[PATCH 5/9] diff: give more detailed messages for bogus diff.* config

From: Jeff King <peff@peff.net>
Date: Dec 7, 2023, 07:25 UTC
Message-ID: <20231207072523.GE1277973@coredump.intra.peff.net>
In-Reply-To: <20231207072338.GA1277727@coredump.intra.peff.net>

The config callbacks for a few diff.* variables simply return -1 when we encounter an error. The message you get mentions the offending location, like:

  fatal: bad config variable 'diff.algorithm' in file '.git/config' at line 7

but is vague about "bad" (as it must be, since the message comes from the generic config code). Most callbacks add their own messages here, so let's do the same. E.g.:

  error: unknown value for config 'diff.algorithm': foo
  fatal: bad config variable 'diff.algorithm' in file '.git/config' at line 7

I've written the string in a way that should be reusable for translators, and matches another similar message in transport.c (there doesn't yet seem to be a popular generic message to reuse here, so hopefully this will get the ball rolling).

Note that in the case of diff.algorithm, our parse_algorithm_value() helper does detect a NULL value string. But it's still worth detecting it ourselves here, since we can give a more specific error message (and which is the usual one for unexpected implicit-bool values).

Signed-off-by: Jeff King <peff@peff.net>
---
 diff.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/diff.c b/diff.c
index 5b213a4b44..a2def45644 100644
--- a/diff.c
+++ b/diff.c
@@ -445,9 +445,12 @@ int git_diff_ui_config(const char *var, const char *value,
 	}
 
 	if (!strcmp(var, "diff.algorithm")) {
+		if (!value)
+			return config_error_nonbool(var);
 		diff_algorithm = parse_algorithm_value(value);
 		if (diff_algorithm < 0)
-			return -1;
+			return error(_("unknown value for config '%s': %s"),
+				     var, value);
 		return 0;
 	}
 
@@ -486,7 +489,8 @@ int git_diff_basic_config(const char *var, const char *value,
 			return config_error_nonbool(var);
 		val = parse_ws_error_highlight(value);
 		if (val < 0)
-			return -1;
+			return error(_("unknown value for config '%s': %s"),
+				     var, value);
 		ws_error_highlight_default = val;
 		return 0;
 	}

-- 
2.43.0.664.ga12c899002