/**
* Updates the first initialization (a.k.a "declaration") of a global name. This involves
* flattening the global name (if it's not just a global variable name already), collapsing object
* literal keys into global variables, declaring stub global variables for properties added later
* in a local scope.
*
* <p>It may seem odd that this function also takes care of declaring stubs for direct children.
* The ultimate goal of this function is to eliminate the global name entirely (when possible), so
* that "middlemen" namespaces disappear, and to do that we need to make sure that all the direct
* children will be collapsed as well.
*
* @param n An object representing a global name (e.g. "a", "a.b.c")
* @param alias The flattened name for {@code n} (e.g. "a", "a$b$c")
* @param canCollapseChildNames Whether it's possible to collapse children of this name. (This is
* mostly passed for convenience; it's equivalent to n.canCollapseChildNames()).
*/
private void updateObjLitOrFunctionDeclaration(
Name n, String alias, boolean canCollapseChildNames) {
Ref decl = n.getDeclaration();
if (decl == null) {
// Some names do not have declarations, because they
// are only defined in local scopes.
return;
}
if (decl.getTwin() != null) {
// Twin declarations will get handled when normal references
// are handled.
return;
}
switch (decl.node.getParent().getType()) {
case Token.ASSIGN:
updateObjLitOrFunctionDeclarationAtAssignNode(n, alias, canCollapseChildNames);
break;
case Token.VAR:
updateObjLitOrFunctionDeclarationAtVarNode(n, canCollapseChildNames);
break;
case Token.FUNCTION:
updateFunctionDeclarationAtFunctionNode(n, canCollapseChildNames);
break;
}
}
/**
* Flattens all references to a collapsible property of a global name except its initial
* definition.
*
* @param n A global property name (e.g. "a.b" or "a.b.c.d")
* @param alias The flattened name (e.g. "a$b" or "a$b$c$d")
*/
private void flattenReferencesTo(Name n, String alias) {
String originalName = n.getFullName();
for (Ref r : n.getRefs()) {
if (r == n.getDeclaration()) {
// Declarations are handled separately.
continue;
}
Node rParent = r.node.getParent();
// There are two cases when we shouldn't flatten a reference:
// 1) Object literal keys, because duplicate keys show up as refs.
// 2) References inside a complex assign. (a = x.y = 0). These are
// called TWIN references, because they show up twice in the
// reference list. Only collapse the set, not the alias.
if (!NodeUtil.isObjectLitKey(r.node) && (r.getTwin() == null || r.isSet())) {
flattenNameRef(alias, r.node, rParent, originalName);
}
}
// Flatten all occurrences of a name as a prefix of its subnames. For
// example, if {@code n} corresponds to the name "a.b", then "a.b" will be
// replaced with "a$b" in all occurrences of "a.b.c", "a.b.c.d", etc.
if (n.props != null) {
for (Name p : n.props) {
flattenPrefixes(alias, p, 1);
}
}
}
/**
* Flattens all occurrences of a name as a prefix of subnames beginning with a particular subname.
*
* @param n A global property name (e.g. "a.b.c.d")
* @param alias A flattened prefix name (e.g. "a$b")
* @param depth The difference in depth between the property name and the prefix name (e.g. 2)
*/
private void flattenPrefixes(String alias, Name n, int depth) {
// Only flatten the prefix of a name declaration if the name being
// initialized is fully qualified (i.e. not an object literal key).
String originalName = n.getFullName();
Ref decl = n.getDeclaration();
if (decl != null && decl.node != null && decl.node.isGetProp()) {
flattenNameRefAtDepth(alias, decl.node, depth, originalName);
}
for (Ref r : n.getRefs()) {
if (r == decl) {
// Declarations are handled separately.
continue;
}
// References inside a complex assign (a = x.y = 0)
// have twins. We should only flatten one of the twins.
if (r.getTwin() == null || r.isSet()) {
flattenNameRefAtDepth(alias, r.node, depth, originalName);
}
}
if (n.props != null) {
for (Name p : n.props) {
flattenPrefixes(alias, p, depth + 1);
}
}
}
/**
* For each qualified name N in the global scope, we check if: (a) No ancestor of N is ever
* aliased or assigned an unknown value type. (If N = "a.b.c", "a" and "a.b" are never aliased).
