enhance unused (#4858)

lib/compress.js

@@ -5817,19 +5817,29 @@ merge(Compressor.prototype, {
             } else if (node instanceof AST_Unary) {
                 if (node.write_only) sym = node.expression;
             }
-            if (/strict/.test(compressor.option("pure_getters"))) {
-                while (sym instanceof AST_PropAccess && !sym.expression.may_throw_on_access(compressor)) {
-                    if (sym instanceof AST_Sub) props.unshift(sym.property);
-                    sym = sym.expression;
-                    nested = true;
-                }
-            }
+            if (/strict/.test(compressor.option("pure_getters"))) sym = extract_reference(sym, props);
             if (!(sym instanceof AST_SymbolRef)) return;
             var def = sym.definition();
             if (export_defaults[def.id]) return;
             if (compressor.exposed(def)) return;
             if (!can_drop_symbol(sym, compressor, nested)) return;
             return sym;
+
+            function extract_reference(node, props) {
+                if (node instanceof AST_PropAccess) {
+                    var expr = node.expression;
+                    if (!expr.may_throw_on_access(compressor)) {
+                        nested = true;
+                        if (props && node instanceof AST_Sub) props.unshift(node.property);
+                        return extract_reference(expr, props);
+                    }
+                } else if (node instanceof AST_Assign && node.operator == "=") {
+                    var ref = extract_reference(node.right);
+                    if (props) props.assign = node;
+                    return ref;
+                }
+                return node;
+            }
         };
         var assign_in_use = Object.create(null);
         var export_defaults = Object.create(null);
@@ -6648,6 +6658,11 @@ merge(Compressor.prototype, {
                         }
                     }, true);
                 }))) {
+                if (props.assign) {
+                    props.assign.write_only = true;
+                    props.assign.walk(tw);
+                    delete props.assign.write_only;
+                }
                 props.forEach(function(prop) {
                     prop.walk(tw);
                 });

test/compress/classes.js

@@ -1541,3 +1541,23 @@ issue_4848: {
     expect_stdout: "PASS"
     node_version: ">=4"
 }
+
+drop_unused_self_reference: {
+    options = {
+        pure_getters: "strict",
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        "use strict";
+        class A {}
+        (A.p = A).q = console.log("PASS");
+    }
+    expect: {
+        "use strict";
+        console.log("PASS");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=4"
+}

test/compress/functions.js

@@ -6021,3 +6021,20 @@ issue_4823: {
     }
     expect_stdout: "function"
 }
+
+drop_unused_self_reference: {
+    options = {
+        pure_getters: "strict",
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        function f() {}
+        (f.p = f).q = console.log("PASS");
+    }
+    expect: {
+        console.log("PASS");
+    }
+    expect_stdout: "PASS"
+}

test/ufuzz/index.js

@@ -1796,7 +1796,7 @@ function createClassLiteral(recurmax, stmtDepth, canThrow, name) {
         if (SUPPORT.class_field && rng(2)) {
             s += internal || createObjectKey(recurmax, stmtDepth, canThrow);
             if (rng(5)) {
-                async = bug_async_class_await && fixed;
+                async = bug_async_class_await && fixed && 0;
                 generator = false;
                 s += " = " + createExpression(recurmax, NO_COMMA, stmtDepth, fixed ? canThrow : CANNOT_THROW);
                 generator = save_generator;
@@ -2000,7 +2000,7 @@ function isBannedKeyword(name) {
       case "arguments":
         return in_class;
       case "await":
-        return async;
+        return async !== false;
       case "yield":
         return generator || in_class;
     }