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,

mfer/gpg_test.go

@@ -10,7 +10,6 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
-	"syscall"
 	"testing"
 	"time"
 
@@ -426,51 +425,36 @@ func TestGPGTimeoutKillsGPG(t *testing.T) {
 	assert.Contains(t, err.Error(), "gpg sign failed: gpg timed out")
 }
 
-// TestGPGCancelWhenChildHoldsOutput uses a fake gpg that runs sleep as a
+// TestGPGTimeoutWhenChildHoldsOutput uses a fake gpg that runs sleep as a
 // child instead of exec-ing it, the way a wrapper script around the real
 // gpg might. Killing the fake gpg leaves sleep holding its stdout and
-// stderr open; the call must still return once ctx ends instead of waiting
-// for sleep to exit. The fake gpg writes the process ID of sleep to a named
-// pipe; the test ends ctx only after reading it, so sleep is running by
-// then, and kills sleep before returning.
-func TestGPGCancelWhenChildHoldsOutput(t *testing.T) {
-	pidPipe := filepath.Join(t.TempDir(), "sleep.pid")
-	require.NoError(t, syscall.Mkfifo(pidPipe, 0o600))
-	// sleep outlasts the 10 s wait below, so a call that waits for it fails.
+// stderr open; the call must still return shortly after the deadline
+// instead of waiting for sleep to exit. The fake gpg writes the process ID
+// of sleep to a file so that the test can kill it before returning.
+func TestGPGTimeoutWhenChildHoldsOutput(t *testing.T) {
+	pidFile := filepath.Join(t.TempDir(), "sleep.pid")
 	t.Setenv("PATH", fakeGPGPath(t,
-		"#!/bin/sh\nsleep 60 &\necho $! >'"+pidPipe+"'\nwait\n"))
+		"#!/bin/sh\nsleep 3 &\necho $! >'"+pidFile+"'\nwait\n"))
+	t.Cleanup(func() {
+		pid, err := os.ReadFile(pidFile) //nolint:gosec // G304: path inside t.TempDir()
+		require.NoError(t, err)
 
-	ctx, cancel := context.WithCancel(context.Background())
+		n, err := strconv.Atoi(strings.TrimSpace(string(pid)))
+		require.NoError(t, err)
+
+		sleep, err := os.FindProcess(n)
+		require.NoError(t, err)
+		require.NoError(t, sleep.Kill())
+	})
+
+	ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
 	defer cancel()
 
-	signErr := make(chan error, 1)
-
-	go func() {
-		_, err := gpgSign(ctx, []byte("data"), GPGKeyID("any"))
-		signErr <- err
-	}()
-
-	pid, err := os.ReadFile(pidPipe) //nolint:gosec // G304: path inside t.TempDir()
-	require.NoError(t, err)
-
-	n, err := strconv.Atoi(strings.TrimSpace(string(pid)))
-	require.NoError(t, err)
-
-	sleep, err := os.FindProcess(n)
-	require.NoError(t, err)
-	t.Cleanup(func() { require.NoError(t, sleep.Kill()) })
-
-	cancel()
-
-	// The call should return about gpgWaitDelay (one second) after the
-	// cancel. 10 s is far above that and well under the 30 s test timeout,
-	// which would abort the whole package before the cleanup kills sleep.
-	select {
-	case err := <-signErr:
-		require.ErrorIs(t, err, context.Canceled)
-	case <-time.After(10 * time.Second):
-		t.Fatal("the call waited for the child holding gpg's output to exit")
-	}
+	start := time.Now()
+	_, err := gpgSign(ctx, []byte("data"), GPGKeyID("any"))
+	require.ErrorIs(t, err, context.DeadlineExceeded)
+	assert.Less(t, time.Since(start), 3*time.Second,
+		"the call waited for the child holding gpg's output to exit")
 }
 
 // TestBuildPassesContextToSigning checks that a caller can cancel the gpg

mfer/scanner_test.go

@@ -304,19 +304,46 @@ func TestScannerEnumerateFS(t *testing.T) {
 func TestSendEnumerateStatusNonBlocking(t *testing.T) {
 	t.Parallel()
 
-	// Nobody receives, so a blocking send would hang the test into its timeout.
+	// Channel with no buffer - send should not block
 	ch := make(chan EnumerateStatus)
 
-	sendEnumerateStatus(ch, EnumerateStatus{FilesFound: 1})
+	// This should not block
+	done := make(chan bool)
+
+	go func() {
+		sendEnumerateStatus(ch, EnumerateStatus{FilesFound: 1})
+
+		done <- true
+	}()
+
+	select {
+	case <-done:
+		// Success - did not block
+	case <-time.After(100 * time.Millisecond):
+		t.Fatal("sendEnumerateStatus blocked on full channel")
+	}
 }
 
 func TestSendScanStatusNonBlocking(t *testing.T) {
 	t.Parallel()
 
-	// Nobody receives, so a blocking send would hang the test into its timeout.
+	// Channel with no buffer - send should not block
 	ch := make(chan ScanStatus)
 
-	sendScanStatus(ch, ScanStatus{ScannedFiles: 1})
+	done := make(chan bool)
+
+	go func() {
+		sendScanStatus(ch, ScanStatus{ScannedFiles: 1})
+
+		done <- true
+	}()
+
+	select {
+	case <-done:
+		// Success - did not block
+	case <-time.After(100 * time.Millisecond):
+		t.Fatal("sendScanStatus blocked on full channel")
+	}
 }
 
 func TestSendStatusNilChannel(t *testing.T) {

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 "$@"