Add merge style fast-forward-only (go-gitea#28954)

chrisnc · algernon · commit 83123b493f3a · 2024-02-14T17:19:19.000+01:00
With this option, it is possible to require a linear commit history with the following benefits over the next best option `Rebase+fast-forward`: The original commits continue existing, with the original signatures continuing to stay valid instead of being rewritten, there is no merge commit, and reverting commits becomes easier. Closes go-gitea#24906
diff --git a/custom/conf/app.example.ini b/custom/conf/app.example.ini
@@ -1061,7 +1061,7 @@ LEVEL = Info
 ;; List of keywords used in Pull Request comments to automatically reopen a related issue
 ;REOPEN_KEYWORDS = reopen,reopens,reopened
 ;;
-;; Set default merge style for repository creating, valid options: merge, rebase, rebase-merge, squash
+;; Set default merge style for repository creating, valid options: merge, rebase, rebase-merge, squash, fast-forward-only
 ;DEFAULT_MERGE_STYLE = merge
 ;;
 ;; In the default merge message for squash commits include at most this many commits
diff --git a/docs/content/administration/config-cheat-sheet.en-us.md b/docs/content/administration/config-cheat-sheet.en-us.md
@@ -126,7 +126,7 @@ In addition, there is _`StaticRootPath`_ which can be set as a built-in at build
  keywords used in Pull Request comments to automatically close a related issue
 - `REOPEN_KEYWORDS`: **reopen**, **reopens**, **reopened**: List of keywords used in Pull Request comments to automatically reopen
  a related issue
-- `DEFAULT_MERGE_STYLE`: **merge**: Set default merge style for repository creating, valid options: `merge`, `rebase`, `rebase-merge`, `squash`
+- `DEFAULT_MERGE_STYLE`: **merge**: Set default merge style for repository creating, valid options: `merge`, `rebase`, `rebase-merge`, `squash`, `fast-forward-only`
 - `DEFAULT_MERGE_MESSAGE_COMMITS_LIMIT`: **50**: In the default merge message for squash commits include at most this many commits. Set to `-1` to include all commits
 - `DEFAULT_MERGE_MESSAGE_SIZE`: **5120**: In the default merge message for squash commits limit the size of the commit messages. Set to `-1` to have no limit. Only used if `POPULATE_SQUASH_COMMENT_WITH_COMMIT_MESSAGES` is `true`.
 - `DEFAULT_MERGE_MESSAGE_ALL_AUTHORS`: **false**: In the default merge message for squash commits walk all commits to include all authors in the Co-authored-by otherwise just use those in the limited list
diff --git a/docs/content/administration/config-cheat-sheet.zh-cn.md b/docs/content/administration/config-cheat-sheet.zh-cn.md
@@ -125,7 +125,7 @@ menu:
 - `CLOSE_KEYWORDS`: **close**, **closes**, **closed**, **fix**, **fixes**, **fixed**, **resolve**, **resolves**, **resolved**: 在拉取请求评论中用于自动关闭相关问题的关键词列表。
 - `REOPEN_KEYWORDS`: **reopen**, **reopens**, **reopened**: 在拉取请求评论中用于自动重新打开相关问题的
 关键词列表。
-- `DEFAULT_MERGE_STYLE`: **merge**: 设置创建仓库的默认合并方式，可选: `merge`, `rebase`, `rebase-merge`, `squash`
+- `DEFAULT_MERGE_STYLE`: **merge**: 设置创建仓库的默认合并方式，可选: `merge`, `rebase`, `rebase-merge`, `squash`, `fast-forward-only`
 - `DEFAULT_MERGE_MESSAGE_COMMITS_LIMIT`: **50**: 在默认合并消息中，对于`squash`提交，最多包括此数量的提交。设置为 -1 以包括所有提交。
 - `DEFAULT_MERGE_MESSAGE_SIZE`: **5120**: 在默认的合并消息中，对于`squash`提交，限制提交消息的大小。设置为 `-1`以取消限制。仅在`POPULATE_SQUASH_COMMENT_WITH_COMMIT_MESSAGES`为`true`时使用。
 - `DEFAULT_MERGE_MESSAGE_ALL_AUTHORS`: **false**: 在默认合并消息中，对于`squash`提交，遍历所有提交以包括所有作者的`Co-authored-by`，否则仅使用限定列表中的作者。
diff --git a/models/error.go b/models/error.go
@@ -493,6 +493,23 @@ func (err ErrMergeUnrelatedHistories) Error() string {
 	return fmt.Sprintf("Merge UnrelatedHistories Error: %v: %s\n%s", err.Err, err.StdErr, err.StdOut)
 }
 
+// ErrMergeDivergingFastForwardOnly represents an error if a fast-forward-only merge fails because the branches diverge
+type ErrMergeDivergingFastForwardOnly struct {
+	StdOut string
+	StdErr string
+	Err    error
+}
+
+// IsErrMergeDivergingFastForwardOnly checks if an error is a ErrMergeDivergingFastForwardOnly.
