alloc: set up an allocator that fails before library init

We require the library to be initialized with git_libgit2_init before it
is functional.  However, if a user tries to uses the library without
doing so - as they might when getting started with the library for the
first time - we will likely crash.

This commit introduces some guard rails - now instead of having _no_
allocator by default, we'll have an allocator that always fails, and
never tries to set an error message (since the thread-local state is
set up by git_libgit2_init).  We've modified the error retrieval
function to (try to) ensure that the library has been initialized before
getting the thread-local error message.

(Unfortunately, we cannot determine if the thread local storage has
actually been configured, this does require initialization by
git_libgit2_init.  But a naive attempt should be good enough for most
cases.)

1 files changed, 10 insertions, 0 deletions

diff --git a/src/errors.c b/src/errors.c
index 5b68dd9cb..3d1d1c9a1 100644
--- a/src/errors.c
+++ b/src/errors.c
@@ -10,6 +10,7 @@
 #include "threadstate.h"
 #include "posix.h"
 #include "buffer.h"
+#include "libgit2.h"
 
 /********************************************
  * New error handling
@@ -20,6 +21,11 @@ static git_error g_git_oom_error = {
 	GIT_ERROR_NOMEMORY
 };
 
+static git_error g_git_uninitialized_error = {
+	"libgit2 has not been initialized; you must call git_libgit2_init",
+	GIT_ERROR_INVALID
+};
+
 static void set_error_from_buffer(int error_class)
 {
 	git_error *error = &GIT_THREADSTATE->error_t;
@@ -131,6 +137,10 @@ void git_error_clear(void)
 
 const git_error *git_error_last(void)
 {
+	/* If the library is not initialized, return a static error. */
+	if (!git_libgit2_init_count())
+		return &g_git_uninitialized_error;
+
 	return GIT_THREADSTATE->last_error;
 }