feat: TC39 decorator proposal support (#22040)

This commit adds support for [TC39 Decorator
Proposal](https://github.com/tc39/proposal-decorators).

These decorators are only available in transpiled sources - ie.
non-JavaScript files (because of lack of support in V8).

This entails that "experimental TypeScript decorators" are not available
by default
and require to be configured, with a configuration like this:
```
{
  "compilerOptions": {
    "experimentalDecorators": true
  }
}
```


Closes https://github.com/denoland/deno/issues/19160

---------

Signed-off-by: Bartek Iwańczuk <biwanczuk@gmail.com>
Co-authored-by: crowlkats <crowlkats@toaxl.com>
Co-authored-by: Divy Srivastava <dj.srivastava23@gmail.com>

Cargo.lock

@@ -1172,9 +1172,9 @@ dependencies = [
 
 [[package]]
 name = "deno_config"
-version = "0.8.1"
+version = "0.8.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "81fec482ce578388108cfd4a7ca900be7b8aea5081e1922ff3c5f87f0767c531"
+checksum = "cb5634c4d8f29f62bc4516a3dc474c1a06a6ce1388a139df08cb2020244e7de7"
 dependencies = [
  "anyhow",
  "glob",

cli/Cargo.toml

@@ -55,7 +55,7 @@ winres.workspace = true
 [dependencies]
 deno_ast = { workspace = true, features = ["bundler", "cjs", "codegen", "dep_graph", "module_specifier", "proposal", "react", "sourcemap", "transforms", "typescript", "view", "visit"] }
 deno_cache_dir = "=0.6.1"
-deno_config = "=0.8.1"
+deno_config = "=0.8.2"
 deno_core = { workspace = true, features = ["include_js_files_for_snapshotting"] }
 deno_doc = { version = "=0.94.1", features = ["html"] }
 deno_emit = "=0.34.0"

cli/args/mod.rs

@@ -158,10 +158,8 @@ pub fn ts_config_to_emit_options(
       _ => (false, false, false, false),
     };
   deno_ast::EmitOptions {
-    // TODO(bartlomieju): change it to default to `false` and only enable
-    // if tsconfig.json enabled experimental decorators
-    use_ts_decorators: true,
-    use_decorators_proposal: false,
+    use_ts_decorators: options.experimental_decorators,
+    use_decorators_proposal: !options.experimental_decorators,
     emit_metadata: options.emit_decorator_metadata,
     imports_not_used_as_values,
     inline_source_map: options.inline_source_map,
@@ -1088,10 +1086,26 @@ impl CliOptions {
     &self,
     config_type: TsConfigType,
   ) -> Result<TsConfigForEmit, AnyError> {
-    deno_config::get_ts_config_for_emit(
+    let result = deno_config::get_ts_config_for_emit(
       config_type,
       self.maybe_config_file.as_ref(),
-    )
+    );
+
+    match result {
+      Ok(mut ts_config_for_emit) => {
+        if matches!(self.flags.subcommand, DenoSubcommand::Bundle(..)) {
+          // For backwards compatibility, force `experimentalDecorators` setting
+          // to true.
+          *ts_config_for_emit
+            .ts_config
+            .0
+            .get_mut("experimentalDecorators")
+            .unwrap() = serde_json::Value::Bool(true);
+        }
+        Ok(ts_config_for_emit)
+      }
+      Err(err) => Err(err),
+    }
   }
 
   pub fn resolve_inspector_server(&self) -> Option<InspectorServer> {

cli/tests/integration/repl_tests.rs

@@ -358,15 +358,26 @@ fn typescript_declarations() {
 
 #[test]
 fn typescript_decorators() {
-  util::with_pty(&["repl"], |mut console| {
-    console
-      .write_line("function dec(target) { target.prototype.test = () => 2; }");
-    console.expect("undefined");
-    console.write_line("@dec class Test {}");
-    console.expect("[class Test]");
-    console.write_line("new Test().test()");
-    console.expect("2");
-  });
+  let context = TestContextBuilder::default().use_temp_cwd().build();
+  let temp_dir = context.temp_dir();
+  temp_dir.write(
+    "./deno.json",
+    r#"{ "compilerOptions": { "experimentalDecorators": true } }"#,
+  );
+  let config_path = temp_dir.target_path().join("./deno.json");
+  util::with_pty(
+    &["repl", "--config", config_path.to_string_lossy().as_ref()],
+    |mut console| {
+      console.write_line(
+        "function dec(target) { target.prototype.test = () => 2; }",
+      );
+      console.expect("undefined");
+      console.write_line("@dec class Test {}");
+      console.expect("[class Test]");
+      console.write_line("new Test().test()");
+      console.expect("2");
+    },
+  );
 }
 
