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, 4 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index 84262f4..71c5ee0 100644
--- a/Makefile
+++ b/Makefile
@@ -2,6 +2,10 @@ TEST_ARGS ?= --count=1
 
 default: test
 
+
+generate: static-build/install/lib/libgit2.a
+	go generate --tags "static" ./...
+
 # System library
 # ==============
 # This uses whatever version of libgit2 can be found in the system.