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/*
* Copyright 2019 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.common.collect.ImmutableSet;
import com.google.javascript.jscomp.AccessorSummary.PropertyAccessKind;
import com.google.javascript.jscomp.colors.Color;
import com.google.javascript.jscomp.colors.StandardColors;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.jstype.JSType;
import com.google.javascript.rhino.jstype.JSTypeNative;
/**
* Logic for answering questions about portions of the AST.
*
* What kind of methods should go here?
*
*
Methods that answer questions about some portion of the AST and that may require global
* information about the compilation, generally taking at least one {@link Node} as an argument. For
* example:
*
*
* - Does a node have side effects?
*
- Can we statically determine the value of a node?
*
*
* What kind of logic should not go here?
*
*
Really simple logic that requires no global information, like finding the parameter list node
* of a function, should be in {@link NodeUtil}. Logic that creates new Nodes or modifies the AST
* should go in {@link AstFactory}.
*/
public class AstAnalyzer {
/**
* The set of builtin constructors that don't have side effects.
*
*
TODO(bradfordcsmith): If all of these are annotated {@code sideefectfree}, can we drop this
* list?
*/
private static final ImmutableSet CONSTRUCTORS_WITHOUT_SIDE_EFFECTS =
ImmutableSet.of("Array", "Date", "Error", "Object", "RegExp", "XMLHttpRequest");
// A list of built-in object creation or primitive type cast functions that
// can also be called as constructors but lack side-effects.
// TODO(johnlenz): consider adding an extern annotation for this.
private static final ImmutableSet BUILTIN_FUNCTIONS_WITHOUT_SIDEEFFECTS =
ImmutableSet.of(
"Object", "Array", "String", "Number", "BigInt", "Boolean", "RegExp", "Error");
private static final ImmutableSet OBJECT_METHODS_WITHOUT_SIDEEFFECTS =
ImmutableSet.of("toString", "valueOf");
private static final ImmutableSet REGEXP_METHODS = ImmutableSet.of("test", "exec");
private static final ImmutableSet STRING_REGEXP_METHODS =
ImmutableSet.of("match", "replace", "search", "split");
private final AbstractCompiler compiler;
private final boolean assumeGettersArePure;
AstAnalyzer(AbstractCompiler compiler, boolean assumeGettersArePure) {
this.compiler = checkNotNull(compiler);
this.assumeGettersArePure = assumeGettersArePure;
}
/**
* Returns true if the node may create new mutable state, or change existing state.
*
* @see XKCD Cartoon
*/
boolean mayEffectMutableState(Node n) {
return checkForStateChangeHelper(n, /* checkForNewObjects= */ true);
}
/**
* Returns true if the node which may have side effects when executed. This version default to the
* "safe" assumptions when the compiler object is not provided (RegExp have side-effects, etc).
*/
public boolean mayHaveSideEffects(Node n) {
return checkForStateChangeHelper(n, /* checkForNewObjects= */ false);
}
/**
* Returns true if this function call may have side effects.
*
* This method is guaranteed to return true all calls that have side-effects, but may also
* return true for calls that have none.
*
* @param callNode - function call node
*/
boolean functionCallHasSideEffects(Node callNode) {
checkState(
callNode.isCall() || callNode.isTaggedTemplateLit() || callNode.isOptChainCall(), callNode);
if (callNode.isNoSideEffectsCall()) {
return false;
}
if (callNode.isOnlyModifiesArgumentsCall() && NodeUtil.allArgsUnescapedLocal(callNode)) {
return false;
}
Node callee = callNode.getFirstChild();
// Built-in functions with no side effects.
if (callee.isName()) {
String name = callee.getString();
if (BUILTIN_FUNCTIONS_WITHOUT_SIDEEFFECTS.contains(name)) {
return false;
}
} else if (callee.isGetProp() || callee.isOptChainGetProp()) {
if (callNode.hasOneChild()
&& OBJECT_METHODS_WITHOUT_SIDEEFFECTS.contains(callee.getString())) {
return false;
}
if (callNode.isOnlyModifiesThisCall()
&& NodeUtil.evaluatesToLocalValue(callee.getFirstChild())) {
return false;
}
// Many common Math functions have no side-effects.
