enhance `join_vars` (#3804)

1 files changed, 24 insertions, 10 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 6742aef3..e40e1d2e 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -2447,6 +2447,7 @@ merge(Compressor.prototype, {
                         statements[++j] = stat;
                         defs = stat;
                     }
+                    continue;
                 } else if (stat instanceof AST_Exit) {
                     stat.value = join_assigns_expr(stat.value);
                 } else if (stat instanceof AST_For) {
@@ -2454,21 +2455,20 @@ merge(Compressor.prototype, {
                     if (exprs) {
                         CHANGED = true;
                         stat.init = exprs.length ? make_sequence(stat.init, exprs) : null;
-                        statements[++j] = stat;
                     } else if (prev instanceof AST_Var && (!stat.init || stat.init.TYPE == prev.TYPE)) {
                         if (stat.init) {
                             prev.definitions = prev.definitions.concat(stat.init.definitions);
                         }
-                        stat.init = prev;
-                        statements[j] = stat;
+                        defs = stat.init = prev;
+                        statements[j] = merge_defns(stat);
                         CHANGED = true;
+                        continue;
                     } else if (defs && stat.init && defs.TYPE == stat.init.TYPE && declarations_only(stat.init)) {
                         defs.definitions = defs.definitions.concat(stat.init.definitions);
                         stat.init = null;
-                        statements[++j] = stat;
                         CHANGED = true;
-                    } else {
-                        statements[++j] = stat;
+                    } else if (stat.init instanceof AST_Definitions) {
+                        defs = stat.init;
                     }
                 } else if (stat instanceof AST_ForIn) {
                     stat.object = join_assigns_expr(stat.object);
@@ -2481,19 +2481,16 @@ merge(Compressor.prototype, {
                         if (!exprs.length) continue;
                         stat.body = make_sequence(stat.body, exprs);
                     }
-                    statements[++j] = stat;
                 } else if (stat instanceof AST_Switch) {
                     stat.expression = join_assigns_expr(stat.expression);
                 } else if (stat instanceof AST_With) {
                     stat.expression = join_assigns_expr(stat.expression);
-                } else {
-                    statements[++j] = stat;
                 }
+                statements[++j] = defs ? merge_defns(stat) : stat;
             }
             statements.length = j + 1;
 
             function join_assigns_expr(value) {
-                statements[++j] = stat;
                 var exprs = join_assigns(prev, value, 1);
                 if (!exprs) return value;
                 CHANGED = true;
@@ -2501,6 +2498,23 @@ merge(Compressor.prototype, {
                 if (exprs[exprs.length - 1] !== tail) exprs.push(tail.left);
                 return make_sequence(value, exprs);
             }
+
+            function merge_defns(stat) {
+                return stat.transform(new TreeTransformer(function(node, descend, in_list) {
+                    if (node instanceof AST_Definitions) {
+                        if (defs === node) return node;
+                        if (defs.TYPE != node.TYPE) return node;
+                        var parent = this.parent();
+                        if (parent instanceof AST_ForIn && parent.init === node) return node;
+                        if (!declarations_only(node)) return node;
+                        defs.definitions = defs.definitions.concat(node.definitions);
+                        CHANGED = true;
+                        return in_list ? List.skip : make_node(AST_EmptyStatement, node);
+                    }
+                    if (node instanceof AST_Scope) return node;
+                    if (!(node instanceof AST_Statement)) return node;
+                }));
+            }
         }
     }