thodg/libgit2

diff --git a/include/git2/common.h b/include/git2/common.h
index 1d2d3a3..2aae648 100644
--- a/include/git2/common.h
+++ b/include/git2/common.h
@@ -173,6 +173,9 @@
 /** Streaming error */
 #define GIT_ESTREAM (GIT_ERROR - 26)
 
+/** invalid arguments to function */
+#define GIT_EINVALIDARGS (GIT_ERROR - 27)
+
 GIT_BEGIN_DECL
 
 typedef struct {
diff --git a/src/common.h b/src/common.h
index 351d669..e5b9f15 100644
--- a/src/common.h
+++ b/src/common.h
@@ -54,7 +54,8 @@ typedef SSIZE_T ssize_t;
 #include "bswap.h"
 
 #define GIT_PATH_MAX 4096
-extern int git__error(int error, const char *, ...) GIT_FORMAT_PRINTF(2, 3);
+extern int git__throw(int error, const char *, ...) GIT_FORMAT_PRINTF(2, 3);
+extern int git__rethrow(int error, const char *, ...) GIT_FORMAT_PRINTF(2, 3);
 
 #include "util.h"
 
diff --git a/src/errors.c b/src/errors.c
index 73df2e2..40b0feb 100644
--- a/src/errors.c
+++ b/src/errors.c
@@ -30,7 +30,25 @@
 
 static GIT_TLS char g_last_error[1024];
 
-int git__error(int error, const char *msg, ...)
+int git__rethrow(int error, const char *msg, ...)
+{
+	char new_error[1024];
+	char *old_error = NULL;
+
+	va_list va;
+
+	va_start(va, msg);
+	vsnprintf(new_error, sizeof(new_error), msg, va);
+	va_end(va);
+
+	old_error = strdup(g_last_error);
+	snprintf(g_last_error, sizeof(g_last_error), "%s \n    - %s", new_error, old_error);
+	free(old_error);
+
+	return error;
+}
+
+int git__throw(int error, const char *msg, ...)
 {
 	va_list va;
 
diff --git a/src/refs.c b/src/refs.c
index ea96819..c4d3d6a 100644
--- a/src/refs.c
+++ b/src/refs.c
@@ -122,7 +122,8 @@ static int reference_create(
 	else if (type == GIT_REF_OID)
 		size = sizeof(reference_oid);
 	else
-		return GIT_EINVALIDREFSTATE;
+		return git__throw(GIT_EINVALIDARGS,
+			"Invalid reference type. Use either GIT_REF_OID or GIT_REF_SYMBOLIC as type specifier");
 
 	reference = git__malloc(size);
 	if (reference == NULL)
@@ -159,11 +160,9 @@ static int reference_read(gitfo_buf *file_content, time_t *mtime, const char *re
 	/* Determine the full path of the file */
 	git__joinpath(path, repo_path, ref_name);
 
-	if (gitfo_stat(path, &st) < 0)
-		return GIT_ENOTFOUND;
-
-	if (S_ISDIR(st.st_mode))
-		return GIT_EOBJCORRUPTED;
+	if (gitfo_stat(path, &st) < 0 || S_ISDIR(st.st_mode))
+		return git__throw(GIT_ENOTFOUND,
+			"Cannot read reference file '%s'", ref_name);
 
 	if (mtime)
 		*mtime = st.st_mtime;
@@ -205,7 +204,8 @@ static int loose_update(git_reference *ref)
 	else if (ref->type == GIT_REF_OID)
 		error = loose_parse_oid(ref, &ref_file);
 	else
-		error = GIT_EINVALIDREFSTATE;
+		error = git__throw(GIT_EOBJCORRUPTED,
+			"Invalid reference type (%d) for loose reference", ref->type);
 
 	gitfo_free_buf(&ref_file);
 
@@ -229,7 +229,8 @@ static int loose_parse_symbolic(git_reference *ref, gitfo_buf *file_content)
 	ref_sym = (reference_symbolic *)ref;
 
 	if (file_content->len < (header_len + 1))
-		return GIT_EREFCORRUPTED;
+		return git__throw(GIT_EOBJCORRUPTED,
+			"Failed to parse loose reference. Object too short");
 
