feat(automerge): implement GitHub --auto-merge-method flag for apply command

runatlantis.io/docs/automerging.md

@@ -29,6 +29,23 @@ Automerging can be enabled either by:
 If automerge is enabled, you can disable it for a single `atlantis apply`
 command with the `--auto-merge-disabled` option.
 
+## How to set the merge method for automerge
+
+If automerge is enabled, you can use the `--auto-merge-method` option
+for the `atlantis apply` command to specify which merge method use.
+
+```shell
+atlantis apply --auto-merge-method <method>
+```
+
+The `method` must be one of:
+
+- merge
+- rebase
+- squash
+
+This is currently only implemented for the GitHub VCS.
+
 ## Requirements
 
 ### All Plans Must Succeed

runatlantis.io/docs/using-atlantis.md

@@ -149,6 +149,7 @@ atlantis apply -w staging
 * `-p project` Apply the plan for this project. Refers to the name of the project configured in the repo's [`atlantis.yaml` file](repo-level-atlantis-yaml.md). Cannot be used at same time as `-d` or `-w`.
 * `-w workspace` Apply the plan for this [Terraform workspace](https://developer.hashicorp.com/terraform/language/state/workspaces). Ignore this if Terraform workspaces are unused.
 * `--auto-merge-disabled` Disable [automerge](automerging.md) for this apply command.
+* `--auto-merge-method method` Specify which [merge method](automerging.md#how-to-set-merge-method-for-automerge) use for the apply command if [automerge](automerging.md) is enabled. Implemented only for GitHub.
 * `--verbose` Append Atlantis log to comment.
 
 ### Additional Terraform flags

server/core/config/valid/global_cfg.go

@@ -104,6 +104,7 @@ type MergedProjectCfg struct {
 	Name                      string
 	AutoplanEnabled           bool
 	AutoMergeDisabled         bool
+	AutoMergeMethod           string
 	TerraformVersion          *version.Version
 	RepoCfgVersion            int
 	PolicySets                PolicySets

server/events/apply_command_runner.go

@@ -181,7 +181,7 @@ func (a *ApplyCommandRunner) Run(ctx *command.Context, cmd *CommentCommand) {
 	a.updateCommitStatus(ctx, pullStatus)
 
 	if a.autoMerger.automergeEnabled(projectCmds) && !cmd.AutoMergeDisabled {
-		a.autoMerger.automerge(ctx, pullStatus, a.autoMerger.deleteSourceBranchOnMergeEnabled(projectCmds))
+		a.autoMerger.automerge(ctx, pullStatus, a.autoMerger.deleteSourceBranchOnMergeEnabled(projectCmds), cmd.AutoMergeMethod)
 	}
 }
 

server/events/automerger.go

@@ -13,7 +13,7 @@ type AutoMerger struct {
 	GlobalAutomerge bool
 }
 
-func (c *AutoMerger) automerge(ctx *command.Context, pullStatus models.PullStatus, deleteSourceBranchOnMerge bool) {
+func (c *AutoMerger) automerge(ctx *command.Context, pullStatus models.PullStatus, deleteSourceBranchOnMerge bool, mergeMethod string) {
 	// We only automerge if all projects have been successfully applied.
 	for _, p := range pullStatus.Projects {
 		if p.Status != models.AppliedPlanStatus {
@@ -32,6 +32,7 @@ func (c *AutoMerger) automerge(ctx *command.Context, pullStatus models.PullStatu
 	ctx.Log.Info("automerging pull request")
 	var pullOptions models.PullRequestOptions
 	pullOptions.DeleteSourceBranchOnMerge = deleteSourceBranchOnMerge
+	pullOptions.MergeMethod = mergeMethod
 	err := c.VCSClient.MergePull(ctx.Log, ctx.Pull, pullOptions)
 
 	if err != nil {

server/events/comment_parser.go

@@ -41,6 +41,8 @@ const (
 	policySetFlagShort           = ""
 	autoMergeDisabledFlagLong    = "auto-merge-disabled"
 	autoMergeDisabledFlagShort   = ""
+	autoMergeMethodFlagLong      = "auto-merge-method"
+	autoMergeMethodFlagShort     = ""
 	verboseFlagLong              = "verbose"
 	verboseFlagShort             = ""
 	clearPolicyApprovalFlagLong  = "clear-policy-approval"
@@ -70,7 +72,7 @@ type CommentBuilder interface {
 	// BuildPlanComment builds a plan comment for the specified args.
 	BuildPlanComment(repoRelDir string, workspace string, project string, commentArgs []string) string
 	// BuildApplyComment builds an apply comment for the specified args.
-	BuildApplyComment(repoRelDir string, workspace string, project string, autoMergeDisabled bool) string
+	BuildApplyComment(repoRelDir string, workspace string, project string, autoMergeDisabled bool, autoMergeMethod string) string
 	// BuildApprovePoliciesComment builds an approve_policies comment for the specified args.
 	BuildApprovePoliciesComment(repoRelDir string, workspace string, project string) string
 }
@@ -226,7 +228,9 @@ func (e *CommentParser) Parse(rawComment string, vcsHost models.VCSHostType) Com
 	var project string
 	var policySet string
 	var clearPolicyApproval bool
-	var verbose, autoMergeDisabled bool
+	var verbose bool
+	var autoMergeDisabled bool
+	var autoMergeMethod string
 	var flagSet *pflag.FlagSet
 	var name command.Name
 