// TODO(nicksantos): This is a terrible terrible hack, until
// I create a definitionProvider that understands namespacing.
if (callee.getFirstChild().isName()
&& callee.isQualifiedName()
&& callee.getFirstChild().getString().equals("Math")) {
switch (callee.getString()) {
case "abs":
case "acos":
case "acosh":
case "asin":
case "asinh":
case "atan":
case "atanh":
case "atan2":
case "cbrt":
case "ceil":
case "cos":
case "cosh":
case "exp":
case "expm1":
case "floor":
case "hypot":
case "log":
case "log10":
case "log1p":
case "log2":
case "max":
case "min":
case "pow":
case "round":
case "sign":
case "sin":
case "sinh":
case "sqrt":
case "tan":
case "tanh":
case "trunc":
return false;
case "random":
return !callNode.hasOneChild(); // no parameters
default:
// Unknown Math.* function, so fall out of this switch statement.
}
}
if (!compiler.hasRegExpGlobalReferences()) {
if (callee.getFirstChild().isRegExp() && REGEXP_METHODS.contains(callee.getString())) {
return false;
} else if (isTypedAsString(callee.getFirstChild())) {
// Unlike regexs, string methods don't need to be hosted on a string literal
// to avoid leaking mutating global state changes, it is just necessary that
// the regex object can't be referenced.
String method = callee.getString();
Node param = callee.getNext();
if (param != null) {
if (param.isStringLit()) {
if (STRING_REGEXP_METHODS.contains(method)) {
return false;
}
} else if (param.isRegExp()) {
if ("replace".equals(method)) {
// Assume anything but a string constant has side-effects
return !param.getNext().isStringLit();
} else if (STRING_REGEXP_METHODS.contains(method)) {
return false;
}
}
}
}
}
}
return true;
}
private boolean isTypedAsString(Node n) {
if (n.isStringLit()) {
return true;
}
if (compiler.getOptions().useTypesForLocalOptimization) {
Color color = n.getColor();
if (color != null) {
return color.equals(StandardColors.STRING);
}
JSType type = n.getJSType();
if (type != null) {
JSType nativeStringType =
compiler.getTypeRegistry().getNativeType(JSTypeNative.STRING_TYPE);
if (type.equals(nativeStringType)) {
return true;
}
}
}
return false;
}
/**
* Returns true if some node in n's subtree changes application state. If {@code
* checkForNewObjects} is true, we assume that newly created mutable objects (like object
* literals) change state. Otherwise, we assume that they have no side effects.
*/
private boolean checkForStateChangeHelper(Node n, boolean checkForNewObjects) {
Node parent = n.getParent();
// Rather than id which ops may have side effects, id the ones
// that we know to be safe
switch (n.getToken()) {
case THROW:
// Throw is a side-effect by definition.
case YIELD:
case AWAIT:
case FOR_AWAIT_OF:
// Context switches can conceal side-effects.
case FOR_OF:
case FOR_IN:
// Enhanced for loops are almost always side-effectful; it's not worth checking them
// further. Particularly, they represent a kind of assignment op.
case VAR:
case LET:
case CONST:
case EXPORT:
// Variable declarations are side-effects.
return true;
// import() expressions have side effects
case DYNAMIC_IMPORT:
return true;
case SUPER:
// The super keyword is a noop on its own.
return false;
case OBJECTLIT:
case ARRAYLIT:
case REGEXP:
if (checkForNewObjects) {
return true;
}
break;
case OBJECT_REST:
case OBJECT_SPREAD:
// Object-rest and object-spread may trigger a getter.
if (assumeGettersArePure) {
break; // We still need to inspect the children.
}
return true;
case ITER_REST:
case ITER_SPREAD:
if (NodeUtil.iteratesImpureIterable(n)) {
return true;
}
break;
case NAME:
// TODO(b/129564961): Consider EXPORT declarations.
if (n.hasChildren()) {
// This is the left side of a var/let/const
return true;
}
break;
case FUNCTION:
// Function expressions don't have side-effects, but function
// declarations change the namespace. Either way, we don't need to
// check the children, since they aren't executed at declaration time.
