Auditing Angular's TypeScript 7 Beta: Diagnostics Parity and Source-Map Fidelity
Angular's TypeScript 7-powered compiler beta is reported to move part of the build pipeline into a native preprocessor, described as Rust-based, while Microsoft's publicly documented TypeScript native port is a Go codebase. This audit skips the faster-builds headline and measures the three properties that actually decide whether a real workspace can adopt the beta: diagnostics parity, source-map fidelity, and transformer compatibility. We build a fixture workspace with one application and one publishable library, strict templates everywhere, and template checks promoted from warnings to errors so the diagnostic surface is diffable at all. Both compilers run from the same lockfile and are selected by environment variable, with exact versions pinned and no carets, so the control can't quietly evaporate between machines. Then we look at where the native-to-JavaScript seam leaks: byte offsets becoming line and column numbers, UTF-16 code units versus UTF-8 bytes, spans expressed as start-length or start-end, and spans that cross the synthetic template boundary. None of those failures crash a build or turn CI red, which is exactly why they matter. Full write-up: https://hackyjs.com/posts/auditing-angulars-typescript-7-beta-diagnostics-parity-source-map-fidelity-and-transformer-compatibility