 #[test]

cli/tests/integration/run_tests.rs

@@ -1508,8 +1508,13 @@ itest!(no_check {
 });
 
 itest!(no_check_decorators {
-  args: "run --quiet --reload --no-check run/no_check_decorators.ts",
-  output: "run/no_check_decorators.ts.out",
+  args: "run --quiet --reload --no-check run/decorators/experimental/no_check/main.ts",
+  output: "run/decorators/experimental/no_check/main.out",
+});
+
+itest!(decorators_tc39_proposal {
+  args: "run --quiet --reload --check run/decorators/tc39_proposal/main.ts",
+  output: "run/decorators/tc39_proposal/main.out",
 });
 
 itest!(check_remote {
@@ -1526,8 +1531,8 @@ itest!(no_check_remote {
 });
 
 itest!(runtime_decorators {
-  args: "run --quiet --reload --no-check run/runtime_decorators.ts",
-  output: "run/runtime_decorators.ts.out",
+  args: "run --quiet --reload --no-check run/decorators/experimental/runtime/main.ts",
+  output: "run/decorators/experimental/runtime/main.out",
 });
 
 itest!(seed_random {
@@ -1591,8 +1596,8 @@ itest!(ts_type_imports {
 });
 
 itest!(ts_decorators {
-  args: "run --reload --check run/ts_decorators.ts",
-  output: "run/ts_decorators.ts.out",
+  args: "run --reload --check run/decorators/experimental/ts/main.ts",
+  output: "run/decorators/experimental/ts/main.out",
 });
 
 itest!(ts_type_only_import {

cli/tests/testdata/run/decorators/experimental/deno.json

@@ -0,0 +1,5 @@
+{
+  "compilerOptions": {
+    "experimentalDecorators": true
+  }
+}

cli/tests/testdata/run/decorators/experimental/runtime/main.out

@@ -0,0 +1,7 @@
+@A evaluated
+@B evaluated
+@B called
+@A called
+fn() called from @A
+fn() called from @B
+C.test() called

cli/tests/testdata/run/decorators/experimental/runtime/main.ts

@@ -0,0 +1,42 @@
+// deno-lint-ignore-file
+function a() {
+  console.log("@A evaluated");
+  return function (
+    target: any,
+    propertyKey: string,
+    descriptor: PropertyDescriptor,
+  ) {
+    console.log("@A called");
+    const fn = descriptor.value;
+    descriptor.value = function () {
+      console.log("fn() called from @A");
+      fn();
+    };
+  };
+}
+
+function b() {
+  console.log("@B evaluated");
+  return function (
+    target: any,
+    propertyKey: string,
+    descriptor: PropertyDescriptor,
+  ) {
+    console.log("@B called");
+    const fn = descriptor.value;
+    descriptor.value = function () {
+      console.log("fn() called from @B");
+      fn();
+    };
+  };
+}
+
+class C {
+  @a()
+  @b()
+  static test() {
+    console.log("C.test() called");
+  }
+}
+
+C.test();

cli/tests/testdata/run/decorators/tc39_proposal/main.out

@@ -0,0 +1,3 @@
+starting m with arguments 1
+C.m 1
+ending m

cli/tests/testdata/run/decorators/tc39_proposal/main.ts

@@ -0,0 +1,21 @@
+// deno-lint-ignore no-explicit-any
+function logged(value: any, { kind, name }: { kind: string; name: string }) {
+  if (kind === "method") {
+    return function (...args: unknown[]) {
+      console.log(`starting ${name} with arguments ${args.join(", ")}`);
+      // @ts-ignore this has implicit any type
+      const ret = value.call(this, ...args);
+      console.log(`ending ${name}`);
+      return ret;
+    };
+  }
+}
+
+class C {
+  @logged
+  m(arg: number) {
+    console.log("C.m", arg);
+  }
+}
+
+new C().m(1);

cli/tests/testdata/run/runtime_decorators.ts

@@ -1,5 +1,5 @@
 // deno-lint-ignore-file
-function A() {
+function a() {
   console.log("@A evaluated");
   return function (
     target: any,
@@ -15,7 +15,7 @@ function A() {
   };
 }
 
-function B() {
+function b() {
   console.log("@B evaluated");
   return function (
     target: any,
@@ -32,8 +32,8 @@ function B() {
 }
 
 class C {
-  @A()
-  @B()
+  @a()
+  @b()
   static test() {
     console.log("C.test() called");
   }

cli/tools/repl/session.rs

@@ -184,6 +184,7 @@ pub struct ReplSession {
   /// This is only optional because it's temporarily taken when evaluating.
   test_event_receiver: Option<tokio::sync::mpsc::UnboundedReceiver<TestEvent>>,
   jsx: ReplJsxState,
+  experimental_decorators: bool,
 }
 
 impl ReplSession {
@@ -240,6 +241,11 @@ impl ReplSession {
       deno_core::resolve_path("./$deno$repl.ts", cli_options.initial_cwd())
         .unwrap();
 
+    let ts_config_for_emit = cli_options
+      .resolve_ts_config_for_emit(deno_config::TsConfigType::Emit)?;
+    let emit_options =
+      crate::args::ts_config_to_emit_options(ts_config_for_emit.ts_config);
+    let experimental_decorators = emit_options.use_ts_decorators;
     let mut repl_session = ReplSession {
       npm_resolver,
       resolver,
@@ -260,6 +266,7 @@ impl ReplSession {
         frag_factory: "React.Fragment".to_string(),
         import_source: None,
       },
+      experimental_decorators,
     };
 
     // inject prelude
@@ -596,10 +603,8 @@ impl ReplSession {
 
     let transpiled_src = parsed_source
       .transpile(&deno_ast::EmitOptions {
-        // TODO(bartlomieju): change it to default to `false` and only enable
-        // if tsconfig.json enabled experimental decorators
-        use_ts_decorators: true,
-        use_decorators_proposal: false,
+        use_ts_decorators: self.experimental_decorators,
+        use_decorators_proposal: !self.experimental_decorators,
         emit_metadata: false,
         source_map: false,
         inline_source_map: false,