+func IsErrMergeDivergingFastForwardOnly(err error) bool {
+	_, ok := err.(ErrMergeDivergingFastForwardOnly)
+	return ok
+}
+
+func (err ErrMergeDivergingFastForwardOnly) Error() string {
+	return fmt.Sprintf("Merge DivergingFastForwardOnly Error: %v: %s\n%s", err.Err, err.StdErr, err.StdOut)
+}
+
 // ErrRebaseConflicts represents an error if rebase fails with a conflict
 type ErrRebaseConflicts struct {
 	Style     repo_model.MergeStyle
diff --git a/models/repo/git.go b/models/repo/git.go
@@ -21,6 +21,8 @@ const (
 	MergeStyleRebaseMerge MergeStyle = "rebase-merge"
 	// MergeStyleSquash squash commits into single commit before merging
 	MergeStyleSquash MergeStyle = "squash"
+	// MergeStyleFastForwardOnly fast-forward merge if possible, otherwise fail
+	MergeStyleFastForwardOnly MergeStyle = "fast-forward-only"
 	// MergeStyleManuallyMerged pr has been merged manually, just mark it as merged directly
 	MergeStyleManuallyMerged MergeStyle = "manually-merged"
 	// MergeStyleRebaseUpdate not a merge style, used to update pull head by rebase
diff --git a/models/repo/repo_unit.go b/models/repo/repo_unit.go
@@ -153,6 +153,7 @@ type PullRequestsConfig struct {
 	AllowRebase                   bool
 	AllowRebaseMerge              bool
 	AllowSquash                   bool
+	AllowFastForwardOnly          bool
 	AllowManualMerge              bool
 	AutodetectManualMerge         bool
 	AllowRebaseUpdate             bool
@@ -179,6 +180,7 @@ func (cfg *PullRequestsConfig) IsMergeStyleAllowed(mergeStyle MergeStyle) bool {
 		mergeStyle == MergeStyleRebase && cfg.AllowRebase ||
 		mergeStyle == MergeStyleRebaseMerge && cfg.AllowRebaseMerge ||
 		mergeStyle == MergeStyleSquash && cfg.AllowSquash ||
+		mergeStyle == MergeStyleFastForwardOnly && cfg.AllowFastForwardOnly ||
 		mergeStyle == MergeStyleManuallyMerged && cfg.AllowManualMerge
 }
 
diff --git a/modules/git/error.go b/modules/git/error.go
@@ -96,7 +96,7 @@ func (err ErrBranchNotExist) Unwrap() error {
 	return util.ErrNotExist
 }
 
-// ErrPushOutOfDate represents an error if merging fails due to unrelated histories
+// ErrPushOutOfDate represents an error if merging fails due to the base branch being updated
 type ErrPushOutOfDate struct {
 	StdOut string
 	StdErr string
diff --git a/modules/repository/create.go b/modules/repository/create.go
@@ -87,7 +87,11 @@ func CreateRepositoryByExample(ctx context.Context, doer, u *user_model.User, re
 			units = append(units, repo_model.RepoUnit{
 				RepoID: repo.ID,
 				Type:   tp,
-				Config: &repo_model.PullRequestsConfig{AllowMerge: true, AllowRebase: true, AllowRebaseMerge: true, AllowSquash: true, DefaultMergeStyle: repo_model.MergeStyle(setting.Repository.PullRequest.DefaultMergeStyle), AllowRebaseUpdate: true},
+				Config: &repo_model.PullRequestsConfig{
+					AllowMerge: true, AllowRebase: true, AllowRebaseMerge: true, AllowSquash: true, AllowFastForwardOnly: true,
+					DefaultMergeStyle: repo_model.MergeStyle(setting.Repository.PullRequest.DefaultMergeStyle),
+					AllowRebaseUpdate: true,
+				},
 			})
 		} else {
 			units = append(units, repo_model.RepoUnit{
diff --git a/modules/structs/repo.go b/modules/structs/repo.go
@@ -99,6 +99,7 @@ type Repository struct {
 	AllowRebase                   bool             `json:"allow_rebase"`
