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>

1 files changed, 20 insertions, 6 deletions

diff --git a/cli/args/mod.rs b/cli/args/mod.rs
index 34448e633..13ee9eeef 100644
--- a/cli/args/mod.rs
+++ b/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> {