feat(transformer/typescript): debug_assert that enum_eval ran in semantic (#22252)

Closes #21667.

Stacked on #22253 (which lands the prerequisite `with_enum_eval(true)` calls in `cargo allocs` and the four transformer benches that this assert would otherwise trip).

## Problem

The TS enum lowering reads pre-computed member values from `Scoping`. Those values are only populated when `SemanticBuilder::with_enum_eval(true)` is set; without it, every `get_enum_member_value` call returns `None`, so string-valued members are treated as opaque expressions and the transform emits incorrect reverse mappings.

Example from #21667:

```ts
enum Theme {
  Light = "Light",
  Dark = "Dark",
  Default = Theme.Light,
}
```

When the transformer runs on a `Scoping` built without `enum_eval`, it does not recognise `Theme.Light` as a string and produces:

```js
Theme[Theme["Default"] = Theme.Light] = "Default";
```

— i.e. a reverse-mapping assignment for a string member, which is wrong (and runtime-observable).

## Fix

Add a `debug_assert!` at the entry of `transform_ts_enum` (after the `decl.declare` early return) verifying that the enum's body scope is registered in `Scoping`.

The check uses `get_enum_body_scopes` as the signal: `add_enum_body_scope` has exactly one caller (`evaluate_enum_members`), which is gated entirely by `enum_eval`. No new state on `Scoping` / `EnumData`.

The internal `Compiler` (`crates/oxc/src/compiler.rs`) and the playground (`napi/playground/src/lib.rs`) already enable `enum_eval`. The benches and `cargo allocs` are fixed in the parent PR. This guard catches the misuse for any other external caller of `Transformer::build_with_scoping`.

## Test plan

- [x] `cargo test -p oxc_transformer` — new integration tests in `tests/integrations/enum_eval.rs` cover both the positive case and the `#[should_panic]` case (debug-only)
- [x] `cargo run -p oxc_transform_conformance` — no snapshot changes (the conformance runner goes through `CompilerInterface`, which already enables `enum_eval`)
- [x] `cargo clippy -p oxc_transformer --tests` — clean

crates/oxc_transformer/src/typescript/enum.rs

@@ -160,6 +160,17 @@ impl<'a> TypeScriptEnum {
             return None;
         }
 
+        // Enum lowering relies on pre-computed member values stored in `Scoping`
+        // by `evaluate_enum_members` (only run when the semantic builder is configured
+        // with `enum_eval`). Without it, string-valued members are not recognized and
+        // the transform emits incorrect reverse mappings (see oxc#21667).
+        debug_assert!(
+            ctx.scoping().get_enum_body_scopes(decl.id.symbol_id()).is_some(),
+            "Transformer requires `Scoping` produced with `SemanticBuilder::with_enum_eval(true)` \
+             to correctly transform `enum {}`.",
+            decl.id.name,
+        );
+
         let ast = ctx.ast;
 
         let is_export = export_span.is_some();

crates/oxc_transformer/tests/integrations/enum_eval.rs

@@ -0,0 +1,31 @@
+use std::path::Path;
+
+use oxc_allocator::Allocator;
+use oxc_parser::Parser;
+use oxc_semantic::SemanticBuilder;
+use oxc_span::SourceType;
+use oxc_transformer::{TransformOptions, Transformer};
+
+fn run(enum_eval: bool) {
+    let source_text = "enum E { A = 1 }";
+    let source_type = SourceType::ts();
+    let allocator = Allocator::default();
+    let ret = Parser::new(&allocator, source_text, source_type).parse();
+    let mut program = ret.program;
+    let scoping =
+        SemanticBuilder::new().with_enum_eval(enum_eval).build(&program).semantic.into_scoping();
+    let _ret = Transformer::new(&allocator, Path::new(""), &TransformOptions::default())
+        .build_with_scoping(scoping, &mut program);
+}
+
+#[test]
+fn transforms_enum_when_enum_eval_enabled() {
+    run(true);
+}
+
+#[test]
+#[should_panic(expected = "SemanticBuilder::with_enum_eval(true)")]
+#[cfg(debug_assertions)]
+fn panics_when_enum_eval_disabled() {
+    run(false);
+}

crates/oxc_transformer/tests/integrations/main.rs

@@ -1,3 +1,4 @@
+mod enum_eval;
 mod es_target;
 mod helper_call;
 mod targets;

tasks/track_memory_allocations/allocs_minifier.snap

@@ -1,6 +1,6 @@
 File                       | File size      || Sys allocs     | Sys reallocs   || Arena allocs   | Arena reallocs | Arena bytes    
 -------------------------------------------------------------------------------------------------------------------------------------------
-checker.ts                 | 2.92 MB        ||            286 |             37 ||         152712 |          28244
+checker.ts                 | 2.92 MB        ||            286 |             37 ||         152659 |          28244
 
 cal.com.tsx                | 1.06 MB        ||          20214 |             46 ||          37153 |           4570
 
@@ -10,5 +10,5 @@ pdf.mjs                    | 567.30 kB      ||           4052 |            417 |
 
 antd.js                    | 6.69 MB        ||           7702 |           1657 ||         331684 |          69349
 
-binder.ts                  | 193.08 kB      ||             66 |             23 ||           7083 |            824
+binder.ts                  | 193.08 kB      ||             66 |             23 ||           7075 |            824
 

tasks/track_memory_allocations/allocs_semantic.snap

@@ -1,8 +1,8 @@
 File                       | File size      || Sys allocs     | Sys reallocs   || Arena allocs   | Arena reallocs | Arena bytes    
 -------------------------------------------------------------------------------------------------------------------------------------------
-checker.ts                 | 2.92 MB        ||           2281 |             18 ||              0 |              0
+checker.ts                 | 2.92 MB        ||           2309 |             18 ||              0 |              0
 
-cal.com.tsx                | 1.06 MB        ||          14966 |             22 ||              0 |              0
+cal.com.tsx                | 1.06 MB        ||          14978 |             22 ||              0 |              0
 
 RadixUIAdoptionSection.jsx | 2.52 kB        ||             10 |              3 ||              0 |              0
 
@@ -10,5 +10,5 @@ pdf.mjs                    | 567.30 kB      ||           1401 |            208 |
 
 antd.js                    | 6.69 MB        ||           2455 |             18 ||              0 |              0
 
-binder.ts                  | 193.08 kB      ||            190 |             11 ||              0 |              0
+binder.ts                  | 193.08 kB      ||            196 |             11 ||              0 |              0
 

tasks/track_memory_allocations/allocs_transformer.snap

@@ -1,8 +1,8 @@
 File                       | File size      || Sys allocs     | Sys reallocs   || Arena allocs   | Arena reallocs | Arena bytes    
 -------------------------------------------------------------------------------------------------------------------------------------------
-checker.ts                 | 2.92 MB        ||            159 |              1 ||           4765 |             64
+checker.ts                 | 2.92 MB        ||             20 |              1 ||           4400 |             64
 
-cal.com.tsx                | 1.06 MB        ||             37 |              3 ||          38190 |           3515
+cal.com.tsx                | 1.06 MB        ||             26 |              3 ||          38212 |           3515
 
 RadixUIAdoptionSection.jsx | 2.52 kB        ||             22 |              3 ||            259 |             24
 
@@ -10,5 +10,5 @@ pdf.mjs                    | 567.30 kB      ||             15 |              0 |
 
 antd.js                    | 6.69 MB        ||             15 |              0 ||              2 |              0
 
-binder.ts                  | 193.08 kB      ||             30 |              1 ||            367 |              6
+binder.ts                  | 193.08 kB      ||             18 |              1 ||            379 |              6