 	AllowRebaseMerge              bool             `json:"allow_rebase_explicit"`
 	AllowSquash                   bool             `json:"allow_squash_merge"`
+	AllowFastForwardOnly          bool             `json:"allow_fast_forward_only_merge"`
 	AllowRebaseUpdate             bool             `json:"allow_rebase_update"`
 	DefaultDeleteBranchAfterMerge bool             `json:"default_delete_branch_after_merge"`
 	DefaultMergeStyle             string           `json:"default_merge_style"`
@@ -198,6 +199,8 @@ type EditRepoOption struct {
 	AllowRebaseMerge *bool `json:"allow_rebase_explicit,omitempty"`
 	// either `true` to allow squash-merging pull requests, or `false` to prevent squash-merging.
 	AllowSquash *bool `json:"allow_squash_merge,omitempty"`
+	// either `true` to allow fast-forward-only merging pull requests, or `false` to prevent fast-forward-only merging.
+	AllowFastForwardOnly *bool `json:"allow_fast_forward_only_merge,omitempty"`
 	// either `true` to allow mark pr as merged manually, or `false` to prevent it.
 	AllowManualMerge *bool `json:"allow_manual_merge,omitempty"`
 	// either `true` to enable AutodetectManualMerge, or `false` to prevent it. Note: In some special cases, misjudgments can occur.
@@ -206,7 +209,7 @@ type EditRepoOption struct {
 	AllowRebaseUpdate *bool `json:"allow_rebase_update,omitempty"`
 	// set to `true` to delete pr branch after merge by default
 	DefaultDeleteBranchAfterMerge *bool `json:"default_delete_branch_after_merge,omitempty"`
-	// set to a merge style to be used by this repository: "merge", "rebase", "rebase-merge", or "squash".
+	// set to a merge style to be used by this repository: "merge", "rebase", "rebase-merge", "squash", or "fast-forward-only".
 	DefaultMergeStyle *string `json:"default_merge_style,omitempty"`
 	// set to `true` to allow edits from maintainers by default
 	DefaultAllowMaintainerEdit *bool `json:"default_allow_maintainer_edit,omitempty"`
diff --git a/options/locale/locale_en-US.ini b/options/locale/locale_en-US.ini
@@ -1816,6 +1816,7 @@ pulls.merge_pull_request = Create merge commit
 pulls.rebase_merge_pull_request = Rebase then fast-forward
 pulls.rebase_merge_commit_pull_request = Rebase then create merge commit
 pulls.squash_merge_pull_request = Create squash commit
+pulls.fast_forward_only_merge_pull_request = Fast-forward only
 pulls.merge_manually = Manually merged
 pulls.merge_commit_id = The merge commit ID
 pulls.require_signed_wont_sign = The branch requires signed commits but this merge will not be signed
diff --git a/routers/api/v1/repo/repo.go b/routers/api/v1/repo/repo.go
@@ -897,6 +897,7 @@ func updateRepoUnits(ctx *context.APIContext, opts api.EditRepoOption) error {
 					AllowRebase:                   true,
 					AllowRebaseMerge:              true,
 					AllowSquash:                   true,
+					AllowFastForwardOnly:          true,
 					AllowManualMerge:              true,
 					AutodetectManualMerge:         false,
 					AllowRebaseUpdate:             true,
@@ -923,6 +924,9 @@ func updateRepoUnits(ctx *context.APIContext, opts api.EditRepoOption) error {
 			if opts.AllowSquash != nil {
 				config.AllowSquash = *opts.AllowSquash
 			}
+			if opts.AllowFastForwardOnly != nil {
+				config.AllowFastForwardOnly = *opts.AllowFastForwardOnly
+			}
 			if opts.AllowManualMerge != nil {
