In #37257 I discussed one way to host TS project references under Bazel, where each build step gets only .d.ts and tsconfig.json files from the referenced projects. This is broken because TS module resolution fails to locate the .d.ts files in their outDir.

In this issue, let's try a different approach for Bazel, to satisfy current TS module resolution, each build step should get the .ts sources of its referenced projects, and the .tsbuildinfo output as well.

Bazel is picky about the setting of --outDir, because it supports cross-compiled builds in distinct output locations. For example if you're on a Mac and building for local platform, the outDir is <workspace root>/bazel-out/darwin-fastbuild/bin. But if you're on a Mac and building for a docker image, you need native binaries to be for the target platform so outDir is <workspace root>/bazel-out/k8-fastbuild/bin and if you want binaries with debug information it's <workspace root>/bazel-out/k8-dbg/bin.

Since the outDir is platform-specific, we don't want to check in a config file that hard-codes it. So we prefer to always have Bazel pass the --outDir option on the command-line to tsc, rather than include it in the tsconfig files.

Now we come to the problem. TypeScript "composite" setting enables up-to-dateness checking in tsc. With this input structure, and trying to tsc -p b

a/a.ts
a/tsconfig.json (no outDir specified; a was compiled with tsc --outDir=bazel-out/darwin-fastbuild/bin/a)
b/b.ts
b/tsconfig.json
bazel-out/darwin-fastbuild/bin/a/a.d.ts
bazel-out/darwin-fastbuild/bin/a/tsconfig.tsbuildinfo

we get b/b.ts(1,17): error TS6305: Output file '/private/var/tmp/_bazel_alx/df60115ea7f2a64e10fb4aa64b7d827f/sandbox/darwin-sandbox/54/execroot/ts_composite/a/a.d.ts' has not been built from source file '/private/var/tmp/_bazel_alx/df60115ea7f2a64e10fb4aa64b7d827f/sandbox/darwin-sandbox/54/execroot/ts_composite/a/a.ts'.

This indicates that TS is looking for a.d.ts next to a.ts. If we hard-code the platform-dependent outDir into a/tsconfig.json like I've done here
https://github.com/alexeagle/ts_composite/pull/5 it solves this problem, but not in a way we can ship.

Note that the compilation of a/tsconfig.json produces a .tsbuildinfo file with a correct "outDir" (based on the --outDir flag that was passed to compilation of a

 "options": {
      "project": "../../../../a/tsconfig.json",
      "outDir": "./",
  }

So it seems like the behavior for compiling b is to read the outDir setting from a/tsconfig.json rather than trust the options.outDir reflected in the .tsbuildinfo output.