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add comments for #1602

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alexlamsl 2017-03-15 23:24:38 +08:00
parent 3787fc1570
commit 200090a38d
1 changed files with 10 additions and 0 deletions
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10
lib/compress.js
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@ -151,7 +151,17 @@ merge(Compressor.prototype, {
node = node.hoist_declarations(this); node = node.hoist_declarations(this);
was_scope = true; was_scope = true;
} }
// Before https://github.com/mishoo/UglifyJS2/pull/1602 AST_Node.optimize()
// would call AST_Node.transform() if a different instance of AST_Node is
// produced after OPT().
// This corrupts TreeWalker.stack, which cause AST look-ups to malfunction.
// Migrate and defer all children's AST_Node.transform() to below, which
// will now happen after this parent AST_Node has been properly substituted
// thus gives a consistent AST snapshot.
descend(node, this); descend(node, this);
// Existing code relies on how AST_Node.optimize() worked, and omitting the
// following replacement call would result in degraded efficiency of both
// output and performance.
descend(node, this); descend(node, this);
var opt = node.optimize(this); var opt = node.optimize(this);
if (was_scope && opt instanceof AST_Scope) { if (was_scope && opt instanceof AST_Scope) {