Add API to get merged PR of a commit (#29243)

Adds a new API `/repos/{owner}/{repo}/commits/{sha}/pull` that allows
you to get the merged PR associated to a commit.

---------

Co-authored-by: 6543 <6543@obermui.de>
(cherry picked from commit 0a426cc575734e5eff410d6a790f40473117f753)

routers/api/v1/api.go

@@ -1300,6 +1300,7 @@ func Routes() *web.Route {
 					m.Group("/{ref}", func() {
 						m.Get("/status", repo.GetCombinedCommitStatusByRef)
 						m.Get("/statuses", repo.GetCommitStatusesByRef)
+						m.Get("/pull", repo.GetCommitPullRequest)
 					}, context.ReferencesGitRepo())
 				}, reqRepoReader(unit.TypeCode))
 				m.Group("/git", func() {

routers/api/v1/repo/commits.go

@@ -10,6 +10,7 @@ import (
 	"net/http"
 	"strconv"
 
+	issues_model "code.gitea.io/gitea/models/issues"
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/context"
 	"code.gitea.io/gitea/modules/git"
@@ -323,3 +324,53 @@ func DownloadCommitDiffOrPatch(ctx *context.APIContext) {
 		return
 	}
 }
+
+// GetCommitPullRequest returns the pull request of the commit
+func GetCommitPullRequest(ctx *context.APIContext) {
+	// swagger:operation GET /repos/{owner}/{repo}/commits/{sha}/pull repository repoGetCommitPullRequest
+	// ---
+	// summary: Get the pull request of the commit
+	// produces:
+	// - application/json
+	// parameters:
+	// - name: owner
+	//   in: path
+	//   description: owner of the repo
+	//   type: string
+	//   required: true
+	// - name: repo
+	//   in: path
+	//   description: name of the repo
+	//   type: string
+	//   required: true
+	// - name: sha
+	//   in: path
+	//   description: SHA of the commit to get
+	//   type: string
+	//   required: true
+	// responses:
+	//   "200":
+	//     "$ref": "#/responses/PullRequest"
+	//   "404":
+	//     "$ref": "#/responses/notFound"
+
+	pr, err := issues_model.GetPullRequestByMergedCommit(ctx, ctx.Repo.Repository.ID, ctx.Params(":sha"))
+	if err != nil {
+		if issues_model.IsErrPullRequestNotExist(err) {
+			ctx.Error(http.StatusNotFound, "GetPullRequestByMergedCommit", err)
+		} else {
+			ctx.Error(http.StatusInternalServerError, "GetPullRequestByIndex", err)
+		}
+		return
+	}
+
+	if err = pr.LoadBaseRepo(ctx); err != nil {
+		ctx.Error(http.StatusInternalServerError, "LoadBaseRepo", err)
+		return
+	}
+	if err = pr.LoadHeadRepo(ctx); err != nil {
+		ctx.Error(http.StatusInternalServerError, "LoadHeadRepo", err)
+		return
+	}
+	ctx.JSON(http.StatusOK, convert.ToAPIPullRequest(ctx, pr, ctx.Doer))
+}