drop odd return value semantics from userdiff_config

When the userdiff_config function was introduced in be58e70
(diff: unify external diff and funcname parsing code,
2008-10-05), it used a return value convention unlike any
other config callback. Like other callbacks, it used "-1" to
signal error. But it returned "1" to indicate that it found
something, and "0" otherwise; other callbacks simply
returned "0" to indicate that no error occurred.

This distinction was necessary at the time, because the
userdiff namespace overlapped slightly with the color
configuration namespace. So "diff.color.foo" could mean "the
'foo' slot of diff coloring" or "the 'foo' component of the
"color" userdiff driver". Because the color-parsing code
would die on an unknown color slot, we needed the userdiff
code to indicate that it had matched the variable, letting
us bypass the color-parsing code entirely.

Later, in 8b8e862 (ignore unknown color configuration,
2009-12-12), the color-parsing code learned to silently
ignore unknown slots. This means we no longer need to
protect userdiff-matched variables from reaching the
color-parsing code.

We can therefore change the userdiff_config calling
convention to a more normal one. This drops some code from
each caller, which is nice. But more importantly, it reduces
the cognitive load for readers who may wonder why
userdiff_config is unlike every other config callback.

There's no need to add a new test confirming that this
works; t4020 already contains a test that sets
diff.color.external.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

3 files changed, 4 insertions, 19 deletions

diff --git a/builtin/blame.c b/builtin/blame.c
index 5a67c202f..01956c808 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -2050,14 +2050,8 @@ static int git_blame_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
-	switch (userdiff_config(var, value)) {
-	case 0:
-		break;
-	case -1:
+	if (userdiff_config(var, value) < 0)
 		return -1;
-	default:
-		return 0;
-	}
 
 	return git_default_config(var, value, cb);
 }
diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index 07bd98408..8ed501f22 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -226,14 +226,8 @@ static const char * const cat_file_usage[] = {
 
 static int git_cat_file_config(const char *var, const char *value, void *cb)
 {
-	switch (userdiff_config(var, value)) {
-	case 0:
-		break;
-	case -1:
+	if (userdiff_config(var, value) < 0)
 		return -1;
-	default:
-		return 0;
-	}
 
 	return git_default_config(var, value, cb);
 }
diff --git a/builtin/grep.c b/builtin/grep.c
index 5c2ae94e5..dc6de83ab 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -325,11 +325,8 @@ static int grep_config(const char *var, const char *value, void *cb)
 	struct grep_opt *opt = cb;
 	char *color = NULL;
 
-	switch (userdiff_config(var, value)) {
-	case 0: break;
-	case -1: return -1;
-	default: return 0;
-	}
+	if (userdiff_config(var, value) < 0)
+		return -1;
 
 	if (!strcmp(var, "grep.extendedregexp")) {
 		if (git_config_bool(var, value))