js_parser: keep the inferred name of lowered anonymous decorated class expressions

src/js_parser/lower/lower_decorators.rs

@@ -5,9 +5,8 @@ use bun_alloc::ArenaVecExt as _;
 
 use bun_collections::{HashMap, VecExt};
 
-use crate::lexer as js_lexer;
 use crate::p::P;
-use crate::parser::{ARGUMENTS_STR as arguments_str, Ref, is_eval_or_arguments};
+use crate::parser::{ARGUMENTS_STR as arguments_str, Ref};
 use bun_ast::g::{DeclList, Property, PropertyKind};
 use bun_ast::{self as js_ast, B, E, Expr, ExprNodeList, Flags, G, S, Stmt};
 
@@ -124,19 +123,21 @@ fn class_copy(c: &G::Class) -> G::Class {
     }
 }
 
-/// Whether a context-inferred name (`export default` → "default", object
-/// property keys, assignment targets) can be attached to a lowered anonymous
-/// class expression as its syntactic binding name. Class bodies are always
-/// strict mode code and the output may be a module, so reserved words
-/// ("default", "let", "await", …), `eval`/`arguments`, and non-identifier
-/// strings would turn `_class = class <name> {}` into a syntax error.
-#[inline]
-fn can_be_class_binding_name(name: &[u8]) -> bool {
-    js_lexer::is_identifier(name)
-        && js_lexer::keyword(name).is_none()
-        && !js_lexer::is_strict_mode_reserved_word(name)
-        && name != b"await"
-        && !is_eval_or_arguments(name)
+/// Installed before static blocks run; a `static name` field instead wins on its own.
+fn defines_static_name_method(props: &[Property]) -> bool {
+    props.iter().any(|prop| {
+        prop.flags.contains(Flags::Property::IsStatic)
+            && (prop.flags.contains(Flags::Property::IsMethod)
+                // A decorated accessor is installed from the suffix instead.
+                || (prop.kind == PropertyKind::AutoAccessor && prop.ts_decorators.len_u32() == 0))
+            && match prop.key {
+                Some(key) => matches!(
+                    key.unwrap_inlined().data,
+                    js_ast::ExprData::EString(s) if s.eql_comptime(b"name")
+                ),
+                None => false,
+            }
+    })
 }
 
 // ── impl P ───────────────────────────────────────────────────────────────────
@@ -1142,19 +1143,14 @@ impl<'a, const TYPESCRIPT: bool, const SCAN_ONLY: bool> P<'a, TYPESCRIPT, SCAN_O
                 class_name_ref = ecr;
                 class_name_loc = loc;
                 expr_class_is_anonymous = true;
-                if let Some(name) = name_from_context
-                    && can_be_class_binding_name(name)
-                {
-                    class.class_name = Some(js_ast::LocRef {
-                        ref_: p.new_sym(js_ast::symbol::Kind::Other, name),
-                        loc,
-                    });
-                }
             }
         } else {
             class_name_ref = class.class_name.as_ref().unwrap().ref_;
             class_name_loc = class.class_name.as_ref().unwrap().loc;
         }
+        // Decided before Phase 2 replaces decorated computed keys with temporaries.
+        let restore_inferred_name =
+            expr_class_is_anonymous && !defines_static_name_method(class.properties.slice());
 
         let mut inner_class_ref: Ref = class_name_ref;
         if !is_expr {
@@ -2422,6 +2418,21 @@ impl<'a, const TYPESCRIPT: bool, const SCAN_ONLY: bool> P<'a, TYPESCRIPT, SCAN_O
             new_properties = merged;
         }
 
+        // A string literal, unlike a class binding, survives the bundler's renaming.
+        if restore_inferred_name {
+            let this_e = p.new_expr(E::This {}, loc);
+            let name_e = p.new_expr(
+                E::EString {
+                    data: name_from_context.unwrap_or(b"").into(),
+                    ..Default::default()
+                },
+                loc,
+            );
+            let set_name = p.call_rt(loc, b"__name", &[this_e, name_e]);
+            let block = p.make_static_block(set_name, loc);
+            new_properties.insert(0, block);
+        }
+
         class.properties = bun_ast::StoreSlice::new_mut(new_properties.into_bump_slice_mut());
         class.has_decorators = false;
         class.should_lower_standard_decorators = false;