@@ -248,6 +252,7 @@ func (e *CommentParser) Parse(rawComment string, vcsHost models.VCSHostType) Com
 		flagSet.StringVarP(&dir, dirFlagLong, dirFlagShort, "", "Apply the plan for this directory, relative to root of repo, ex. 'child/dir'.")
 		flagSet.StringVarP(&project, projectFlagLong, projectFlagShort, "", "Apply the plan for this project. Refers to the name of the project configured in a repo config file. Cannot be used at same time as workspace or dir flags.")
 		flagSet.BoolVarP(&autoMergeDisabled, autoMergeDisabledFlagLong, autoMergeDisabledFlagShort, false, "Disable automerge after apply.")
+		flagSet.StringVarP(&autoMergeMethod, autoMergeMethodFlagLong, autoMergeMethodFlagShort, "", "Specifies the merge method for the VCS if automerge is enabled. (Currently only implemented for GitHub)")
 		flagSet.BoolVarP(&verbose, verboseFlagLong, verboseFlagShort, false, "Append Atlantis log to comment.")
 	case command.ApprovePolicies.String():
 		name = command.ApprovePolicies
@@ -317,8 +322,20 @@ func (e *CommentParser) Parse(rawComment string, vcsHost models.VCSHostType) Com
 		return CommentParseResult{CommentResponse: e.errMarkdown(err, cmd, flagSet)}
 	}
 
+	if autoMergeMethod != "" {
+		if autoMergeDisabled {
+			err := fmt.Sprintf("cannot use --%s at the same time as --%s", autoMergeMethodFlagLong, autoMergeDisabledFlagLong)
+			return CommentParseResult{CommentResponse: e.errMarkdown(err, cmd, flagSet)}
+		}
+
+		if vcsHost != models.Github {
+			err := fmt.Sprintf("--%s is not currently implemented for %s", autoMergeMethodFlagLong, vcsHost.String())
+			return CommentParseResult{CommentResponse: e.errMarkdown(err, cmd, flagSet)}
+		}
+	}
+
 	return CommentParseResult{
-		Command: NewCommentCommand(dir, extraArgs, name, subName, verbose, autoMergeDisabled, workspace, project, policySet, clearPolicyApproval),
+		Command: NewCommentCommand(dir, extraArgs, name, subName, verbose, autoMergeDisabled, autoMergeMethod, workspace, project, policySet, clearPolicyApproval),
 	}
 }
 
@@ -387,7 +404,7 @@ func (e *CommentParser) parseArgs(name command.Name, args []string, flagSet *pfl
 
 // BuildPlanComment builds a plan comment for the specified args.
 func (e *CommentParser) BuildPlanComment(repoRelDir string, workspace string, project string, commentArgs []string) string {
-	flags := e.buildFlags(repoRelDir, workspace, project, false)
+	flags := e.buildFlags(repoRelDir, workspace, project, false, "")
 	commentFlags := ""
 	if len(commentArgs) > 0 {
 		var flagsWithoutQuotes []string
@@ -402,18 +419,18 @@ func (e *CommentParser) BuildPlanComment(repoRelDir string, workspace string, pr
 }
 
 // BuildApplyComment builds an apply comment for the specified args.
-func (e *CommentParser) BuildApplyComment(repoRelDir string, workspace string, project string, autoMergeDisabled bool) string {
-	flags := e.buildFlags(repoRelDir, workspace, project, autoMergeDisabled)
+func (e *CommentParser) BuildApplyComment(repoRelDir string, workspace string, project string, autoMergeDisabled bool, autoMergeMethod string) string {
+	flags := e.buildFlags(repoRelDir, workspace, project, autoMergeDisabled, autoMergeMethod)
 	return fmt.Sprintf("%s %s%s", e.ExecutableName, command.Apply.String(), flags)
 }
 
