feat(api): support ref suffixes in compare (#38148)

Compare API requests with a `^` or `~N` revision suffix (for example
`compare/main...feature^`) were rejected with `400 Unsupported
comparison syntax: ref with suffix`. The fix resolves the suffix to a
commit before comparing, so `base...head^` and `~N` work on either side,
the same as git.

Only `^`/`~N` navigation is resolved. Pull request creation still
requires plain branch refs, and the web compare page keeps rejecting
suffixes since its branch selectors need separate UI work.

Closes #33943

modules/git/ref.go

@@ -228,13 +228,16 @@ func (ref RefName) RefWebLinkPath() string {
 	return string(refType) + "/" + util.PathEscapeSegments(ref.ShortName())
 }
 
-func ParseRefSuffix(ref string) (string, string) {
+func ParseRefSuffix(ref string) (refName, refSuffix string) {
 	// Partially support https://git-scm.com/docs/gitrevisions
-	if idx := strings.Index(ref, "@{"); idx != -1 {
-		return ref[:idx], ref[idx:]
+	suffixIdx := -1 // earliest suffix mark, so a combined suffix like "main~2^" stays intact
+	for _, mark := range []string{"@{", "^", "~"} {
+		if idx := strings.Index(ref, mark); idx != -1 && (suffixIdx == -1 || idx < suffixIdx) {
+			suffixIdx = idx
+		}
 	}
-	if idx := strings.Index(ref, "^"); idx != -1 {
-		return ref[:idx], ref[idx:]
+	if suffixIdx == -1 {
+		return ref, ""
 	}
-	return ref, ""
+	return ref[:suffixIdx], ref[suffixIdx:]
 }

modules/git/ref_test.go

@@ -37,3 +37,22 @@ func TestRefWebLinkPath(t *testing.T) {
 	assert.Equal(t, "tag/foo", RefName("refs/tags/foo").RefWebLinkPath())
 	assert.Equal(t, "commit/c0ffee", RefName("c0ffee").RefWebLinkPath())
 }
+
+func TestParseRefSuffix(t *testing.T) {
+	cases := []struct {
+		ref, name, suffix string
+	}{
+		{"main", "main", ""},
+		{"main^", "main", "^"},
+		{"main^2", "main", "^2"},
+		{"main~3", "main", "~3"},
+		{"main@{yesterday}", "main", "@{yesterday}"},
+		{"main~2^", "main", "~2^"},
+		{"main^~2", "main", "^~2"},
+	}
+	for _, c := range cases {
+		name, suffix := ParseRefSuffix(c.ref)
+		assert.Equal(t, c.name, name, "ref: %s", c.ref)
+		assert.Equal(t, c.suffix, suffix, "ref: %s", c.ref)
+	}
+}

routers/api/v1/repo/compare.go

@@ -38,7 +38,7 @@ func CompareDiff(ctx *context.APIContext) {
 	//   required: true
 	// - name: basehead
 	//   in: path
-	//   description: compare two refs as `base...head` (or `base..head`); refs may be branches, tags, full or short SHAs, including branch names that contain slashes.
+	//   description: compare two refs as `base...head` (or `base..head`); refs may be branches, tags, full or short SHAs (including branch names that contain slashes), optionally with a `^` or `~N` revision suffix.
 	//   type: string
 	//   required: true
 	// - name: output
@@ -51,6 +51,8 @@ func CompareDiff(ctx *context.APIContext) {
 	// responses:
 	//   "200":
 	//     "$ref": "#/responses/Compare"
+	//   "400":
+	//     "$ref": "#/responses/error"
 	//   "404":
 	//     "$ref": "#/responses/notFound"
 

routers/api/v1/repo/pull.go

@@ -1087,12 +1087,6 @@ func parseCompareInfo(ctx *context.APIContext, compareParam string) (result *git
 	baseRepo := ctx.Repo.Repository
 	compareReq := common.ParseCompareRouterParam(compareParam)
 
