Merge branch '4612-add-support-for-patch-id-generation' into 'master'

Add new GetPatchID RPC

Closes #4612

See merge request https://gitlab.com/gitlab-org/gitaly/-/merge_requests/5174

Merged-by: karthik nayak <knayak@gitlab.com>
Approved-by: Patrick Steinhardt <psteinhardt@gitlab.com>
Approved-by: karthik nayak <knayak@gitlab.com>
Reviewed-by: Patrick Steinhardt <psteinhardt@gitlab.com>
Reviewed-by: Sincheol (David) Kim <dkim@gitlab.com>
Co-authored-by: David Kim <dkim@gitlab.com>

6 files changed, 545 insertions, 77 deletions

diff --git a/internal/git/command_description.go b/internal/git/command_description.go
index 99a932cc4..0ed09e7f9 100644
--- a/internal/git/command_description.go
+++ b/internal/git/command_description.go
@@ -202,6 +202,9 @@ var commandDescriptions = map[string]commandDescription{
 		flags: scNoRefUpdates,
 		opts:  packConfiguration(),
 	},
+	"patch-id": {
+		flags: scNoRefUpdates | scNoEndOfOptions,
+	},
 	"prune": {
 		flags: scNoRefUpdates,
 	},
diff --git a/internal/gitaly/service/diff/patch_id.go b/internal/gitaly/service/diff/patch_id.go
new file mode 100644
index 000000000..aa8e5f50a
--- /dev/null
+++ b/internal/gitaly/service/diff/patch_id.go
@@ -0,0 +1,84 @@
+package diff
+
+import (
+	"context"
+	"errors"
+	"strings"
+
+	"gitlab.com/gitlab-org/gitaly/v15/internal/git"
+	"gitlab.com/gitlab-org/gitaly/v15/internal/gitaly/service"
+	"gitlab.com/gitlab-org/gitaly/v15/internal/structerr"
+	"gitlab.com/gitlab-org/gitaly/v15/proto/go/gitalypb"
+)
+
+func (s *server) GetPatchID(ctx context.Context, in *gitalypb.GetPatchIDRequest) (*gitalypb.GetPatchIDResponse, error) {
+	if err := validatePatchIDRequest(in); err != nil {
+		return nil, structerr.NewInvalidArgument("%w", err)
+	}
+
+	var diffCmdStderr strings.Builder
+
+	diffCmd, err := s.gitCmdFactory.New(ctx, in.Repository,
+		git.Command{
+			Name: "diff",
+			Args: []string{string(in.GetOldRevision()), string(in.GetNewRevision())},
+		},
+		git.WithStderr(&diffCmdStderr),
+	)
+	if err != nil {
+		return nil, structerr.New("spawning diff: %w", err)
+	}
+
+	var patchIDStdout strings.Builder
+	var patchIDStderr strings.Builder
+
+	patchIDCmd, err := s.gitCmdFactory.NewWithoutRepo(ctx,
+		git.Command{
+			Name:  "patch-id",
+			Flags: []git.Option{git.Flag{Name: "--stable"}},
+		},
+		git.WithStdin(diffCmd),
+		git.WithStdout(&patchIDStdout),
+		git.WithStderr(&patchIDStderr),
+	)
+	if err != nil {
+		return nil, structerr.New("spawning patch-id: %w", err)
+	}
+
+	if err := patchIDCmd.Wait(); err != nil {
+		return nil, structerr.New("waiting for patch-id: %w", err).WithMetadata("stderr", patchIDStderr.String())
+	}
+
+	if err := diffCmd.Wait(); err != nil {
+		return nil, structerr.New("waiting for git-diff: %w", err).WithMetadata("stderr", diffCmdStderr.String())
+	}
+
+	if patchIDStdout.Len() == 0 {
+		return nil, structerr.NewFailedPrecondition("no difference between old and new revision")
+	}
+
+	// When computing patch IDs for commits directly via e.g. `git show | git patch-id` then the second
+	// field printed by git-patch-id(1) denotes the commit of the patch ID. As we only generate patch IDs
+	// from a diff here the second field will always be the zero OID, so we ignore it.
+	patchID, _, found := strings.Cut(patchIDStdout.String(), " ")
+
+	if !found {
+		return nil, structerr.NewFailedPrecondition("unexpected patch ID format")
+	}
+
+	return &gitalypb.GetPatchIDResponse{PatchId: patchID}, nil
+}
+
+func validatePatchIDRequest(in *gitalypb.GetPatchIDRequest) error {
+	if err := service.ValidateRepository(in.GetRepository()); err != nil {
+		return err
+	}
+	if string(in.GetOldRevision()) == "" {
+		return errors.New("empty OldRevision")
+	}
+	if string(in.GetNewRevision()) == "" {
+		return errors.New("empty NewRevision")
+	}
+
+	return nil
+}
diff --git a/internal/gitaly/service/diff/patch_id_test.go b/internal/gitaly/service/diff/patch_id_test.go
new file mode 100644
index 000000000..432cc47cd
--- /dev/null
+++ b/internal/gitaly/service/diff/patch_id_test.go
@@ -0,0 +1,138 @@
+//go:build !gitaly_test_sha256
+
+package diff
+
+import (
+	"testing"
+
+	"gitlab.com/gitlab-org/gitaly/v15/internal/structerr"
+	"gitlab.com/gitlab-org/gitaly/v15/internal/testhelper"