 // BuildApprovePoliciesComment builds an apply comment for the specified args.
 func (e *CommentParser) BuildApprovePoliciesComment(repoRelDir string, workspace string, project string) string {
-	flags := e.buildFlags(repoRelDir, workspace, project, false)
+	flags := e.buildFlags(repoRelDir, workspace, project, false, "")
 	return fmt.Sprintf("%s %s%s", e.ExecutableName, command.ApprovePolicies.String(), flags)
 }
 
-func (e *CommentParser) buildFlags(repoRelDir string, workspace string, project string, autoMergeDisabled bool) string {
+func (e *CommentParser) buildFlags(repoRelDir string, workspace string, project string, autoMergeDisabled bool, autoMergeMethod string) string {
 	// Add quotes if dir has spaces.
 	if strings.Contains(repoRelDir, " ") {
 		repoRelDir = fmt.Sprintf("%q", repoRelDir)
@@ -441,6 +458,9 @@ func (e *CommentParser) buildFlags(repoRelDir string, workspace string, project
 	if autoMergeDisabled {
 		flags = fmt.Sprintf("%s --%s", flags, autoMergeDisabledFlagLong)
 	}
+	if autoMergeMethod != "" {
+		flags = fmt.Sprintf("%s --%s %s", flags, autoMergeMethodFlagLong, autoMergeMethod)
+	}
 	return flags
 }
 

server/events/comment_parser_test.go

@@ -729,6 +729,7 @@ func TestBuildPlanApplyVersionComment(t *testing.T) {
 		workspace         string
 		project           string
 		autoMergeDisabled bool
+		autoMergeMethod   string
 		commentArgs       []string
 		expPlanFlags      string
 		expApplyFlags     string
@@ -824,6 +825,16 @@ func TestBuildPlanApplyVersionComment(t *testing.T) {
 			expApplyFlags:     "-d dir -w workspace --auto-merge-disabled",
 			expVersionFlags:   "-d dir -w workspace",
 		},
+		{
+			repoRelDir:      "dir",
+			workspace:       "workspace",
+			project:         "",
+			autoMergeMethod: "squash",
+			commentArgs:     []string{`"arg1"`, `"arg2"`, `arg3`},
+			expPlanFlags:    "-d dir -w workspace -- arg1 arg2 arg3",
+			expApplyFlags:   "-d dir -w workspace --auto-merge-method squash",
+			expVersionFlags: "-d dir -w workspace",
+		},
 	}
 
 	for _, c := range cases {
@@ -834,7 +845,7 @@ func TestBuildPlanApplyVersionComment(t *testing.T) {
 					actComment := commentParser.BuildPlanComment(c.repoRelDir, c.workspace, c.project, c.commentArgs)
 					Equals(t, fmt.Sprintf("atlantis plan %s", c.expPlanFlags), actComment)
 				case command.Apply:
-					actComment := commentParser.BuildApplyComment(c.repoRelDir, c.workspace, c.project, c.autoMergeDisabled)
+					actComment := commentParser.BuildApplyComment(c.repoRelDir, c.workspace, c.project, c.autoMergeDisabled, c.autoMergeMethod)
 					Equals(t, fmt.Sprintf("atlantis apply %s", c.expApplyFlags), actComment)
 				}
 			}
@@ -1020,14 +1031,18 @@ var PlanUsage = `Usage of plan:
 `
 
 var ApplyUsage = `Usage of apply:
-      --auto-merge-disabled   Disable automerge after apply.
-  -d, --dir string            Apply the plan for this directory, relative to root of
-                              repo, ex. 'child/dir'.
-  -p, --project string        Apply the plan for this project. Refers to the name of
-                              the project configured in a repo config file. Cannot
-                              be used at same time as workspace or dir flags.
-      --verbose               Append Atlantis log to comment.
-  -w, --workspace string      Apply the plan for this Terraform workspace.
+      --auto-merge-disabled        Disable automerge after apply.
+      --auto-merge-method string   Specifies the merge method for the VCS if
+                                   automerge is enabled. (Currently only implemented
+                                   for GitHub)
+  -d, --dir string                 Apply the plan for this directory, relative to
+                                   root of repo, ex. 'child/dir'.
+  -p, --project string             Apply the plan for this project. Refers to the
+                                   name of the project configured in a repo config
+                                   file. Cannot be used at same time as workspace or
+                                   dir flags.
+      --verbose                    Append Atlantis log to comment.
+  -w, --workspace string           Apply the plan for this Terraform workspace.
 `
 
 var ApprovePolicyUsage = `Usage of approve_policies:

server/events/event_parser.go

@@ -128,6 +128,8 @@ type CommentCommand struct {
 	SubName string
 	// AutoMergeDisabled is true if the command should not automerge after apply.
 	AutoMergeDisabled bool
+	// AutoMergeMethod specified the merge method for the VCS if automerge enabled.
+	AutoMergeMethod string
 	// Verbose is true if the command should output verbosely.
 	Verbose bool
 	// Workspace is the name of the Terraform workspace to run the command in.
@@ -177,11 +179,11 @@ func (c CommentCommand) IsAutoplan() bool {
 
