chore: rewrite prepare-release script as a go cmd

This change allows release engineers to generate the changelog PR via
the local gh command thus inheriting the user's credentials. This fixes
permissions issues in the release process. The script is added as a go
tool via go.mod.

Signed-off-by: crozzy <joseph.crosland@gmail.com>

Author: crozzy

.github/scripts/changelog-render

@@ -14,7 +14,7 @@ On rare occasions when a fix is time-sensitive, it is possible to create a relea
 
 ```sh
 NEW_VERSION=v0.999.999
-.github/scripts/prepare-release -b main -r upstream "$NEW_VERSION"
+go tool prepare-release -remote=upstream -branch=main "$NEW_VERSION"
 ```
 
 Follow the `prepare-release` command's instructions to merge changelog updates and release the tag.
@@ -42,7 +42,7 @@ Finally, prepare the release specifying the release branch.
 LAST_MINOR=v0.999.0
 NEW_VERSION=v0.999.1
 BRANCH=release-${LAST_MINOR%.*} # e.g. release-v0.999
-.github/scripts/prepare-release -b $BRANCH -r upstream $NEW_VERSION
+go tool prepare-release -remote=upstream -branch=$BRANCH $NEW_VERSION
 ```
 
 Follow the `prepare-release` command's instructions to merge changelog updates and release the tag.

.github/scripts/changelog-update

@@ -62,3 +62,5 @@ require (
 )
 
 replace github.com/quay/claircore/updater/driver => ./updater/driver
+
+tool github.com/quay/claircore/internal/cmd/prepare-release

.github/scripts/prepare-release

@@ -0,0 +1,173 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"time"
+)
+
+const (
+	notesRef   = "refs/notes/changelog"
+	compareURL = "https://github.com/quay/claircore/compare"
+)
+
+// getPreviousTag finds the most recent version tag merged into the current branch.
+func getPreviousTag() (string, error) {
+	out, err := exec.Command("git", "tag", "--sort=-taggerdate", "--merged").Output()
+	if err != nil {
+		return "", fmt.Errorf("listing tags: %w", err)
+	}
+	for _, line := range strings.Split(string(out), "\n") {
+		if strings.HasPrefix(line, "v") {
+			return line, nil
+		}
+	}
+	return "", fmt.Errorf("no version tags found")
+}
+
+// renderChangelog generates the changelog content for a new release.
+// It reads git notes from commits between previous tag and the branch.
+func renderChangelog(w io.Writer, prevTag, nextTag, branch string) error {
+	// Write header
+	fmt.Fprintf(w, "<a name=\"%s\"></a>\n", nextTag)
+	fmt.Fprintf(w, "## [%s] - %s\n", nextTag, time.Now().Format("2006-01-02"))
+	fmt.Fprintf(w, "[%s]: %s/%s...%s\n\n", nextTag, compareURL, prevTag, nextTag)
+
+	// Get commits since prevTag on the target branch
+	out, err := exec.Command("git", "rev-list", prevTag+".."+branch).Output()
+	if err != nil {
+		return fmt.Errorf("listing commits: %w", err)
+	}
+
+	hasNotes := false
+	for _, commit := range strings.Split(strings.TrimSpace(string(out)), "\n") {
+		if commit == "" {
+			continue
+		}
+		note, err := getCommitNote(commit)
+		if err != nil || note == "" {
+			continue
+		}
+		hasNotes = true
+		formatted := formatNote(note)
+		fmt.Fprint(w, formatted)
+	}
+
+	if !hasNotes {
+		fmt.Fprintln(w, "Nothing interesting happened this release.")
+		fmt.Fprintln(w)
+	}
+
+	return nil
+}
+
+// getCommitNote retrieves the changelog note for a commit.
+func getCommitNote(commit string) (string, error) {
+	cmd := exec.Command("git", "notes", "--ref="+notesRef, "show", commit)
+	out, err := cmd.Output()
+	if err != nil {
+		// No soup for you
+		return "", err
+	}
+	return string(out), nil
+}
+
+// formatNote formats a changelog note into markdown.
+func formatNote(note string) string {
+	var sb strings.Builder
+	lines := strings.Split(strings.TrimSpace(note), "\n")
+
+	hasEmptyLine := false
+	for _, line := range lines {
+		if line == "" {
+			hasEmptyLine = true
+			break
+		}
+	}
+
+	if hasEmptyLine {
+		// Do the details thing
+		first := true
+		inDetails := false
+		for _, line := range lines {
+			line = linkifyJira(line)
+			if first {
+				sb.WriteString("- ")
+				sb.WriteString(line)
+				sb.WriteString("\n")
+				first = false
+			} else if line == "" && !inDetails {
+				sb.WriteString("  <details>\n")
+				inDetails = true
+			} else {
+				sb.WriteString("  ")
+				sb.WriteString(line)
+				sb.WriteString("\n")
+			}
+		}
+		if inDetails {
+			sb.WriteString("  </details>\n")
+		}
+	} else {
+		// Just print it
+		for _, line := range lines {
+			line = linkifyJira(line)
+			sb.WriteString(line)
+			sb.WriteString("\n")
+		}
+	}
+	sb.WriteString("\n")
+
+	return sb.String()
+}
+
+var jiraPattern = regexp.MustCompile(`(PROJQUAY|CLAIRDEV)-[0-9]+`)
+
+const jiraURL = "https://redhat.atlassian.net/browse"
+
+// linkifyJira replaces PROJQUAY-XXX with markdown links.
+func linkifyJira(s string) string {
+	return jiraPattern.ReplaceAllStringFunc(s, func(match string) string {
+		return fmt.Sprintf("[%s](%s/%s)", match, jiraURL, match)
+	})
+}
+
+// updateChangelogFile renders the new changelog section, reads the existing changelog
+// into memory and then writes the new changelog section then the existing changelog.
+func updateChangelogFile(repoRoot, prevTag, nextTag, branch string) error {
+	changelogPath := filepath.Join(repoRoot, "CHANGELOG.md")
+
+	// Render new content
+	var newChangelog strings.Builder
+	if err := renderChangelog(&newChangelog, prevTag, nextTag, branch); err != nil {
+		return fmt.Errorf("rendering changelog: %w", err)
+	}
+
+	// Read existing changelog
+	existing, err := os.ReadFile(changelogPath)
+	if err != nil && !os.IsNotExist(err) {
+		return fmt.Errorf("reading existing changelog: %w", err)
+	}
+
+	// Write new changelog (prepend new content)
+	f, err := os.Create(changelogPath)
+	if err != nil {
+		return fmt.Errorf("creating changelog: %w", err)
+	}
+	defer f.Close()
+
+	bw := bufio.NewWriter(f)
+	bw.WriteString(newChangelog.String())
+	bw.Write(existing)
+	if err := bw.Flush(); err != nil {
+		return fmt.Errorf("writing changelog: %w", err)
+	}
+
+	return nil
+}