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/*
* Copyright 2020 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.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.javascript.jscomp.parsing.parser.FeatureSet.Feature;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import java.util.ArrayDeque;
import org.jspecify.nullness.Nullable;
/**
* Rewrites a single optional chain as one or more nested hook expressions.
*
* Optional chains contained in OPTCHAIN_GETELEM indices or OPTCHAIN_CALL arguments are not
* rewritten.
*
*
Example:
*
*
* a?.b[obj?.index]?.c?.(obj?.arg)
* // becomes
* (tmp0 = a) == null
* ? void 0
* : (tmp1 = tmp0.b[obj?.index]) == null
* ? void 0
* : (tmp2 = tmp1.c) == null
* ? void 0
* : tmp2.call(tmp1, obj?.arg);
*
*
* The unit tests for this class are in RewriteOptionalChainingOperatorTest, because it's most
* convenient to test this class as part of the transpilation pass that uses it.
*/
class OptionalChainRewriter {
final AbstractCompiler compiler;
final AstFactory astFactory;
final TmpVarNameCreator tmpVarNameCreator;
// If a scope is provided, newly created variables will be declared in that scope
final @Nullable Scope scope;
final Node chainParent;
final Node wholeChain;
final Node insertionPoint;
final ArrayDeque deletesToDelete;
/** Creates unique names to be used for temporary variables. */
interface TmpVarNameCreator {
/** Creates a unique temporary variable name each time it is called. */
String createTmpVarName();
}
static class Builder {
final AbstractCompiler compiler;
final AstFactory astFactory;
TmpVarNameCreator tmpVarNameCreator;
Scope scope;
private Builder(AbstractCompiler compiler) {
this.compiler = checkNotNull(compiler);
this.astFactory = compiler.createAstFactory();
}
@CanIgnoreReturnValue
Builder setTmpVarNameCreator(TmpVarNameCreator tmpVarNameCreator) {
this.tmpVarNameCreator = checkNotNull(tmpVarNameCreator);
return this;
}
/** Optionally sets a scope in which the rewriter will declare all temporary variables */
@CanIgnoreReturnValue
Builder setScope(Scope scope) {
this.scope = checkNotNull(scope);
return this;
}
/** @param wholeChain The last Node in the optional chain. Parent of all the rest. */
OptionalChainRewriter build(Node wholeChain) {
return new OptionalChainRewriter(this, wholeChain);
}
}
static Builder builder(AbstractCompiler compiler) {
return new Builder(compiler);
}
private OptionalChainRewriter(Builder builder, Node wholeChain) {
// This class will only operate on an entire chain.
checkArgument(NodeUtil.isEndOfFullOptChain(wholeChain), wholeChain);
this.compiler = builder.compiler;
this.astFactory = builder.astFactory;
this.tmpVarNameCreator = checkNotNull(builder.tmpVarNameCreator);
this.scope = builder.scope;
this.wholeChain = wholeChain;
this.chainParent = checkNotNull(wholeChain.getParent(), wholeChain);
// Insert temporaries just before the enclosing statement.
Node enclosingStatement = NodeUtil.getEnclosingStatement(wholeChain);
if (enclosingStatement.getPrevious() != null
&& enclosingStatement.getPrevious().isLabelName()) {
// Do not insert temporaries between a label name and its statement.
// e.g. `{ label: for (const a of b?.c) {...}`
// AST shape is
// BLOCK
// LABEL // parent of enclosingStatement - insert above this
// LABEL_NAME
// enclosingStatement
this.insertionPoint = enclosingStatement.getParent();
} else {
this.insertionPoint = enclosingStatement;
}
this.deletesToDelete = new ArrayDeque<>();
}
/** Rewrites the optional chain as a hook with temporary variables introduced as needed. */
void rewrite() {
checkState(NodeUtil.isOptChainNode(wholeChain), "already rewritten: %s", wholeChain);
// `first?.start.second?.start`
// We search from the end of the chain and push the start nodes onto the stack, so the first
// one ends up on top.
ArrayDeque startNodeStack = new ArrayDeque<>();
Node subchainEnd = wholeChain;
while (NodeUtil.isOptChainNode(subchainEnd)) {
final Node subchainStart = NodeUtil.getStartOfOptChainSegment(subchainEnd);
startNodeStack.push(subchainStart);
subchainEnd = subchainStart.getFirstChild();
}
checkState(!startNodeStack.isEmpty());
// Each time we rewrite the initial segment of the chain, the remaining chain gets wrapped
// in a hook statement like `(tmp0 = a.b) == null ? void 0 : tmp0.rest?.of.chain?.()`,
// So wholeChain ends up more deeply nested on each rewrite.
