## Summary
Introduces `oxc_diagnostics::Diagnostics` — a `Vec<OxcDiagnostic>` newtype that knows the difference between errors and warnings — and makes it the standard diagnostics return value across oxc.
- **New type**: `Diagnostics` with `has_errors()`, `has_warnings()`, `errors()`, `warnings()`, plus `Vec`-like ergonomics (Deref, `IntoIterator`, `Extend`, `From`/`Into<Vec>`) so most call sites are unchanged.
- **Return types**: `ParserReturn`, `SemanticBuilderReturn`, `IsolatedDeclarationsReturn`, the React Compiler `TransformResult`/`LintResult`, and `TransformerReturn` now expose `diagnostics: Diagnostics` instead of `errors: Vec<OxcDiagnostic>` (the React Compiler's separate `errors`/`warnings` are merged into one severity-tagged list).
- **Behaviour**: a React Compiler **error** now stops the transform (no output), while **warnings** flow through and the transform continues. `compile()` aborts codegen only when `diagnostics.has_errors()` — warnings alone no longer abort (previously any diagnostic did).
## Breaking change
Consumers reading `*.errors` on these return values must read `*.diagnostics`. React Compiler consumers that read `.errors`/`.warnings` separately should use `diagnostics.has_errors()` / `diagnostics.errors()` / `diagnostics.warnings()`.
Parser/semantic/isolated-declarations fatality is otherwise unchanged. Builds on the React Compiler transform feature (#23201).
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Pre-requisite for #22252.
## Why
#22252 adds a `debug_assert!` in the transformer that requires `Scoping` to be built with `SemanticBuilder::with_enum_eval(true)` whenever a `TSEnumDeclaration` reaches the transform pass. The internal `Compiler` (`crates/oxc/src/compiler.rs`) and the playground already enable it; the CI run on #22252 surfaced a few internal callers that don't.
Land that fix on its own first, so the assert PR doesn't trip CI on these tasks.
## Sites updated
Every `SemanticBuilder` site that feeds `Transformer::build_with_scoping`:
- `tasks/track_memory_allocations/src/lib.rs` — both call sites (`cargo allocs`).
- `tasks/benchmark/benches/transformer.rs`
- `tasks/benchmark/benches/pipeline.rs`
- `tasks/benchmark/benches/minifier.rs`
- `tasks/benchmark/benches/codegen.rs`
Other semantic builders in these files that feed only the minifier / codegen / compressor are left alone — they don't go through enum lowering.
## Test plan
- [x] `cargo check -p oxc_track_memory_allocations` — clean
- [x] `cargo check --benches -p oxc_benchmark` — clean
The benchmark jobs take too long to run, change them to a minimal set.
This set of files are smaller but should provide basic coverage to real
world examples.
Cameron