-	// remove the check when we support compare with carets
-	if compareReq.BaseOriRefSuffix != "" {
-		ctx.APIError(http.StatusBadRequest, "Unsupported comparison syntax: ref with suffix")
-		return nil, nil
-	}
-
 	_, headRepo, err := common.GetHeadOwnerAndRepo(ctx, baseRepo, compareReq)
 	switch {
 	case errors.Is(err, util.ErrInvalidArgument):
@@ -1152,10 +1146,18 @@ func parseCompareInfo(ctx *context.APIContext, compareParam string) (result *git
 		return nil, nil
 	}
 
-	baseRef := ctx.Repo.GitRepo.UnstableGuessRefByShortName(util.IfZero(compareReq.BaseOriRef, baseRepo.GetPullRequestTargetBranch(ctx)))
-	headRef := headGitRepo.UnstableGuessRefByShortName(util.IfZero(compareReq.HeadOriRef, headRepo.DefaultBranch))
+	baseRef, err := common.ResolveRefWithSuffix(ctx.Repo.GitRepo, util.IfZero(compareReq.BaseOriRef, baseRepo.GetPullRequestTargetBranch(ctx)), compareReq.BaseOriRefSuffix)
+	if err != nil {
+		ctx.APIErrorAuto(err)
+		return nil, nil
+	}
+	headRef, err := common.ResolveRefWithSuffix(headGitRepo, util.IfZero(compareReq.HeadOriRef, headRepo.DefaultBranch), compareReq.HeadOriRefSuffix)
+	if err != nil {
+		ctx.APIErrorAuto(err)
+		return nil, nil
+	}
 
-	log.Trace("Repo path: %q, base ref: %q->%q, head ref: %q->%q", ctx.Repo.Repository.RelativePath(), compareReq.BaseOriRef, baseRef, compareReq.HeadOriRef, headRef)
+	log.Trace("Repo path: %q, base ref: %q->%q, head ref: %q->%q", ctx.Repo.Repository.RelativePath(), compareReq.BaseOriRef+compareReq.BaseOriRefSuffix, baseRef, compareReq.HeadOriRef+compareReq.HeadOriRefSuffix, headRef)
 
 	baseRefValid := baseRef.IsBranch() || baseRef.IsTag() || git.IsStringLikelyCommitID(git.ObjectFormatFromName(ctx.Repo.Repository.ObjectFormatName), baseRef.ShortName())
 	headRefValid := headRef.IsBranch() || headRef.IsTag() || git.IsStringLikelyCommitID(git.ObjectFormatFromName(headRepo.ObjectFormatName), headRef.ShortName())

routers/common/compare.go

@@ -5,7 +5,9 @@ package common
 
 import (
 	"context"
+	"regexp"
 	"strings"
+	"sync"
 
 	repo_model "gitea.dev/models/repo"
 	user_model "gitea.dev/models/user"
@@ -19,9 +21,10 @@ type CompareRouterReq struct {
 
 	CompareSeparator string
 
-	HeadOwner    string
-	HeadRepoName string
-	HeadOriRef   string
+	HeadOwner        string
+	HeadRepoName     string
+	HeadOriRef       string
+	HeadOriRefSuffix string
 }
 