 // String returns a string representation of the command.
 func (c CommentCommand) String() string {
-	return fmt.Sprintf("command=%q verbose=%t dir=%q workspace=%q project=%q policyset=%q, clear-policy-approval=%t, flags=%q", c.Name.String(), c.Verbose, c.RepoRelDir, c.Workspace, c.ProjectName, c.PolicySet, c.ClearPolicyApproval, strings.Join(c.Flags, ","))
+	return fmt.Sprintf("command=%q, verbose=%t, dir=%q, workspace=%q, project=%q, policyset=%q, auto-merge-disabled=%t, auto-merge-method=%s, clear-policy-approval=%t, flags=%q", c.Name.String(), c.Verbose, c.RepoRelDir, c.Workspace, c.ProjectName, c.PolicySet, c.AutoMergeDisabled, c.AutoMergeMethod, c.ClearPolicyApproval, strings.Join(c.Flags, ","))
 }
 
 // NewCommentCommand constructs a CommentCommand, setting all missing fields to defaults.
-func NewCommentCommand(repoRelDir string, flags []string, name command.Name, subName string, verbose, autoMergeDisabled bool, workspace string, project string, policySet string, clearPolicyApproval bool) *CommentCommand {
+func NewCommentCommand(repoRelDir string, flags []string, name command.Name, subName string, verbose, autoMergeDisabled bool, autoMergeMethod string, workspace string, project string, policySet string, clearPolicyApproval bool) *CommentCommand {
 	// If repoRelDir was empty we want to keep it that way to indicate that it
 	// wasn't specified in the comment.
 	if repoRelDir != "" {
@@ -198,6 +200,7 @@ func NewCommentCommand(repoRelDir string, flags []string, name command.Name, sub
 		Verbose:             verbose,
 		Workspace:           workspace,
 		AutoMergeDisabled:   autoMergeDisabled,
+		AutoMergeMethod:     autoMergeMethod,
 		ProjectName:         project,
 		PolicySet:           policySet,
 		ClearPolicyApproval: clearPolicyApproval,

server/events/event_parser_test.go

@@ -750,14 +750,14 @@ func TestNewCommand_CleansDir(t *testing.T) {
 
 	for _, c := range cases {
 		t.Run(c.RepoRelDir, func(t *testing.T) {
-			cmd := events.NewCommentCommand(c.RepoRelDir, nil, command.Plan, "", false, false, "workspace", "", "", false)
+			cmd := events.NewCommentCommand(c.RepoRelDir, nil, command.Plan, "", false, false, "", "workspace", "", "", false)
 			Equals(t, c.ExpDir, cmd.RepoRelDir)
 		})
 	}
 }
 
 func TestNewCommand_EmptyDirWorkspaceProject(t *testing.T) {
-	cmd := events.NewCommentCommand("", nil, command.Plan, "", false, false, "", "", "", false)
+	cmd := events.NewCommentCommand("", nil, command.Plan, "", false, false, "", "", "", "", false)
 	Equals(t, events.CommentCommand{
 		RepoRelDir:  "",
 		Flags:       nil,
@@ -769,7 +769,7 @@ func TestNewCommand_EmptyDirWorkspaceProject(t *testing.T) {
 }
 
 func TestNewCommand_AllFieldsSet(t *testing.T) {
-	cmd := events.NewCommentCommand("dir", []string{"a", "b"}, command.Plan, "", true, false, "workspace", "project", "policyset", false)
+	cmd := events.NewCommentCommand("dir", []string{"a", "b"}, command.Plan, "", true, false, "", "workspace", "project", "policyset", false)
 	Equals(t, events.CommentCommand{
 		Workspace:   "workspace",
 		RepoRelDir:  "dir",
@@ -816,7 +816,7 @@ func TestCommentCommand_IsAutoplan(t *testing.T) {
 }
 
 func TestCommentCommand_String(t *testing.T) {
-	exp := `command="plan" verbose=true dir="mydir" workspace="myworkspace" project="myproject" policyset="", clear-policy-approval=false, flags="flag1,flag2"`
+	exp := `command="plan", verbose=true, dir="mydir", workspace="myworkspace", project="myproject", policyset="", auto-merge-disabled=false, auto-merge-method=, clear-policy-approval=false, flags="flag1,flag2"`
 	Equals(t, exp, (events.CommentCommand{
 		RepoRelDir:  "mydir",
 		Flags:       []string{"flag1", "flag2"},