+	"gitlab.com/gitlab-org/gitaly/v15/proto/go/gitalypb"
+)
+
+func TestGetPatchID(t *testing.T) {
+	t.Parallel()
+	ctx := testhelper.Context(t)
+	_, repoProto, _, client := setupDiffService(t, ctx)
+
+	testCases := []struct {
+		desc             string
+		setup            func() *gitalypb.GetPatchIDRequest
+		expectedResponse *gitalypb.GetPatchIDResponse
+		expectedErr      error
+	}{
+		{
+			desc: "returns patch-id successfully",
+			setup: func() *gitalypb.GetPatchIDRequest {
+				return &gitalypb.GetPatchIDRequest{
+					Repository:  repoProto,
+					OldRevision: []byte("HEAD~3"),
+					NewRevision: []byte("HEAD"),
+				}
+			},
+			expectedResponse: &gitalypb.GetPatchIDResponse{PatchId: "1d108b99acd03f94e015c5237afa7bc24382f1f6"},
+		},
+		{
+			desc: "returns patch-id successfully with commit ids",
+			setup: func() *gitalypb.GetPatchIDRequest {
+				return &gitalypb.GetPatchIDRequest{
+					Repository:  repoProto,
+					OldRevision: []byte("55bc176024cfa3baaceb71db584c7e5df900ea65"),
+					NewRevision: []byte("c1c67abbaf91f624347bb3ae96eabe3a1b742478"),
+				}
+			},
+			expectedResponse: &gitalypb.GetPatchIDResponse{PatchId: "1c5c57c2b6ef85b3cd248c34318bcce5bec3b540"},
+		},
+		{
+			desc: "returns patch-id successfully for a specific file",
+			setup: func() *gitalypb.GetPatchIDRequest {
+				return &gitalypb.GetPatchIDRequest{
+					Repository:  repoProto,
+					OldRevision: []byte("HEAD~3:.gitattributes"),
+					NewRevision: []byte("HEAD:.gitattributes"),
+				}
+			},
+			expectedResponse: &gitalypb.GetPatchIDResponse{PatchId: "ed52511a91dd53dcf58acf6e85be5456b54f2f8a"},
+		},
+		{
+			desc: "file didn't exist in the old revision",
+			setup: func() *gitalypb.GetPatchIDRequest {
+				return &gitalypb.GetPatchIDRequest{
+					Repository:  repoProto,
+					OldRevision: []byte("HEAD~3:files/flat/path/correct/content.txt"),
+					NewRevision: []byte("HEAD:files/flat/path/correct/content.txt"),
+				}
+			},
+			expectedErr: structerr.New("waiting for git-diff: exit status 128"),
+		},
+		{
+			desc: "unknown revisions",
+			setup: func() *gitalypb.GetPatchIDRequest {
+				return &gitalypb.GetPatchIDRequest{
+					Repository:  repoProto,
+					OldRevision: []byte("0000000000000000000000000000000000000000"),
+					NewRevision: []byte("1111111111111111111111111111111111111111"),
+				}
+			},
+			expectedErr: structerr.New("waiting for git-diff: exit status 128").WithMetadata("stderr", ""),
+		},
+		{
+			desc: "no diff from the given revisions",
+			setup: func() *gitalypb.GetPatchIDRequest {
+				return &gitalypb.GetPatchIDRequest{
+					Repository:  repoProto,
+					OldRevision: []byte("HEAD"),
+					NewRevision: []byte("HEAD"),
+				}
+			},
+			expectedErr: structerr.NewFailedPrecondition("no difference between old and new revision"),
+		},
+		{
+			desc: "empty repository",
+			setup: func() *gitalypb.GetPatchIDRequest {
+				return &gitalypb.GetPatchIDRequest{
+					Repository:  nil,
+					OldRevision: []byte("HEAD~1"),
+					NewRevision: []byte("HEAD"),
+				}
+			},
+			expectedErr: structerr.NewInvalidArgument(testhelper.GitalyOrPraefect(
+				"empty Repository",
+				"repo scoped: empty Repository",
+			)),
+		},
+		{
+			desc: "empty old revision",
+			setup: func() *gitalypb.GetPatchIDRequest {
+				return &gitalypb.GetPatchIDRequest{
+					Repository:  repoProto,
+					NewRevision: []byte("HEAD"),
+				}
+			},
+			expectedErr: structerr.NewInvalidArgument("empty OldRevision"),
+		},
+		{
+			desc: "empty new revision",
+			setup: func() *gitalypb.GetPatchIDRequest {
+				return &gitalypb.GetPatchIDRequest{
+					Repository:  repoProto,
+					OldRevision: []byte("HEAD~1"),
+				}
+			},
+			expectedErr: structerr.NewInvalidArgument("empty NewRevision"),
+		},
+	}
+
+	for _, tc := range testCases {
+		tc := tc
+		t.Run(tc.desc, func(t *testing.T) {
+			t.Parallel()
+
+			request := tc.setup()
+			response, err := client.GetPatchID(ctx, request)
+
+			testhelper.RequireGrpcError(t, tc.expectedErr, err)
+			testhelper.ProtoEqual(t, tc.expectedResponse, response)
+		})
+	}
+}
diff --git a/proto/diff.proto b/proto/diff.proto
index 3247ceb57..6905af2c4 100644
--- a/proto/diff.proto
+++ b/proto/diff.proto
@@ -53,6 +53,15 @@ service DiffService {
     };
   }
 