 	/* 
 	 * Assume we have already checked for the header
@@ -246,7 +247,8 @@ static int loose_parse_symbolic(git_reference *ref, gitfo_buf *file_content)
 	/* remove newline at the end of file */
 	eol = strchr(ref_sym->target, '\n');
 	if (eol == NULL)
-		return GIT_EREFCORRUPTED;
+		return git__throw(GIT_EOBJCORRUPTED,
+			"Failed to parse loose reference. Missing EOL");
 
 	*eol = '\0';
 	if (eol[-1] == '\r')
@@ -257,6 +259,7 @@ static int loose_parse_symbolic(git_reference *ref, gitfo_buf *file_content)
 
 static int loose_parse_oid(git_reference *ref, gitfo_buf *file_content)
 {
+	int error;
 	reference_oid *ref_oid;
 	char *buffer;
 
@@ -265,17 +268,19 @@ static int loose_parse_oid(git_reference *ref, gitfo_buf *file_content)
 
 	/* File format: 40 chars (OID) + newline */
 	if (file_content->len < GIT_OID_HEXSZ + 1)
-		return GIT_EREFCORRUPTED;
+		return git__throw(GIT_EOBJCORRUPTED,
+			"Failed to parse loose reference. Reference too short");
 
-	if (git_oid_mkstr(&ref_oid->oid, buffer) < GIT_SUCCESS)
-		return GIT_EREFCORRUPTED;
+	if ((error = git_oid_mkstr(&ref_oid->oid, buffer)) < GIT_SUCCESS)
+		return git__rethrow(GIT_EOBJCORRUPTED, "Failed to parse loose reference.");
 
 	buffer = buffer + GIT_OID_HEXSZ;
 	if (*buffer == '\r')
 		buffer++;
 
 	if (*buffer != '\n')
-		return GIT_EREFCORRUPTED;
+		return git__throw(GIT_EOBJCORRUPTED,
+			"Failed to parse loose reference. Missing EOL");
 
 	return GIT_SUCCESS;
 }
@@ -387,7 +392,7 @@ static int loose_write(git_reference *ref)
 		strcpy(ref_contents, GIT_SYMREF);
 		strcat(ref_contents, ref_sym->target);
 	} else {
-		error = GIT_EINVALIDREFSTATE;
+		error = git__throw(GIT_EOBJCORRUPTED, "Failed to write reference. Invalid reference type");
 		goto unlock;
 	}
 
diff --git a/src/util.h b/src/util.h
index f5f0b86..6724e8d 100644
--- a/src/util.h
+++ b/src/util.h
@@ -14,7 +14,7 @@ GIT_INLINE(void *) git__malloc(size_t len)
 {
 	void *ptr = malloc(len);
 	if (!ptr)
-		git__error(GIT_ENOMEM, "Out of memory. Failed to allocate %d bytes.", (int)len);
+		git__throw(GIT_ENOMEM, "Out of memory. Failed to allocate %d bytes.", (int)len);
 	return ptr;
 }
 
@@ -22,7 +22,7 @@ GIT_INLINE(void *) git__calloc(size_t nelem, size_t elsize)
 {
 	void *ptr = calloc(nelem, elsize);
 	if (!ptr)
-		git__error(GIT_ENOMEM, "Out of memory. Failed to allocate %d bytes.", (int)elsize);
+		git__throw(GIT_ENOMEM, "Out of memory. Failed to allocate %d bytes.", (int)elsize);
 	return ptr;
 }
 
@@ -30,7 +30,7 @@ GIT_INLINE(char *) git__strdup(const char *str)
 {
 	char *ptr = strdup(str);
 	if (!ptr)
-		git__error(GIT_ENOMEM, "Out of memory. Failed to duplicate string");
+		git__throw(GIT_ENOMEM, "Out of memory. Failed to duplicate string");
 	return ptr;
 }
 
@@ -38,7 +38,7 @@ GIT_INLINE(void *) git__realloc(void *ptr, size_t size)
 {
 	void *new_ptr = realloc(ptr, size);
 	if (!new_ptr)
-		git__error(GIT_ENOMEM, "Out of memory. Failed to allocate %d bytes.", (int)size);
+		git__throw(GIT_ENOMEM, "Out of memory. Failed to allocate %d bytes.", (int)size);
 	return new_ptr;
 }