chore: refactor LineBlame (#8419)

- Refactor arguments of the function to make more sense.
  - `path` can be inferred from `repo` receiver.
  - `line` can be `uint64`.
- The two calls to this function check for specific errors, do this error checking in the function.
- The ID of a object format is not 40 in the case of SHA256, get the object format and use the correct length.
- Add test coverage for `LineBlame`, notably it checks for the errors that can legitimately happen.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/8419
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>

modules/git/repo_blame.go

@@ -4,20 +4,46 @@
 package git
 
 import (
+	"errors"
 	"fmt"
+	"regexp"
+)
+
+var (
+	ErrBlameFileDoesNotExist   = errors.New("the blamed file does not exist")
+	ErrBlameFileNotEnoughLines = errors.New("the blamed file has not enough lines")
+
+	notEnoughLinesRe = regexp.MustCompile(`^fatal: file .+ has only \d+ lines?\n$`)
 )
 
 // LineBlame returns the latest commit at the given line
-func (repo *Repository) LineBlame(revision, path, file string, line uint) (*Commit, error) {
-	res, _, err := NewCommand(repo.Ctx, "blame").
+func (repo *Repository) LineBlame(revision, file string, line uint64) (*Commit, error) {
+	res, _, gitErr := NewCommand(repo.Ctx, "blame").
 		AddOptionFormat("-L %d,%d", line, line).
 		AddOptionValues("-p", revision).
-		AddDashesAndList(file).RunStdString(&RunOpts{Dir: path})
+		AddDashesAndList(file).RunStdString(&RunOpts{Dir: repo.Path})
+	if gitErr != nil {
+		stdErr := gitErr.Stderr()
+
+		if stdErr == fmt.Sprintf("fatal: no such path %s in %s\n", file, revision) {
+			return nil, ErrBlameFileDoesNotExist
+		}
+		if notEnoughLinesRe.MatchString(stdErr) {
+			return nil, ErrBlameFileNotEnoughLines
+		}
+
+		return nil, gitErr
+	}
+
+	objectFormat, err := repo.GetObjectFormat()
 	if err != nil {
 		return nil, err
 	}
-	if len(res) < 40 {
-		return nil, fmt.Errorf("invalid result of blame: %s", res)
+
+	objectIDLen := objectFormat.FullLength()
+	if len(res) < objectIDLen {
+		return nil, fmt.Errorf("output of blame is invalid, cannot contain commit ID: %s", res)
 	}
-	return repo.GetCommit(res[:40])
+
+	return repo.GetCommit(res[:objectIDLen])
 }