry() && NodeUtil.hasFinally(cur) && cur.getLastChild() != previous) {
if (lastJump == node) {
createEdge(lastJump, Branch.UNCOND, cur.getLastChild());
} else {
finallyMap.put(lastJump, computeFallThrough(cur.getLastChild()));
}
lastJump = cur;
}
checkState(cur.hasParent(), "Cannot find continue target.");
previous = cur;
}
Node iter = cur;
if (cur.isVanillaFor()) {
// the increment expression happens after the continue
iter = cur.getChildAtIndex(2);
}
if (lastJump == node) {
createEdge(node, Branch.UNCOND, iter);
} else {
finallyMap.put(lastJump, iter);
}
}
private void handleReturn(Node node) {
Node lastJump = null;
for (Node curHandler : exceptionHandler) {
if (curHandler.isFunction()) {
break;
}
if (NodeUtil.hasFinally(curHandler)) {
if (lastJump == null) {
createEdge(node, Branch.UNCOND, curHandler.getLastChild());
} else {
finallyMap.put(lastJump, computeFallThrough(curHandler.getLastChild()));
}
lastJump = curHandler;
}
}
if (node.hasChildren()) {
connectToPossibleExceptionHandler(node, node.getFirstChild());
}
if (lastJump == null) {
createEdge(node, Branch.UNCOND, null);
} else {
finallyMap.put(lastJump, null);
}
}
private void handleStmt(Node node) {
// Simply transfer to the next line.
createEdge(node, Branch.UNCOND, computeFollowNode(node, this));
connectToPossibleExceptionHandler(node, node);
}
static Node computeFollowNode(Node node, ControlFlowAnalysis cfa) {
return computeFollowNode(node, node, cfa);
}
static Node computeFollowNode(Node node) {
return computeFollowNode(node, node, null);
}
/**
* Computes the follow() node of a given node and its parent. There is a side effect when calling
* this function. If this function computed an edge that exists a FINALLY, it'll attempt to
* connect the fromNode to the outer FINALLY according to the finallyMap.
*
* @param fromNode The original source node since {@code node} is changed during recursion.
* @param node The node that follow() should compute.
*/
private static @Nullable Node computeFollowNode(
Node fromNode, Node node, @Nullable ControlFlowAnalysis cfa) {
/*
* This is the case where:
*
* 1. Parent is null implies that we are transferring control to the end of
* the script.
*
* 2. Parent is a function implies that we are transferring control back to
* the caller of the function.
*
* 3. If the node is a return statement, we should also transfer control
* back to the caller of the function.
*
* 4. If the node is root then we have reached the end of what we have been
* asked to traverse.
*
* In all cases we should transfer control to a "symbolic return" node.
* This will make life easier for DFAs.
*/
Node parent = node.getParent();
if (parent == null || parent.isFunction() || (cfa != null && node == cfa.root)) {
return null;
}
// If we are just before a IF/WHILE/DO/FOR:
switch (parent.getToken()) {
// The follow() of any of the path from IF would be what follows IF.
case IF:
return computeFollowNode(fromNode, parent, cfa);
case CASE:
case DEFAULT_CASE:
// After the body of a CASE, the control goes to the body of the next
// case, without having to go to the case condition.
if (parent.getNext() != null) {
if (parent.getNext().isCase()) {
return parent.getNext().getSecondChild();
} else if (parent.getNext().isDefaultCase()) {
return parent.getNext().getFirstChild();
} else {
throw new IllegalStateException("Not reachable");
}
} else {
return computeFollowNode(fromNode, parent, cfa);
}
case FOR_IN:
case FOR_OF:
case FOR_AWAIT_OF:
return parent;
case FOR:
return parent.getSecondChild().getNext();
case WHILE:
case DO:
return parent;
case TRY:
// If we are coming out of the TRY block...
if (parent.getFirstChild() == node) {
if (NodeUtil.hasFinally(parent)) { // and have FINALLY block.
return computeFallThrough(parent.getLastChild());
} else { // and have no FINALLY.
return computeFollowNode(fromNode, parent, cfa);
}
// CATCH block.
} else if (NodeUtil.getCatchBlock(parent) == node) {
if (NodeUtil.hasFinally(parent)) { // and have FINALLY block.
return computeFallThrough(node.getNext());
} else {
return computeFollowNode(fromNode, parent, cfa);
}
// If we are coming out of the FINALLY block...
} else if (parent.getLastChild() == node) {
if (cfa != null) {
for (Node finallyNode : cfa.finallyMap.get(parent)) {
cfa.createEdge(fromNode, Branch.ON_EX, finallyNode);
}
}
return computeFollowNode(fromNode, parent, cfa);
}
// fall through
default:
break;
}
// Now that we are done with the special cases follow should be its
// immediate sibling, unless its sibling is a function
Node nextSibling = node.getNext();
// Skip function declarations because control doesn't get pass into it.
while (nextSibling != null && nextSibling.isFunction()) {
nextSibling = nextSibling.getNext();
}
if (nextSibling != null) {
return computeFallThrough(nextSibling);
} else {
// If there are no more siblings, control is transferred up the AST.
return computeFollowNode(fromNode, parent, cfa);
}
}
/**
* Computes the destination node of n when we want to fallthrough into the subtree of n. We don't
* always create a CFG edge into n itself because of DOs and FORs.
*/
static Node computeFallThrough(Node n) {
switch (n.getToken()) {
case DO:
case FOR:
return computeFallThrough(n.getFirstChild());
case FOR_IN:
case FOR_OF:
case FOR_AWAIT_OF:
return n.getSecondChild();
case LABEL:
return computeFallThrough(n.getLastChild());
default:
return n;
}
}
/**
* Connects the two nodes in the control flow graph.
*
* @param fromNode Source.