 func (cr *CompareRouterReq) DirectComparison() bool {
@@ -79,9 +82,11 @@ func ParseCompareRouterParam(routerParam string) *CompareRouterReq {
 		sep = ".."
 		basePart, headPart, ok = strings.Cut(routerParam, sep)
 		if !ok {
-			headOwnerName, headRepoName, headRef := parseHead(routerParam)
+			headOwnerName, headRepoName, headOriRef := parseHead(routerParam)
+			headOriRef, headOriRefSuffix := git.ParseRefSuffix(headOriRef)
 			return &CompareRouterReq{
-				HeadOriRef:       headRef,
+				HeadOriRef:       headOriRef,
+				HeadOriRefSuffix: headOriRefSuffix,
 				HeadOwner:        headOwnerName,
 				HeadRepoName:     headRepoName,
 				CompareSeparator: "...",
@@ -92,9 +97,36 @@ func ParseCompareRouterParam(routerParam string) *CompareRouterReq {
 	ci := &CompareRouterReq{CompareSeparator: sep}
 	ci.BaseOriRef, ci.BaseOriRefSuffix = git.ParseRefSuffix(basePart)
 	ci.HeadOwner, ci.HeadRepoName, ci.HeadOriRef = parseHead(headPart)
+	ci.HeadOriRef, ci.HeadOriRefSuffix = git.ParseRefSuffix(ci.HeadOriRef)
 	return ci
 }
 
+// validRefSuffix matches only ^/~ ancestry navigation. The ^{...}, @{...} and :path forms address
+// other objects (trees, blobs) or reflog/upstream state that compare does not resolve, so they are rejected.
+var validRefSuffix = sync.OnceValue(func() *regexp.Regexp {
+	return regexp.MustCompile(`^(?:[~^][0-9]*)+$`)
+})
+
+// ResolveRefWithSuffix resolves oriRef plus an optional revision suffix (^, ~N) to a RefName.
+// A nil error guarantees a usable RefName: an unsupported suffix yields an invalid-argument error
+// and an unresolvable ref yields a not-found error.
+func ResolveRefWithSuffix(gitRepo *git.Repository, oriRef, refSuffix string) (git.RefName, error) {
+	if refSuffix == "" {
+		if refName := gitRepo.UnstableGuessRefByShortName(oriRef); refName != "" {
+			return refName, nil
+		}
+		return "", util.NewNotExistErrorf("ref %q does not exist", oriRef)
+	}
+	if !validRefSuffix().MatchString(refSuffix) {
+		return "", util.NewInvalidArgumentErrorf("unsupported ref suffix %q", refSuffix)
+	}
+	commit, err := gitRepo.GetCommit(oriRef + refSuffix)
+	if err != nil {
+		return "", util.NewNotExistErrorf("ref %q does not exist", oriRef+refSuffix)
+	}
+	return git.RefNameFromCommit(commit.ID.String()), nil
+}
+
 // maxForkTraverseLevel defines the maximum levels to traverse when searching for the head repository.
 const maxForkTraverseLevel = 10
 

routers/common/compare_test.go

@@ -6,6 +6,8 @@ package common
 import (
 	"testing"
 
+	"gitea.dev/modules/util"
+
 	"github.com/stretchr/testify/assert"
 )
 
@@ -97,9 +99,56 @@ func TestCompareRouterReq(t *testing.T) {
 				HeadOriRef:       "develop",
 			},
 		},
+		{
+			input: "main...develop^",
+			CompareRouterReq: &CompareRouterReq{
+				BaseOriRef:       "main",
+				CompareSeparator: "...",
+				HeadOriRef:       "develop",
+				HeadOriRefSuffix: "^",
+			},
+		},
+		{
+			input: "main~2...develop",
+			CompareRouterReq: &CompareRouterReq{
+				BaseOriRef:       "main",
+				BaseOriRefSuffix: "~2",
+				CompareSeparator: "...",
+				HeadOriRef:       "develop",
+			},
+		},
+		{
+			input: "main...lunny/forked_repo:develop~3",
+			CompareRouterReq: &CompareRouterReq{
+				BaseOriRef:       "main",
+				CompareSeparator: "...",
+				HeadOwner:        "lunny",
+				HeadRepoName:     "forked_repo",
+				HeadOriRef:       "develop",
+				HeadOriRefSuffix: "~3",
+			},
+		},
+		{
+			input: "develop^",
+			CompareRouterReq: &CompareRouterReq{
+				CompareSeparator: "...",
+				HeadOriRef:       "develop",
+				HeadOriRefSuffix: "^",
+			},
+		},
 	}
 
