`--no-cache-filter=lint` is silently ignored by BuildKit when no stage
matches the name, so the entire anti-false-green mechanism hung on one
unvalidated magic string: renaming or mistyping the `lint` stage would
have left the lint layer served from cache and `script/lint` reporting
green having linted nothing. Reproduced here — with the filter pointed at
a nonexistent stage and no `--target`, an unchanged tree built with
`RUN golangci-lint run ... CACHED` and exited 0.
`--target lint` closes it: a stage name that does not exist now fails
loudly (`target stage "nosuchstage" could not be found`, exit 1) instead
of passing. The two flags name the same stage from the same string and
validate each other; both the script and the stage definition in
Dockerfile.lint carry a comment saying they must be kept in sync.
`--output=type=cacheonly` drops the image export. Nothing consumes the
image — the deliverable of this build is an exit code — and the export
cost seconds per run and left one dangling image behind every time, on a
host where pruning is prohibited. The lint stage still executes and a
lint failure still exits non-zero, both verified rather than assumed.
TODO.md: the 2026-08-07 entry's claim that the repo has no linter pin and
lints on the host is marked superseded in place rather than rewritten;
the narrowed scaffold exemption now names `.dockerignore` alongside
`Dockerfile.lint` and `script/lint`; and the specific wall-clock timings
are replaced by the durable property they were evidence for, since they
vary per host and per run.
golangci-lint is no longer invoked on the host anywhere in the repo.
Dockerfile.lint pins golangci/golangci-lint:v2.12.2 by digest and runs
the linter as a build step, so a successful build IS a clean lint, and
`make lint` becomes a thin shim over script/lint. This removes the host
linter install that produced a false green here, where a branch that was
genuinely red with a goconst finding reported "0 issues" off the shared
host cache; a container per run has its own cache and lock.
Two deliberate divergences from the sneak/homoicon reference shape:
- Two stages rather than one. A cached `deps` stage holds
`go mod download`, then `FROM deps AS lint` carries the source copy
and the lint run, and script/lint builds with
`--no-cache-filter=lint`. Caching of the lint result is explicitly
waived (a cached build lints nothing), and splitting the stages means
busting the lint layer does not re-fetch the module cache over the
network on every run.
- No `golangci-lint config verify` step. It resolves its JSON schema
over a live, unpinned HTTPS call: an unpinned network input inside
the one step whose purpose is a pinned, reproducible gate, and a
schema-host outage would surface as a red build. `golangci-lint run`
already fails on a malformed config. The reason is recorded in a
comment in Dockerfile.lint.
.dockerignore excludes .git only; the lint reads the Go sources,
go.mod/go.sum and .golangci.yml, none of which come from there.
The TODO.md scaffold-exemption note is narrowed rather than dropped:
Dockerfile.lint and script/lint are now permitted and required, while CI
config, REPO_POLICIES.md, an application Dockerfile and any other
script/ entrypoint still are not.
Verified, since a green docker build is the classic false green: two
consecutive script/lint runs on an unchanged tree each showed the
`golangci-lint run` layer executing (9.8s and 7.9s, both "0 issues.")
while the deps layers reported CACHED; a deliberate indent-error-flow
violation failed the build naming that finding and the unused one, and a
revert went clean again. `make check` green.
