[clang-tools-extra] [clangd] Test background index file contents (PR #179956)

[Justin Cady via cfe-commits]

justincady wrote:

I understand the concern. I suspect we just view the value of the explicit test differently. As someone previously unfamiliar with the clangd codebase, I was surprised that I couldn't find any validation of on-disk representation (at least, not in the way I was expecting it). Adding this test was helpful in growing my understanding, and I thought desirable to keep (even if there is already implicit coverage via round-trip testing).

> I am simply trying to understand what specific potential problem is not covered by the existing tests, where a bug might occur that will be missed by the existing tests.

There may or may not be a potential problem exclusively identified by this test. I don't think I can prove that either way. I'm happy to update the test to validate the full path as you pointed out, but I also don't want to waste anyone's time. If you and other maintainers would rather not add the test I'll close this PR.

Again, I apologize for making things more complex in my attempt to simplify a future review. Thanks again for taking a look.

https://github.com/llvm/llvm-project/pull/179956