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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 com.google.auto.value.AutoValue;
import com.google.common.base.Splitter;
import com.google.common.collect.ImmutableCollection;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableMultimap;
import com.google.common.collect.ImmutableSet;
import com.google.javascript.jscomp.AbstractCompiler.LifeCycleStage;
import com.google.javascript.rhino.Node;
import java.util.ArrayDeque;
import java.util.List;
import java.util.function.Consumer;
import java.util.stream.Collectors;
import org.jspecify.nullness.Nullable;
/** Detects all potential usages of polyfilled classes or methods */
final class PolyfillUsageFinder {
/**
* Represents a single polyfill: specifically, for a native symbol, a set of native and polyfill
* versions, and a library to ensure is injected if the output version is less than the native
* version.
*/
static final class Polyfill {
/** The full name of the polyfill, e.g `Map` or `String.prototype.includes` */
final String nativeSymbol;
/**
* The language version at (or above) which the native symbol is available and sufficient. If
* the language out flag is at least as high as {@code nativeVersion} then the polyfill is not
* needed. This string should be one of those returned by FeatureSet.version().
*/
final String nativeVersion;
/**
* The required language version for the polyfill to work. This should not be higher than {@code
* nativeVersion}, but may be the same in cases where there is no polyfill provided. This is
* used to emit a warning if the language out flag is too low. This string should be one of
* those returned by FeatureSet.version().
*/
final String polyfillVersion;
/**
* Runtime library to inject for the polyfill, e.g. "es6/map".
*/
final String library;
final Kind kind;
enum Kind {
STATIC, // Map or Array.of
METHOD // String.prototype.includes
}
Polyfill(
String nativeSymbol,
String nativeVersion,
String polyfillVersion,
String library,
Kind kind) {
this.nativeSymbol = nativeSymbol;
this.nativeVersion = nativeVersion;
this.polyfillVersion = polyfillVersion;
this.library = library;
this.kind = kind;
}
}
/** Maps from polyfill names to the actual Polyfill object. */
static final class Polyfills {
// Map of method polyfills, keyed by native method name.
private final ImmutableMultimap methods;
// Map of static polyfills, keyed by fully-qualified native name.
private final ImmutableMap statics;
// Set of suffixes of qualified names.
private final ImmutableSet suffixes;
private Polyfills(
ImmutableMultimap methods, ImmutableMap statics) {
this.methods = methods;
this.statics = statics;
this.suffixes =
ImmutableSet.copyOf(
statics.keySet().stream()
.map(arg -> arg.substring(arg.lastIndexOf('.') + 1))
.collect(Collectors.toList()));
}
/**
* Builds a Polyfills instance from a polyfill table, which is a simple
* text file with lines containing space-separated tokens:
* [NATIVE_SYMBOL] [NATIVE_VERSION] [POLYFILL_VERSION] [LIBRARY]
* For example,
* Array.prototype.fill es6 es3 es6/array/fill
* Map es6 es3 es6/map
* WeakMap es6 es6
* The last line, WeakMap, does not have a polyfill available, so the
* library token is empty.
*/
static Polyfills fromTable(String table) {
ImmutableMultimap.Builder methods = ImmutableMultimap.builder();
ImmutableMap.Builder statics = ImmutableMap.builder();
for (String line : Splitter.on('\n').omitEmptyStrings().split(table)) {
List tokens = Splitter.on(' ').omitEmptyStrings().splitToList(line.trim());
if (tokens.size() == 1 && tokens.get(0).isEmpty()) {
continue;
} else if (tokens.size() < 3) {
throw new IllegalArgumentException("Invalid table: too few tokens on line: " + line);
}
String symbol = tokens.get(0);
boolean isPrototypeMethod = symbol.contains(".prototype.");
final String nativeVersionStr = tokens.get(1);
final String polyfillVersionStr = tokens.get(2);
Polyfill polyfill =
new Polyfill(
symbol,
nativeVersionStr,
polyfillVersionStr,
tokens.size() > 3 ? tokens.get(3) : "",
isPrototypeMethod ? Polyfill.Kind.METHOD : Polyfill.Kind.STATIC);
