Reflink shared/copy subtrees in a single syscall#22
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ApplyCopy previously walked every file under shared/copy/ and reflinked each one individually — ~4 syscalls per file, so a Composer vendor/ with 20k files took ~4s of pure syscall overhead after "copied vendor/" printed. APFS clonefile(2) accepts directories and clones the whole hierarchy in one syscall, so fast-path each template-free top-level subtree via a new fscopy.CopyTree and fall through to the existing per-file walk for top-level files, template-containing subtrees, pre-existing destinations, and non-APFS/Linux volumes. Measured 6.2s → 2.0s wall-clock for `wt add --skip-setup` in a 20,762-file project; system CPU drops 4.94s → 0.98s.
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Summary
ApplyCopynow tries a singleclonefile(2)per template-free top-level directory inshared/copy/via a newfscopy.CopyTree, collapsing the ~20k per-file reflinks for a Composer vendor/ into one syscall.WalkDir+CopyFilepath for top-level files, subtrees containing.templatefiles, destinations that already exist, and any filesystem/platform that returnserrReflinkUnsupported(Linux FICLONE is file-only and stays on the per-file path).wt add --skip-setupin a 20,762-file project: 6.18s → 2.04s wall-clock, 4.94s → 0.98s system CPU.Test plan
make dev(fmt + vet + test + build)GOOS=linux go build ./...cross-compileTestCopyTreeNested,TestCopyTreePreservesSymlink,TestCopyTreeExistingDst,TestIsReflinkUnsupportedin fscopy;TestApplyCopyFastPathForDirectories,TestApplyCopyFallsBackWhenTreeContainsTemplate,TestApplyCopyFastPathPreservedWhenVarsNilin project~/Sites/affiliatedwith--skip-setup— pause aftercopied vendor/is gone