 				config.AllowManualMerge = *opts.AllowManualMerge
 			}
diff --git a/routers/api/v1/repo/repo_test.go b/routers/api/v1/repo/repo_test.go
@@ -35,6 +35,7 @@ func TestRepoEdit(t *testing.T) {
 	allowRebase := false
 	allowRebaseMerge := false
 	allowSquashMerge := false
+	allowFastForwardOnlyMerge := false
 	archived := true
 	opts := api.EditRepoOption{
 		Name:                      &ctx.Repo.Repository.Name,
@@ -50,6 +51,7 @@ func TestRepoEdit(t *testing.T) {
 		AllowRebase:               &allowRebase,
 		AllowRebaseMerge:          &allowRebaseMerge,
 		AllowSquash:               &allowSquashMerge,
+		AllowFastForwardOnly:      &allowFastForwardOnlyMerge,
 		Archived:                  &archived,
 	}
 
diff --git a/routers/web/repo/issue.go b/routers/web/repo/issue.go
@@ -1871,6 +1871,8 @@ func ViewIssue(ctx *context.Context) {
 				mergeStyle = repo_model.MergeStyleRebaseMerge
 			} else if prConfig.AllowSquash {
 				mergeStyle = repo_model.MergeStyleSquash
+			} else if prConfig.AllowFastForwardOnly {
+				mergeStyle = repo_model.MergeStyleFastForwardOnly
 			} else if prConfig.AllowManualMerge {
 				mergeStyle = repo_model.MergeStyleManuallyMerged
 			}
diff --git a/routers/web/repo/setting/setting.go b/routers/web/repo/setting/setting.go
@@ -251,6 +251,7 @@ func UnitsPost(ctx *context.Context) {
 				AllowRebase:                   form.PullsAllowRebase,
 				AllowRebaseMerge:              form.PullsAllowRebaseMerge,
 				AllowSquash:                   form.PullsAllowSquash,
+				AllowFastForwardOnly:          form.PullsAllowFastForwardOnly,
 				AllowManualMerge:              form.PullsAllowManualMerge,
 				AutodetectManualMerge:         form.EnableAutodetectManualMerge,
 				AllowRebaseUpdate:             form.PullsAllowRebaseUpdate,
diff --git a/services/convert/repository.go b/services/convert/repository.go
@@ -93,6 +93,7 @@ func innerToRepo(ctx context.Context, repo *repo_model.Repository, permissionInR
 	allowRebase := false
 	allowRebaseMerge := false
 	allowSquash := false
+	allowFastForwardOnly := false
 	allowRebaseUpdate := false
 	defaultDeleteBranchAfterMerge := false
 	defaultMergeStyle := repo_model.MergeStyleMerge
@@ -105,6 +106,7 @@ func innerToRepo(ctx context.Context, repo *repo_model.Repository, permissionInR
 		allowRebase = config.AllowRebase
 		allowRebaseMerge = config.AllowRebaseMerge
 		allowSquash = config.AllowSquash
+		allowFastForwardOnly = config.AllowFastForwardOnly
 		allowRebaseUpdate = config.AllowRebaseUpdate
 		defaultDeleteBranchAfterMerge = config.DefaultDeleteBranchAfterMerge
 		defaultMergeStyle = config.GetDefaultMergeStyle()
@@ -220,6 +222,7 @@ func innerToRepo(ctx context.Context, repo *repo_model.Repository, permissionInR
 		AllowRebase:                   allowRebase,
 		AllowRebaseMerge:              allowRebaseMerge,
 		AllowSquash:                   allowSquash,
+		AllowFastForwardOnly:          allowFastForwardOnly,
 		AllowRebaseUpdate:             allowRebaseUpdate,
 		DefaultDeleteBranchAfterMerge: defaultDeleteBranchAfterMerge,
 		DefaultMergeStyle:             string(defaultMergeStyle),
diff --git a/services/forms/repo_form.go b/services/forms/repo_form.go
@@ -170,6 +170,7 @@ type RepoUnitSettingForm struct {
 	PullsAllowRebase                      bool
