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/*
* Copyright 2018 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.ImmutableMap;
import com.google.common.collect.Maps;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.StaticScope;
import java.io.Serializable;
import java.util.Collections;
import java.util.EnumMap;
import java.util.LinkedHashMap;
import java.util.Map;
import javax.annotation.Nullable;
/**
* Scope contains information about a variable scope in JavaScript. Scopes can be nested, a scope
* points back to its parent scope. A Scope contains information about variables defined in that
* scope.
*
* ES 2015 introduces new scoping rules, which adds some complexity to this class. In particular,
* scopes fall into two mutually exclusive categories: block and container. Block
* scopes are all scopes whose roots are blocks, as well as any control structures whose optional
* blocks are omitted. These scopes did not exist at all prior to ES 2015. Container scopes comprise
* function scopes, global scopes, and module scopes, and (aside from modules, which didn't exist in
* ES5) corresponds to the ES5 scope rules. This corresponds roughly to one container scope per CFG
* root (but not exactly, due to SCRIPT-level CFGs).
*
*
All container scopes, plus the outermost block scope within a function (i.e. the function
* block scope) are considered hoist scopes. All functions thus have two hoist scopes:
* the function scope and the function block scope. Hoist scopes are relevant because "var"
* declarations are hoisted to the closest hoist scope, as opposed to "let" and "const" which always
* apply to the specific scope in which they occur.
*
*
Note that every function actually has two distinct hoist scopes: a container scope on the
* FUNCTION node, and a block-scope on the top-level BLOCK in the function (the "function block").
* Local variables are declared on the function block, while parameters and optionally the function
* name (if it bleeds, i.e. from a named function expression) are declared on the container scope.
* This is required so that default parameter initializers can refer to names from outside the
* function that could possibly be shadowed in the function block. But these scopes are not fully
* independent of one another, since the language does not allow a top-level local variable to
* shadow a parameter name - so in some situations these scopes must be treated as a single scope.
*
* @see NodeTraversal
*/
public abstract class AbstractScope, V extends AbstractVar>
implements StaticScope, Serializable {
private Map vars = ImmutableMap.of();
private Map implicitVars = ImmutableMap.of();
private final Node rootNode;
AbstractScope(Node rootNode) {
this.rootNode = checkNotNull(rootNode);
}
/** The depth of the scope. The global scope has depth 0. */
public abstract int getDepth();
/** Returns the parent scope, or null if this is the global scope. */
public abstract S getParent();
@Override
public final String toString() {
return "Scope@" + rootNode;
}
public Scope untyped() {
throw new IllegalStateException("untyped() called, but not an untyped scope.");
}
public TypedScope typed() {
throw new IllegalStateException("typed() called, but not a typed scope.");
}
/**
* @return True if this scope contains {@code other}, or is the same scope as {@code other}.
*/
final boolean contains(S other) {
S s = checkNotNull(other);
while (s != null) {
if (s == this) {
return true;
}
s = s.getParent();
}
return false;
}
/**
* Gets the container node of the scope. This is typically the FUNCTION node or the global
* BLOCK/SCRIPT node.
*/
@Override
public final Node getRootNode() {
return rootNode;
}
/** Walks up the tree to find the global scope. */
public final S getGlobalScope() {
S result = thisScope();
while (result.getParent() != null) {
result = result.getParent();
}
return result;
}
@Override
public final S getParentScope() {
return getParent();
}
abstract V makeImplicitVar(ImplicitVar type);
/**
* Undeclares a variable, to be used when the compiler optimizes out
* a variable and removes it from the scope.
