Add a TypeScript 7 backend for Glint type extraction

[johanrd]

Type-aware linting on TypeScript 7. TS7 ships no in-process API, so the existing pipeline (typescript as a library + Glint's rewriteModule) cannot run on it. TS7's typescript/unstable/sync is a synchronous IPC API, which is what html-validate's synchronous transformer needs.

Design

One extraction algorithm (lib/glint.ts) over two backends (lib/backend/):

• ts6 — the existing pipeline, moved to lib/backend/ts6.ts. It now always adds ember-source/types / @glint/ember-tsc/types to its program, so projects that dropped them from compilerOptions.types for the content mapper keep their types.
• tsgo — lib/backend/tsgo.ts. Opens the project with runExternalCode, so the tsconfig's contentMappers (ember-content-mapper) transform .gts inside the compiler; sourceFile.spanMap maps template ranges to the virtual text. No Glint rewrite, no typescript library in-process. The resolver's syntactic parses use the same API through an fs overlay.
• TsSyntax facade (predicates, enum tables, parseFile, union/literal helpers) replaces typeof TS in lib/resolver/*; boundary casts are confined to tsgo.ts.
• Selection per tsconfig: tsgo when it declares contentMappers and a TS7 package resolves (typescript 7.x, @typescript/native, typescript-7, or HVE_TSGO=<name>); HVE_TS_BACKEND=tsgo|ts6 forces. Node 22.12+ for require() of the ESM API. Cache entries carry the backend.

Verification

• pnpm test (ts6) and pnpm test:tsgo (same suite, vitest.tsgo.config.ts): 289 passed, 1 expected fail each. vitest.config.ts excludes ecosystem/**.
• 244-template app, both backends from dist/: 23 string-literal unions and 24 literals identical as sets, componentAttrMap 272/272, componentTagMap 617 identical + 8 where tsgo resolves a real tag the TS6 program reported as any, 0 missing.

Behaviour differences

• tsgo returns union members in checker order, so values[0] may be a different (equally valid) member than under TS6.
• Files outside a tsconfig's include have no project under tsgo, same as tsc; examples/ got its own tsconfig.
• A signature-less template-only component's Element is null under tsgo (unknown under TS6); both now resolve to transparent.

Cowritten by Claude

[Copilot]

🔵 Needs a closer look

It introduces a large new backend built on an unstable TypeScript 7 dev API with subtle snapshot-lifetime and span-mapping semantics that cannot be fully verified from the diff and warrant human review.

Pull request overview

This PR adds a second type-extraction backend so the plugin can perform type-aware Ember/Glint linting on TypeScript 7 (tsgo), which ships no in-process library API. It refactors the previously monolithic lib/glint.ts into a shared extraction algorithm over a TypeBackend abstraction (lib/backend/), with the existing TS5/6 + Glint rewriteModule pipeline moved to ts6.ts and a new tsgo.ts backend built on typescript/unstable/sync. A TsSyntax facade replaces direct typeof TS usage across the resolver so the syntactic walks work against either backend.

Changes:

• Introduce lib/backend/ (types.ts, ts6.ts, tsgo.ts, index.ts) with per-tsconfig backend selection driven by contentMappers detection, TS7 package resolution, and HVE_TS_BACKEND / HVE_TSGO overrides.
• Refactor lib/glint.ts and the resolver to consume TemplateSites and the TsSyntax/CheckerLike/ProgramLike interfaces instead of the typescript module directly; add the backend to the disk-cache key.
• Add the test:tsgo suite (vitest.tsgo.config.ts), the typescript-7/ember-content-mapper dev deps, example/fixture tsconfigs declaring contentMappers, and README docs.

File summaries

File	Description
lib/backend/types.ts	New shared interfaces (TsSyntax, TypeBackend, TemplateSite, etc.)
lib/backend/index.ts	Backend selection, tsconfig discovery, syntax fallback
lib/backend/ts6.ts	Existing pipeline extracted; always adds ember/glint types
lib/backend/tsgo.ts	New TS7 IPC backend: snapshots, span mapping, site collection
lib/glint.ts	Refactored to iterate backend sites; adds Element: null handling
lib/cache.ts	Adds backend to cache entry + read/write signatures
lib/resolver/walk.ts, template-source.ts, build-maps.ts	Switch to TsSyntax/syntaxFor
lib/cache.ts, run.ts	Backend threaded through cache key and summary line
test/*.ts, *fixtures	Updated call signatures, backend-selection test, contentMappers fixtures
package.json, pnpm-lock.yaml	New deps, test:tsgo script, optional typescript peer
README.md, examples/tsconfig.json, vitest*.config.ts	Docs and dual-backend test config

Review details

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• Comments generated: 2
• Review effort level: Balanced

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