 	PullsAllowRebaseMerge                 bool
 	PullsAllowSquash                      bool
+	PullsAllowFastForwardOnly             bool
 	PullsAllowManualMerge                 bool
 	PullsDefaultMergeStyle                string
 	EnableAutodetectManualMerge           bool
@@ -609,8 +610,8 @@ func (f *InitializeLabelsForm) Validate(req *http.Request, errs binding.Errors)
 // swagger:model MergePullRequestOption
 type MergePullRequestForm struct {
 	// required: true
-	// enum: merge,rebase,rebase-merge,squash,manually-merged
-	Do                     string `binding:"Required;In(merge,rebase,rebase-merge,squash,manually-merged)"`
+	// enum: merge,rebase,rebase-merge,squash,fast-forward-only,manually-merged
+	Do                     string `binding:"Required;In(merge,rebase,rebase-merge,squash,fast-forward-only,manually-merged)"`
 	MergeTitleField        string
 	MergeMessageField      string
 	MergeCommitID          string // only used for manually-merged
diff --git a/services/pull/merge.go b/services/pull/merge.go
@@ -273,6 +273,10 @@ func doMergeAndPush(ctx context.Context, pr *issues_model.PullRequest, doer *use
 		if err := doMergeStyleSquash(mergeCtx, message); err != nil {
 			return "", err
 		}
+	case repo_model.MergeStyleFastForwardOnly:
+		if err := doMergeStyleFastForwardOnly(mergeCtx); err != nil {
+			return "", err
+		}
 	default:
 		return "", models.ErrInvalidMergeStyle{ID: pr.BaseRepo.ID, Style: mergeStyle}
 	}
@@ -383,6 +387,13 @@ func runMergeCommand(ctx *mergeContext, mergeStyle repo_model.MergeStyle, cmd *g
 				StdErr: ctx.errbuf.String(),
 				Err:    err,
 			}
+		} else if mergeStyle == repo_model.MergeStyleFastForwardOnly && strings.Contains(ctx.errbuf.String(), "Not possible to fast-forward, aborting") {
+			log.Debug("MergeDivergingFastForwardOnly %-v: %v\n%s\n%s", ctx.pr, err, ctx.outbuf.String(), ctx.errbuf.String())
+			return models.ErrMergeDivergingFastForwardOnly{
+				StdOut: ctx.outbuf.String(),
+				StdErr: ctx.errbuf.String(),
+				Err:    err,
+			}
 		}
 		log.Error("git merge %-v: %v\n%s\n%s", ctx.pr, err, ctx.outbuf.String(), ctx.errbuf.String())
 		return fmt.Errorf("git merge %v: %w\n%s\n%s", ctx.pr, err, ctx.outbuf.String(), ctx.errbuf.String())
diff --git a/services/pull/merge_ff_only.go b/services/pull/merge_ff_only.go
@@ -0,0 +1,21 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package pull
+
+import (
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/log"
+)
+
+// doMergeStyleFastForwardOnly merges the tracking into the current HEAD - which is assumed to be staging branch (equal to the pr.BaseBranch)
+func doMergeStyleFastForwardOnly(ctx *mergeContext) error {
+	cmd := git.NewCommand(ctx, "merge", "--ff-only").AddDynamicArguments(trackingBranch)
+	if err := runMergeCommand(ctx, repo_model.MergeStyleFastForwardOnly, cmd); err != nil {
+		log.Error("%-v Unable to merge tracking into base: %v", ctx.pr, err)
+		return err
+	}
+
+	return nil
+}
diff --git a/services/pull/merge_merge.go b/services/pull/merge_merge.go
@@ -9,7 +9,7 @@ import (
 	"code.gitea.io/gitea/modules/log"
 )
 
-// doMergeStyleMerge merges the tracking into the current HEAD - which is assumed to tbe staging branch (equal to the pr.BaseBranch)
+// doMergeStyleMerge merges the tracking branch into the current HEAD - which is assumed to be the staging branch (equal to the pr.BaseBranch)
