lint: enable custom linters from go-lint project

ops/build-lint.sh

@@ -0,0 +1,39 @@
+#!/usr/bin/env sh
+
+set -e
+
+SCRIPT_DIR=$(cd "$(dirname "$0")" && pwd)
+PROJECT_ROOT=$(cd "$SCRIPT_DIR/.." && pwd)
+cd "$PROJECT_ROOT" # .custom-gcl.yaml is only discovered in the project root.
+
+# go-lint is public, but the public checksum database has not indexed it yet.
+# Preserve existing exclusions while fetching the module through the normal
+# proxy-then-direct resolution path.
+export GONOSUMDB="${GONOSUMDB:+$GONOSUMDB,}git.offline-twitter.com"
+
+BIN="bin/golint"
+STAMP="bin/.golint.stamp"
+
+# The pinned plugin version is recorded in .custom-gcl.yaml.
+current_stamp() {
+    sha256sum .custom-gcl.yaml | cut -d' ' -f1
+}
+
+if [ "$1" = "--if-needed" ] &&
+   [ -x "$BIN" ] &&
+   [ -f "$STAMP" ] &&
+   [ "$(cat "$STAMP")" = "$(current_stamp)" ]; then
+    exit 0
+fi
+
+if ! [ -x "$(command -v golangci-lint)" ]; then
+    echo "golangci-lint is not installed. Please install it from https://golangci-lint.run/welcome/install/"
+    exit 1
+fi
+
+mkdir -p bin
+echo "Building golint (golangci-lint + shared custom linters)..."
+golangci-lint custom
+current_stamp > "$STAMP"
+
+echo "Done: $PROJECT_ROOT/$BIN"