test/bundler/bundler_edgecase.test.ts

@@ -3170,6 +3170,51 @@ describe("bundler", () => {
     },
     run: { stdout: "try:false" },
   });
+  // Standard-decorator lowering rewrites `const Bar = class { ... }` into
+  // `_class = class { ... }`, so the class no longer infers its name from the
+  // binding. The name the lowering attaches instead has to survive the
+  // bundler's renaming of symbols that collide in the enclosing scope (the
+  // function-local `Bar` here, the CommonJS-wrapped module scope below) and
+  // identifier minification.
+  const decoratedAnonymousClassNames = /* js */ `
+    function dec() {}
+    function f() {
+      const Bar = class { @dec m() {} };
+      const Baz = class { accessor x; };
+      let Qux; Qux = class { @dec static s() {} };
+      const obj = { "not-an-identifier": class { @dec m() {} } };
+      return [Bar.name, Baz.name, Qux.name, obj["not-an-identifier"].name];
+    }
+    console.log(JSON.stringify(f()));
+  `;
+  itBundled("edgecase/DecoratedAnonymousClassExprKeepsInferredName", {
+    files: {
+      "/entry.js": decoratedAnonymousClassNames,
+    },
+    run: { stdout: '["Bar","Baz","Qux","not-an-identifier"]' },
+  });
+  itBundled("edgecase/DecoratedAnonymousClassExprKeepsInferredNameMinified", {
+    files: {
+      "/entry.js": decoratedAnonymousClassNames,
+    },
+    minifyIdentifiers: true,
+    minifySyntax: true,
+    minifyWhitespace: true,
+    run: { stdout: '["Bar","Baz","Qux","not-an-identifier"]' },
+  });
+  itBundled("edgecase/DecoratedAnonymousClassExprKeepsInferredNameInCJSWrapper", {
+    files: {
+      "/entry.js": /* js */ `
+        console.log(require("./mod.cjs").name);
+      `,
+      "/mod.cjs": /* js */ `
+        function dec() {}
+        const Bar = class { @dec m() {} };
+        module.exports = Bar;
+      `,
+    },
+    run: { stdout: "Bar" },
+  });
 });
 
 for (const backend of ["api", "cli"] as const) {

test/bundler/transpiler/es-decorators.test.ts

@@ -845,6 +845,7 @@ describe("ES Decorators", () => {
           import Cls from "./mod.js";
           const c = new Cls();
           console.log(c.foo());
+          console.log(Cls.name);
         `,
         "mod.js": `
           function dec(fn, ctx) { console.log("decorated", ctx.name); return fn; }
@@ -863,7 +864,7 @@ describe("ES Decorators", () => {
 
       const [stdout, rawStderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
       expect(filterStderr(rawStderr)).toBe("");
-      expect(stdout).toBe("decorated foo\n42\n");
+      expect(stdout).toBe("decorated foo\n42\ndefault\n");
       expect(exitCode).toBe(0);
     });
 
@@ -982,6 +983,191 @@ describe("ES Decorators", () => {
     });
   });
 