+  // GetPatchID computes a patch ID for a patch. Patch IDs are a unique ID computed by hashing
+  // a patch with some parameters like line numbers ignored. The patch ID can thus be used to compare
+  // whether diffs make the same change. Please refer to git-patch-id(1) for further information.
+  // If the difference between old and new change is empty then this RPC returns an error.
+  rpc GetPatchID(GetPatchIDRequest) returns (GetPatchIDResponse) {
+    option (op_type) = {
+      op: ACCESSOR
+    };
+  }
 }
 
 // This comment is left unintentionally blank.
@@ -312,3 +321,24 @@ message ChangedPaths {
   // new_mode is the mode of the changed path after the change. Please refer to `old_mode` for a list of potential values.
   int32 new_mode = 4;
 }
+
+// GetPatchIDRequest is a request for the GetPatchID RPC.
+message GetPatchIDRequest {
+  // Repository is the repository the patch ID shall be computed in.
+  Repository repository = 1 [(target_repository)=true];
+  // OldRevision is the old revision that shall be used to compute the patch
+  // from that will then be passed to git-patch-id(1). Accepts revisions as
+  // specified in gitrevisions(5).
+  bytes old_revision = 2;
+  // newRevision is the new revision that shall be used to compute the patch
+  // from that will then be passed to git-patch-id(1). Accepts revisions as
+  // specified in gitrevisions(5).
+  bytes new_revision = 3;
+}
+
+// GetPatchIDResponse is a response for the GetPatchID RPC.
+message GetPatchIDResponse {
+  // PatchId is the patch ID that was generated by hashing the diff of the
+  // given old and new revision.
+  string patch_id = 1;
+}
diff --git a/proto/go/gitalypb/diff.pb.go b/proto/go/gitalypb/diff.pb.go
index ad38fd178..10d55083b 100644
--- a/proto/go/gitalypb/diff.pb.go
+++ b/proto/go/gitalypb/diff.pb.go
@@ -1306,6 +1306,127 @@ func (x *ChangedPaths) GetNewMode() int32 {
 	return 0
 }
 
