[Tyrie Vella (tyrielv)]

Problem and Context

libgit2 does not read the config that GIT_CONFIG_GLOBAL, GIT_CONFIG_SYSTEM, GIT_CONFIG_NOSYSTEM, GIT_CONFIG, GIT_CONFIG_COUNT, or GIT_CONFIG_PARAMETERS select or supply. RetryConfig already detects these variables with LibGit2Repo.EnvironmentChangesGitConfig() and reads its settings with git.exe. The boolean gvfs.* settings did not. They read the user's real config and ignored the value from the environment.

This affects gvfs.trust-pack-indexes, gvfs.prefetch-offload, gvfs.prefetch-use-idx, gvfs.enable-packfile-recovery, gvfs.background-cache-auth, gvfs.mount-progress, and gvfs.show-hydration-status. Git sets GIT_CONFIG_PARAMETERS for every git -c <key>=<value> command, so the hooks see these variables often. For example, CloneNetworkTests sets gvfs.trust-pack-indexes through GIT_CONFIG_GLOBAL. The clone ignores that value. The test passes only because its value matches the default.

Changes

• When EnvironmentChangesGitConfig() is true, read boolean settings with git config --type=bool. Git normalizes the value, exits with 1 when the key is unset, and fails when the value is not a boolean. When the environment does not change config, the reads still use libgit2.
• Add the LibGit2Repo.TryReadConfigBoolWithGit delegate. The static LibGit2Repo.GetConfigBoolOrDefault and every LibGit2RepoInvoker constructor require it. Remove the invoker constructors that took no reader.
• Keep the failure policy of each read path. The static helper logs the failure and returns the default. The invoker throws when git cannot read the key, as its libgit2 read does. Thus an invalid gvfs.enable-packfile-recovery value stops maintenance instead of enabling pack recovery.
• Add GitProcess.TryGetBoolFromConfig. GitRepo, CloneVerb, PrefetchVerb, BlobPrefetcher, and InProcessMount pass it as the reader. GitRepo supplies the reader that PrefetchStep, PackfileMaintenanceStep, and GitStatusCache use. gvfs.mount-progress now uses the static helper instead of its own LibGit2Repo read.
• In GVFS.Hooks, read gvfs.show-hydration-status with the parent Git executable, as the alias check does. The query sets COMMAND_HOOK_LOCK, and it does not search the current directory or PATH for git. The alias check and this read share the config query and retry code.
• Close the redirected standard input of every ProcessHelper.Run child. No caller writes to it. With GIT_CONFIG=-, git reads config from standard input, and a hook query waited for input forever.
• Parse the git output in LibGit2Repo, because GVFS.Hooks compiles LibGit2Repo.cs but not GitProcess.cs.
• Add unit tests for the git route, the libgit2 route, an unset key, a failed git read through the static helper and through the invoker, a git reader that throws, the output parser, the git config command lines in GitProcess and the hook, and the closed standard input in ProcessHelper.

Known gaps and deliberate decisions

• No functional test with a non-default value. The new unit tests verify the routing and the parser. No functional test yet runs a GVFS command with an environment-supplied value that differs from the default. Deferred to keep this change focused. No follow-up is planned yet.
• Relative config paths in GitProcess. GitProcess runs git from Environment.SystemDirectory. Thus a relative GIT_CONFIG_GLOBAL or GIT_CONFIG path resolves against that directory, and git reports the key as unset. RetryConfig and every other GitProcess config read already behave this way. Deferred to a separate change.
• libgit2 string and multi-value reads. GitRepo.TryGetConfigValue (gvfs.max-active-enumerations), GetConfigString, and ForEachMultiVarConfig still ignore these environment variables. This change covers only boolean settings.
• Other hook launches. The hooks still launch git and gvfs by name for the worktree and prefetch commands. Windows searches the current directory before PATH for those names. This change does not alter those launches.

[Nathan Baird (ShiningMassXAcc)]

Please add the end-to-end validation requested in the inline comment.

[Nathan Baird (ShiningMassXAcc)]

Please add an end-to-end test where an environment-supplied boolean disagrees with local gvfs.* config and assert actual GVFS behavior. For example, with a completed prefetch baseline, override gvfs.prefetch-offload in both directions and assert mount offload versus direct execution. The mock-based routing tests do not prove the compiled runtime path honors the effective value.