return checkForNewObjects || NodeUtil.isFunctionDeclaration(n);
case GETTER_DEF:
case SETTER_DEF:
case MEMBER_FUNCTION_DEF:
// simply defining a member function, getter, or setter has no side effects
return false;
case COMPUTED_PROP:
if (n.getParent().isClassMembers()) {
return checkForStateChangeHelper(n.getFirstChild(), checkForNewObjects);
}
break; // Assume that COMPUTED_PROP keys in OBJECT_PATTERN never trigger getters.
case MEMBER_FIELD_DEF:
if (n.isStaticMember()
&& n.hasChildren()
&& checkForStateChangeHelper(n.getFirstChild(), checkForNewObjects)) {
return true;
}
return false;
case COMPUTED_FIELD_DEF:
if (checkForStateChangeHelper(n.getFirstChild(), checkForNewObjects)
|| (n.isStaticMember()
&& n.getSecondChild() != null
&& checkForStateChangeHelper(n.getSecondChild(), checkForNewObjects))) {
return true;
}
return false;
case CLASS:
return checkForNewObjects
|| NodeUtil.isClassDeclaration(n)
// Check the extends clause for side effects.
|| checkForStateChangeHelper(n.getSecondChild(), checkForNewObjects)
// Check for class members that are computed properties with side effects.
|| checkForStateChangeHelper(n.getLastChild(), checkForNewObjects);
case CLASS_MEMBERS:
for (Node member = n.getFirstChild(); member != null; member = member.getNext()) {
if (checkForStateChangeHelper(member, checkForNewObjects)) {
return true;
}
}
return false;
case NEW:
if (checkForNewObjects) {
return true;
}
if (!constructorCallHasSideEffects(n)) {
// loop below will see if the constructor parameters have
// side-effects
break;
}
return true;
case CALL:
case OPTCHAIN_CALL:
// calls to functions that have no side effects have the no
// side effect property set.
if (!functionCallHasSideEffects(n)) {
// loop below will see if the function parameters have
// side-effects
break;
}
return true;
case TAGGED_TEMPLATELIT:
if (functionCallHasSideEffects(n)) {
return true;
}
// Need to look at the children for their possible side-effects.
break;
case CAST:
case AND:
case BLOCK:
case ROOT:
case EXPR_RESULT:
case HOOK:
case IF:
case PARAM_LIST:
case DEFAULT_VALUE:
// Any context that supports DEFAULT_VALUE is already an assignment. The possiblity of a
// default doesn't itself create a side-effect. Therefore, we prefer to defer the decision.
case NUMBER:
case BIGINT:
case OR:
case COALESCE:
case THIS:
case TRUE:
case FALSE:
case NULL:
case STRINGLIT:
case SWITCH:
case TEMPLATELIT_SUB:
case TRY:
case EMPTY:
case TEMPLATELIT:
case TEMPLATELIT_STRING:
break;
case STRING_KEY:
if (parent.isObjectPattern()) {
// This STRING_KEY names a property being read from.
// Assumption: GETELEM (via a COMPUTED_PROP) never triggers a getter or setter.
if (getPropertyKind(n.getString()).hasGetter()) {
return true;
} else if (parent.getLastChild().isObjectRest()) {
// Due to language syntax, only the last child can be an OBJECT_REST.
// `({ thisKey: target, ...rest} = something())`
// The presence of `thisKey` affects what properties get put into `rest`.
return true;
}
}
break;
case GETELEM:
case OPTCHAIN_GETELEM:
// Since we can't see what property is accessed we cannot tell whether
// obj[someProp]/obj?.[someProp] will
// trigger a getter or setter, and thus could have side effects.
// We will assume it does not. This introduces some risk of code breakage, but the code
// size cost of assuming all GETELEM/OPTCHAIN_GETELEM nodes have side effects is completely
// unacceptable.
break;
case GETPROP:
case OPTCHAIN_GETPROP:
if (getPropertyKind(n.getString()).hasGetterOrSetter()) {
// TODO(b/135640150): Use the parent nodes to determine whether this is a get or set.
return true;
}
break;
default:
if (NodeUtil.isSimpleOperator(n) || n.isGetProp() || n.isGetElem()) {
break;
}
if (NodeUtil.isAssignmentOp(n)) {
Node assignTarget = n.getFirstChild();
if (assignTarget.isName()) {
return true;
}
// Assignments will have side effects if
// a) The RHS has side effects, or
// b) The LHS has side effects, or
// c) A name on the LHS will exist beyond the life of this statement.
if (checkForStateChangeHelper(n.getFirstChild(), checkForNewObjects)
|| checkForStateChangeHelper(n.getLastChild(), checkForNewObjects)) {
return true;
}
if (NodeUtil.isNormalGet(assignTarget)) {
// If the object being assigned to is a local object, don't
// consider this a side-effect as it can't be referenced
// elsewhere. Don't do this recursively as the property might
// be an alias of another object, unlike a literal below.
