Anchor patch hunks as git apply does, refuse patches touching non-100644 files by their real mode, survive bare-CR context lines (issue 1604 review)

modules/gitea/cmd/forge/commit.go

@@ -340,7 +340,14 @@ func commit(ctx context.Context, f *Forge, a CommitAsk) (*Committed, error) {
 			forgeApplied = true
 		case errors.As(err, &status) && status.Status >= 500:
 			delete(on, "content")
-			read := func(p string) ([]byte, bool, error) { return f.contentAt(ctx, repo, p, ref) }
+			read := func(p string) ([]byte, string, bool, error) {
+				b, ok, err := f.contentAt(ctx, repo, p, ref)
+				if err != nil || !ok {
+					return nil, "", false, err
+				}
+				mode, err := f.modeAt(ctx, repo, ref, p)
+				return b, mode, true, err
+			}
 			var perr error
 			if files, perr = patchAsFiles(a.Patch, read); perr != nil {
 				return nil, fmt.Errorf("the forge did not take the patch: %w; the tool could not apply it itself: %v", err, perr)
@@ -545,3 +552,43 @@ func (f *Forge) contentAt(ctx context.Context, repo, path, ref string) ([]byte,
 	}
 	return raw, true, nil
 }
+
+// modeAt is the git mode of a file at a commit, read through the git trees API: the contents API carries none.
+func (f *Forge) modeAt(ctx context.Context, repo, ref, path string) (string, error) {
+	parts := strings.Split(path, "/")
+	tree := ref
+	for depth, name := range parts {
+		found := false
+		for page := 1; ; page++ {
+			var got struct {
+				Tree []struct {
+					Path string `json:"path"`
+					Mode string `json:"mode"`
+					Type string `json:"type"`
+					SHA  string `json:"sha"`
+				} `json:"tree"`
+				Total int `json:"total_count"`
+			}
+			if err := f.GetJSON(ctx, fmt.Sprintf("%s/git/trees/%s?per_page=1000&page=%d", repo, url.PathEscape(tree), page), &got); err != nil {
+				return "", fmt.Errorf("the mode of %s could not be read: %w", path, err)
+			}
+			for _, e := range got.Tree {
+				if e.Path != name {
+					continue
+				}
+				if depth == len(parts)-1 {
+					return e.Mode, nil
+				}
+				tree, found = e.SHA, true
+				break
+			}
+			if found || len(got.Tree) == 0 || page*1000 >= got.Total {
+				break
+			}
+		}
+		if !found && depth < len(parts)-1 {
+			return "", fmt.Errorf("the mode of %s could not be read: %s is not a folder at %s", path, name, short(ref))
+		}
+	}
+	return "", fmt.Errorf("the mode of %s could not be read: not in the tree of %s", path, short(ref))
+}