// We only care about the top-most replacement here.
final Node optChainReplacement = rewriteInitialSegment(startNodeStack.pop(), wholeChain);
while (!startNodeStack.isEmpty()) {
rewriteInitialSegment(startNodeStack.pop(), wholeChain);
}
// Handle a non-optional call to an optional chain that ends in an element or property
// access.
// `(a?.optional.chain)(arg1)`
// Writing JavaScript code like this is a bad idea, but it might get automatically
// generated, so we must handle it.
// The optional chain could evaluate to `undefined`, which we then try to call as a
// function. However, if it isn't undefined, we have to preserve the correct `this` value
// for the call.
if (chainParent.isCall()
// The chain will have been replaced by optChainReplacement during the rewriting above.
&& optChainReplacement.isFirstChildOf(chainParent)
// The wholeChain variable will still point to the rewritten final Node of the
// chain. It will no longer be optional.
&& NodeUtil.isNormalGet(wholeChain)) {
final Node thisValue = wholeChain.getFirstChild();
final Node tmpThisNode = getSubExprNameNode(thisValue);
optChainReplacement.detach();
chainParent.addChildToFront(tmpThisNode);
final Node dotCallNode =
astFactory
.createGetPropWithUnknownType(optChainReplacement, "call")
.srcrefTreeIfMissing(optChainReplacement);
chainParent.addChildToFront(dotCallNode);
}
// Report changes here; chainParent can get deleted below this.
// E.g. code `(p = a?.b)=>{ return p}` changes to `let tmp0; (p = (tmp0=a)==null?void
// 0:tmp0.b)=>{return p}`
// This requires recording scope changes at two places:
// 1. the function scope changed from rewriting to HOOK (recorded here),
// 2. SCRIPT scope changed due to the `let tmp0` inserted (recorded in `declareTempVarName`
// where declarations are created).
compiler.reportChangeToEnclosingScope(chainParent);
if (chainParent.isDelProp()) {
// With rewriting above,
// `delete a?.b?.c`
// synthesizes additional deletes
// `delete (tmp0 = a) == null ? true : delete (tmp1 = tmp0.b) == null ? true : delete tmp1.c;`
// ^^^^^^ ^^^^^^
//
// But we must generate only:
// `(tmp0 = a) == null ? true : (tmp1 = tmp0.b) == null ? true : delete tmp1.c;`
// That is, the preceding deletes for every hook must be removed.
while (!deletesToDelete.isEmpty()) {
Node delete = deletesToDelete.removeFirst();
checkState(delete.getFirstChild().isHook(), delete);
Node hook = delete.getFirstChild();
hook.detach();
delete.replaceWith(hook);
compiler.reportChangeToEnclosingScope(hook);
}
}
// Transpilation of the optional chain adds `let` declarations for temporary variables.
// NOTE: If this class is being used before transpilation, it's OK to use `let`, since it will
// be transpiled away, if necessary. If it is being used after transpilation, then using `let`
// must be OK, because optional chains weren't transpiled away and `let` existed before they
// did.
final Node enclosingScript = NodeUtil.getEnclosingScript(insertionPoint);
NodeUtil.addFeatureToScript(enclosingScript, Feature.LET_DECLARATIONS, compiler);
}
/**
* Rewrites the first part of a possibly-multi-part optional chain.
*
* e.g.
*
*
{@code
* a()?.b.c?.d;
* // becomes
* let tmp0;
* (tmp0 = a()) == null
* ? void 0
* : tmp0.b.c?d;
* }
*
* If this optional chain is under a delete, the l-r rewriting must synthesize another `delete` to
* ensure the next chain(if present), knows that it must delete the `fullChainEnd`.
*
* e.g. * *
*
*
{@code
* * delete a?.b.c?.d;
* * // becomes
* * let tmp0;
* * (tmp0 = a()) == null
* * ? true
* * : delete tmp0.b.c?d;
* *
* }
*
* @param fullChainStart The very first `?.` node
* @param fullChainEnd The very last optional chain node.
* @return The hook expression that replaced the chain.
