repowalk

Overview ¶

Package repowalk walks this repository's tree for the tests that scan it (the guard tests: goexec's toolchain guards, trimpathguard, vacuousguard), in a way Go's test cache can replay.

THE PROBLEM. `go test` keys a cached result on every file and directory the test opened or stat'ed inside the module. For a directory it LISTED, the key is the directory's own stat plus the stat of every entry in it, so a test that walks the repository root with filepath.WalkDir keys on the mtime of every top-level entry — .git, .forge, tmp, bin included. Those change all the time without any tracked file changing: git rewrites .git/index on a status refresh, `forge ci verify-generated` and `forge generate` record their cache in .forge/, a build writes bin/. Every such write made the scanning packages re-run on an unchanged tree, so a second `task ci` on the same commit re-paid them, and a CI runner (whose fresh .git has the checkout's mtime) never replayed them at all.

WHAT THIS DOES INSTEAD. WalkDir lists the root WITHOUT the read reaching the test log, and keys on the root's own stat instead (os.Stat, which is logged). A directory's mtime changes exactly when an entry is created, removed or renamed in it, so a new or deleted top-level entry still invalidates the result. Each top-level entry the callback descends into is walked with the ordinary, logged calls, so a change anywhere below it does too; an entry the callback skips (fs.SkipDir) is never read, and so never keys the result. What the callback learns of a top-level entry without opening it is its name and type, which only a rename can change.

The callback must therefore READ (open or stat) whatever it decides on, beyond a top-level entry's name and type. DirEntry.Info does stat, so it is part of the key.

On Windows the root listing cannot be read outside package os, and WalkDir is plain filepath.WalkDir: correct, keyed on more than it needs.