* (b) N has exactly one write, and it lives in the global scope. (c) N is aliased in a local
* scope. (d) N is aliased in global scope
*
* <p>If (a) is true, then GlobalNamespace must know all the writes to N. If (a) and (b) are true,
* then N cannot change during the execution of a local scope. If (a) and (b) and (c) are true,
* then the alias can be inlined if the alias obeys the usual rules for how we decide whether a
* variable is inlineable. If (a) and (b) and (d) are true, then inline the alias if possible (if
* it is assigned exactly once unconditionally).
*
* @see InlineVariables
*/
private void inlineAliases(GlobalNamespace namespace) {
// Invariant: All the names in the worklist meet condition (a).
Deque<Name> workList = new ArrayDeque<>(namespace.getNameForest());
while (!workList.isEmpty()) {
Name name = workList.pop();
// Don't attempt to inline a getter or setter property as a variable.
if (name.type == Name.Type.GET || name.type == Name.Type.SET) {
continue;
}
if (!name.inExterns && name.globalSets == 1 && name.localSets == 0 && name.aliasingGets > 0) {
// {@code name} meets condition (b). Find all of its local aliases
// and try to inline them.
List<Ref> refs = new ArrayList<>(name.getRefs());
for (Ref ref : refs) {
if (ref.type == Type.ALIASING_GET && ref.scope.isLocal()) {
// {@code name} meets condition (c). Try to inline it.
// TODO(johnlenz): consider picking up new aliases at the end
// of the pass instead of immediately like we do for global
// inlines.
if (inlineAliasIfPossible(name, ref, namespace)) {
name.removeRef(ref);
}
} else if (ref.type == Type.ALIASING_GET
&& ref.scope.isGlobal()
&& ref.getTwin() == null) { // ignore aliases in chained assignments
if (inlineGlobalAliasIfPossible(name, ref, namespace)) {
name.removeRef(ref);
}
}
}
}
// Check if {@code name} has any aliases left after the
// local-alias-inlining above.
if ((name.type == Name.Type.OBJECTLIT || name.type == Name.Type.FUNCTION)
&& name.aliasingGets == 0
&& name.props != null) {
// All of {@code name}'s children meet condition (a), so they can be
// added to the worklist.
workList.addAll(name.props);
}
}
}
/**
* Updates the initial assignment to a collapsible property at global scope by changing it to a
* variable declaration (e.g. a.b = 1 -> var a$b = 1). The property's value may either be a
* primitive or an object literal or function whose properties aren't collapsible.
*
* @param alias The flattened property name (e.g. "a$b")
* @param refName The name for the reference being updated.
* @param ref An object containing information about the assignment getting updated
*/
private void updateSimpleDeclaration(String alias, Name refName, Ref ref) {
Node rvalue = ref.node.getNext();
Node parent = ref.node.getParent();
Node grandparent = parent.getParent();
Node greatGrandparent = grandparent.getParent();
if (rvalue != null && rvalue.isFunction()) {
checkForHosedThisReferences(rvalue, refName.docInfo, refName);
}
// Create the new alias node.
Node nameNode =
NodeUtil.newName(compiler, alias, grandparent.getFirstChild(), refName.getFullName());
NodeUtil.copyNameAnnotations(ref.node.getLastChild(), nameNode);
if (grandparent.isExprResult()) {
// BEFORE: a.b.c = ...;
// exprstmt
// assign
// getprop
// getprop
// name a
// string b
// string c
// NODE
// AFTER: var a$b$c = ...;
// var
// name a$b$c
// NODE
// Remove the r-value (NODE).
parent.removeChild(rvalue);
nameNode.addChildToFront(rvalue);
Node varNode = IR.var(nameNode);
greatGrandparent.replaceChild(grandparent, varNode);
} else {
// This must be a complex assignment.
Preconditions.checkNotNull(ref.getTwin());
// BEFORE:
// ... (x.y = 3);
//
// AFTER:
// var x$y;
// ... (x$y = 3);
Node current = grandparent;
Node currentParent = grandparent.getParent();
for (;
!currentParent.isScript() && !currentParent.isBlock();
current = currentParent, currentParent = currentParent.getParent()) {}
// Create a stub variable declaration right
// before the current statement.
Node stubVar = IR.var(nameNode.cloneTree()).useSourceInfoIfMissingFrom(nameNode);
currentParent.addChildBefore(stubVar, current);
parent.replaceChild(ref.node, nameNode);
}
compiler.reportCodeChange();
}
