ci: Add codeowners validator

ci/codeowners-validator/default.nix

···
+{
+  buildGoModule,
+  fetchFromGitHub,
+  fetchpatch,
+}:
+buildGoModule {
+  name = "codeowners-validator";
+  src = fetchFromGitHub {
+    owner = "mszostok";
+    repo = "codeowners-validator";
+    rev = "f3651e3810802a37bd965e6a9a7210728179d076";
+    hash = "sha256-5aSmmRTsOuPcVLWfDF6EBz+6+/Qpbj66udAmi1CLmWQ=";
+  };
+  patches = [
+    # https://github.com/mszostok/codeowners-validator/pull/222
+    (fetchpatch {
+      name = "user-write-access-check";
+      url = "https://github.com/mszostok/codeowners-validator/compare/f3651e3810802a37bd965e6a9a7210728179d076...840eeb88b4da92bda3e13c838f67f6540b9e8529.patch";
+      hash = "sha256-t3Dtt8SP9nbO3gBrM0nRE7+G6N/ZIaczDyVHYAG/6mU=";
+    })
+    # Undoes part of the above PR: We don't want to require write access
+    # to the repository, that's only needed for GitHub's native CODEOWNERS.
+    # Furthermore, it removes an unneccessary check from the code
+    # that breaks tokens generated for GitHub Apps.
+    ./permissions.patch
+    # Allows setting a custom CODEOWNERS path using the OWNERS_FILE env var
+    ./owners-file-name.patch
+  ];
+  postPatch = "rm -r docs/investigation";
+  vendorHash = "sha256-R+pW3xcfpkTRqfS2ETVOwG8PZr0iH5ewroiF7u8hcYI=";
+}

ci/codeowners-validator/owners-file-name.patch

···
+diff --git a/pkg/codeowners/owners.go b/pkg/codeowners/owners.go
+index 6910bd2..e0c95e9 100644
+--- a/pkg/codeowners/owners.go
++++ b/pkg/codeowners/owners.go
+@@ -39,6 +39,10 @@ func NewFromPath(repoPath string) ([]Entry, error) {
+ // openCodeownersFile finds a CODEOWNERS file and returns content.
+ // see: https://help.github.com/articles/about-code-owners/#codeowners-file-location
+ func openCodeownersFile(dir string) (io.Reader, error) {
++	if file, ok := os.LookupEnv("OWNERS_FILE"); ok {
++		return fs.Open(file)
++	}
++
+ 	var detectedFiles []string
+ 	for _, p := range []string{".", "docs", ".github"} {
+ 		pth := path.Join(dir, p)

ci/codeowners-validator/permissions.patch

···
+diff --git a/internal/check/valid_owner.go b/internal/check/valid_owner.go
+index a264bcc..610eda8 100644
+--- a/internal/check/valid_owner.go
++++ b/internal/check/valid_owner.go
+@@ -16,7 +16,6 @@ import (
+ const scopeHeader = "X-OAuth-Scopes"
+ 
+ var reqScopes = map[github.Scope]struct{}{
+-	github.ScopeReadOrg: {},
+ }
+ 
+ type ValidOwnerConfig struct {
+@@ -223,10 +222,7 @@ func (v *ValidOwner) validateTeam(ctx context.Context, name string) *validateErr
+ 	for _, t := range v.repoTeams {
+ 		// GitHub normalizes name before comparison
+ 		if strings.EqualFold(t.GetSlug(), team) {
+-			if t.Permissions["push"] {
+-				return nil
+-			}
+-			return newValidateError("Team %q cannot review PRs on %q as neither it nor any parent team has write permissions.", team, v.orgRepoName)
++			return nil
+ 		}
+ 	}
+ 
+@@ -245,10 +241,7 @@ func (v *ValidOwner) validateGitHubUser(ctx context.Context, name string) *valid
+ 	for _, u := range v.repoUsers {
+ 		// GitHub normalizes name before comparison
+ 		if strings.EqualFold(u.GetLogin(), userName) {
+-			if u.Permissions["push"] {
+-				return nil
+-			}
+-			return newValidateError("User %q cannot review PRs on %q as they don't have write permissions.", userName, v.orgRepoName)
++			return nil
+ 		}
+ 	}
+ 

ci/default.nix

···
 {
   inherit pkgs;
   requestReviews = pkgs.callPackage ./request-reviews { };
+  codeownersValidator = pkgs.callPackage ./codeowners-validator { };
 }