*/
final void undeclare(V var) {
checkState(var.getScope() == this);
checkState(vars.get(var.getName()).equals(var));
undeclareInteral(var);
}
/** Without any safety checks */
final void undeclareInteral(V var) {
// Assume that vars must contain var, and thus not be empty
vars.remove(var.getName());
}
final void declareInternal(String name, V var) {
checkState(hasOwnSlot(name) || canDeclare(name), "Illegal shadow: %s", var.getNode());
// For memory savings, only initialize the map once it needs to add its first element
Map emptySentinel = ImmutableMap.of();
if (vars == emptySentinel) {
vars = Maps.newLinkedHashMapWithExpectedSize(1);
}
vars.put(name, var);
}
final void clearVarsInternal() {
if (!vars.isEmpty()) {
vars.clear();
}
}
/** Returns true iff this scope implies a slot with the given name. */
protected boolean hasOwnImplicitSlot(@Nullable ImplicitVar name) {
return name != null && name.isMadeByScope(this);
}
/** Returns true if a variable is declared in this scope, with no recursion. */
public final boolean hasOwnSlot(String name) {
return vars.containsKey(name) || hasOwnImplicitSlot(ImplicitVar.of(name));
}
/** Returns true if a variable is declared in this or any parent scope. */
public final boolean hasSlot(String name) {
for (S scope = thisScope(); scope != null; scope = scope.getParent()) {
if (scope.hasOwnSlot(name)) {
return true;
}
}
return false;
}
@Nullable
private final V getOwnImplicitSlot(@Nullable ImplicitVar name) {
if (!hasOwnImplicitSlot(name)) {
return null;
}
// For memory savings, only initialize the map once it needs to add its first element
Map emptySentinel = ImmutableMap.of();
if (implicitVars == emptySentinel) {
implicitVars = new EnumMap<>(ImplicitVar.class);
}
return implicitVars.computeIfAbsent(name, this::makeImplicitVar);
}
@Override
public final V getOwnSlot(String name) {
V var = vars.get(name);
if (var != null) {
return var;
}
return getOwnImplicitSlot(ImplicitVar.of(name));
}
@Override
public final V getSlot(String name) {
return getVar(name);
}
/**
* Returns the variable, may be null
*
* Non-final for {@link TypedScope} which needs to handle qualified names.
*/
public V getVar(String name) {
for (AbstractScope scope = thisScope(); scope != null; scope = scope.getParent()) {
@Nullable V var = scope.getOwnSlot(name);
if (var != null) {
return var;
}
}
return null;
}
/**
* Get a unique Var object to represent "arguments" within this scope.
*
* This explicitly excludes user declared variables that are names "arguments". It only returns
* special "arguments" variable that is inherent to a function.
*/
public final V getArgumentsVar() {
for (AbstractScope scope = thisScope(); scope != null; scope = scope.getParent()) {
@Nullable V arguments = scope.getOwnImplicitSlot(ImplicitVar.ARGUMENTS);
if (arguments != null) {
return arguments;
}
}
return null;
}
/**
* Returns true if the name can be declared on this scope without causing illegal shadowing.
* Specifically, this is aware of the connection between function container scopes and function
* block scopes and returns false for redeclaring parameters on the block scope.
*/
final boolean canDeclare(String name) {
return !hasOwnSlot(name)
&& (!isFunctionBlockScope()
|| !getParent().hasOwnSlot(name)
|| isBleedingFunctionName(name));
}
/**
* Returns true if the given name is a bleeding function name in this scope. Local variables in
* the function block are not allowed to shadow parameters, but they are allowed to shadow a
* bleeding function name.
*/
private boolean isBleedingFunctionName(String name) {
V var = getVar(name);
return var != null //
&& var.getNode() != null //
&& var.getNode().getParent().isFunction();
}
/**
* Return an iterable over all of the variables declared in this scope (except the special
* 'arguments' variable).
*/
public final Iterable getVarIterable() {
return vars.values();
}
/**
* Return an iterable over all of the variables accessible to this scope (i.e. the variables in
* this scope and its parent scopes). Any variables declared in the local scope with the same name
* as a variable declared in a parent scope gain precedence - if let x exists in the block scope,
* a declaration let x from the parent scope would not be included because the parent scope's
* variable gets shadowed.
*
* The iterable contains variables from inner scopes before adding variables from outer parent
* scopes.
*
*
We do not include the special 'arguments' variable.
*/
public final Iterable getAllAccessibleVariables() {
Map accessibleVars = new LinkedHashMap<>();
S s = thisScope();
while (s != null) {
for (V v : s.getVarIterable()) {
accessibleVars.putIfAbsent(v.getName(), v);
}
s = s.getParent();
}
return accessibleVars.values();
}
public final Iterable getAllSymbols() {
return Collections.unmodifiableCollection(vars.values());
}
/** Returns number of variables in this scope (excluding the special 'arguments' variable) */
public final int getVarCount() {
return vars.size();
}
/** Returns whether this is the global scope. */
public final boolean isGlobal() {
return getParent() == null;
}
/** Returns whether this is a local scope (i.e. not the global scope). */
public final boolean isLocal() {
return getParent() != null;
}
public final boolean isBlockScope() {
return NodeUtil.createsBlockScope(rootNode);
}
public final boolean isFunctionBlockScope() {
return NodeUtil.isFunctionBlock(getRootNode());
}
public final boolean isFunctionScope() {
return getRootNode().isFunction();
}
public final boolean isModuleScope() {
return getRootNode().isModuleBody();
}
public final boolean isCatchScope() {
return getRootNode().isBlock()
&& getRootNode().hasOneChild()
&& getRootNode().getFirstChild().isCatch();
}
/**
* If a var were declared in this scope, would it belong to this scope (as opposed to some
* enclosing scope)?
