com.google.javascript.jscomp.LinkedFlowScope Maven / Gradle / Ivy
/*
* 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 com.google.javascript.jscomp.type.FlowScope;
import com.google.javascript.rhino.HamtPMap;
import com.google.javascript.rhino.JSDocInfo;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.PMap;
import com.google.javascript.rhino.jstype.JSType;
import com.google.javascript.rhino.jstype.StaticTypedRef;
import com.google.javascript.rhino.jstype.StaticTypedScope;
import com.google.javascript.rhino.jstype.StaticTypedSlot;
/**
* A flow scope that tries to store as little symbol information as possible,
* instead delegating to its parents. Optimized for low memory use.
*
* @author [email protected] (Nick Santos)
*/
class LinkedFlowScope implements FlowScope {
// Map from TypedScope to OverlayScope.
private final PMap scopes;
private final TypedScope functionScope;
// The TypedScope for the block that this flow scope is defined for.
private final TypedScope syntacticScope;
/**
* Creates a flow scope without a direct parent. This can happen in three cases: (1) the "bottom"
* scope for a CFG root, (2) a direct child of a parent at the maximum depth, or (3) a joined
* scope with more than one direct parent. The parent is non-null only in the second case.
*/
private LinkedFlowScope(
PMap scopes,
TypedScope syntacticScope,
TypedScope functionScope) {
this.scopes = scopes;
this.syntacticScope = syntacticScope;
this.functionScope = functionScope;
}
/**
* Returns the scope map, trimmed to the common ancestor between this FlowScope's syntacticScope
* and the given scope. Any inferred types on variables in deeper scopes cannot be propagated past
* this point (since they're no longer in scope), and trimming them eagerly allows us to ignore
* these irrelevant types when checking equality and joining.
*/
private PMap trimScopes(TypedScope scope) {
TypedScope thisScope = syntacticScope;
TypedScope thatScope = scope;
int thisDepth = thisScope.getDepth();
int thatDepth = thatScope.getDepth();
PMap result = scopes;
while (thatDepth > thisDepth) {
thatScope = thatScope.getParent();
thatDepth--;
}
while (thisDepth > thatDepth) {
result = result.minus(thisScope);
thisScope = thisScope.getParent();
thisDepth--;
}
while (thisScope != thatScope && thisScope != null && thatScope != null) {
result = result.minus(thisScope);
thisScope = thisScope.getParent();
thatScope = thatScope.getParent();
}
return result;
}
/** Whether this flows from a bottom scope. */
private boolean flowsFromBottom() {
return functionScope.isBottom();
}
/**
* Creates an entry lattice for the flow.
*/
public static LinkedFlowScope createEntryLattice(TypedScope scope) {
return new LinkedFlowScope(HamtPMap.empty(), scope, scope);
}
@Override
public LinkedFlowScope inferSlotType(String symbol, JSType type) {
OverlayScope scope = getOverlayScopeForName(symbol, true);
OverlayScope newScope = scope.infer(symbol, type);
// Aggressively remove empty scopes to maintain a reasonable equivalence.
PMap newScopes =
!newScope.slots.isEmpty() ? scopes.plus(scope.scope, newScope) : scopes.minus(scope.scope);
return newScopes != scopes
? new LinkedFlowScope(newScopes, syntacticScope, functionScope)
: this;
}
@Override
public LinkedFlowScope inferQualifiedSlot(
Node node, String symbol, JSType bottomType, JSType inferredType, boolean declared) {
if (functionScope.isGlobal()) {
// Do not infer qualified names on the global scope. Ideally these would be
// added to the scope by TypedScopeCreator, but if they are not, adding them
// here causes scaling problems (large projects can have tens of thousands of
// undeclared qualified names in the global scope) with no real benefit.
return this;
}
TypedVar v = syntacticScope.getVar(symbol);
if (v == null && !functionScope.isBottom()) {
// NOTE(sdh): Qualified names are declared on scopes lazily via this method.