 	for _, c := range cases {
 		assert.Equal(t, c.CompareRouterReq, ParseCompareRouterParam(c.input), "input: %s", c.input)
 	}
 }
+
+func TestResolveRefWithSuffix(t *testing.T) {
+	// The ^{...}, @{...} and :path forms address non-commit objects or reflog state, so they are
+	// rejected before any repository access and a nil repo is fine here.
+	for _, refSuffix := range []string{"^{/Add}", "^{commit}", "@{upstream}", "~1:path"} {
+		ref, err := ResolveRefWithSuffix(nil, "branch", refSuffix)
+		assert.ErrorIs(t, err, util.ErrInvalidArgument, "suffix %q", refSuffix)
+		assert.Empty(t, ref, "suffix %q", refSuffix)
+	}
+}

routers/web/repo/compare.go

@@ -208,11 +208,6 @@ func (cpi *comparePageInfoType) parseCompareInfo(ctx *context.Context, comparePa
 	// 1 Parse compare router param
 	compareReq := common.ParseCompareRouterParam(compareParam)
 
-	// remove the check when we support compare with carets
-	if compareReq.BaseOriRefSuffix != "" {
-		return util.NewInvalidArgumentErrorf("unsupported comparison syntax: ref with suffix")
-	}
-
 	// 2 get repository and owner for head
 	headOwner, headRepo, err := common.GetHeadOwnerAndRepo(ctx, baseRepo, compareReq)
 	if err != nil {
@@ -241,18 +236,18 @@ func (cpi *comparePageInfoType) parseCompareInfo(ctx *context.Context, comparePa
 	baseRefName := util.IfZero(compareReq.BaseOriRef, baseRepo.GetPullRequestTargetBranch(ctx))
 	headRefName := util.IfZero(compareReq.HeadOriRef, headRepo.DefaultBranch)
 
-	baseRef := ctx.Repo.GitRepo.UnstableGuessRefByShortName(baseRefName)
-	if baseRef == "" {
-		return util.NewNotExistErrorf("no base ref: %s", baseRefName)
+	baseRef, err := common.ResolveRefWithSuffix(ctx.Repo.GitRepo, baseRefName, compareReq.BaseOriRefSuffix)
+	if err != nil {
+		return err
 	}
 	headGitRepo, err := gitrepo.RepositoryFromRequestContextOrOpen(ctx, headRepo)
 	if err != nil {
 		return err
 	}
 
-	headRef := headGitRepo.UnstableGuessRefByShortName(headRefName)
-	if headRef == "" {
-		return util.NewNotExistErrorf("no head ref: %s", headRefName)
+	headRef, err := common.ResolveRefWithSuffix(headGitRepo, headRefName, compareReq.HeadOriRefSuffix)
+	if err != nil {
+		return err
 	}
 
 	ctx.Data["BaseName"] = baseRepo.OwnerName

templates/swagger/v1_json.tmpl

@@ -8135,7 +8135,7 @@
           },
           {
             "type": "string",
-            "description": "compare two refs as `base...head` (or `base..head`); refs may be branches, tags, full or short SHAs, including branch names that contain slashes.",
+            "description": "compare two refs as `base...head` (or `base..head`); refs may be branches, tags, full or short SHAs (including branch names that contain slashes), optionally with a `^` or `~N` revision suffix.",
             "name": "basehead",
             "in": "path",
             "required": true
@@ -8155,6 +8155,9 @@
           "200": {
             "$ref": "#/responses/Compare"
           },
+          "400": {
+            "$ref": "#/responses/error"
+          },
           "404": {
             "$ref": "#/responses/notFound"
           }

