fix corner case in collapse_vars (#5018)

fixes #5017

lib/compress.js

@@ -1820,7 +1820,7 @@ merge(Compressor.prototype, {
                     if (is_lhs(node, parent)) {
                         if (value_def && !hit_rhs) {
                             assign_used = true;
-                            replaced++;
+                            if (node.definition().last_ref === node) replaced++;
                         }
                         return node;
                     } else if (value_def) {
@@ -1946,10 +1946,9 @@ merge(Compressor.prototype, {
                     }
                 }
                 // Replace variable when found
-                if (node instanceof AST_SymbolRef
-                    && node.name == def.name) {
-                    if (!--replaced) abort = true;
+                if (node instanceof AST_SymbolRef && node.definition() === def) {
                     if (is_lhs(node, multi_replacer.parent())) return node;
+                    if (!--replaced) abort = true;
                     var ref = rvalue.clone();
                     ref.scope = node.scope;
                     ref.reference();

test/compress/collapse_vars.js

@@ -4658,6 +4658,7 @@ replace_all_var_scope: {
     rename = true
     options = {
         collapse_vars: true,
+        reduce_vars: true,
         unused: true,
     }
     mangle = {}
@@ -4676,7 +4677,7 @@ replace_all_var_scope: {
         (function(c, o) {
             switch (~a) {
               case (b += a):
-              case o++:
+              case +o:
             }
         })(--b, a);
         console.log(a, b);
@@ -4728,7 +4729,7 @@ cascade_statement: {
         }
         function f3(a, b) {
             for (; a < b; a++)
-                if (c = a, a && b)
+                if ((c = a) && b)
                     var c = c = b(a);
         }
     }

test/compress/destructured.js

@@ -2625,3 +2625,25 @@ issue_4994: {
     expect_stdout: "PASS"
     node_version: ">=6"
 }
+
+issue_5017: {
+    options = {
+        collapse_vars: true,
+        reduce_vars: true,
+        toplevel: true,
+    }
+    input: {
+        var a = function() {};
+        var b = c = a;
+        var c = [ c ] = [ c ];
+        console.log(c[0] === a ? "PASS" : "FAIL");
+    }
+    expect: {
+        var a = function() {};
+        var b = a;
+        var c = [ c ] = [ c = a ];
+        console.log(c[0] === a ? "PASS" : "FAIL");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}

test/compress/keep_fargs.js

@@ -1151,6 +1151,7 @@ replace_all_var_scope: {
     options = {
         collapse_vars: true,
         keep_fargs: false,
+        reduce_vars: true,
         unused: true,
     }
     mangle = {}
@@ -1169,7 +1170,7 @@ replace_all_var_scope: {
         (function(c) {
             switch (~a) {
               case (b += a):
-            case c++:
+              case +c:
             }
         })((--b, a));
         console.log(a, b);