private boolean isRemovableVar(Var var) {
// Global variables are off-limits if the user might be using them.
if (!removeGlobals && var.isGlobal()) {
return false;
}
// Referenced variables are off-limits.
if (referenced.contains(var)) {
return false;
}
// Exported variables are off-limits.
if (codingConvention.isExported(var.getName())) {
return false;
}
return true;
}
/**
* Traverses everything in the current scope and marks variables that are referenced.
*
* <p>During traversal, we identify subtrees that will only be referenced if their enclosing
* variables are referenced. Instead of traversing those subtrees, we create a continuation for
* them, and traverse them lazily.
*/
private void traverseNode(Node n, Node parent, Scope scope) {
int type = n.getType();
Var var = null;
switch (type) {
case Token.FUNCTION:
// If this function is a removable var, then create a continuation
// for it instead of traversing immediately.
if (NodeUtil.isFunctionDeclaration(n)) {
var = scope.getVar(n.getFirstChild().getString());
}
if (var != null && isRemovableVar(var)) {
continuations.put(var, new Continuation(n, scope));
} else {
traverseFunction(n, scope);
}
return;
case Token.ASSIGN:
Assign maybeAssign = Assign.maybeCreateAssign(n);
if (maybeAssign != null) {
// Put this in the assign map. It might count as a reference,
// but we won't know that until we have an index of all assigns.
var = scope.getVar(maybeAssign.nameNode.getString());
if (var != null) {
assignsByVar.put(var, maybeAssign);
assignsByNode.put(maybeAssign.nameNode, maybeAssign);
if (isRemovableVar(var) && !maybeAssign.mayHaveSecondarySideEffects) {
// If the var is unreferenced and performing this assign has
// no secondary side effects, then we can create a continuation
// for it instead of traversing immediately.
continuations.put(var, new Continuation(n, scope));
return;
}
}
}
break;
case Token.CALL:
// Look for calls to inheritance-defining calls (such as goog.inherits).
SubclassRelationship subclassRelationship = codingConvention.getClassesDefinedByCall(n);
if (subclassRelationship != null) {
Var subclassVar = scope.getVar(subclassRelationship.subclassName);
// Don't try to track the inheritance calls for non-globals. It would
// be more correct to only not track when the subclass does not
// reference a constructor, but checking that it is a global is
// easier and mostly the same.
if (subclassVar != null && subclassVar.isGlobal() && !referenced.contains(subclassVar)) {
// Save a reference to the EXPR node.
inheritsCalls.put(subclassVar, parent);
continuations.put(subclassVar, new Continuation(n, scope));
return;
}
}
break;
case Token.NAME:
var = scope.getVar(n.getString());
if (parent.getType() == Token.VAR) {
Node value = n.getFirstChild();
if (value != null
&& var != null
&& isRemovableVar(var)
&& !NodeUtil.mayHaveSideEffects(value)) {
// If the var is unreferenced and creating its value has no side
// effects, then we can create a continuation for it instead
// of traversing immediately.
continuations.put(var, new Continuation(n, scope));
return;
}
} else {
// If arguments is escaped, we just assume the worst and continue
// on all the parameters.
if ("arguments".equals(n.getString()) && scope.isLocal()) {
Node lp = scope.getRootNode().getFirstChild().getNext();
for (Node a = lp.getFirstChild(); a != null; a = a.getNext()) {
markReferencedVar(scope.getVar(a.getString()));
}
}
// All name references that aren't declarations or assigns
// are references to other vars.
if (var != null) {
// If that var hasn't already been marked referenced, then
// start tracking it. If this is an assign, do nothing
// for now.
if (isRemovableVar(var)) {
if (!assignsByNode.containsKey(n)) {
markReferencedVar(var);
}
} else {
markReferencedVar(var);
}
}
}
break;
}
for (Node c = n.getFirstChild(); c != null; c = c.getNext()) {
traverseNode(c, n, scope);
}
}