if (isPrototypeMethod) {
methods.put(symbol.replaceAll(".*\\.prototype\\.", ""), polyfill);
} else {
statics.put(symbol, polyfill);
}
}
return new Polyfills(methods.build(), statics.buildOrThrow());
}
}
@AutoValue
abstract static class PolyfillUsage {
abstract Polyfill polyfill();
abstract Node node();
abstract String name();
abstract boolean isExplicitGlobal();
private static PolyfillUsage createExplicit(Polyfill polyfill, Node node, String name) {
return new AutoValue_PolyfillUsageFinder_PolyfillUsage(
polyfill, node, name, /* isExplicitGlobal= */ true);
}
private static PolyfillUsage createNonExplicit(Polyfill polyfill, Node node, String name) {
return new AutoValue_PolyfillUsageFinder_PolyfillUsage(
polyfill, node, name, /* isExplicitGlobal= */ false);
}
}
private final AbstractCompiler compiler;
private final Polyfills polyfills;
PolyfillUsageFinder(AbstractCompiler compiler, Polyfills polyfills) {
this.polyfills = polyfills;
this.compiler = compiler;
}
/**
* Passes all polyfill usages found, in postorder, to the given polyfillConsumer
*
* Excludes polyfill usages behind a guard, like {@code if (Promise) return
* Promise.resolve('ok');}
*/
void traverseExcludingGuarded(Node root, Consumer polyfillConsumer) {
NodeTraversal.traverse(
compiler, root, new Traverser(this.compiler, polyfillConsumer, Guard.ONLY_UNGUARDED));
}
/**
* Passes all polyfill usages found, in postorder, to the given polyfillConsumer
*
* Includes polyfill usages that are behind a guard, like {@code if (Promise) return
* Promise.resolve('ok');}
*/
void traverseIncludingGuarded(Node root, Consumer polyfillConsumer) {
NodeTraversal.traverse(
compiler, root, new Traverser(this.compiler, polyfillConsumer, Guard.ALL));
}
/**
* Passes all polyfill usages found, in postorder, to the given polyfillConsumer
*
* Only includes polyfill usages that are behind a guard, like {@code if (Promise) return
* Promise.resolve('ok');}
*/
void traverseOnlyGuarded(Node root, Consumer polyfillConsumer) {
NodeTraversal.traverse(
compiler, root, new Traverser(this.compiler, polyfillConsumer, Guard.ONLY_GUARDED));
}
private enum Guard {
ONLY_GUARDED,
ONLY_UNGUARDED,
ALL;
boolean shouldInclude(boolean isGuarded) {
switch (this) {
case ALL:
return true;
case ONLY_GUARDED:
return isGuarded;
case ONLY_UNGUARDED:
return !isGuarded;
}
throw new AssertionError();
}
};
private class Traverser extends GuardedCallback {
private final Consumer polyfillConsumer;
// Whether to emit usages like Promise in `if (Promise) return Promise.resolve('ok');}`
private final Guard includeGuardedUsages;
Traverser(
AbstractCompiler compiler,
Consumer polyfillConsumer,
Guard includeGuardedUsages) {
super(compiler);
this.polyfillConsumer = polyfillConsumer;
this.includeGuardedUsages = includeGuardedUsages;
}
@Override
public void visitGuarded(NodeTraversal traversal, Node node, Node parent) {
switch (node.getToken()) {
case NAME:
visitName(traversal, node);
break;
case GETPROP:
case OPTCHAIN_GETPROP:
visitGetPropChain(traversal, node);
break;
default:
// nothing to do
}
}
private void visitName(NodeTraversal traversal, Node nameNode) {
String name = nameNode.getString();
Polyfill polyfill = polyfills.statics.get(name);
if (polyfill == null) {
// no polyfill exists for this name
return;
}
if (isPolyfillVisibleInScope(traversal, name)
&& includeGuardedUsages.shouldInclude(isGuarded(name))) {
this.polyfillConsumer.accept(PolyfillUsage.createNonExplicit(polyfill, nameNode, name));
}
}
private void visitGetPropChain(NodeTraversal traversal, Node getPropNode) {
// First see if we have a usage that matches a full static polyfill name.
// e.g. `Array.from` or `globalThis.Promise.allSettled`
PolyfillUsage staticPolyfillUsage =
maybeCreateStaticPolyfillUsageForGetPropChain(traversal, getPropNode);
if (staticPolyfillUsage != null) {
if (includeGuardedUsages.shouldInclude(isGuarded(staticPolyfillUsage.name()))) {
this.polyfillConsumer.accept(staticPolyfillUsage);
}
} else {
// We don't have a static polyfill usage, but this could still be a reference to one of
// several possible method polyfills.