*/
private Node rewriteInitialSegment(final Node fullChainStart, final Node fullChainEnd) {
// `receiverNode?.restOfChain`
Node receiverNode = fullChainStart.getFirstChild();
// for `a?.b.c?.d`, this will be `a?.b.c`, because the NodeUtil method finds the end
// of the sub-chain, not the full chain.
final Node initialChainEnd = NodeUtil.getEndOfOptChainSegment(fullChainStart);
// Is this optional chain under delete
boolean isBeingDeleted = fullChainEnd.getParent().isDelProp();
if (isBeingDeleted) {
deletesToDelete.addLast(fullChainEnd.getParent());
}
// If the receiver is an optional chain, we weren't really given the start of a full
// chain.
checkArgument(!NodeUtil.isOptChainNode(receiverNode), receiverNode);
// change the initial chain's nodes to be non-optional
NodeUtil.convertToNonOptionalChainSegment(initialChainEnd);
final Node placeholder = IR.empty();
fullChainEnd.replaceWith(placeholder);
// NOTE: convertToNonOptionalChain() above will have made the chain start
// and all the other nodes in the first segment of the chain non-optional,
// so fullChainStart.isCall() is the right test here.
if (NodeUtil.isNormalGet(receiverNode) && fullChainStart.isCall()) {
// `expr.prop?.(x).y`
// Needs to become
// `(t1 = (t0 = expr).prop) == null ? void 0 : t1.call(t0, x).y`
final Node thisValue = receiverNode.getFirstChild();
final Node tmpThisNode = getSubExprNameNode(thisValue);
final Node tmpReceiverNode = getSubExprNameNode(receiverNode);
receiverNode = fullChainStart.removeFirstChild();
fullChainStart.addChildToFront(tmpThisNode);
fullChainStart.addChildToFront(
astFactory
.createGetPropWithUnknownType(tmpReceiverNode, "call")
.srcrefTreeIfMissing(receiverNode));
} else {
// `expr?.x.y`
// needs to become
// `((t0 = expr) == null) ? void 0 : t0.x.y`
final Node tmpReceiverNode = getSubExprNameNode(receiverNode);
receiverNode = fullChainStart.getFirstChild();
receiverNode.replaceWith(tmpReceiverNode);
}
final Node optChainReplacement =
astFactory
.createHook(
astFactory.createEq(receiverNode, astFactory.createNull()),
isBeingDeleted ? astFactory.createBoolean(true) : astFactory.createUndefinedValue(),
isBeingDeleted ? astFactory.createDelProp(fullChainEnd) : fullChainEnd)
.srcrefTreeIfMissing(fullChainEnd);
placeholder.replaceWith(optChainReplacement);
return optChainReplacement;
}
/**
* Given an expression node, declare a temporary variable to hold that expression and replace the
* expression with `(tmp = expr)`.
*
* e.g. `subExpr.moreExpr` becomes `(tmp = subExpr).moreExpr`, and `let tmp;` gets inserted
* before the enclosing statement of this optional chain.
*
* @param subExpr The sub expression Node
* @return A detached NAME node for the temporary variable name and with source info and type
* matching `subExpr`, that may be inserted where needed.
*/
Node getSubExprNameNode(Node subExpr) {
String tempVarName = declareTempVarName(subExpr);
Node placeholder = IR.empty();
subExpr.replaceWith(placeholder);
Node replacement = astFactory.createAssign(tempVarName, subExpr).srcrefTreeIfMissing(subExpr);
placeholder.replaceWith(replacement);
return replacement.getFirstChild().cloneNode();
}
/**
* Declare a temporary variable name that will be used to hold the given value.
*
*
The generated declaration has no assignment, it's just `let tmp;`.
*
* @param valueNode A node from which to copy the source info and type to be used for the new
* variable.
* @return the name used for the new temporary variable.
*/
String declareTempVarName(Node valueNode) {
String tempVarName = tmpVarNameCreator.createTmpVarName();
Node declarationStatement =
astFactory.createSingleLetNameDeclaration(tempVarName).srcrefTree(valueNode);
declarationStatement.getFirstChild().setInferredConstantVar(true);
declarationStatement.insertBefore(insertionPoint);
compiler.reportChangeToEnclosingScope(declarationStatement);
if (scope != null) {
scope.declare(tempVarName, declarationStatement.getFirstChild(), /* input= */ null);
}
return tempVarName;
}
}