GeezerVison

PR Checklist

• The PR title follows our guidelines.
• There is an issue for the bug/feature this PR is for.
• All existing tests are passing (packages/vite: 169 files / 1963 tests).
• Tests for the changes are included.

What is the current behavior?

Under HMR, the /ns/m route serves app modules without a source map. Vite's transform does produce one, but the device pipeline then changes the code: it prepends guards and boot code, rewrites and hoists imports, and for some modules re-prints the whole file with Babel ([ast-normalized]). Then it sends the result without the map. The runtime reports scripts like http://<host>:5173/ns/m/src/app with an empty sourceMapURL, so a debugger (VS Code / js-debug, Chrome DevTools) cannot bind breakpoints in .ts/.tsx sources. This is why the NativeScript VS Code extension forces --no-hmr for Vite projects.

What is the new behavior?

App modules (not library/node_modules ones) served by /ns/m carry an inline source map:

• hmr/server/served-module-sourcemap.ts aligns Vite's transform output with the served body using a Myers line diff (whitespace-insensitive), then carries Vite's mappings over:
  • Lines with the same text apart from indentation keep Vite's segments, with columns shifted by the indentation change. This covers the Babel re-print, which uses retainLines.
  • Hunks rewritten in place (same line count on both sides) map each line to the start of its original line.
  • Injected preamble and hoisted imports stay unmapped.
• Sources are emitted as absolute file:// URLs, because the device URL doesn't mirror the project layout. js-debug and DevTools resolve them with no path overrides.
• The map is appended before the response memo, so cached responses include it. Code that already has a sourceMappingURL is left as is.
• New dependency: @jridgewell/sourcemap-codec (already in the tree through Babel).

Verified

On a Solid app (ns debug ios --watch, iOS simulator), driving js-debug 1.140 (the version VS Code bundles) over DAP:

• Breakpoints in app.tsx, state/ui.ts, and a Babel-normalized data/music.ts bind at the requested lines.
• After an HMR edit, the breakpoint re-binds to the new module version and pauses in App at app.tsx:15, with scopes and evaluation working.
• The iOS and Android inspector clients pass data: source map URLs through unchanged.

Cost

• About 0.3 ms to build the map for a 600-line module, only for responses not already cached.
• About 40% more bytes per app module. Library modules, core, and the deps bundle are unchanged.

Not covered

Vue SFCs are served by /ns/sfc / /ns/asm and still have no maps. That can follow separately.

Related: the VS Code extension stops forcing --no-hmr once this ships: nativescript-community/nativescript-vscode-extension#303.