templates/swagger/v1_openapi3_json.tmpl

@@ -19490,7 +19490,7 @@
             }
           },
           {
-            "description": "compare two refs as `base...head` (or `base..head`); refs may be branches, tags, full or short SHAs, including branch names that contain slashes.",
+            "description": "compare two refs as `base...head` (or `base..head`); refs may be branches, tags, full or short SHAs (including branch names that contain slashes), optionally with a `^` or `~N` revision suffix.",
             "in": "path",
             "name": "basehead",
             "required": true,
@@ -19515,6 +19515,9 @@
           "200": {
             "$ref": "#/components/responses/Compare"
           },
+          "400": {
+            "$ref": "#/components/responses/error"
+          },
           "404": {
             "$ref": "#/components/responses/notFound"
           }

tests/integration/api_repo_compare_test.go

@@ -45,6 +45,40 @@ func TestAPICompareBranches(t *testing.T) {
 			assert.Len(t, apiResp.Commits, 1)
 		})
 
+		t.Run("CompareWithRefSuffix", func(t *testing.T) {
+			defer tests.PrintCurrentTest(t)()
+
+			// remove-files-b^ is the parent of the tip, so the range drops the tip and ends at that parent
+			const parentSHA = "b67e43a07d48243a5f670ace063acd5e13f719df"
+			req := NewRequestf(t, "GET", "/api/v1/repos/user2/repo20/compare/add-csv...remove-files-b^").AddTokenAuth(token2)
+			resp := MakeRequest(t, req, http.StatusOK)
+			apiResp := DecodeJSON(t, resp, &api.Compare{})
+			assert.Equal(t, 1, apiResp.TotalCommits)
+			assert.Len(t, apiResp.Commits, 1)
+			assert.Equal(t, parentSHA, apiResp.Commits[0].SHA)
+
+			// the same suffix on the direct ".." comparison resolves to the same commit
+			req = NewRequestf(t, "GET", "/api/v1/repos/user2/repo20/compare/add-csv..remove-files-b^").AddTokenAuth(token2)
+			resp = MakeRequest(t, req, http.StatusOK)
+			apiResp = DecodeJSON(t, resp, &api.Compare{})
+			assert.Equal(t, 1, apiResp.TotalCommits)
+			assert.Equal(t, parentSHA, apiResp.Commits[0].SHA)
+
+			req = NewRequestf(t, "GET", "/api/v1/repos/user2/repo20/compare/add-csv~1...add-csv").AddTokenAuth(token2)
+			resp = MakeRequest(t, req, http.StatusOK)
+			apiResp = DecodeJSON(t, resp, &api.Compare{})
+			assert.Equal(t, 1, apiResp.TotalCommits)
+			assert.Len(t, apiResp.Commits, 1)
+
+			// a valid but unresolvable suffix is not found, while an unsupported suffix (^{...}) is a bad request
+			req = NewRequestf(t, "GET", "/api/v1/repos/user2/repo20/compare/add-csv...remove-files-b~50").AddTokenAuth(token2)
+			MakeRequest(t, req, http.StatusNotFound)
+			req = NewRequestf(t, "GET", "/api/v1/repos/user2/repo20/compare/add-csv...remove-files-b^{/Add}").AddTokenAuth(token2)
+			MakeRequest(t, req, http.StatusBadRequest)
+			req = NewRequestf(t, "GET", "/api/v1/repos/user2/repo20/compare/add-csv^{/Add}...remove-files-b").AddTokenAuth(token2)
+			MakeRequest(t, req, http.StatusBadRequest)
+		})
+
 		t.Run("CompareForkOnlyCommit", func(t *testing.T) {
 			defer tests.PrintCurrentTest(t)()
 

tests/integration/compare_test.go

@@ -14,7 +14,10 @@ import (
 	"gitea.dev/models/unittest"
 	user_model "gitea.dev/models/user"
 	"gitea.dev/modules/git/gitcmd"
+	"gitea.dev/modules/gitrepo"
 	"gitea.dev/modules/test"
+	"gitea.dev/modules/util"
+	"gitea.dev/routers/common"
 	repo_service "gitea.dev/services/repository"
 	"gitea.dev/tests"
 
