Cache typed config with git config list --type=<X>

[derrickstolee]

In certain repos and on the Windows platform, git-credential-manager can take 8-15 seconds before looking up a credential or having any user-facing interaction. This is due to dozens of git config --get processes that take 150-250 milliseconds each. The config keys that cause this pain are http.<url>.sslCAinfo and http.<url>.cookieFile. When credential.useHttpPath is enabled, each key is checked as <url> is incrementally truncated by directory segment.

It would be best if we could call a single Git process to send multiple config queries instead of running multiple processes. gitgitgadget/git#2033 suggested this direction of a single process solution, but it's very complicated! During review of that effort, it was recommended to use git config list instead.

But then there's a different problem! In all released versions of Git, git config list silently ignores the --type argument. We need the --type argument to guarantee that the resulting output string matches the bool or path formats.

The core Git change in gitgitgadget/git#2044 is now merged to next and thus is queued for Git 2.54.0. (We should wait until it merges to master before merging this change, just in case.) We can only check compatibility using a version check since the original command silently misbehaves.

This pull request allows for caching the list of all config values that match the given types: bool, path, or none. These are loaded lazily so if a command doesn't need one of the types then the command doesn't run. We are also careful to clear this cache if GCM mutates the config.

Since we ask for Git config values using --type=bool, --type=path, and --no-type, we may launch three git config list commands to satisfy these needs.

There is a possibility that this feature is fast-tracked into microsoft/git, in which case the version check would need augmentation. I have that available in derrickstolee#1 as an example.

Disclaimer: I used Claude Code and GitHub Copilot CLI to assist with this change. I carefully reviewed the changes and made adjustments based on my own taste and testing.

I did an end-to-end performance test on a local monorepo and got these results for improvements to no-op git fetch calls:

Command	Mean [s]	Min [s]	Max [s]	Relative
Without Cache	14.986 ± 0.255	14.558	15.192	3.29 ± 0.17
With Cache	4.561 ± 0.223	4.390	4.935	1.00

[derrickstolee]

The Git change is now merged into master so it's locked-in for Git 2.54.0.

[mjcheetham]

This is a rather involved change (caches!) and is Git version dependant. I'll need a few iterations to fully grok the implications.

At this point, I'm also strongly considering the effort compared to writing our own Git config file parser (including support for all the include and includeIf logic) rather than continuing to patch more layers on the git config handling.

One thing I've spotted so far is a blocker on the use of --show-scope that would also need to be version-gated sadly 😢

[mjcheetham]

Unfortunately --show-scope was only introduced in 2020 with Git 2.26.0 (commit 145d59f4823) so we cannot always use this option else Git exits with an error.

I originally used --show-scope but had to drop it to support older Git versions: #318

[derrickstolee]

I force-pushed to drop the commit that added --show-scope and the only impact was to remove --show-scope from the new code path. It reuses the existing parsing of --show-origin.

Range diff:

1:  cfd3298c = 1:  cfd3298c refactor: Add config caching to reduce git process calls
2:  625d2541 = 2:  625d2541 test: Add cache tests and fix precedence bug
3:  eb0d445a < -:  -------- refactor: Use git config --show-scope for reliable level detection
4:  c7687ad7 ! 3:  4f37e544 feat: Cache config entries by type for typed queries
    @@ src/shared/Core/GitConfiguration.cs: namespace GitCredentialManager
                      return;
     +            }

    --            using (ChildProcess git = _git.CreateProcess("config list --show-scope --show-origin -z"))
    -+            using (ChildProcess git = _git.CreateProcess($"config list --show-scope --show-origin -z {typeArg}"))
    +-            using (ChildProcess git = _git.CreateProcess("config list --show-origin -z"))
    ++            using (ChildProcess git = _git.CreateProcess($"config list --show-origin -z {typeArg}"))
                  {
                      git.Start(Trace2ProcessClass.Git);
                      // To avoid deadlocks, always read the output stream first and then wait
    @@ src/shared/Core/GitConfiguration.cs: namespace GitCredentialManager
     +                        cache.Load(data, _trace);
                              break;
                          default:
    -                         _trace.WriteLine($"Failed to load config cache (exit={git.ExitCode}), will use individual git config commands");
    +                         _trace.WriteLine($"Failed to load config cache (exit={git.ExitCode})");
     @@ src/shared/Core/GitConfiguration.cs: namespace GitCredentialManager
              {
                  if (_useCache)
5:  0fea6faf = 4:  3125246e feat: Gate config cache on Git 2.54.0+ version check