fix corner case reduce_vars (#4706)

fixes #4705

lib/compress.js

@@ -938,7 +938,8 @@ merge(Compressor.prototype, {
             node.variables.each(function(def) {
                 reset_def(tw, compressor, def);
             });
-            if (!node.name) return;
+            if (node.extends) node.extends.walk(tw);
+            if (node.name) {
                 var d = node.name.definition();
                 var parent = tw.parent();
                 if (parent instanceof AST_ExportDeclaration || parent instanceof AST_ExportDefault) d.single_use = false;
@@ -953,16 +954,19 @@ merge(Compressor.prototype, {
                 } else {
                     d.fixed = false;
                 }
-        });
+            }
-        def(AST_ClassField, function(tw) {
+            node.properties.filter(function(prop) {
-            var node = this;
+                if (prop.key instanceof AST_Node) prop.key.walk(tw);
-            if (node.static) return;
+                return prop.value;
-            if (node.key instanceof AST_Node) node.key.walk(tw);
+            }).forEach(function(prop) {
-            if (node.value) {
+                if (prop.static) {
+                    prop.value.walk(tw);
+                } else {
                     push(tw);
-                node.value.walk(tw);
+                    prop.value.walk(tw);
                     pop(tw);
                 }
+            });
             return true;
         });
         def(AST_Conditional, function(tw) {

test/compress/classes.js

@@ -747,3 +747,24 @@ issue_4687_2: {
     expect_stdout: "PASS"
     node_version: ">=4"
 }
+
+issue_4705: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = "PASS";
+        class A {
+            p = a = "FAIL";
+            [console.log(a)];
+        }
+    }
+    expect: {
+        console.log("PASS");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=12"
+}