 func doMergeStyleMerge(ctx *mergeContext, message string) error {
 	cmd := git.NewCommand(ctx, "merge", "--no-ff", "--no-commit").AddDynamicArguments(trackingBranch)
 	if err := runMergeCommand(ctx, repo_model.MergeStyleMerge, cmd); err != nil {
diff --git a/templates/repo/issue/view_content/pull.tmpl b/templates/repo/issue/view_content/pull.tmpl
@@ -197,7 +197,7 @@
 				{{if .AllowMerge}} {{/* user is allowed to merge */}}
 					{{$prUnit := .Repository.MustGetUnit $.Context $.UnitTypePullRequests}}
 					{{$approvers := (.Issue.PullRequest.GetApprovers ctx)}}
-					{{if or $prUnit.PullRequestsConfig.AllowMerge $prUnit.PullRequestsConfig.AllowRebase $prUnit.PullRequestsConfig.AllowRebaseMerge $prUnit.PullRequestsConfig.AllowSquash}}
+					{{if or $prUnit.PullRequestsConfig.AllowMerge $prUnit.PullRequestsConfig.AllowRebase $prUnit.PullRequestsConfig.AllowRebaseMerge $prUnit.PullRequestsConfig.AllowSquash $prUnit.PullRequestsConfig.AllowFastForwardOnly}}
 						{{$hasPendingPullRequestMergeTip := ""}}
 						{{if .HasPendingPullRequestMerge}}
 							{{$createdPRMergeStr := TimeSinceUnix .PendingPullRequestMerge.CreatedUnix ctx.Locale}}
@@ -268,6 +268,13 @@
 									'mergeMessageFieldText': {{.GetCommitMessages}} + defaultSquashMergeMessage,
 									'hideAutoMerge': generalHideAutoMerge,
 								},
+								{
+									'name': 'fast-forward-only',
+									'allowed': {{and $prUnit.PullRequestsConfig.AllowFastForwardOnly (eq .Issue.PullRequest.CommitsBehind 0)}},
+									'textDoMerge': {{ctx.Locale.Tr "repo.pulls.fast_forward_only_merge_pull_request"}},
+									'hideMergeMessageTexts': true,
+									'hideAutoMerge': generalHideAutoMerge,
+								},
 								{
 									'name': 'manually-merged',
 									'allowed': {{$prUnit.PullRequestsConfig.AllowManualMerge}},
diff --git a/templates/repo/issue/view_content/pull_merge_instruction.tmpl b/templates/repo/issue/view_content/pull_merge_instruction.tmpl
@@ -35,6 +35,10 @@
 			<div>git checkout {{.PullRequest.BaseBranch}}</div>
 			<div>git merge --squash {{$localBranch}}</div>
 		</div>
+		<div class="gt-hidden" data-pull-merge-style="fast-forward-only">
+			<div>git checkout {{.PullRequest.BaseBranch}}</div>
+			<div>git merge --ff-only {{$localBranch}}</div>
+		</div>
 		<div class="gt-hidden" data-pull-merge-style="manually-merged">
 			<div>git checkout {{.PullRequest.BaseBranch}}</div>
 			<div>git merge {{$localBranch}}</div>
diff --git a/templates/repo/settings/units/pulls.tmpl b/templates/repo/settings/units/pulls.tmpl
diff --git a/templates/swagger/v1_json.tmpl b/templates/swagger/v1_json.tmpl
diff --git a/tests/integration/api_repo_edit_test.go b/tests/integration/api_repo_edit_test.go
diff --git a/tests/integration/pull_merge_test.go b/tests/integration/pull_merge_test.go

Original file line number	Diff line number	Diff line change
`@@ -96,7 +96,7 @@ func (err ErrBranchNotExist) Unwrap() error {`
`96`	`96`	`return util.ErrNotExist`
`97`	`97`	`}`
`98`	`98`
`99`		`-// ErrPushOutOfDate represents an error if merging fails due to unrelated histories`
	`99`	`+// ErrPushOutOfDate represents an error if merging fails due to the base branch being updated`
`100`	`100`	`type ErrPushOutOfDate struct {`
`101`	`101`	`StdOut string`
`102`	`102`	`StdErr string`