// e.g. `obj.includes(x)` could be a usage of `Array.prototype.includes` or
// `String.prototype.includes`.
final String propertyName = getPropNode.getString();
ImmutableCollection methodPolyfills = polyfills.methods.get(propertyName);
// Note that we use ".foo" as the guard check for methods to keep them distinct in case
// there is also a static "foo" polyfill.
if (!methodPolyfills.isEmpty()
&& includeGuardedUsages.shouldInclude(isGuarded("." + propertyName))) {
for (Polyfill polyfill : methodPolyfills) {
this.polyfillConsumer.accept(
PolyfillUsage.createNonExplicit(polyfill, getPropNode, propertyName));
}
}
}
}
}
private @Nullable PolyfillUsage maybeCreateStaticPolyfillUsageForGetPropChain(
NodeTraversal traversal, final Node getPropNode) {
checkArgument(getPropNode.isGetProp() || getPropNode.isOptChainGetProp(), getPropNode);
final String lastComponent = getPropNode.getString();
if (!polyfills.suffixes.contains(lastComponent)) {
// Save execution time by bailing out early if the property name at the end of the chain
// doesn't match any of the known polyfills.
return null;
}
// NOTE: We are not using isQualifiedName() and getQualifiedName() here, because we want to
// locate the owner node and also have this code work for optional chains.
final ArrayDeque components = new ArrayDeque<>();
components.addFirst(lastComponent);
Node ownerNode;
for (ownerNode = getPropNode.getFirstChild();
ownerNode.isGetProp() || ownerNode.isOptChainGetProp();
ownerNode = ownerNode.getFirstChild()) {
components.addFirst(ownerNode.getString());
}
if (!ownerNode.isName()) {
// Static polyfills are always fully qualified names beginning with a NAME node.
// e.g. `Array.from` or `globalThis.Promise`
return null;
}
final String rootName = ownerNode.getString();
components.addFirst(rootName);
final String fullName = String.join(".", components);
final String globalPrefix = findGlobalPrefix(fullName);
if (globalPrefix != null) {
// The full name starts with a known global value, like `goog.global.` or `globalThis.`.
// We must strip that off before matching with the known polyfill names.
// (Note that the connecting '.' is included and will also be stripped.)
// Also, the presence of the explicit global value name means we don't have to check the
// scope for a shadowing variable as we do below.
Polyfill polyfill = polyfills.statics.get(fullName.substring(globalPrefix.length()));
if (polyfill != null) {
return PolyfillUsage.createExplicit(polyfill, getPropNode, polyfill.nativeSymbol);
}
} else {
Polyfill polyfill = polyfills.statics.get(fullName);
if (polyfill != null) {
// If we see a declaration of the name, then it is defined by the source code,
// and we won't count it as a reference to our polyfill.
// Checking the scope is relatively expensive, so we don't want to do it until
// we've confirmed that this node looks like it could be a polyfill reference.
if (isPolyfillVisibleInScope(traversal, rootName)) {
return PolyfillUsage.createNonExplicit(polyfill, getPropNode, polyfill.nativeSymbol);
}
}
}
return null;
}
/** @return Whether the Polyfill name is visible in the current scope. */
private boolean isPolyfillVisibleInScope(NodeTraversal t, String globalName) {
// This class is only supposed to traverse over actual sources, not externs,
// so it shouldn't see the declarations of the things being polyfilled.
// If the AST is normalized we can avoid building the scope (which is relatively expensive)
// and rely on the normalization guarantee that every name in AST is unique.
// NOTE: there is an edge case that we are purposely ignoring here. This pass expects
// the traverse the AST without externs, this creates a distinction between undeclared variables
// (externs) and symbols in the global scope (internal globals). So then against the
// un-normalized AST for detecting whether to inject Polyfills, it won't inject, if there is a
// global declaration of the same name. But when removing Polyfills (which happens when the
// AST is normalized), it won't try to remove these same Polyfills if they were present,
// because the scope distinction isn't used. This doesn't change behavior because they
// wouldn't have been injected in the first place.
return (compiler.getLifeCycleStage() == LifeCycleStage.NORMALIZED
|| t.getScope().getVar(globalName) == null);
}
private static @Nullable String findGlobalPrefix(String qualifiedName) {
for (String global : GLOBAL_NAMES) {
if (qualifiedName.startsWith(global)) {
return global;
}
}
return null;
}
private static final ImmutableSet GLOBAL_NAMES =
ImmutableSet.of("goog.global.", "window.", "goog$global.", "globalThis.");
}