// The difficulty is that it's not always clear which scope they need to be
// defined on. In particular, syntacticScope is wrong because it is often a
// nested block scope that is ignored when branches are joined; functionScope
// is also wrong because it could lead to ambiguity if the same root name is
// declared in multiple different blocks. Instead, the qualified name is declared
// on the scope that owns the root, when possible. When the root is undeclared, the qualified
// name is declared in the global scope, as only global variables can be undeclared.
TypedVar rootVar = syntacticScope.getVar(getRootOfQualifiedName(symbol));
TypedScope rootScope = rootVar != null ? rootVar.getScope() : syntacticScope.getGlobalScope();
v = rootScope.declare(symbol, node, bottomType, null, !declared);
}
JSType declaredType = v != null ? v.getType() : null;
if (v != null) {
if (!v.isTypeInferred()) {
// Use the inferred type over the declared type only if the
// inferred type is a strict subtype of the declared type.
if (declaredType == null
|| !inferredType.isSubtypeOf(declaredType)
|| declaredType.isSubtypeOf(inferredType)
|| inferredType.isEquivalentTo(declaredType)) {
return this;
}
} else if (declaredType != null && !inferredType.isSubtypeOf(declaredType)) {
// If this inferred type is incompatible with another type previously
// inferred and stored on the scope, then update the scope.
v.setType(v.getType().getLeastSupertype(inferredType));
}
}
return inferSlotType(symbol, inferredType);
}
@Override
public JSType getTypeOfThis() {
return functionScope.getTypeOfThis();
}
@Override
public Node getRootNode() {
return syntacticScope.getRootNode();
}
@Override
public StaticTypedScope getParentScope() {
throw new UnsupportedOperationException();
}
/** Get the slot for the given symbol. */
@Override
public StaticTypedSlot getSlot(String name) {
TypedVar var = syntacticScope.getVar(name);
OverlayScope scope =
var == null
? getOverlayScopeForName(name, false)
: getOverlayScopeForScope(var.getScope(), false);
return scope != null ? scope.getSlot(name) : var;
}
private static String getRootOfQualifiedName(String name) {
int index = name.indexOf('.');
return index < 0 ? name : name.substring(0, index);
}
/**
* Returns the overlay scope corresponding to this qualified name
*
* @param create whether to create a new OverlayScope if one does not already exist.
*/
private OverlayScope getOverlayScopeForName(String name, boolean create) {
TypedVar rootVar = syntacticScope.getVar(getRootOfQualifiedName(name));
TypedScope scope = rootVar != null ? rootVar.getScope() : null;
scope = scope != null ? scope : functionScope;
return getOverlayScopeForScope(scope, create);
}
/**
* Returns the overlay scope corresponding to this syntactic scope.
*
* Use instead of {@link #getOverlayScopeForName(String, boolean)} if you already know the
* correct scope in order to avoid a variable lookup.
*
* @param scope the syntactic scope
* @param create whether to create a new OverlayScope if one does not already exist.
*/
private OverlayScope getOverlayScopeForScope(TypedScope scope, boolean create) {
OverlayScope overlay = scopes.get(scope);
if (overlay == null && create) {
overlay = new OverlayScope(scope);
}
return overlay;
}
@Override
public StaticTypedSlot getOwnSlot(String name) {
throw new UnsupportedOperationException();
}
@Override
public FlowScope withSyntacticScope(StaticTypedScope scope) {
TypedScope typedScope = (TypedScope) scope;
return scope != syntacticScope
? new LinkedFlowScope(trimScopes(typedScope), typedScope, functionScope)
: this;
}
@Override
public TypedScope getDeclarationScope() {
return syntacticScope;
}
/** Join the two FlowScopes. */
static class FlowScopeJoinOp extends JoinOp.BinaryJoinOp {
// NOTE(sdh): When joining flow scopes with different syntactic scopes,
// we do not attempt to recover the correct syntactic scope. This is
// okay because joins only occur in two situations: (1) performed by
// the DataFlowAnalysis class automatically between CFG nodes, and (2)
// requested manually while traversing a single expression within a CFG
// node. The syntactic scope is always set at the beginning of flowing
// through a CFG node. In the case of (1), the join result's syntactic
// scope is immediately replaced with the correct one when we flow through
// the next node. In the case of (2), both inputs will always have the
// same syntactic scope. So simply propagating either input's scope is
// perfectly fine.