+// GetPatchIDRequest is a request for the GetPatchID RPC.
+type GetPatchIDRequest struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// Repository is the repository the patch ID shall be computed in.
+	Repository *Repository `protobuf:"bytes,1,opt,name=repository,proto3" json:"repository,omitempty"`
+	// OldRevision is the old revision that shall be used to compute the patch
+	// from that will then be passed to git-patch-id(1). Accepts revisions as
+	// specified in gitrevisions(5).
+	OldRevision []byte `protobuf:"bytes,2,opt,name=old_revision,json=oldRevision,proto3" json:"old_revision,omitempty"`
+	// newRevision is the new revision that shall be used to compute the patch
+	// from that will then be passed to git-patch-id(1). Accepts revisions as
+	// specified in gitrevisions(5).
+	NewRevision []byte `protobuf:"bytes,3,opt,name=new_revision,json=newRevision,proto3" json:"new_revision,omitempty"`
+}
+
+func (x *GetPatchIDRequest) Reset() {
+	*x = GetPatchIDRequest{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_diff_proto_msgTypes[15]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *GetPatchIDRequest) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*GetPatchIDRequest) ProtoMessage() {}
+
+func (x *GetPatchIDRequest) ProtoReflect() protoreflect.Message {
+	mi := &file_diff_proto_msgTypes[15]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use GetPatchIDRequest.ProtoReflect.Descriptor instead.
+func (*GetPatchIDRequest) Descriptor() ([]byte, []int) {
+	return file_diff_proto_rawDescGZIP(), []int{15}
+}
+
+func (x *GetPatchIDRequest) GetRepository() *Repository {
+	if x != nil {
+		return x.Repository
+	}
+	return nil
+}
+
+func (x *GetPatchIDRequest) GetOldRevision() []byte {
+	if x != nil {
+		return x.OldRevision
+	}
+	return nil
+}
+
+func (x *GetPatchIDRequest) GetNewRevision() []byte {
+	if x != nil {
+		return x.NewRevision
+	}
+	return nil
+}
+
+// GetPatchIDResponse is a response for the GetPatchID RPC.
+type GetPatchIDResponse struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// PatchId is the patch ID that was generated by hashing the diff of the
+	// given old and new revision.
+	PatchId string `protobuf:"bytes,1,opt,name=patch_id,json=patchId,proto3" json:"patch_id,omitempty"`
+}
+
+func (x *GetPatchIDResponse) Reset() {
+	*x = GetPatchIDResponse{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_diff_proto_msgTypes[16]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *GetPatchIDResponse) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*GetPatchIDResponse) ProtoMessage() {}
+
+func (x *GetPatchIDResponse) ProtoReflect() protoreflect.Message {
+	mi := &file_diff_proto_msgTypes[16]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use GetPatchIDResponse.ProtoReflect.Descriptor instead.
+func (*GetPatchIDResponse) Descriptor() ([]byte, []int) {
+	return file_diff_proto_rawDescGZIP(), []int{16}
+}
+
+func (x *GetPatchIDResponse) GetPatchId() string {
+	if x != nil {
+		return x.PatchId
+	}
+	return ""
+}
+
 // Request is a single request to pass to git diff-tree.
 type FindChangedPathsRequest_Request struct {
 	state         protoimpl.MessageState
@@ -1322,7 +1443,7 @@ type FindChangedPathsRequest_Request struct {
 func (x *FindChangedPathsRequest_Request) Reset() {
 	*x = FindChangedPathsRequest_Request{}
 	if protoimpl.UnsafeEnabled {
-		mi := &file_diff_proto_msgTypes[15]
+		mi := &file_diff_proto_msgTypes[17]
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		ms.StoreMessageInfo(mi)
 	}
@@ -1335,7 +1456,7 @@ func (x *FindChangedPathsRequest_Request) String() string {
 func (*FindChangedPathsRequest_Request) ProtoMessage() {}
 
 func (x *FindChangedPathsRequest_Request) ProtoReflect() protoreflect.Message {
-	mi := &file_diff_proto_msgTypes[15]
+	mi := &file_diff_proto_msgTypes[17]
 	if protoimpl.UnsafeEnabled && x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -1407,7 +1528,7 @@ type FindChangedPathsRequest_Request_TreeRequest struct {
 func (x *FindChangedPathsRequest_Request_TreeRequest) Reset() {
 	*x = FindChangedPathsRequest_Request_TreeRequest{}
 	if protoimpl.UnsafeEnabled {
-		mi := &file_diff_proto_msgTypes[16]
+		mi := &file_diff_proto_msgTypes[18]
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		ms.StoreMessageInfo(mi)
 	}
@@ -1420,7 +1541,7 @@ func (x *FindChangedPathsRequest_Request_TreeRequest) String() string {
 func (*FindChangedPathsRequest_Request_TreeRequest) ProtoMessage() {}
 
