Add DefaultMergeStyle option to repository (#14789)

Fixes #12293

routers/api/v1/repo/repo.go

@@ -731,6 +731,7 @@ func updateRepoUnits(ctx *context.APIContext, opts api.EditRepoOption) error {
 					AllowSquash:               true,
 					AllowManualMerge:          true,
 					AutodetectManualMerge:     false,
+					DefaultMergeStyle:         models.MergeStyleMerge,
 				}
 			} else {
 				config = unit.PullRequestsConfig()
@@ -757,6 +758,9 @@ func updateRepoUnits(ctx *context.APIContext, opts api.EditRepoOption) error {
 			if opts.AutodetectManualMerge != nil {
 				config.AutodetectManualMerge = *opts.AutodetectManualMerge
 			}
+			if opts.DefaultMergeStyle != nil {
+				config.DefaultMergeStyle = models.MergeStyle(*opts.DefaultMergeStyle)
+			}
 
 			units = append(units, models.RepoUnit{
 				RepoID: repo.ID,

routers/repo/issue.go

@@ -1484,7 +1484,10 @@ func ViewIssue(ctx *context.Context) {
 		// Check correct values and select default
 		if ms, ok := ctx.Data["MergeStyle"].(models.MergeStyle); !ok ||
 			!prConfig.IsMergeStyleAllowed(ms) {
-			if prConfig.AllowMerge {
+			defaultMergeStyle := prConfig.GetDefaultMergeStyle()
+			if prConfig.IsMergeStyleAllowed(defaultMergeStyle) && !ok {
+				ctx.Data["MergeStyle"] = defaultMergeStyle
+			} else if prConfig.AllowMerge {
 				ctx.Data["MergeStyle"] = models.MergeStyleMerge
 			} else if prConfig.AllowRebase {
 				ctx.Data["MergeStyle"] = models.MergeStyleRebase

routers/repo/setting.go

@@ -322,6 +322,7 @@ func SettingsPost(ctx *context.Context) {
 					AllowSquash:               form.PullsAllowSquash,
 					AllowManualMerge:          form.PullsAllowManualMerge,
 					AutodetectManualMerge:     form.EnableAutodetectManualMerge,
+					DefaultMergeStyle:         models.MergeStyle(form.PullsDefaultMergeStyle),
 				},
 			})
 		} else if !models.UnitTypePullRequests.UnitGlobalDisabled() {