fix corner case in merge_vars (#5424)

fixes #5423

lib/compress.js

@@ -6081,18 +6081,15 @@ Compressor.prototype.compress = function(node) {
             }
             if (node instanceof AST_Call) {
                 var exp = node.expression;
-                var tail = exp.tail_node();
-                if (!(tail instanceof AST_LambdaExpression)) {
+                if (exp instanceof AST_LambdaExpression) {
+                    node.args.forEach(function(arg) {
+                        arg.walk(tw);
+                    });
+                    exp.walk(tw);
+                } else {
                     descend();
-                    return mark_expression(exp);
+                    mark_expression(exp);
                 }
-                if (exp !== tail) exp.expressions.slice(0, -1).forEach(function(node) {
-                    node.walk(tw);
-                });
-                node.args.forEach(function(arg) {
-                    arg.walk(tw);
-                });
-                tail.walk(tw);
                 return true;
             }
             if (node instanceof AST_Class) {
@@ -6172,6 +6169,8 @@ Compressor.prototype.compress = function(node) {
                 if (node === self) root = segment;
                 if (node instanceof AST_Lambda) {
                     if (node.name) references[node.name.definition().id] = false;
+                    var parent = tw.parent();
+                    var in_iife = parent && parent.TYPE == "Call" && parent.expression === node;
                     var marker = node.uses_arguments && !tw.has_directive("use strict") ? function(node) {
                         if (node instanceof AST_SymbolFunarg) references[node.definition().id] = false;
                     } : function(node) {
@@ -6187,11 +6186,13 @@ Compressor.prototype.compress = function(node) {
                             || node.parent_scope.find_variable(ref.name) === def)) {
                             references[def.id] = false;
                             references[ldef.id] = false;
-                        } else {
+                        } else if (in_iife) {
                             var save = segment;
                             pop();
                             mark(ref, true);
                             segment = save;
+                        } else {
+                            mark(ref, true);
                         }
                         return true;
                     });
@@ -6214,7 +6215,8 @@ Compressor.prototype.compress = function(node) {
                 } else {
                     descend();
                 }
-                return mark_expression(exp);
+                mark_expression(exp);
+                return true;
             }
             if (node instanceof AST_Switch) {
                 node.expression.walk(tw);
@@ -6313,11 +6315,9 @@ Compressor.prototype.compress = function(node) {
             }
 
             function mark_expression(exp) {
-                if (compressor.option("ie")) {
-                    var sym = root_expr(exp);
-                    if (sym instanceof AST_SymbolRef) sym.walk(tw);
-                }
-                return true;
+                if (!compressor.option("ie")) return;
+                var sym = root_expr(exp);
+                if (sym instanceof AST_SymbolRef) sym.walk(tw);
             }
 
             function walk_cond(condition, consequent, alternative) {

test/compress/destructured.js

@@ -3535,3 +3535,34 @@ issue_5405_2: {
     expect_stdout: "PASS"
     node_version: ">=6"
 }
+
+issue_5423: {
+    options = {
+        merge_vars: true,
+        toplevel: true,
+    }
+    input: {
+        var a, b;
+        function f({
+            [function() {
+                if (++a)
+                    return 42;
+            }()]: c
+        }) {}
+        f(b = f);
+        console.log(typeof b);
+    }
+    expect: {
+        var a, b;
+        function f({
+            [function() {
+                if (++a)
+                    return 42;
+            }()]: c
+        }) {}
+        f(b = f);
+        console.log(typeof b);
+    }
+    expect_stdout: "function"
+    node_version: ">=6"
+}