consolidate & enhance `unused` (#2439)

- defer declaration removal in `collapse_vars`
- account for `AST_SymbolFunarg` in deduplication
- private accounting for `collapse_vars`
- avoid issues with identity reference due to deep cloning

fixes #2437

1 files changed, 74 insertions, 68 deletions

diff --git a/lib/compress.js b/lib/compress.js
index ba7c10f4..d8482337 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -788,6 +788,14 @@ merge(Compressor.prototype, {
             || compressor.option("unsafe") && global_names(this.name);
     });
 
+    function drop_decl(def) {
+        def._eliminiated = (def._eliminiated || 0) + 1;
+        if (def.orig.length == def._eliminiated) {
+            def.scope.functions.del(def.name);
+            def.scope.variables.del(def.name);
+        }
+    }
+
     function tighten_body(statements, compressor) {
         var CHANGED, max_iter = 10;
         do {
@@ -1000,7 +1008,8 @@ merge(Compressor.prototype, {
             function get_lhs(expr) {
                 if (expr instanceof AST_VarDef) {
                     var def = expr.name.definition();
-                    if (def.orig.length > 1 && !(expr.name instanceof AST_SymbolFunarg)
+                    if (def.orig.length - (def._eliminiated || 0) > 1
+                            && !(expr.name instanceof AST_SymbolFunarg)
                         || def.references.length == 1 && !compressor.exposed(def)) {
                         return make_node(AST_SymbolRef, expr.name, expr.name);
                     }
@@ -1009,6 +1018,10 @@ merge(Compressor.prototype, {
                 }
             }
 
+            function get_rvalue(expr) {
+                return expr[expr instanceof AST_Assign ? "right" : "value"];
+            }
+
             function get_lvalues(expr) {
                 var lvalues = Object.create(null);
                 if (expr instanceof AST_Unary) return lvalues;
@@ -1019,7 +1032,7 @@ merge(Compressor.prototype, {
                         lvalues[sym.name] = lvalues[sym.name] || is_lhs(node, tw.parent());
                     }
                 });
-                expr[expr instanceof AST_Assign ? "right" : "value"].walk(tw);
+                get_rvalue(expr).walk(tw);
                 return lvalues;
             }
 
@@ -1043,7 +1056,9 @@ merge(Compressor.prototype, {
                     if (node === expr) {
                         found = true;
                         if (node instanceof AST_VarDef) {
-                            remove(node.name.definition().orig, node.name);
+                            drop_decl(node.name.definition());
+                            node.value = null;
+                            return node;
                         }
                         return in_list ? MAP.skip : null;
                     }
@@ -1052,16 +1067,13 @@ merge(Compressor.prototype, {
                       case 0: return null;
                       case 1: return node.expressions[0];
                     }
-                    if (node instanceof AST_Definitions && node.definitions.length == 0
-                        || node instanceof AST_SimpleStatement && !node.body) {
-                        return null;
-                    }
+                    if (node instanceof AST_SimpleStatement && !node.body) return null;
                 }));
             }
 
             function value_has_side_effects(expr) {
                 if (expr instanceof AST_Unary) return false;
-                return expr[expr instanceof AST_Assign ? "right" : "value"].has_side_effects(compressor);
+                return get_rvalue(expr).has_side_effects(compressor);
             }
 
