Support .git-blame-ignore-revs file (#26395)

Closes #26329

This PR adds the ability to ignore revisions specified in the
`.git-blame-ignore-revs` file in the root of the repository.


![grafik](https://github.com/go-gitea/gitea/assets/1666336/9e91be0c-6e9c-431c-bbe9-5f80154251c8)

The banner is displayed in this case. I intentionally did not add a UI
way to bypass the ignore file (same behaviour as Github) but you can add
`?bypass-blame-ignore=true` to the url manually.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/web/repo/blame.go

@@ -8,9 +8,9 @@ import (
 	gotemplate "html/template"
 	"net/http"
 	"net/url"
+	"strconv"
 	"strings"
 
-	repo_model "code.gitea.io/gitea/models/repo"
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/charset"
 	"code.gitea.io/gitea/modules/context"
@@ -45,10 +45,6 @@ func RefBlame(ctx *context.Context) {
 		return
 	}
 
-	userName := ctx.Repo.Owner.Name
-	repoName := ctx.Repo.Repository.Name
-	commitID := ctx.Repo.CommitID
-
 	branchLink := ctx.Repo.RepoLink + "/src/" + ctx.Repo.BranchNameSubURL()
 	treeLink := branchLink
 	rawLink := ctx.Repo.RepoLink + "/raw/" + ctx.Repo.BranchNameSubURL()
@@ -101,26 +97,16 @@ func RefBlame(ctx *context.Context) {
 		return
 	}
 
-	blameReader, err := git.CreateBlameReader(ctx, repo_model.RepoPath(userName, repoName), commitID, fileName)
+	bypassBlameIgnore, _ := strconv.ParseBool(ctx.FormString("bypass-blame-ignore"))
+
+	result, err := performBlame(ctx, ctx.Repo.Repository.RepoPath(), ctx.Repo.Commit, fileName, bypassBlameIgnore)
 	if err != nil {
 		ctx.NotFound("CreateBlameReader", err)
 		return
 	}
-	defer blameReader.Close()
 
-	blameParts := make([]git.BlamePart, 0)
-
-	for {
-		blamePart, err := blameReader.NextPart()
-		if err != nil {
-			ctx.NotFound("NextPart", err)
-			return
-		}
-		if blamePart == nil {
-			break
-		}
-		blameParts = append(blameParts, *blamePart)
-	}
+	ctx.Data["UsesIgnoreRevs"] = result.UsesIgnoreRevs
+	ctx.Data["FaultyIgnoreRevsFile"] = result.FaultyIgnoreRevsFile
 
 	// Get Topics of this repo
 	renderRepoTopics(ctx)
@@ -128,16 +114,77 @@ func RefBlame(ctx *context.Context) {
 		return
 	}
 
-	commitNames, previousCommits := processBlameParts(ctx, blameParts)
+	commitNames, previousCommits := processBlameParts(ctx, result.Parts)
 	if ctx.Written() {
 		return
 	}
 
-	renderBlame(ctx, blameParts, commitNames, previousCommits)
+	renderBlame(ctx, result.Parts, commitNames, previousCommits)
 
 	ctx.HTML(http.StatusOK, tplRepoHome)
 }
 
+type blameResult struct {
+	Parts                []git.BlamePart
+	UsesIgnoreRevs       bool
+	FaultyIgnoreRevsFile bool
+}
+
+func performBlame(ctx *context.Context, repoPath string, commit *git.Commit, file string, bypassBlameIgnore bool) (*blameResult, error) {
+	blameReader, err := git.CreateBlameReader(ctx, repoPath, commit, file, bypassBlameIgnore)
+	if err != nil {
+		return nil, err
+	}
+
+	r := &blameResult{}
+	if err := fillBlameResult(blameReader, r); err != nil {
+		_ = blameReader.Close()
+		return nil, err
+	}
+
+	err = blameReader.Close()
+	if err != nil {
+		if len(r.Parts) == 0 && r.UsesIgnoreRevs {
+			// try again without ignored revs
+
+			blameReader, err = git.CreateBlameReader(ctx, repoPath, commit, file, true)
+			if err != nil {
+				return nil, err
+			}
+
+			r := &blameResult{
+				FaultyIgnoreRevsFile: true,
+			}
+			if err := fillBlameResult(blameReader, r); err != nil {
+				_ = blameReader.Close()
+				return nil, err
+			}
+
+			return r, blameReader.Close()
+		}
+		return nil, err
+	}
+	return r, nil
+}
+
+func fillBlameResult(br *git.BlameReader, r *blameResult) error {
+	r.UsesIgnoreRevs = br.UsesIgnoreRevs()
+
+	r.Parts = make([]git.BlamePart, 0, 5)
+	for {
+		blamePart, err := br.NextPart()
+		if err != nil {
+			return fmt.Errorf("BlameReader.NextPart failed: %w", err)
+		}
+		if blamePart == nil {
+			break
+		}
+		r.Parts = append(r.Parts, *blamePart)
+	}
+
+	return nil
+}
+
 func processBlameParts(ctx *context.Context, blameParts []git.BlamePart) (map[string]*user_model.UserCommit, map[string]string) {
 	// store commit data by SHA to look up avatar info etc
 	commitNames := make(map[string]*user_model.UserCommit)