CI: add _readme-gofmt tool to reformat Go code in README

.ci.gofmt.sh

@@ -1,11 +1,15 @@
 #!/usr/bin/env bash
 
+set -euo pipefail
+
 if [ -n "$(gofmt -l .)" ]; then
   echo "Go code is not formatted:"
   gofmt -d .
   exit 1
 fi
 
+go run ./_readme-gofmt/main.go
+
 go generate ./...
 if [ -n "$(git status -s -uno)" ]; then
   echo "Go generate output does not match commit."

.github/workflows/main.yml

@@ -15,10 +15,8 @@ jobs:
         uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c # v6.4.0
         with:
           go-version: ${{ matrix.go_version }}
-      - run: npm install -g mdsf-cli
       - run: ./.ci.gogenerate.sh
       - run: ./.ci.gofmt.sh
-      - run: ./.ci.readme.fmt.sh
       - run: ./.ci.govet.sh
       - run: go test -v -race ./...
   test:

_readme-gofmt/main.go

@@ -0,0 +1,91 @@
+//go:build go1.21
+
+/*
+MIT License
+
+Copyright (c) 2026 Olivier Mengué and contributors.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+*/
+
+// Command readme-gofmt applies 'gofmt -s' to all Go block in README.md.
+package main
+
+import (
+	"bytes"
+	"log"
+	"os"
+	"os/exec"
+	"regexp"
+	"slices"
+)
+
+func main() {
+	log.SetFlags(0)
+	log.SetPrefix("readme-gofmt: ")
+
+	buf, err := os.ReadFile("README.md")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	gofmt, err := exec.LookPath("gofmt")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	buf = bytes.ReplaceAll(buf, []byte("\r"), nil) // CRLF -> LF
+
+	reBlock := regexp.MustCompile("(?s)\n```go\n(.*?\n)```")
+
+	matches := reBlock.FindAllSubmatchIndex(buf, -1)
+
+	changes := 0
+
+	for i := len(matches) - 1; i >= 0; i-- {
+		match := matches[i]
+		block := buf[match[2]:match[3]]
+
+		cmd := exec.Command(gofmt, "-s")
+		cmd.Stdin = bytes.NewReader(block)
+		var output bytes.Buffer
+		cmd.Stdout = &output
+		cmd.Stderr = os.Stderr
+		err := cmd.Run()
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		outputBytes := bytes.ReplaceAll(output.Bytes(), []byte("\r"), []byte("")) // CRLF -> LF
+		if !bytes.Equal(outputBytes, block) {
+			changes++
+			buf = slices.Replace(buf, match[2], match[3], outputBytes...)
+		}
+	}
+
+	if changes > 0 {
+		cmd := exec.Command("diff", "-a", "-u", "README.md", "-")
+		cmd.Stdin = bytes.NewReader(buf)
+		cmd.Stdout = os.Stdout
+		cmd.Stderr = os.Stderr
+		cmd.Run()
+
+		os.Exit(2)
+	}
+}