feat: edit commit message after merging through PR

Closes #5

prbody.go

@@ -0,0 +1,57 @@
+package rp
+
+import (
+	"strings"
+
+	"github.com/apricote/releaser-pleaser/internal/git"
+	"github.com/apricote/releaser-pleaser/internal/markdown"
+)
+
+func parsePRBodyForCommitOverrides(commits []git.Commit) ([]git.Commit, error) {
+	result := make([]git.Commit, 0, len(commits))
+
+	for _, commit := range commits {
+		singleResult, err := parseSinglePRBodyForCommitOverrides(commit)
+		if err != nil {
+			return nil, err
+		}
+
+		result = append(result, singleResult...)
+	}
+
+	return result, nil
+}
+
+func parseSinglePRBodyForCommitOverrides(commit git.Commit) ([]git.Commit, error) {
+	if commit.PullRequest == nil {
+		return []git.Commit{commit}, nil
+	}
+
+	source := []byte(commit.PullRequest.Description)
+	var overridesText string
+	var found bool
+	err := markdown.WalkAST(source, markdown.GetCodeBlockText(source, "rp-commits", &overridesText, &found))
+	if err != nil {
+		return nil, err
+	}
+
+	if !found {
+		return []git.Commit{commit}, nil
+	}
+
+	lines := strings.Split(overridesText, "\n")
+	result := make([]git.Commit, 0, len(lines))
+	for _, line := range lines {
+		// Only consider lines with text
+		line = strings.TrimSpace(line)
+		if line == "" {
+			continue
+		}
+
+		newCommit := commit
+		newCommit.Message = line
+		result = append(result, newCommit)
+	}
+
+	return result, nil
+}