config: add `git_die_config()` to the config-set API

Add `git_die_config` that dies printing the line number and the file name
of the highest priority value for the configuration variable `key`. A custom
error message is also printed before dying, specified by the caller, which can
be skipped if `err` argument is set to NULL.

It has usage in non-callback based config value retrieval where we can
raise an error and die if there is a semantic error.
For example,

	if (!git_config_get_value(key, &value)){
		if (!strcmp(value, "foo"))
			git_config_die(key, "value: `%s` is illegal", value);
		else
			/* do work */
	}

Signed-off-by: Tanay Abhra <tanayabh@gmail.com>
Reviewed-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/cache.h b/cache.h
index f11ce41956..89a0d51515 100644
--- a/cache.h
+++ b/cache.h
@@ -1388,6 +1388,9 @@ struct key_value_info {
 	int linenr;
 };
 
+extern NORETURN void git_die_config(const char *key, const char *err, ...) __attribute__((format(printf, 2, 3)));
+extern NORETURN void git_die_config_linenr(const char *key, const char *filename, int linenr);
+
 extern int committer_ident_sufficiently_given(void);
 extern int author_ident_sufficiently_given(void);