Run all linting in Docker via the Dockerfile lint stage (closes #90)

script/lint now builds only the lint stage of the main Dockerfile
(docker build --no-cache --target lint), whose build runs the linter, so
a successful build is a clean lint. It is uncached because a cached
build runs no linter, and a trap removes the image it tagged; the tag
carries the process ID so concurrent runs do not collide. The lint stage
calls golangci-lint directly, since make lint now needs Docker. Nothing
installs or runs golangci-lint on the host any more: bootstrap and the
Makefile drop the install, and script/fmt drops golangci-lint run --fix.

Model: opus-5-5

Dockerfile

@@ -14,7 +14,9 @@ RUN touch mfer/mf.pb.go
 # Go half of fmt-check only: this image has no node, so no prettier. The
 # markdown half runs in the mdfmt stage below.
 RUN make fmt-check-go
-RUN make lint
+# The linter directly, not `make lint`: script/lint builds this stage, and
+# there is no docker inside this build.
+RUN golangci-lint run --config .golangci.yml ./...
 
 # Markdown/JSON format stage — prettier needs node, which the Go images
 # do not have. node:22.17.0-bookworm-slim (2026-08-09); ships node

Makefile

@@ -58,9 +58,6 @@ fmt-check-md:
 hooks:
 	@script/install-precommit
 
-devprereqs:
-	which golangci-lint || go install -v github.com/golangci/golangci-lint/v2/cmd/golangci-lint@v2.12.2
-
 mfer/mf.pb.go: mfer/mf.proto
 	cd mfer && go generate .
 

README.md

@@ -65,9 +65,9 @@ standard: normalized scripts in `script/` are the entrypoints for the
 development workflow, and the Makefile targets are thin shims that call them. We
 provide:
 
-- `script/bootstrap` — install all dependencies (Go, golangci-lint, Go module
-  download, and node/yarn plus the prettier version pinned in
-  `package.json`/`yarn.lock`), idempotently
+- `script/bootstrap` — install all dependencies (Go, Go module download, and
+  node/yarn plus the prettier version pinned in `package.json`/`yarn.lock`),
+  idempotently; golangci-lint is not installed, it runs only in Docker
 - `script/setup` — make a fresh clone ready for development: runs
   `script/bootstrap`, then `script/install-precommit`
 - `script/projectname` — output the project name (`mfer`); used by other scripts
@@ -77,9 +77,11 @@ provide:
 - `script/fuzz` — fuzz the manifest parser for one minute; run by hand
   (`make fuzz`), never by CI, while `script/test` runs its committed seed corpus
   as ordinary tests
-- `script/lint` — run `golangci-lint` and verify `gofmt` cleanliness
-- `script/fmt` — format all code and docs (writes): `gofumpt`,
-  `golangci-lint run --fix`, and `script/prettier --write`
+- `script/lint` — run `golangci-lint` in Docker: builds only the `lint` stage of
+  the `Dockerfile` (the Go format check, then the linter), uncached so it runs
+  every time, then removes the image
+- `script/fmt` — format all code and docs (writes): `gofumpt` and
+  `script/prettier --write`
 - `script/prettier` — run prettier over the repository's canonical file set
   (Markdown and JSON, minus `.prettierignore`) in the given mode, `--write` or
   `--check`; the single definition of that file set, so `script/fmt` and
@@ -105,11 +107,10 @@ yet. Primary development happens on a privately-run Gitea instance at
 [tracked there](https://git.eeqj.de/sneak/mfer/issues).
 
 Changes must always be formatted with a standard `go fmt`, syntactically valid,
-and must pass the linting defined in the repository (presently only the
-`golangci-lint` defaults), which can be run with a `make lint`. The `main`
-branch is protected and all changes must be made via
-[pull requests](https://git.eeqj.de/sneak/mfer/pulls) and pass CI to be merged.
-Any changes submitted to this project must also be
+and must pass the linting defined in the repository's `.golangci.yml`, which
+`make lint` runs in Docker. The `main` branch is protected and all changes must
+be made via [pull requests](https://git.eeqj.de/sneak/mfer/pulls) and pass CI to
+be merged. Any changes submitted to this project must also be
 [WTFPL-licensed](https://wtfpl.net) to be considered.
 
 See [`REPO_POLICIES.md`](REPO_POLICIES.md) for detailed coding standards,

script/bootstrap

@@ -140,12 +140,7 @@ main() {
 
     # ---- Go repos ----
     if missing go; then pkg_install go golang go go; fi
-    # golangci-lint: packaged in nix, brew, and apk. On apt there is no
-    # package: download a specific release archive from GitHub and
-    # verify its hash (verify_sha256), never curl | sh.
-    if missing golangci-lint; then
-        pkg_install golangci-lint golangci-lint golangci-lint golangci-lint
-    fi
+    # No golangci-lint: script/lint runs it in Docker only.
     go mod download
 
     # ---- Python repos ----

script/fmt

@@ -19,7 +19,6 @@ main() {
     cd "$ROOT"
     ensure_pb
     gofumpt -l -w mfer internal cmd
-    golangci-lint run --fix
     # Markdown and JSON, over the same file set script/fmt-check verifies.
     "$SCRIPT_DIR/prettier" --write
 }

script/lint

@@ -1,17 +1,20 @@
 #!/bin/sh
-# script/lint: run the linter.
+# script/lint: run golangci-lint, in Docker only. Builds the lint stage of
+# the Dockerfile, whose build runs the linter, so a successful build is a
+# clean lint. --no-cache because a cached build runs no linter. The image
+# is removed afterwards, whatever the outcome.
 set -eu
 
-ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
+ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    golangci-lint run
-    if [ -n "$(gofmt -l .)" ]; then
-        echo "gofmt: files need formatting:" >&2
-        gofmt -l . >&2
-        exit 1
-    fi
+    # Tagged per run, so concurrent runs never remove each other's image.
+    image="$("$SCRIPT_DIR/projectname")-lint:$$"
+    # A failed build leaves no image, so there is nothing to remove then.
+    trap 'docker image rm "$image" >/dev/null 2>&1 || true' EXIT INT TERM
+    docker build --no-cache --target lint -t "$image" .
 }
 
 main "$@"