Node current = assignTarget.getFirstChild();
if (NodeUtil.evaluatesToLocalValue(current)) {
return false;
}
// A literal value as defined by "isLiteralValue" is guaranteed
// not to be an alias, or any components which are aliases of
// other objects.
// If the root object is a literal don't consider this a
// side-effect.
while (NodeUtil.isNormalGet(current)) {
current = current.getFirstChild();
}
return !NodeUtil.isLiteralValue(current, true);
} else {
// TODO(johnlenz): remove this code and make this an exception. This
// is here only for legacy reasons, the AST is not valid but
// preserve existing behavior.
return !NodeUtil.isLiteralValue(assignTarget, true);
}
}
return true;
}
for (Node c = n.getFirstChild(); c != null; c = c.getNext()) {
if (checkForStateChangeHelper(c, checkForNewObjects)) {
return true;
}
}
return false;
}
/**
* Do calls to this constructor have side effects?
*
* @param newNode - constructor call node
*/
boolean constructorCallHasSideEffects(Node newNode) {
checkArgument(newNode.isNew(), "Expected NEW node, got %s", newNode.getToken());
if (newNode.isNoSideEffectsCall()) {
return false;
}
// allArgsUnescapedLocal() is actually confirming that all of the arguments are literals or
// values created at the point they are passed in to the call and are not saved anywhere in the
// calling scope.
// TODO(bradfordcsmith): It would be good to rename allArgsUnescapedLocal() to something
// that makes this clearer.
if (newNode.isOnlyModifiesArgumentsCall() && NodeUtil.allArgsUnescapedLocal(newNode)) {
return false;
}
Node nameNode = newNode.getFirstChild();
return !nameNode.isName() || !CONSTRUCTORS_WITHOUT_SIDE_EFFECTS.contains(nameNode.getString());
}
/**
* Returns true if the current node's type implies side effects.
*
*
This is a non-recursive version of the may have side effects check; used to check wherever
* the current node's type is one of the reasons why a subtree has side effects.
*/
boolean nodeTypeMayHaveSideEffects(Node n) {
checkNotNull(compiler);
if (NodeUtil.isAssignmentOp(n)) {
return true;
}
switch (n.getToken()) {
case DELPROP:
case DEC:
case INC:
case YIELD:
case THROW:
case AWAIT:
case FOR_IN: // assigns to a loop LHS
case FOR_OF: // assigns to a loop LHS, runs an iterator
case FOR_AWAIT_OF: // assigns to a loop LHS, runs an iterator, async operations.
case DYNAMIC_IMPORT:
return true;
case OPTCHAIN_CALL:
case CALL:
case TAGGED_TEMPLATELIT:
return functionCallHasSideEffects(n);
case NEW:
return constructorCallHasSideEffects(n);
case NAME:
// A variable definition that assigns a value.
// TODO(b/129564961): Consider EXPORT declarations.
return n.hasChildren();
case DESTRUCTURING_LHS:
// A destructuring declaration statement or assignment. Technically these might contain no
// lvalues but that case is rare enough to be ignored.
return true;
case OBJECT_REST:
case OBJECT_SPREAD:
// Object-rest and object-spread may trigger a getter.
return !assumeGettersArePure;
case ITER_REST:
case ITER_SPREAD:
return NodeUtil.iteratesImpureIterable(n);
case STRING_KEY:
if (n.getParent().isObjectPattern()) {
return getPropertyKind(n.getString()).hasGetter();
}
break;
case GETPROP:
case OPTCHAIN_GETPROP:
return getPropertyKind(n.getString()).hasGetterOrSetter();
default:
break;
}
return false;
}
private PropertyAccessKind getPropertyKind(String name) {
return assumeGettersArePure
? PropertyAccessKind.NORMAL
: compiler.getAccessorSummary().getKind(name);
}
}