feat: Add CHANGELOG generation capability (chu gen changelog)

Generate CHANGELOG entries from conventional commits
- Parse git history (feat, fix, docs, etc)
- Group by commit type
- LLM improves clarity and professionalism
- Supports tag ranges (v1.0.0..v1.1.0)
- E2E test with real git repo

Autonomy: 66% (42/64 scenarios)

Author: jadercorrea

cmd/chu/main.go

@@ -55,6 +55,7 @@ $0-5/month vs $20-30/month subscriptions.
 
 ## SPECIALIZED TOOLS
   chu gen test <file>     - Generate unit tests for a file
+  chu gen changelog       - Generate CHANGELOG from git commits
   chu tdd                 - Test-driven development mode
   chu feature "desc"      - Generate tests + implementation
   chu review [target]     - Code review for bugs, security, improvements

docs/reference/capabilities.md

@@ -205,17 +205,28 @@ Not implemented:
 
 ---
 
-### ❌ Documentation Updates (0/3 scenarios)
+### 🟡 Documentation Updates (1/3 scenarios)
 
-Chuchu cannot automatically:
+**Implemented:**
+
+- ✅ Generate CHANGELOG entries (`chu gen changelog`)
+
+**Not yet implemented:**
 
 - Update README files
-- Generate CHANGELOG entries
 - Update API documentation
 
-**Why:** Documentation requires understanding of user impact and communication style. Coming soon.
+**Example:**
+```bash
+chu gen changelog           # All commits since last tag
+chu gen changelog v1.0.0    # From v1.0.0 to HEAD
+```
+
+**Limitations:**
+- README and API docs require contextual understanding
+- Uses conventional commits format
 
-**Workaround:** Use `chu chat` mode to draft documentation, then review and commit manually.
+**Workaround:** Use `chu chat` mode to draft README updates and API docs.
 
 ---
 
@@ -235,9 +246,9 @@ Chuchu cannot automatically:
 - Coverage gap identification
 - Mock generation
 
-**Phase 9: Documentation (3 scenarios)**
+**Phase 9: Documentation (2 remaining scenarios)**
+- ✅ CHANGELOG generation (DONE)
 - README updates
-- CHANGELOG generation
 - API docs synchronization
 
 ---
@@ -268,7 +279,8 @@ Skipped tests (t.Skip()) represent features not yet implemented.
 - ✅ CI failure handling
 - ✅ PR review iteration
 - ✅ Unit test generation
-- **Autonomy:** 41/64 (64%)
+- ✅ CHANGELOG generation
+- **Autonomy:** 42/64 (66%)
 - **MVAA Critical Path:** 17/17 (100%)
 