+  describe("inferred names of lowered anonymous class expressions", () => {
+    // Lowering turns `const Bar = class { ... }` into `_class = class { ... }`,
+    // which would otherwise make the class infer the name "_class". The name
+    // the source position would have inferred must be restored without adding
+    // a class binding: a binding can only hold identifier names, shadows the
+    // outer variable inside the class body, and is renamed by the bundler.
+    test.concurrent("names that are not valid identifiers", async () => {
+      const { stdout, stderr, exitCode } = await runDecorator(`
+        function dec() {}
+        const obj = {
+          "foo-bar": class { @dec m() {} },
+          "": class { @dec m() {} },
+          default: class { @dec m() {} },
+          "with space": class { accessor x; },
+        };
+        console.log(JSON.stringify([obj["foo-bar"].name, obj[""].name, obj.default.name, obj["with space"].name]));
+      `);
+      expect(stderr).toBe("");
+      expect(stdout).toBe('["foo-bar","","default","with space"]\n');
+      expect(exitCode).toBe(0);
+    });
+
+    test.concurrent("console.log and Bun.inspect show the inferred name", async () => {
+      const { stdout, stderr, exitCode } = await runDecorator(`
+        function dec() {}
+        const Item = class { accessor id; };
+        const Decorated = class { @dec m() {} };
+        class Child extends Item {}
+        console.log(Item, Bun.inspect(new Item(), { compact: true }), Bun.inspect({ item: new Item() }, { compact: true }));
+        console.log(Decorated, Bun.inspect(new Decorated(), { compact: true }), Child);
+        const id = x => x;
+        const Nameless = id(class { @dec m() {} });
+        console.log(Nameless, Bun.inspect(new Nameless(), { compact: true }));
+      `);
+      expect(stderr).toBe("");
+      expect(stdout).toBe(
+        [
+          "[class Item] Item { id: [Getter/Setter] } { item: Item { id: [Getter/Setter] } }",
+          "[class Decorated] Decorated { m: [Function: m] } [class Child extends Item]",
+          "[class (anonymous)] { m: [Function: m] }",
+        ].join("\n") + "\n",
+      );
+      expect(exitCode).toBe(0);
+    });
+
+    test.concurrent("every naming context", async () => {
+      const { stdout, stderr, exitCode } = await runDecorator(`
+        function dec() {}
+        const A = class { @dec m() {} };
+        let B; B = class { @dec m() {} };
+        const { C = class { @dec m() {} } } = {};
+        const [D = class { @dec m() {} }] = [];
+        const obj = { E: class { @dec m() {} } };
+        class Holder {
+          static F = class { @dec m() {} };
+          G = class { @dec m() {} };
+        }
+        const H = @dec class {};
+        console.log(JSON.stringify([A.name, B.name, C.name, D.name, obj.E.name, Holder.F.name, new Holder().G.name, H.name]));
+      `);
+      expect(stderr).toBe("");
+      expect(stdout).toBe('["A","B","C","D","E","F","G","H"]\n');
+      expect(exitCode).toBe(0);
+    });
+
+    test.concurrent("no naming context leaves the name empty", async () => {
+      const { stdout, stderr, exitCode } = await runDecorator(`
+        function dec() {}
+        const id = x => x;
+        console.log(JSON.stringify([id(class { @dec m() {} }).name, id(@dec class {}).name, id(class { accessor x; }).name]));
+      `);
+      expect(stderr).toBe("");
+      expect(stdout).toBe('["","",""]\n');
+      expect(exitCode).toBe(0);
+    });
+
+    test.concurrent("class body still refers to the outer binding", async () => {
+      const { stdout, stderr, exitCode } = await runDecorator(`
+        function dec() {}
+        let Bar = class {
+          @dec m() { return Bar; }
+          static s() { return Bar; }
+        };
+        const Original = Bar;
+        Bar = "reassigned";
+        console.log(Original.name, new Original().m(), Original.s());
+      `);
+      expect(stderr).toBe("");
+      expect(stdout).toBe("Bar reassigned reassigned\n");
+      expect(exitCode).toBe(0);
+    });
+
+    test.concurrent("name is set before static initializers run", async () => {
+      const { stdout, stderr, exitCode } = await runDecorator(`
+        function dec() {}
+        const Bar = class {
+          static field = this.name;
+          static #priv = this.name;
+          static priv() { return this.#priv; }
+          static { console.log("static block:", this.name); }
+          @dec m() {}
+        };
+        console.log(Bar.name, Bar.field, Bar.priv());
+        const Baz = @dec class {
+          static field = this.name;
+        };
+        console.log(Baz.name, Baz.field);
+      `);
+      expect(stderr).toBe("");
+      expect(stdout).toBe("static block: Bar\nBar Bar Bar\nBaz Baz\n");
+      expect(exitCode).toBe(0);
+    });
+
+    test.concurrent("a static member named `name` declared by the class wins", async () => {
+      const { stdout, stderr, exitCode } = await runDecorator(`
+        function dec() {}
+        const Getter = class { static get name() { return "from getter"; } @dec m() {} };
+        const Setter = class { static set name(v) {} @dec m() {} };
+        const Method = class { static name() {} @dec m() {} };
+        const DecoratedMethod = class { @dec static name() {} };
+        const DecoratedComputed = class { @dec static ["name"]() {} };
+        const Accessor = class { static accessor name = "from accessor"; @dec m() {} };
+        const Field = class { static seenBefore = this.name; static name = "from field"; @dec m() {} };
+        const Uninitialized = class { static name; @dec m() {} };
+        const Instance = class { name = "instance"; @dec m() {} };
+        console.log(JSON.stringify([
+          Getter.name,
+          Setter.name,
+          typeof Method.name,
+          typeof DecoratedMethod.name,
+          typeof DecoratedComputed.name,
+          Accessor.name,
+          Field.seenBefore,
+          Field.name,
+          Uninitialized.name,
+          Instance.name,
+        ]));
+      `);
+      expect(stderr).toBe("");
+      expect(stdout).toBe(
+        '["from getter",null,"function","function","function","from accessor","Field","from field",null,"Instance"]\n',
+      );
+      expect(exitCode).toBe(0);
+    });
+
+    test.concurrent("a decorated static accessor named `name` is installed after the body runs", async () => {
+      const { stdout, stderr, exitCode } = await runDecorator(`
+        function dec() {}
+        const Foo = class {
+          static seenBefore = this.name;
+          @dec static accessor name = "from accessor";
+        };
+        console.log(JSON.stringify([Foo.seenBefore, Foo.name]));
+      `);
+      expect(stderr).toBe("");
+      expect(stdout).toBe('["Foo","from accessor"]\n');
+      expect(exitCode).toBe(0);
+    });
+
+    test.concurrent("a static `name` method keyed by an inlined TypeScript enum member wins too", async () => {
+      using dir = tempDir("es-dec-enum-name-key", {
+        "tsconfig.json": JSON.stringify({ compilerOptions: {} }),
+        "test.ts": `
+          enum Key { Name = "name" }
+          function dec() {}
+          const Foo = class {
+            static [Key.Name]() { return "method"; }
+            @dec m() {}
+          };
+          console.log(typeof Foo.name);
+        `,
+      });
+      await using proc = Bun.spawn({
+        cmd: [bunExe(), "test.ts"],
+        env: bunEnv,
+        cwd: String(dir),
+        stderr: "pipe",
+      });
+      const [stdout, rawStderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+      expect(filterStderr(rawStderr)).toBe("");
+      expect(stdout).toBe("function\n");
+      expect(exitCode).toBe(0);
+    });
+  });
+
   describe("private member calls in lowered classes", () => {
     // When a class is lowered for standard decorators, `recv.#m(...)` becomes
     // `__privateGet(recv, _m).call(recv, ...)`. The receiver must be evaluated