@@ -135,6 +138,73 @@ func TestCompareBranches(t *testing.T) {
 	inspectCompare(t, htmlDoc, diffCount, diffChanges)
 }
 
+func TestCompareWithRefSuffix(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	session := loginUser(t, "user2")
+
+	// remove-files-b^ resolves to the tip's parent, so the test.txt added by the tip is excluded
+	req := NewRequest(t, "GET", "/user2/repo20/compare/add-csv...remove-files-b^")
+	resp := session.MakeRequest(t, req, http.StatusOK)
+	htmlDoc := NewHTMLParser(t, resp.Body)
+	inspectCompare(t, htmlDoc, 2, []string{"link_hi", "test.csv"})
+
+	// a suffix resolves to a commit rather than a branch, so the page offers no pull request to create
+	assert.Equal(t, 0, htmlDoc.doc.Find(".pullrequest-form").Length())
+
+	// the same suffix on the direct ".." comparison resolves to the same commit
+	req = NewRequest(t, "GET", "/user2/repo20/compare/add-csv..remove-files-b^")
+	resp = session.MakeRequest(t, req, http.StatusOK)
+	htmlDoc = NewHTMLParser(t, resp.Body)
+	inspectCompare(t, htmlDoc, 2, []string{"link_hi", "test.csv"})
+
+	// a ~N suffix on the base side resolves and renders the compare page, but also
+	// resolves to a commit rather than a branch, so no pull request form is offered
+	req = NewRequest(t, "GET", "/user2/repo20/compare/add-csv~1...remove-files-b")
+	resp = session.MakeRequest(t, req, http.StatusOK)
+	assert.True(t, test.IsNormalPageCompleted(resp.Body.String()))
+	htmlDoc = NewHTMLParser(t, resp.Body)
+	assert.Equal(t, 0, htmlDoc.doc.Find(".pullrequest-form").Length())
+
+	// the web handler folds an unsupported (^{...}) and an unresolvable (~50) suffix alike into 404
+	for _, basehead := range []string{
+		"add-csv...remove-files-b~50",
+		"add-csv...remove-files-b^{/Add}",
+		"add-csv^{/Add}...remove-files-b",
+	} {
+		req = NewRequest(t, "GET", "/user2/repo20/compare/"+basehead).SetHeader("Accept", "text/html")
+		resp = session.MakeRequest(t, req, http.StatusNotFound)
+		assert.True(t, test.IsNormalPageCompleted(resp.Body.String()))
+	}
+}
+
+func TestResolveRefWithSuffixContract(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	repo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 31})
+	gitRepo, err := gitrepo.OpenRepository(t.Context(), repo)
+	require.NoError(t, err)
+	defer gitRepo.Close()
+
+	// a nil error guarantees a usable RefName
+	ref, err := common.ResolveRefWithSuffix(gitRepo, "add-csv", "^")
+	require.NoError(t, err)
+	assert.NotEmpty(t, ref)
+	// a ref resolved with a suffix must be a commit SHA, not a branch ref
+	// (branch refs would break "New Pull Request" logic)
+	assert.False(t, ref.IsBranch(), "ref with suffix must not resolve to a branch")
+
+	// a missing ref and an unresolvable suffix both report not-found instead of an empty RefName
+	for _, tc := range []struct{ oriRef, suffix string }{
+		{"does-not-exist", ""},
+		{"add-csv", "~50"},
+	} {
+		ref, err := common.ResolveRefWithSuffix(gitRepo, tc.oriRef, tc.suffix)
+		assert.ErrorIs(t, err, util.ErrNotExist, "ref %q suffix %q", tc.oriRef, tc.suffix)
+		assert.Empty(t, ref, "ref %q suffix %q", tc.oriRef, tc.suffix)
+	}
+}
+
 func TestCompareBranchesNoCommonMergeBase(t *testing.T) {
 	defer tests.PrepareTestEnv(t)()