             function references_in_scope(def) {
@@ -2303,61 +2315,63 @@ merge(Compressor.prototype, {
         // this scope (not in nested scopes).
         var scope = this;
         var tw = new TreeWalker(function(node, descend){
-            if (node !== self) {
-                if (node instanceof AST_Defun) {
-                    if (!drop_funcs && scope === self) {
-                        var node_def = node.name.definition();
+            if (node === self) return;
+            if (node instanceof AST_Defun) {
+                if (!drop_funcs && scope === self) {
+                    var node_def = node.name.definition();
+                    if (!(node_def.id in in_use_ids)) {
+                        in_use_ids[node_def.id] = true;
+                        in_use.push(node_def);
+                    }
+                }
+                initializations.add(node.name.name, node);
+                return true; // don't go in nested scopes
+            }
+            if (node instanceof AST_SymbolFunarg && scope === self) {
+                var_defs_by_id.add(node.definition().id, node);
+            }
+            if (node instanceof AST_Definitions && scope === self) {
+                node.definitions.forEach(function(def){
+                    var node_def = def.name.definition();
+                    if (def.name instanceof AST_SymbolVar) {
+                        var_defs_by_id.add(node_def.id, def);
+                    }
+                    if (!drop_vars) {
                         if (!(node_def.id in in_use_ids)) {
                             in_use_ids[node_def.id] = true;
                             in_use.push(node_def);
                         }
                     }
-                    initializations.add(node.name.name, node);
-                    return true; // don't go in nested scopes
-                }
-                if (node instanceof AST_Definitions && scope === self) {
-                    node.definitions.forEach(function(def){
-                        var node_def = def.name.definition();
-                        if (def.name instanceof AST_SymbolVar) {
-                            var_defs_by_id.add(node_def.id, def);
-                        }
-                        if (!drop_vars) {
-                            if (!(node_def.id in in_use_ids)) {
-                                in_use_ids[node_def.id] = true;
-                                in_use.push(node_def);
-                            }
+                    if (def.value) {
+                        initializations.add(def.name.name, def.value);
+                        if (def.value.has_side_effects(compressor)) {
+                            def.value.walk(tw);
                         }
-                        if (def.value) {
-                            initializations.add(def.name.name, def.value);
-                            if (def.value.has_side_effects(compressor)) {
-                                def.value.walk(tw);
-                            }
-                        }
-                    });
-                    return true;
-                }
-                var sym;
-                if (scope === self
-                    && (sym = assign_as_unused(node)) instanceof AST_SymbolRef
-                    && self.variables.get(sym.name) === sym.definition()) {
-                    if (node instanceof AST_Assign) node.right.walk(tw);
-                    return true;
-                }
-                if (node instanceof AST_SymbolRef) {
-                    var node_def = node.definition();
-                    if (!(node_def.id in in_use_ids)) {
-                        in_use_ids[node_def.id] = true;
-                        in_use.push(node_def);
                     }
-                    return true;
-                }
-                if (node instanceof AST_Scope) {
-                    var save_scope = scope;
-                    scope = node;
-                    descend();
-                    scope = save_scope;
-                    return true;
+                });
+                return true;
+            }
+            var sym;
+            if (scope === self
+                && (sym = assign_as_unused(node)) instanceof AST_SymbolRef
+                && self.variables.get(sym.name) === sym.definition()) {
+                if (node instanceof AST_Assign) node.right.walk(tw);
+                return true;
+            }
+            if (node instanceof AST_SymbolRef) {
+                var node_def = node.definition();
+                if (!(node_def.id in in_use_ids)) {
+                    in_use_ids[node_def.id] = true;
+                    in_use.push(node_def);
                 }
+                return true;
+            }
+            if (node instanceof AST_Scope) {
+                var save_scope = scope;
+                scope = node;
+                descend();
+                scope = save_scope;
+                return true;
             }
         });
         self.walk(tw);
@@ -2415,7 +2429,7 @@ merge(Compressor.prototype, {
                     var def = node.name.definition();
                     if (!(def.id in in_use_ids)) {
                         compressor[node.name.unreferenced() ? "warn" : "info"]("Dropping unused function {name} [{file}:{line},{col}]", template(node.name));
-                        drop_decl(def, node.name);
+                        drop_decl(def);
                         return make_node(AST_EmptyStatement, node);
                     }
                     return node;
@@ -2437,7 +2451,7 @@ merge(Compressor.prototype, {
                                 if (var_defs.length > 1 && !def.value) {
                                     compressor.warn("Dropping duplicated definition of variable {name} [{file}:{line},{col}]", template(def.name));
                                     remove(var_defs, def);
-                                    drop_decl(sym, def.name);
+                                    drop_decl(sym);
                                     return;
                                 }
                             }
@@ -2470,7 +2484,7 @@ merge(Compressor.prototype, {
                             } else {
                                 compressor[def.name.unreferenced() ? "warn" : "info"]("Dropping unused variable {name} [{file}:{line},{col}]", template(def.name));
                             }
-                            drop_decl(sym, def.name);
+                            drop_decl(sym);
                         }
                     });
                     if (head.length == 0 && tail.length == 1 && tail[0].name instanceof AST_SymbolVar) {
@@ -2479,7 +2493,7 @@ merge(Compressor.prototype, {
                             var def = tail.pop();
                             compressor.warn("Converting duplicated definition of variable {name} to assignment [{file}:{line},{col}]", template(def.name));
                             remove(var_defs, def);
-                            drop_decl(def.name.definition(), def.name);
+                            drop_decl(def.name.definition());
                             side_effects.unshift(make_node(AST_Assign, def, {
                                 operator: "=",
                                 left: make_node(AST_SymbolRef, def.name, def.name),
@@ -2561,14 +2575,6 @@ merge(Compressor.prototype, {
                         col  : sym.start.col
                     };
                 }
-
-                function drop_decl(def, decl) {
-                    remove(def.orig, decl);
-                    if (!def.orig.length) {
-                        def.scope.functions.del(def.name);
-                        def.scope.variables.del(def.name);
-                    }
-                }
             }
         );
         self.transform(tt);
@@ -3288,7 +3294,7 @@ merge(Compressor.prototype, {
                 }));
                 if (reduce_vars) name.definition().fixed = false;
             }
-            remove(def.name.definition().orig, def.name);
+            drop_decl(def.name.definition());
             return a;
         }, []);
         if (assignments.length == 0) return null;