Generate stringer files automatically (#841)

Added `stringer` annotations to `git.go` for `ErrorClass` and
`ErrorCode`. Added `generate` rule for `Makefile` to generate
string representations for these types (first building cgo files
in `_obj` dir to get C constants). Finally, updated `ci` actions
workflow to check that generated files are up to date.

Fixes: #543

1 files changed, 2 insertions, 0 deletions

diff --git a/git.go b/git.go
index 383c492..b7c8b3c 100644
--- a/git.go
+++ b/git.go
@@ -14,6 +14,7 @@ import (
 	"unsafe"
 )
 
+//go:generate stringer -type ErrorClass -trimprefix ErrorClass -tags static
 type ErrorClass int
 
 const (
@@ -48,6 +49,7 @@ const (
 	ErrorClassPatch      ErrorClass = C.GIT_ERROR_PATCH
 )
 
+//go:generate stringer -type ErrorCode -trimprefix ErrorCode -tags static
 type ErrorCode int
 
 const (