Bring back `git_strerror`

We cannot totally deprecate this until the new error handling mechanisms
are all in place.

include/git2/errors.h

@@ -40,6 +40,18 @@ GIT_BEGIN_DECL
  */
 GIT_EXTERN(const char *) git_lasterror(void);
 
+/**
+ * strerror() for the Git library
+ *
+ * Get a string description for a given error code.
+ * NOTE: This method will be eventually deprecated in favor
+ * of the new `git_lasterror`.
+ *
+ * @param num The error code to explain
+ * @return a string explaining the error code
+ */
+GIT_EXTERN(const char *) git_strerror(int num);
+
 /** @} */
 GIT_END_DECL
 #endif

src/errors.c

@@ -30,6 +30,52 @@
 
 static GIT_TLS char g_last_error[1024];
 
+static struct {
+	int num;
+	const char *str;
+} error_codes[] = {
+	{GIT_ERROR, "Unspecified error"},
+	{GIT_ENOTOID, "Input was not a properly formatted Git object id."},
+	{GIT_ENOTFOUND, "Object does not exist in the scope searched."},
+	{GIT_ENOMEM, "Not enough space available."},
+	{GIT_EOSERR, "Consult the OS error information."},
+	{GIT_EOBJTYPE, "The specified object is of invalid type"},
+	{GIT_EOBJCORRUPTED, "The specified object has its data corrupted"},
+	{GIT_ENOTAREPO, "The specified repository is invalid"},
+	{GIT_EINVALIDTYPE, "The object type is invalid or doesn't match"},
+	{GIT_EMISSINGOBJDATA, "The object cannot be written that because it's missing internal data"},
+	{GIT_EPACKCORRUPTED, "The packfile for the ODB is corrupted"},
+	{GIT_EFLOCKFAIL, "Failed to adquire or release a file lock"},
+	{GIT_EZLIB, "The Z library failed to inflate/deflate an object's data"},
+	{GIT_EBUSY, "The queried object is currently busy"},
+	{GIT_EINVALIDPATH, "The path is invalid"},
+	{GIT_EBAREINDEX, "The index file is not backed up by an existing repository"},
+	{GIT_EINVALIDREFNAME, "The name of the reference is not valid"},
+	{GIT_EREFCORRUPTED, "The specified reference has its data corrupted"},
+	{GIT_ETOONESTEDSYMREF, "The specified symbolic reference is too deeply nested"},
+	{GIT_EPACKEDREFSCORRUPTED, "The pack-refs file is either corrupted of its format is not currently supported"},
+	{GIT_EINVALIDPATH, "The path is invalid" },
+	{GIT_EREVWALKOVER, "The revision walker is empty; there are no more commits left to iterate"},
+	{GIT_EINVALIDREFSTATE, "The state of the reference is not valid"},
+	{GIT_ENOTIMPLEMENTED, "This feature has not been implemented yet"},
+	{GIT_EEXISTS, "A reference with this name already exists"},
+	{GIT_EOVERFLOW, "The given integer literal is too large to be parsed"},
+	{GIT_ENOTNUM, "The given literal is not a valid number"},
+};
+
+const char *git_strerror(int num)
+{
+	size_t i;
+
+	if (num == GIT_EOSERR)
+		return strerror(errno);
+	for (i = 0; i < ARRAY_SIZE(error_codes); i++)
+		if (num == error_codes[i].num)
+			return error_codes[i].str;
+
+	return "Unknown error";
+}
+
 int git__rethrow(int error, const char *msg, ...)
 {
 	char new_error[1024];