 ### Future Releases

internal/changelog/generator.go

@@ -0,0 +1,245 @@
+package changelog
+
+import (
+	"context"
+	"fmt"
+	"os/exec"
+	"regexp"
+	"sort"
+	"strings"
+	"time"
+
+	"chuchu/internal/llm"
+)
+
+type ChangelogGenerator struct {
+	provider llm.Provider
+	model    string
+	workDir  string
+}
+
+type CommitGroup struct {
+	Type    string
+	Commits []Commit
+}
+
+type Commit struct {
+	Hash     string
+	Type     string
+	Scope    string
+	Message  string
+	Body     string
+	Breaking bool
+}
+
+func NewChangelogGenerator(provider llm.Provider, model, workDir string) *ChangelogGenerator {
+	return &ChangelogGenerator{
+		provider: provider,
+		model:    model,
+		workDir:  workDir,
+	}
+}
+
+var commitPattern = regexp.MustCompile(`^(\w+)(?:\(([^)]+)\))?(!)?:\s*(.+)$`)
+
+func (g *ChangelogGenerator) Generate(ctx context.Context, fromTag, toTag string) (string, error) {
+	commits, err := g.getCommits(fromTag, toTag)
+	if err != nil {
+		return "", fmt.Errorf("failed to get commits: %w", err)
+	}
+
+	if len(commits) == 0 {
+		return "", fmt.Errorf("no commits found between %s and %s", fromTag, toTag)
+	}
+
+	parsed := g.parseCommits(commits)
+	grouped := g.groupCommits(parsed)
+
+	changelog := g.formatChangelog(grouped, fromTag, toTag)
+
+	improved, err := g.improveWithLLM(ctx, changelog, commits)
+	if err != nil {
+		return changelog, nil
+	}
+
+	return improved, nil
+}
+
+func (g *ChangelogGenerator) getCommits(fromTag, toTag string) ([]string, error) {
+	var args []string
+	if fromTag == "" {
+		args = []string{"log", "--pretty=format:%H|||%s|||%b", toTag}
+	} else {
+		args = []string{"log", "--pretty=format:%H|||%s|||%b", fmt.Sprintf("%s..%s", fromTag, toTag)}
+	}
+
+	cmd := exec.Command("git", args...)
+	cmd.Dir = g.workDir
+	output, err := cmd.Output()
+	if err != nil {
+		return nil, fmt.Errorf("git log failed: %w", err)
+	}
+
+	lines := strings.Split(string(output), "\n")
+	var commits []string
+	for _, line := range lines {
+		if strings.TrimSpace(line) != "" {
+			commits = append(commits, line)
+		}
+	}
+
+	return commits, nil
+}
+
+func (g *ChangelogGenerator) parseCommits(commits []string) []Commit {
+	var parsed []Commit
+
+	for _, commit := range commits {
+		parts := strings.Split(commit, "|||")
+		if len(parts) < 2 {
+			continue
+		}
+
+		hash := parts[0]
+		subject := parts[1]
+		body := ""
+		if len(parts) > 2 {
+			body = parts[2]
+		}
+
+		matches := commitPattern.FindStringSubmatch(subject)
+		if matches == nil {
+			continue
+		}
+
+		commitType := matches[1]
+		scope := matches[2]
+		breaking := matches[3] == "!"
+		message := matches[4]
+
+		if strings.Contains(body, "BREAKING CHANGE:") {
+			breaking = true
+		}
+
+		parsed = append(parsed, Commit{
+			Hash:     hash[:7],
+			Type:     commitType,
+			Scope:    scope,
+			Message:  message,
+			Body:     body,
+			Breaking: breaking,
+		})
+	}
+
+	return parsed
+}
+
+func (g *ChangelogGenerator) groupCommits(commits []Commit) map[string][]Commit {
+	groups := make(map[string][]Commit)
+
+	for _, commit := range commits {
+		groups[commit.Type] = append(groups[commit.Type], commit)
+	}
+
+	return groups
+}
+
+func (g *ChangelogGenerator) formatChangelog(groups map[string][]Commit, fromTag, toTag string) string {
+	var sb strings.Builder
+
+	version := toTag
+	if version == "HEAD" || version == "" {
+		version = "Unreleased"
+	}
+
+	sb.WriteString(fmt.Sprintf("## [%s] - %s\n\n", version, time.Now().Format("2006-01-02")))
+
+	typeOrder := []string{"feat", "fix", "perf", "refactor", "docs", "test", "chore", "build", "ci"}
+	typeNames := map[string]string{
+		"feat":     "Features",
+		"fix":      "Bug Fixes",
+		"perf":     "Performance",
+		"refactor": "Code Refactoring",
+		"docs":     "Documentation",
+		"test":     "Tests",
+		"chore":    "Chores",
+		"build":    "Build System",
+		"ci":       "CI/CD",
+	}
+
+	breaking := []Commit{}
+	for _, commits := range groups {
+		for _, commit := range commits {
+			if commit.Breaking {
+				breaking = append(breaking, commit)
+			}
+		}
+	}
+
+	if len(breaking) > 0 {
+		sb.WriteString("### ⚠ BREAKING CHANGES\n\n")
+		for _, commit := range breaking {
+			sb.WriteString(fmt.Sprintf("- **%s**: %s (%s)\n", commit.Scope, commit.Message, commit.Hash))
+		}
+		sb.WriteString("\n")
+	}
+
+	for _, typ := range typeOrder {
+		commits, ok := groups[typ]
+		if !ok || len(commits) == 0 {
+			continue
+		}
+
+		sort.Slice(commits, func(i, j int) bool {
+			return commits[i].Scope < commits[j].Scope
+		})
+
+		name := typeNames[typ]
+		if name == "" {
+			if len(typ) > 0 {
+				name = strings.ToUpper(typ[:1]) + typ[1:]
+			}
+		}
+
+		sb.WriteString(fmt.Sprintf("### %s\n\n", name))
+
+		for _, commit := range commits {
+			if commit.Scope != "" {
+				sb.WriteString(fmt.Sprintf("- **%s**: %s (%s)\n", commit.Scope, commit.Message, commit.Hash))
+			} else {
+				sb.WriteString(fmt.Sprintf("- %s (%s)\n", commit.Message, commit.Hash))
+			}
+		}
+		sb.WriteString("\n")
+	}
+
+	return sb.String()
+}
+
+func (g *ChangelogGenerator) improveWithLLM(ctx context.Context, changelog string, commits []string) (string, error) {
+	prompt := fmt.Sprintf(`You are a technical writer. Improve this CHANGELOG entry for clarity and professionalism.
+
+Rules:
+- Keep the structure (headings, bullets)
+- Keep commit hashes
+- Improve wording for clarity
+- Group related changes if appropriate
+- Add brief context where helpful
+- Keep it concise
+
+Original CHANGELOG:
+%s
+
+Return ONLY the improved CHANGELOG, no explanations.`, changelog)
+
+	resp, err := g.provider.Chat(ctx, llm.ChatRequest{
+		UserPrompt: prompt,
+		Model:      g.model,
+	})
+
+	if err != nil {
+		return "", err
+	}
+
+	return strings.TrimSpace(resp.Text), nil
+}