 func (x *FindChangedPathsRequest_Request_TreeRequest) ProtoReflect() protoreflect.Message {
-	mi := &file_diff_proto_msgTypes[16]
+	mi := &file_diff_proto_msgTypes[18]
 	if protoimpl.UnsafeEnabled && x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -1469,7 +1590,7 @@ type FindChangedPathsRequest_Request_CommitRequest struct {
 func (x *FindChangedPathsRequest_Request_CommitRequest) Reset() {
 	*x = FindChangedPathsRequest_Request_CommitRequest{}
 	if protoimpl.UnsafeEnabled {
-		mi := &file_diff_proto_msgTypes[17]
+		mi := &file_diff_proto_msgTypes[19]
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		ms.StoreMessageInfo(mi)
 	}
@@ -1482,7 +1603,7 @@ func (x *FindChangedPathsRequest_Request_CommitRequest) String() string {
 func (*FindChangedPathsRequest_Request_CommitRequest) ProtoMessage() {}
 
 func (x *FindChangedPathsRequest_Request_CommitRequest) ProtoReflect() protoreflect.Message {
-	mi := &file_diff_proto_msgTypes[17]
+	mi := &file_diff_proto_msgTypes[19]
 	if protoimpl.UnsafeEnabled && x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -1711,41 +1832,59 @@ var file_diff_proto_rawDesc = []byte{
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+	0x6f, 0x74, 0x6f, 0x33,
 }
 
