fix corner case in collapse_vars

fixes #5389

lib/ast.js

@@ -851,6 +851,9 @@ var AST_DefClass = DEFNODE("DefClass", null, {
     $propdoc: {
         name: "[AST_SymbolDefClass] the name of this class",
     },
+    resolve: function(def_class) {
+        return def_class ? this : this.parent_scope.resolve();
+    },
     _validate: function() {
         if (!(this.name instanceof AST_SymbolDefClass)) throw new Error("name must be AST_SymbolDefClass");
     },

lib/compress.js

@@ -3269,7 +3269,7 @@ Compressor.prototype.compress = function(node) {
                 if (def.scope.resolve() !== scope) return true;
                 if (modify_toplevel && compressor.exposed(def)) return true;
                 return !all(def.references, function(ref) {
-                    return ref.scope.resolve() === scope;
+                    return ref.scope.resolve(true) === scope;
                 });
             }
 

test/compress/classes.js

@@ -2538,3 +2538,34 @@ issue_5387: {
     expect_stdout: "PASS"
     node_version: ">=4"
 }
+
+issue_5389: {
+    options = {
+        collapse_vars: true,
+        toplevel: true,
+    }
+    input: {
+        function log(m, n) {
+            console.log(m, n);
+        }
+        var a = log;
+        class A {
+            [a = "FAIL"] = a = "PASS";
+        }
+        var b = new A();
+        log(a, b.FAIL);
+    }
+    expect: {
+        function log(m, n) {
+            console.log(m, n);
+        }
+        var a = log;
+        class A {
+            [a = "FAIL"] = a = "PASS";
+        }
+        var b = new A();
+        log(a, b.FAIL);
+    }
+    expect_stdout: "PASS PASS"
+    node_version: ">=12"
+}