* @param toNode Destination.
*/
private void createEdge(Node fromNode, ControlFlowGraph.Branch branch, @Nullable Node toNode) {
cfg.createNode(fromNode);
cfg.createNode(toNode);
cfg.connectIfNotFound(fromNode, branch, toNode);
}
/**
* Connects cfgNode to the proper CATCH block if target subtree might throw an exception. If there
* are FINALLY blocks reached before a CATCH, it will make the corresponding entry in finallyMap.
*/
private void connectToPossibleExceptionHandler(Node cfgNode, Node target) {
if (mayThrowException(target) && !exceptionHandler.isEmpty()) {
Node lastJump = cfgNode;
for (Node handler : exceptionHandler) {
if (handler.isFunction()) {
return;
}
checkState(handler.isTry());
Node catchBlock = NodeUtil.getCatchBlock(handler);
boolean lastJumpInCatchBlock = false;
for (Node ancestor : lastJump.getAncestors()) {
if (ancestor == handler) {
break;
} else if (ancestor == catchBlock) {
lastJumpInCatchBlock = true;
break;
}
}
// No catch but a FINALLY, or lastJump is inside the catch block.
if (!NodeUtil.hasCatchHandler(catchBlock) || lastJumpInCatchBlock) {
if (lastJump == cfgNode) {
createEdge(cfgNode, Branch.ON_EX, handler.getLastChild());
} else {
finallyMap.put(lastJump, handler.getLastChild());
}
} else { // Has a catch.
if (lastJump == cfgNode) {
createEdge(cfgNode, Branch.ON_EX, catchBlock);
return;
} else {
finallyMap.put(lastJump, catchBlock);
}
}
lastJump = handler;
}
}
}
/** Get the next sibling (including itself) of one of the given types. */
private static @Nullable Node getNextSiblingOfType(Node first, Token... types) {
for (Node c = first; c != null; c = c.getNext()) {
for (Token type : types) {
if (c.getToken() == type) {
return c;
}
}
}
return null;
}
/**
* Checks if target is actually the break target of labeled continue. The label can be null if it
* is an unlabeled break.
*/
public static boolean isBreakTarget(Node target, String label) {
return isBreakStructure(target, label != null) && matchLabel(target.getParent(), label);
}
/**
* Checks if target is actually the continue target of labeled continue. The label can be null if
* it is an unlabeled continue.
*/
static boolean isContinueTarget(Node target, String label) {
return NodeUtil.isLoopStructure(target) && matchLabel(target.getParent(), label);
}
/**
* Check if label is actually referencing the target control structure. If label is null, it
* always returns true.
*/
private static boolean matchLabel(Node target, String label) {
if (label == null) {
return true;
}
while (target.isLabel()) {
if (target.getFirstChild().getString().equals(label)) {
return true;
}
target = target.getParent();
}
return false;
}
/** Determines if the subtree might throw an exception. */
public static boolean mayThrowException(Node n) {
switch (n.getToken()) {
case CALL:
case TAGGED_TEMPLATELIT:
case GETPROP:
case GETELEM:
case THROW:
case NEW:
case ASSIGN:
case INC:
case DEC:
case INSTANCEOF:
case IN:
case YIELD:
case AWAIT:
return true;
case FUNCTION:
return false;
default:
break;
}
for (Node c = n.getFirstChild(); c != null; c = c.getNext()) {
if (!ControlFlowGraph.isEnteringNewCfgNode(c) && mayThrowException(c)) {
return true;
}
}
return false;
}
/** Determines whether the given node can be terminated with a BREAK node. */
static boolean isBreakStructure(Node n, boolean labeled) {
switch (n.getToken()) {
case FOR:
case FOR_IN:
case FOR_OF:
case FOR_AWAIT_OF:
case DO:
case WHILE:
case SWITCH:
return true;
case BLOCK:
case ROOT:
case IF:
case TRY:
return labeled;
default:
return false;
}
}
/**
* Get the TRY block with a CATCH that would be run if n throws an exception.
*
* @return The CATCH node or null if it there isn't a CATCH before the function terminates.
*/
static @Nullable Node getExceptionHandler(Node n) {
for (Node cur = n; !cur.isScript() && !cur.isFunction(); cur = cur.getParent()) {
Node catchNode = getCatchHandlerForBlock(cur);
if (catchNode != null) {
return catchNode;
}
}
return null;
}
/**
* Locate the catch BLOCK given the first block in a TRY.
*
* @return The CATCH node or null there is no catch handler.
*/
static @Nullable Node getCatchHandlerForBlock(Node block) {
if (block.isBlock()
&& block.getParent().isTry()
&& block.getParent().getFirstChild() == block) {
for (Node s = block.getNext(); s != null; s = s.getNext()) {
if (NodeUtil.hasCatchHandler(s)) {
return s.getFirstChild();
}
}
}
return null;
}
/**
* A {@link ControlFlowGraph} which provides a node comparator based on the pre-order traversal of
* the AST.
*/
private static final class AstControlFlowGraph extends ControlFlowGraph {
/**
* Constructs this graph.
*
* @param entry The entry node.
* @param edgeAnnotations Annotation
*/
private AstControlFlowGraph(Node entry, boolean edgeAnnotations) {
super(entry, /* nodeAnnotations = */ true, edgeAnnotations);
}
/**
* Returns a node comparator based on the pre-order traversal of the AST.
*
* @param isForward x 'before' y in the pre-order traversal implies x 'less than' y (if true)
* and x 'greater than' y (if false).
*/
@Override
public Comparator> getOptionalNodeComparator(boolean isForward) {
return isForward
? Comparator.>comparingInt(DiGraphNode::getPriority)
: Comparator.>comparingInt(DiGraphNode::getPriority).reversed();
}
}
}