 var (
@@ -1761,7 +1900,7 @@ func file_diff_proto_rawDescGZIP() []byte {
 }
 
 var file_diff_proto_enumTypes = make([]protoimpl.EnumInfo, 2)
-var file_diff_proto_msgTypes = make([]protoimpl.MessageInfo, 18)
+var file_diff_proto_msgTypes = make([]protoimpl.MessageInfo, 20)
 var file_diff_proto_goTypes = []interface{}{
 	(CommitDiffRequest_DiffMode)(0),                       // 0: gitaly.CommitDiffRequest.DiffMode
 	(ChangedPaths_Status)(0),                              // 1: gitaly.ChangedPaths.Status
@@ -1780,43 +1919,48 @@ var file_diff_proto_goTypes = []interface{}{
 	(*FindChangedPathsRequest)(nil),                       // 14: gitaly.FindChangedPathsRequest
 	(*FindChangedPathsResponse)(nil),                      // 15: gitaly.FindChangedPathsResponse
 	(*ChangedPaths)(nil),                                  // 16: gitaly.ChangedPaths
-	(*FindChangedPathsRequest_Request)(nil),               // 17: gitaly.FindChangedPathsRequest.Request
-	(*FindChangedPathsRequest_Request_TreeRequest)(nil),   // 18: gitaly.FindChangedPathsRequest.Request.TreeRequest
-	(*FindChangedPathsRequest_Request_CommitRequest)(nil), // 19: gitaly.FindChangedPathsRequest.Request.CommitRequest
-	(*Repository)(nil),                                    // 20: gitaly.Repository
+	(*GetPatchIDRequest)(nil),                             // 17: gitaly.GetPatchIDRequest
+	(*GetPatchIDResponse)(nil),                            // 18: gitaly.GetPatchIDResponse
+	(*FindChangedPathsRequest_Request)(nil),               // 19: gitaly.FindChangedPathsRequest.Request
+	(*FindChangedPathsRequest_Request_TreeRequest)(nil),   // 20: gitaly.FindChangedPathsRequest.Request.TreeRequest
+	(*FindChangedPathsRequest_Request_CommitRequest)(nil), // 21: gitaly.FindChangedPathsRequest.Request.CommitRequest
+	(*Repository)(nil),                                    // 22: gitaly.Repository
 }
 var file_diff_proto_depIdxs = []int32{
-	20, // 0: gitaly.CommitDiffRequest.repository:type_name -> gitaly.Repository
+	22, // 0: gitaly.CommitDiffRequest.repository:type_name -> gitaly.Repository
 	0,  // 1: gitaly.CommitDiffRequest.diff_mode:type_name -> gitaly.CommitDiffRequest.DiffMode
-	20, // 2: gitaly.CommitDeltaRequest.repository:type_name -> gitaly.Repository
+	22, // 2: gitaly.CommitDeltaRequest.repository:type_name -> gitaly.Repository
 	5,  // 3: gitaly.CommitDeltaResponse.deltas:type_name -> gitaly.CommitDelta
-	20, // 4: gitaly.RawDiffRequest.repository:type_name -> gitaly.Repository
-	20, // 5: gitaly.RawPatchRequest.repository:type_name -> gitaly.Repository
-	20, // 6: gitaly.DiffStatsRequest.repository:type_name -> gitaly.Repository
+	22, // 4: gitaly.RawDiffRequest.repository:type_name -> gitaly.Repository
+	22, // 5: gitaly.RawPatchRequest.repository:type_name -> gitaly.Repository
+	22, // 6: gitaly.DiffStatsRequest.repository:type_name -> gitaly.Repository
 	12, // 7: gitaly.DiffStatsResponse.stats:type_name -> gitaly.DiffStats
-	20, // 8: gitaly.FindChangedPathsRequest.repository:type_name -> gitaly.Repository
-	17, // 9: gitaly.FindChangedPathsRequest.requests:type_name -> gitaly.FindChangedPathsRequest.Request
+	22, // 8: gitaly.FindChangedPathsRequest.repository:type_name -> gitaly.Repository
+	19, // 9: gitaly.FindChangedPathsRequest.requests:type_name -> gitaly.FindChangedPathsRequest.Request
 	16, // 10: gitaly.FindChangedPathsResponse.paths:type_name -> gitaly.ChangedPaths
 	1,  // 11: gitaly.ChangedPaths.status:type_name -> gitaly.ChangedPaths.Status
-	18, // 12: gitaly.FindChangedPathsRequest.Request.tree_request:type_name -> gitaly.FindChangedPathsRequest.Request.TreeRequest
-	19, // 13: gitaly.FindChangedPathsRequest.Request.commit_request:type_name -> gitaly.FindChangedPathsRequest.Request.CommitRequest
-	2,  // 14: gitaly.DiffService.CommitDiff:input_type -> gitaly.CommitDiffRequest
-	4,  // 15: gitaly.DiffService.CommitDelta:input_type -> gitaly.CommitDeltaRequest
-	7,  // 16: gitaly.DiffService.RawDiff:input_type -> gitaly.RawDiffRequest
-	9,  // 17: gitaly.DiffService.RawPatch:input_type -> gitaly.RawPatchRequest
-	11, // 18: gitaly.DiffService.DiffStats:input_type -> gitaly.DiffStatsRequest
-	14, // 19: gitaly.DiffService.FindChangedPaths:input_type -> gitaly.FindChangedPathsRequest
-	3,  // 20: gitaly.DiffService.CommitDiff:output_type -> gitaly.CommitDiffResponse
-	6,  // 21: gitaly.DiffService.CommitDelta:output_type -> gitaly.CommitDeltaResponse
-	8,  // 22: gitaly.DiffService.RawDiff:output_type -> gitaly.RawDiffResponse
-	10, // 23: gitaly.DiffService.RawPatch:output_type -> gitaly.RawPatchResponse
-	13, // 24: gitaly.DiffService.DiffStats:output_type -> gitaly.DiffStatsResponse
-	15, // 25: gitaly.DiffService.FindChangedPaths:output_type -> gitaly.FindChangedPathsResponse
-	20, // [20:26] is the sub-list for method output_type
-	14, // [14:20] is the sub-list for method input_type
-	14, // [14:14] is the sub-list for extension type_name
-	14, // [14:14] is the sub-list for extension extendee
-	0,  // [0:14] is the sub-list for field type_name
+	22, // 12: gitaly.GetPatchIDRequest.repository:type_name -> gitaly.Repository
+	20, // 13: gitaly.FindChangedPathsRequest.Request.tree_request:type_name -> gitaly.FindChangedPathsRequest.Request.TreeRequest
+	21, // 14: gitaly.FindChangedPathsRequest.Request.commit_request:type_name -> gitaly.FindChangedPathsRequest.Request.CommitRequest
+	2,  // 15: gitaly.DiffService.CommitDiff:input_type -> gitaly.CommitDiffRequest
+	4,  // 16: gitaly.DiffService.CommitDelta:input_type -> gitaly.CommitDeltaRequest
+	7,  // 17: gitaly.DiffService.RawDiff:input_type -> gitaly.RawDiffRequest
+	9,  // 18: gitaly.DiffService.RawPatch:input_type -> gitaly.RawPatchRequest
+	11, // 19: gitaly.DiffService.DiffStats:input_type -> gitaly.DiffStatsRequest
+	14, // 20: gitaly.DiffService.FindChangedPaths:input_type -> gitaly.FindChangedPathsRequest
+	17, // 21: gitaly.DiffService.GetPatchID:input_type -> gitaly.GetPatchIDRequest
+	3,  // 22: gitaly.DiffService.CommitDiff:output_type -> gitaly.CommitDiffResponse
+	6,  // 23: gitaly.DiffService.CommitDelta:output_type -> gitaly.CommitDeltaResponse
+	8,  // 24: gitaly.DiffService.RawDiff:output_type -> gitaly.RawDiffResponse
+	10, // 25: gitaly.DiffService.RawPatch:output_type -> gitaly.RawPatchResponse
+	13, // 26: gitaly.DiffService.DiffStats:output_type -> gitaly.DiffStatsResponse
+	15, // 27: gitaly.DiffService.FindChangedPaths:output_type -> gitaly.FindChangedPathsResponse
+	18, // 28: gitaly.DiffService.GetPatchID:output_type -> gitaly.GetPatchIDResponse
+	22, // [22:29] is the sub-list for method output_type
+	15, // [15:22] is the sub-list for method input_type
+	15, // [15:15] is the sub-list for extension type_name
+	15, // [15:15] is the sub-list for extension extendee
+	0,  // [0:15] is the sub-list for field type_name
 }
 
