Let branch/tag name be a valid ref to get CI status (#16400)

* fix #16384#

* refactor: move shared helper func to utils package

* extend Tests

* use ctx.Repo.GitRepo if not nil

routers/api/v1/utils/git.go

@@ -0,0 +1,61 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package utils
+
+import (
+	"net/http"
+
+	"code.gitea.io/gitea/modules/context"
+	"code.gitea.io/gitea/modules/git"
+)
+
+// ResolveRefOrSha resolve ref to sha if exist
+func ResolveRefOrSha(ctx *context.APIContext, ref string) string {
+	if len(ref) == 0 {
+		ctx.Error(http.StatusBadRequest, "ref not given", nil)
+		return ""
+	}
+
+	// Search branches and tags
+	for _, refType := range []string{"heads", "tags"} {
+		refSHA, lastMethodName, err := searchRefCommitByType(ctx, refType, ref)
+		if err != nil {
+			ctx.Error(http.StatusInternalServerError, lastMethodName, err)
+			return ""
+		}
+		if refSHA != "" {
+			return refSHA
+		}
+	}
+	return ref
+}
+
+// GetGitRefs return git references based on filter
+func GetGitRefs(ctx *context.APIContext, filter string) ([]*git.Reference, string, error) {
+	if ctx.Repo.GitRepo == nil {
+		var err error
+		ctx.Repo.GitRepo, err = git.OpenRepository(ctx.Repo.Repository.RepoPath())
+		if err != nil {
+			return nil, "OpenRepository", err
+		}
+		defer ctx.Repo.GitRepo.Close()
+	}
+	if len(filter) > 0 {
+		filter = "refs/" + filter
+	}
+	refs, err := ctx.Repo.GitRepo.GetRefsFiltered(filter)
+	return refs, "GetRefsFiltered", err
+}
+
+func searchRefCommitByType(ctx *context.APIContext, refType, filter string) (string, string, error) {
+	refs, lastMethodName, err := GetGitRefs(ctx, refType+"/"+filter) //Search by type
+	if err != nil {
+		return "", lastMethodName, err
+	}
+	if len(refs) > 0 {
+		return refs[0].Object.String(), "", nil //Return found SHA
+	}
+	return "", "", nil
+}