Show conflicts to parent branch

conflicts.go

@@ -0,0 +1,190 @@
+package main
+
+import (
+	"bytes"
+	"context"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"os"
+	"os/exec"
+	"sort"
+	"strconv"
+	"strings"
+	"time"
+)
+
+type conflictFileLoader func(
+	context.Context, string, int, string, string, string, string,
+) ([]string, error)
+
+type conflictFileResult struct {
+	files     []string
+	err       error
+	checkedAt time.Time
+}
+
+func (c *GitHubClient) loadConflictFiles(
+	ctx context.Context,
+	repositoryURL string,
+	number int,
+	baseRef, baseOID, headOID string,
+) ([]string, error) {
+	key := strings.Join([]string{repositoryURL, baseOID, headOID}, "\x00")
+	c.conflictMu.Lock()
+	cached, ok := c.conflictCache[key]
+	c.conflictMu.Unlock()
+	if ok && (cached.err == nil || time.Since(cached.checkedAt) < time.Minute) {
+		return append([]string(nil), cached.files...), cached.err
+	}
+
+	files, err := c.conflicts(ctx, repositoryURL, number, baseRef, baseOID, headOID, c.token)
+	result := conflictFileResult{
+		files: append([]string(nil), files...), err: err, checkedAt: time.Now(),
+	}
+	c.conflictMu.Lock()
+	c.conflictCache[key] = result
+	c.conflictMu.Unlock()
+	return files, err
+}
+
+func analyzeConflictFiles(
+	ctx context.Context,
+	repositoryURL string,
+	number int,
+	baseRef, _, _, token string,
+) ([]string, error) {
+	if repositoryURL == "" || baseRef == "" || number <= 0 {
+		return nil, errors.New("missing repository merge metadata")
+	}
+	gitDir, err := os.MkdirTemp("", "gh-threads-conflicts-*")
+	if err != nil {
+		return nil, fmt.Errorf("create temporary merge repository: %w", err)
+	}
+	defer os.RemoveAll(gitDir)
+
+	run := func(args ...string) ([]byte, error) {
+		command := exec.CommandContext(ctx, "git", args...)
+		command.Env = gitAuthenticationEnvironment(callerEnvironment(), token)
+		return command.CombinedOutput()
+	}
+	if output, runErr := run("init", "--bare", gitDir); runErr != nil {
+		return nil, commandError("initialize merge analysis", output, runErr)
+	}
+	cloneURL := strings.TrimSuffix(strings.TrimSuffix(repositoryURL, "/"), ".git") + ".git"
+	if output, runErr := run("-C", gitDir, "remote", "add", "origin", cloneURL); runErr != nil {
+		return nil, commandError("configure merge analysis remote", output, runErr)
+	}
+	if output, runErr := run("-C", gitDir, "config", "remote.origin.promisor", "true"); runErr != nil {
+		return nil, commandError("configure partial clone", output, runErr)
+	}
+	if output, runErr := run("-C", gitDir, "config", "remote.origin.partialclonefilter", "blob:none"); runErr != nil {
+		return nil, commandError("configure partial clone filter", output, runErr)
+	}
+
+	refspecs := []string{
+		"+refs/heads/" + baseRef + ":refs/gh-threads/base",
+		"+refs/pull/" + strconv.Itoa(number) + "/head:refs/gh-threads/head",
+	}
+	fetch := func(depthArgs ...string) error {
+		args := []string{"-C", gitDir, "fetch", "--quiet", "--no-tags", "--filter=blob:none"}
+		args = append(args, depthArgs...)
+		args = append(args, "origin")
+		args = append(args, refspecs...)
+		output, runErr := run(args...)
+		return commandError("fetch merge inputs", output, runErr)
+	}
+	if err := fetch("--depth=64"); err != nil {
+		return nil, err
+	}
+	for _, deepen := range []string{"192", "768"} {
+		if mergeBaseExists(run, gitDir) {
+			break
+		}
+		if err := fetch("--deepen=" + deepen); err != nil {
+			return nil, err
+		}
+	}
+	if !mergeBaseExists(run, gitDir) {
+		if err := fetch("--unshallow"); err != nil {
+			return nil, err
+		}
+	}
+
+	output, runErr := run(
+		"-C", gitDir, "merge-tree", "--write-tree", "--name-only", "--no-messages", "-z",
+		"refs/gh-threads/base", "refs/gh-threads/head",
+	)
+	if runErr == nil {
+		return nil, nil
+	}
+	var exitErr *exec.ExitError
+	if !errors.As(runErr, &exitErr) || exitErr.ExitCode() != 1 {
+		return nil, commandError("analyze merge conflicts", output, runErr)
+	}
+	return parseConflictFiles(output)
+}
+
+func mergeBaseExists(
+	run func(...string) ([]byte, error),
+	gitDir string,
+) bool {
+	_, err := run(
+		"-C", gitDir, "merge-base", "refs/gh-threads/base", "refs/gh-threads/head",
+	)
+	return err == nil
+}
+
+func parseConflictFiles(output []byte) ([]string, error) {
+	parts := bytes.Split(output, []byte{0})
+	if len(parts) < 2 || len(parts[0]) == 0 {
+		return nil, errors.New("git merge-tree returned malformed conflict data")
+	}
+	files := make([]string, 0, len(parts)-2)
+	seen := make(map[string]bool)
+	for _, raw := range parts[1:] {
+		name := string(raw)
+		if name == "" || seen[name] {
+			continue
+		}
+		seen[name] = true
+		files = append(files, name)
+	}
+	sort.Strings(files)
+	return files, nil
+}
+
+func commandError(action string, output []byte, err error) error {
+	if err == nil {
+		return nil
+	}
+	message := strings.TrimSpace(string(output))
+	if message == "" {
+		return fmt.Errorf("%s: %w", action, err)
+	}
+	return fmt.Errorf("%s: %s", action, message)
+}
+
+func callerEnvironment() []string {
+	const prefix = "GIT_CONFIG_"
+	environment := make([]string, 0, len(os.Environ())+5)
+	for _, item := range os.Environ() {
+		if !strings.HasPrefix(item, prefix) && !strings.HasPrefix(item, "GIT_TERMINAL_PROMPT=") {
+			environment = append(environment, item)
+		}
+	}
+	return environment
+}
+
+func gitAuthenticationEnvironment(environment []string, token string) []string {
+	environment = append(environment, "GIT_TERMINAL_PROMPT=0")
+	if token == "" {
+		return environment
+	}
+	credentials := base64.StdEncoding.EncodeToString([]byte("x-access-token:" + token))
+	return append(environment,
+		"GIT_CONFIG_COUNT=1",
+		"GIT_CONFIG_KEY_0=http.extraHeader",
+		"GIT_CONFIG_VALUE_0=Authorization: Basic "+credentials,
+	)
+}