@Override
public FlowScope apply(FlowScope a, FlowScope b) {
// To join the two scopes, we have to
LinkedFlowScope linkedA = (LinkedFlowScope) a;
LinkedFlowScope linkedB = (LinkedFlowScope) b;
if (linkedA.scopes == linkedB.scopes && linkedA.functionScope == linkedB.functionScope) {
return linkedA;
}
// NOTE: it would be nice to put 'null' as the syntactic scope if they're not
// equal, but this is not currently feasible. For joins that occur within a
// single CFG node's flow, it's irrelevant, but for joins between separate
// CFG nodes, there is *one* place where the syntactic scope is actually used:
// when joining more than two scopes, the first two scopes are joined, and
// then the join result is joined with the third. When joining, we look up
// the types (and existence) of vars in one scope in the other; so when a var
// from the third scope (say, a local) is missing from the join result, it
// looks through the syntactic scope before realizing this. A quick fix
// might be to just check that the scope is non-null before trying to join;
// a better long-term fix would be to improve how we do joins to avoid
// excessive map entry creation: find a common ancestor, etc. One
// interesting consequence of the current approach is that we may end up
// adding irrelevant block-local variables to the joined scope unnecessarily.
TypedScope common = getCommonParentDeclarationScope(linkedA, linkedB);
return new LinkedFlowScope(
join(linkedA, linkedB, common),
common,
linkedA.flowsFromBottom() ? linkedB.functionScope : linkedA.functionScope);
}
}
static TypedScope getCommonParentDeclarationScope(LinkedFlowScope left, LinkedFlowScope right) {
if (left.flowsFromBottom()) {
return right.syntacticScope;
} else if (right.flowsFromBottom()) {
return left.syntacticScope;
}
return left.syntacticScope.getCommonParent(right.syntacticScope);
}
@Override
public boolean equals(Object other) {
if (!(other instanceof LinkedFlowScope)) {
return false;
}
LinkedFlowScope that = (LinkedFlowScope) other;
// If two flow scopes are in the same function, then they could have
// two possible function scopes: the real one and the BOTTOM scope.
// If they have different function scopes, we *should* iterate through all
// the variables in each scope and compare. However, 99.9% of the time,
// they're not equal. And the other .1% of the time, we can pretend
// they're equal--this just means that data flow analysis will have
// to propagate the entry lattice a little bit further than it
// really needs to. Everything will still come out ok.
return this.functionScope == that.functionScope
&& this.scopes.equivalent(that.scopes, LinkedFlowScope::equalScopes);
}
private static boolean equalScopes(OverlayScope left, OverlayScope right) {
if (left == right) {
return true;
}
return left.slots.equivalent(right.slots, LinkedFlowScope::equalSlots);
}
/**
* Determines whether two slots are meaningfully different for the purposes of data flow analysis.
*/
private static boolean equalSlots(StaticTypedSlot slotA, StaticTypedSlot slotB) {
return slotA == slotB || !slotA.getType().differsFrom(slotB.getType());
}
@Override
public int hashCode() {
throw new UnsupportedOperationException();
}
@SuppressWarnings("ReferenceEquality") // JSType comparisons are expensive, so just use identity.
private static PMap join(
LinkedFlowScope linkedA, LinkedFlowScope linkedB, TypedScope commonParent) {
return linkedA
.trimScopes(commonParent)
.reconcile(
linkedB.trimScopes(commonParent),
(scopeA, scopeB) -> {
PMap slotsA = scopeA != null ? scopeA.slots : EMPTY_SLOTS;
PMap slotsB = scopeB != null ? scopeB.slots : EMPTY_SLOTS;
// TODO(sdh): Simplify this logic: we want the best non-bottom scope we can get,
// for the purpose of (a) passing to the joined OverlayScope constructor, and
// (b) joining types only present in one scope.
