src/build/private_code_test

Private Code Test

This directory provides a mechanism for testing that native does not link in object files from unwanted directories. The test finds all linker inputs, and checks that none live inside a list of internal paths.

Original bug: https://bugs.chromium.org/p/chromium/issues/detail?id=1266989

Determining Internal Directories

This is done by parsing the .gclient_entries file for all paths coming from https://chrome-internal.googlesource.com. I chose this approach since it is simple.

The main alternative I found was to use gclient flatten. Example output:

  # src -> src/internal
  "src/internal": {
    "url": "https://chrome-internal.googlesource.com/chrome/src-internal.git@c649c6a155fe65c3730e2d663d7d2058d33bf1f9",
    "condition": 'checkout_src_internal',
  },

• Paths could be found in this way by looking for checkout_src_internal within condition, and by looking for the comment line for recurse_deps that went through an internal repo.

Determining Linker Inputs

This is done by parsing build.ninja to find all inputs to an executable. This approach is pretty fast & simple, but does not catch the case where a public .cc file has an #include a private .h file.

Alternatives considered:

1. Dump paths found in debug information.

• Hard to do cross-platform.

2. Scan a linker map file for input paths.

• LTO causes paths in linker map to be inaccurate.

3. Use a fake link step to capture all object file inputs

• Object files paths are relative to GN target, so this does not catch internal sources referenced by public GN targets.

4. Query GN / Ninja for transitive inputs

• This ends up listing non-linker inputs as well, which we do not want.

5. Parse depfiles to find all headers, and add them to the list of inputs

• Additional work, but would give us full coverage.