 func init() { file_diff_proto_init() }
@@ -2008,7 +2152,7 @@ func file_diff_proto_init() {
 			}
 		}
 		file_diff_proto_msgTypes[15].Exporter = func(v interface{}, i int) interface{} {
-			switch v := v.(*FindChangedPathsRequest_Request); i {
+			switch v := v.(*GetPatchIDRequest); i {
 			case 0:
 				return &v.state
 			case 1:
@@ -2020,7 +2164,7 @@ func file_diff_proto_init() {
 			}
 		}
 		file_diff_proto_msgTypes[16].Exporter = func(v interface{}, i int) interface{} {
-			switch v := v.(*FindChangedPathsRequest_Request_TreeRequest); i {
+			switch v := v.(*GetPatchIDResponse); i {
 			case 0:
 				return &v.state
 			case 1:
@@ -2032,6 +2176,30 @@ func file_diff_proto_init() {
 			}
 		}
 		file_diff_proto_msgTypes[17].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*FindChangedPathsRequest_Request); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_diff_proto_msgTypes[18].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*FindChangedPathsRequest_Request_TreeRequest); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_diff_proto_msgTypes[19].Exporter = func(v interface{}, i int) interface{} {
 			switch v := v.(*FindChangedPathsRequest_Request_CommitRequest); i {
 			case 0:
 				return &v.state
@@ -2044,7 +2212,7 @@ func file_diff_proto_init() {
 			}
 		}
 	}
-	file_diff_proto_msgTypes[15].OneofWrappers = []interface{}{
+	file_diff_proto_msgTypes[17].OneofWrappers = []interface{}{
 		(*FindChangedPathsRequest_Request_TreeRequest_)(nil),
 		(*FindChangedPathsRequest_Request_CommitRequest_)(nil),
 	}
@@ -2054,7 +2222,7 @@ func file_diff_proto_init() {
 			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
 			RawDescriptor: file_diff_proto_rawDesc,
 			NumEnums:      2,
-			NumMessages:   18,
+			NumMessages:   20,
 			NumExtensions: 0,
 			NumServices:   1,
 		},
diff --git a/proto/go/gitalypb/diff_grpc.pb.go b/proto/go/gitalypb/diff_grpc.pb.go
index f2e7f843b..5cbcaa875 100644
--- a/proto/go/gitalypb/diff_grpc.pb.go
+++ b/proto/go/gitalypb/diff_grpc.pb.go
@@ -34,6 +34,11 @@ type DiffServiceClient interface {
 	DiffStats(ctx context.Context, in *DiffStatsRequest, opts ...grpc.CallOption) (DiffService_DiffStatsClient, error)
 	// Return a list of files changed along with the status of each file
 	FindChangedPaths(ctx context.Context, in *FindChangedPathsRequest, opts ...grpc.CallOption) (DiffService_FindChangedPathsClient, error)
+	// GetPatchID computes a patch ID for a patch. Patch IDs are a unique ID computed by hashing
+	// a patch with some parameters like line numbers ignored. The patch ID can thus be used to compare
+	// whether diffs make the same change. Please refer to git-patch-id(1) for further information.
+	// If the difference between old and new change is empty then this RPC returns an error.
+	GetPatchID(ctx context.Context, in *GetPatchIDRequest, opts ...grpc.CallOption) (*GetPatchIDResponse, error)
 }
 