TypedScope typedScopeA =
linkedA.flowsFromBottom() ? null : scopeA != null ? scopeA.scope : scopeB.scope;
TypedScope typedScopeB =
linkedB.flowsFromBottom() ? null : scopeB != null ? scopeB.scope : scopeA.scope;
TypedScope bestScope = typedScopeA != null ? typedScopeA : typedScopeB;
bestScope =
bestScope != null ? bestScope : scopeA != null ? scopeA.scope : scopeB.scope;
return new OverlayScope(
bestScope,
slotsA.reconcile(
slotsB,
(slotA, slotB) -> {
// There are 5 different join cases:
// 1) The type is present in joinedScopeA, not in joinedScopeB,
// and not in functionScope. Just use the one in A.
// 2) The type is present in joinedScopeB, not in joinedScopeA,
// and not in functionScope. Just use the one in B.
// 3) The type is present in functionScope and joinedScopeA, but
// not in joinedScopeB. Join the two types.
// 4) The type is present in functionScope and joinedScopeB, but
// not in joinedScopeA. Join the two types.
// 5) The type is present in joinedScopeA and joinedScopeB. Join
// the two types.
String name = slotA != null ? slotA.getName() : slotB.getName();
if (slotB == null || slotB.getType() == null) {
TypedVar fnSlot = typedScopeB != null ? typedScopeB.getSlot(name) : null;
JSType fnSlotType = fnSlot != null ? fnSlot.getType() : null;
if (fnSlotType != null && fnSlotType != slotA.getType()) {
// Case #3
JSType joinedType = slotA.getType().getLeastSupertype(fnSlotType);
return joinedType != slotA.getType()
? new OverlaySlot(name, joinedType)
: slotA;
} else {
// Case #1
return slotA;
}
} else if (slotA == null || slotA.getType() == null) {
TypedVar fnSlot = typedScopeA != null ? typedScopeA.getSlot(name) : null;
JSType fnSlotType = fnSlot != null ? fnSlot.getType() : null;
if (fnSlotType != null && fnSlotType != slotB.getType()) {
// Case #4
JSType joinedType = slotB.getType().getLeastSupertype(fnSlotType);
return joinedType != slotB.getType()
? new OverlaySlot(name, joinedType)
: slotB;
} else {
// Case #2
return slotB;
}
}
// Case #5
if (slotA.getType() == slotB.getType()) {
return slotA;
}
JSType joinedType = slotA.getType().getLeastSupertype(slotB.getType());
return joinedType != slotA.getType()
? new OverlaySlot(name, joinedType)
: slotA;
}));
});
}
private static class OverlayScope {
final TypedScope scope;
final PMap slots;
OverlayScope(TypedScope scope) {
this.scope = checkNotNull(scope);
this.slots = EMPTY_SLOTS;
}
OverlayScope(TypedScope scope, PMap slots) {
this.scope = checkNotNull(scope);
this.slots = slots;
}
@SuppressWarnings("ReferenceEquality") // JSType#equals is expensive, so use identity.
OverlayScope infer(String name, JSType type) {
// TODO(sdh): variants that do or don't clobber properties (i.e. look up and modify instead)
OverlaySlot slot = slots.get(name);
if (slot != null && type == slot.type) {
return this;
}
return new OverlayScope(scope, slots.plus(name, new OverlaySlot(name, type)));
}
StaticTypedSlot getSlot(String name) {
OverlaySlot slot = slots.get(name);
return slot != null ? slot : scope.getSlot(name);
}
}
private static class OverlaySlot implements StaticTypedSlot {
// TODO(sdh): add a final PMap for properties
final String name;
final JSType type;
OverlaySlot(String name, JSType type) {
this.name = name;
this.type = type;
}
@Override
public String getName() {
return name;
}
@Override
public JSType getType() {
return type;
}
@Override
public boolean isTypeInferred() {
return true;
}
@Override
public StaticTypedRef getDeclaration() {
return null;
}
@Override
public JSDocInfo getJSDocInfo() {
return null;
}
@Override
public StaticTypedScope getScope() {
throw new UnsupportedOperationException();
}
}
private static final PMap EMPTY_SLOTS = HamtPMap.empty();
}