*
* We consider function scopes to be hoist scopes. Even though it's impossible to declare a var
* inside function parameters, it would make less sense to say that if you did declare one in
* the function parameters, it would be hoisted somewhere else.
*/
final boolean isHoistScope() {
return isFunctionScope() || isFunctionBlockScope() || isGlobal() || isModuleScope();
}
/**
* If a var were declared in this scope, return the scope it would be hoisted to.
*
* For function scopes, we return back the scope itself, since even though there is no way to
* declare a var inside function parameters, it would make even less sense to say that such
* declarations would be "hoisted" somewhere else.
*/
public final S getClosestHoistScope() {
S current = thisScope();
while (current != null) {
if (current.isHoistScope()) {
return current;
}
current = current.getParent();
}
return null;
}
/**
* Returns the closest container scope. This is equivalent to what the current scope would have
* been for non-ES6 scope creators, and is thus useful for migrating code to use block scopes.
*/
public final S getClosestContainerScope() {
S scope = getClosestHoistScope();
if (scope.isBlockScope()) {
scope = scope.getParent();
checkState(!scope.isBlockScope());
}
return scope;
}
// This is safe because any concrete subclass of AbstractScope should be assignable to S.
// While it's theoretically possible to do otherwise, such a class would be very awkward to
// implement, and is therefore not worth worrying about.
@SuppressWarnings("unchecked")
private S thisScope() {
return (S) this;
}
/** Performs simple validity checks on when constructing a child scope. */
final void checkChildScope(S parent) {
checkNotNull(parent);
checkArgument(NodeUtil.createsScope(rootNode), rootNode);
checkArgument(
rootNode != parent.getRootNode(),
"rootNode should not be the parent's root node: %s", rootNode);
}
/** Performs simple validity checks on when constructing a root scope. */
final void checkRootScope() {
// TODO(tbreisacher): Can we tighten this to just NodeUtil.createsScope?
checkArgument(
NodeUtil.createsScope(rootNode) || rootNode.isScript() || rootNode.isRoot(), rootNode);
}
/** Returns the nearest common parent between two scopes. */
S getCommonParent(S other) {
S left = thisScope();
S right = other;
while (left != null && right != null && left != right) {
int leftDepth = left.getDepth();
int rightDepth = right.getDepth();
if (leftDepth >= rightDepth) {
left = left.getParent();
}
if (leftDepth <= rightDepth) {
right = right.getParent();
}
}
checkState(left != null && left == right);
return left;
}
/**
* Whether {@code this} and the {@code other} scope have the same container scope (i.e. are in the
* same function, or else both in the global hoist scope). This is equivalent to asking whether
* the two scopes would be equivalent in a pre-ES2015-block-scopes view of the world.
*/
boolean hasSameContainerScope(S other) {
// Do identity check first as a shortcut.
return this == other || getClosestContainerScope() == other.getClosestContainerScope();
}
/**
* Returns the closest scope upon which `this` is defined, which is either the global scope or a
* non-arrow-function scope.
*/
final S getScopeOfThis() {
S scope = getClosestContainerScope();
while (!scope.isGlobal() && !NodeUtil.isNonArrowFunction(scope.getRootNode())) {
scope = scope.getParent().getClosestContainerScope();
}
return scope;
}
/**
* The three implicit var types, which are defined implicitly (at least) in
* every vanilla function scope without actually being declared.
*/
enum ImplicitVar {
ARGUMENTS("arguments"),
EXPORTS("exports"),
SUPER("super"),
// TODO(sdh): Expand THIS.isMadeByScope to check super.isMadeByScope(scope) || scope.isGlobal()
// Currently this causes a number of problems (see b/74980936), but could eventually lead to
// better type information. We might also want to restrict this so that module-root scopes
// explicitly *don't* have access to the global this, though I think this is more than just
// returning false in isMadeByScope - rather, getVar() needs to stop checking and immediately
// return null.
THIS("this");
final String name;
ImplicitVar(String name) {
this.name = name;
}
/** Whether this kind of implicit variable is created/owned by the given scope. */
boolean isMadeByScope(AbstractScope scope) {
if (this.equals(EXPORTS)) {
return scope.isModuleScope()
&& scope.getRootNode().getParent().getBooleanProp(Node.GOOG_MODULE);
}
return NodeUtil.isNonArrowFunction(scope.getRootNode());
}
static ImplicitVar of(String name) {
switch (name) {
case "arguments":
return ARGUMENTS;
case "super":
return SUPER;
case "this":
return THIS;
case "exports":
return EXPORTS;
default:
return null;
}
}
}
}