Add a flag to only allow teams as owners (#127)

README.md

@@ -129,6 +129,7 @@ Use the following environment variables to configure the application:
 | <tt>OWNER_CHECKER_REPOSITORY</tt>  <b>*</b>    | | The owner and repository name separated by slash. For example, gh-codeowners/codeowners-samples. Used to check if GitHub owner is in the given organization.                                                                                                                                                                                                                                                                                                    |
 | <tt>OWNER_CHECKER_IGNORED_OWNERS</tt>          | `@ghost`| The comma-separated list of owners that should not be validated. Example: `"@owner1,@owner2,@org/team1,example@email.com"`.                                                                                                                                                                                                                                                                                                                                     |
 | <tt>OWNER_CHECKER_ALLOW_UNOWNED_PATTERNS</tt> | `true` | 	Specifies whether CODEOWNERS may have unowned files. For example: <br> <br>  `/infra/oncall-rotator/                    @sre-team` <br>  `/infra/oncall-rotator/oncall-config.yml` <br> <br>  The `/infra/oncall-rotator/oncall-config.yml` file is not owned by anyone.                                                                                                                                                                                           |
+| <tt>OWNER_CHEKER_OWNERS_MUST_BE_TEAMS</tt>     | `false` | Specifies whether only teams are allowed as owners of files |
 | <tt>NOT_OWNED_CHECKER_SKIP_PATTERNS</tt>       | - | The comma-separated list of patterns that should be ignored by `not-owned-checker`. For example, you can specify `*` and as a result, the `*` pattern from the **CODEOWNERS** file will be ignored and files owned by this pattern will be reported as unowned unless a later specific pattern will match that path. It's useful because often we have default owners entry at the begging of the CODOEWNERS file, e.g. `*       @global-owner1 @global-owner2` |
 
  <b>*</b> - Required

internal/check/valid_owner.go

@@ -26,6 +26,8 @@ type ValidOwnerConfig struct {
 	//
 	//  The `/infra/oncall-rotator/oncall-config.yml` this file is not owned by anyone.
 	AllowUnownedPatterns bool `envconfig:"default=true"`
+	// OwnersMustBeTeams specifies whether owners must be teams in the same org as the repository
+	OwnersMustBeTeams bool `envconfig:"default=false"`
 }
 
 // ValidOwner validates each owner
@@ -37,6 +39,7 @@ type ValidOwner struct {
 	orgRepoName          string
 	ignOwners            map[string]struct{}
 	allowUnownedPatterns bool
+	ownersMustBeTeams    bool
 }
 
 // NewValidOwner returns new instance of the ValidOwner
@@ -57,6 +60,7 @@ func NewValidOwner(cfg ValidOwnerConfig, ghClient *github.Client) (*ValidOwner,
 		orgRepoName:          split[1],
 		ignOwners:            ignOwners,
 		allowUnownedPatterns: cfg.AllowUnownedPatterns,
+		ownersMustBeTeams:    cfg.OwnersMustBeTeams,
 	}, nil
 }
 
@@ -133,10 +137,10 @@ func (v *ValidOwner) isIgnoredOwner(name string) bool {
 
 func (v *ValidOwner) selectValidateFn(name string) func(context.Context, string) *validateError {
 	switch {
+	case v.ownersMustBeTeams || isGitHubTeam(name):
+		return v.validateTeam
 	case isGitHubUser(name):
 		return v.validateGitHubUser
-	case isGitHubTeam(name):
-		return v.validateTeam
 	case isEmailAddress(name):
 		// TODO(mszostok): try to check if e-mail really exists
 		return func(context.Context, string) *validateError { return nil }
@@ -186,6 +190,10 @@ func (v *ValidOwner) validateTeam(ctx context.Context, name string) *validateErr
 		}
 	}
 
+	if !isGitHubTeam(name) {
+		return newValidateError("%s is not a team", name)
+	}
+
 	// called after validation it's safe to work on `parts` slice
 	parts := strings.SplitN(name, "/", 2)
 	org := parts[0]