 type diffServiceClient struct {
@@ -236,6 +241,15 @@ func (x *diffServiceFindChangedPathsClient) Recv() (*FindChangedPathsResponse, e
 	return m, nil
 }
 
+func (c *diffServiceClient) GetPatchID(ctx context.Context, in *GetPatchIDRequest, opts ...grpc.CallOption) (*GetPatchIDResponse, error) {
+	out := new(GetPatchIDResponse)
+	err := c.cc.Invoke(ctx, "/gitaly.DiffService/GetPatchID", in, out, opts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
 // DiffServiceServer is the server API for DiffService service.
 // All implementations must embed UnimplementedDiffServiceServer
 // for forward compatibility
@@ -252,6 +266,11 @@ type DiffServiceServer interface {
 	DiffStats(*DiffStatsRequest, DiffService_DiffStatsServer) error
 	// Return a list of files changed along with the status of each file
 	FindChangedPaths(*FindChangedPathsRequest, DiffService_FindChangedPathsServer) error
+	// GetPatchID computes a patch ID for a patch. Patch IDs are a unique ID computed by hashing
+	// a patch with some parameters like line numbers ignored. The patch ID can thus be used to compare
+	// whether diffs make the same change. Please refer to git-patch-id(1) for further information.
+	// If the difference between old and new change is empty then this RPC returns an error.
+	GetPatchID(context.Context, *GetPatchIDRequest) (*GetPatchIDResponse, error)
 	mustEmbedUnimplementedDiffServiceServer()
 }
 
@@ -277,6 +296,9 @@ func (UnimplementedDiffServiceServer) DiffStats(*DiffStatsRequest, DiffService_D
 func (UnimplementedDiffServiceServer) FindChangedPaths(*FindChangedPathsRequest, DiffService_FindChangedPathsServer) error {
 	return status.Errorf(codes.Unimplemented, "method FindChangedPaths not implemented")
 }
+func (UnimplementedDiffServiceServer) GetPatchID(context.Context, *GetPatchIDRequest) (*GetPatchIDResponse, error) {
+	return nil, status.Errorf(codes.Unimplemented, "method GetPatchID not implemented")
+}
 func (UnimplementedDiffServiceServer) mustEmbedUnimplementedDiffServiceServer() {}
 
 // UnsafeDiffServiceServer may be embedded to opt out of forward compatibility for this service.
@@ -416,13 +438,36 @@ func (x *diffServiceFindChangedPathsServer) Send(m *FindChangedPathsResponse) er
 	return x.ServerStream.SendMsg(m)
 }
 
+func _DiffService_GetPatchID_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(GetPatchIDRequest)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(DiffServiceServer).GetPatchID(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: "/gitaly.DiffService/GetPatchID",
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(DiffServiceServer).GetPatchID(ctx, req.(*GetPatchIDRequest))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
 // DiffService_ServiceDesc is the grpc.ServiceDesc for DiffService service.
 // It's only intended for direct use with grpc.RegisterService,
 // and not to be introspected or modified (even as a copy)
 var DiffService_ServiceDesc = grpc.ServiceDesc{
 	ServiceName: "gitaly.DiffService",
 	HandlerType: (*DiffServiceServer)(nil),
-	Methods:     []grpc.MethodDesc{},
+	Methods: []grpc.MethodDesc{
+		{
+			MethodName: "GetPatchID",
+			Handler:    _DiffService_GetPatchID_Handler,
+		},
+	},
 	Streams: []grpc.StreamDesc{
 		{
 			StreamName:    "CommitDiff",