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88cb6f58f8
Consolidate go.mod.sri and go.toolchain.rev.sri into a single flakehashes.json file at the repo root, owned by a new Go program at tool/updateflakes. The JSON is consumed by flake.nix via builtins.fromJSON and by any future Go code via the FlakeHashes struct that defines its schema. Each block records its input fingerprint alongside the SRI it produced: the goModSum (a sha256 over go.mod and go.sum) for the vendor block, and the literal rev string from go.toolchain.rev for the toolchain block. updateflakes regenerates a block only when its recorded fingerprint disagrees with the current input. Doing the gating by content rather than file mtimes avoids the usual mtime hazards across git checkouts, clones, and merges. It also means re-runs with no input changes are essentially free, and a re-run that touches only one input pays only for that one block. The two blocks have no shared state -- vendor invokes go mod vendor into one tempdir, toolchain fetches and extracts a tarball into another -- so they run concurrently via errgroup. Cold time is bounded by the slower of the two rather than their sum. Also takes the opportunity to fold the toolchain fetch into a single curl|tar pipeline (no intermediate .tar.gz on disk). Split cmd/nardump into a thin package main and a new package nardump library at cmd/nardump/nardump that holds the NAR encoder and SRI helper. tool/updateflakes imports the library directly rather than building and exec'ing the nardump binary at runtime. The library uses fs.ReadLink (Go 1.25+) instead of os.Readlink, so it no longer requires the caller to chdir into the FS root for symlink targets to resolve. WriteNAR now wraps its writer in a bufio.Writer internally (unless the caller already passed one) and flushes on return, so callers don't pay for tiny writes against slow underlying writers. The cache-busting line in flake.nix and shell.nix is known to live at end of file, so updateCacheBust walks the lines in reverse. make tidy timings on this machine, before: ~14s every run. After: warm (no input changes): 0.05s vendor block stale only: 1.4s toolchain block stale only: 5.0s cold (no flakehashes.json): 5.0s Updates #6845 Change-Id: I0340608798f1614abf147a491bf7c68a198a0db4 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
nardump
nardump is like nix-store --dump, but in Go, writing a NAR file (tar-like, but focused on being reproducible) to stdout or to a hash with the --sri flag.
It lets us calculate the Nix sha256 in shell.nix without the person running git-pull-oss.sh having Nix available.