[PATCH 2/2] fix clang -Wtautological-compare with unsigned enum

[Antoine Pelisse <apelisse@gmail.com>]

Create a GREP_HEADER_FIELD_MIN so we can check that the field value is
sane and silent the clang warning.

Clang warning happens because the enum is unsigned (this is
implementation-defined, and there is no negative fields) and the check
is then tautological.

Signed-off-by: Antoine Pelisse <apelisse@gmail.com>
---
I tried to consider discussion [1] and this [2] discussion on clang's list

With these two patches and the patch from Max Horne, I'm finally able to
compile with CC=clang CFLAGS=-Werror.

 [1]: http://thread.gmane.org/gmane.comp.version-control.git/184908
 [2]: http://clang-developers.42468.n3.nabble.com/Possibly-invalid-enum-tautology-warning-td3233140.html

 grep.c | 3 ++-
 grep.h | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/grep.c b/grep.c
index 4bd1b8b..bb548ca 100644
--- a/grep.c
+++ b/grep.c
@@ -625,7 +625,8 @@ static struct grep_expr *prep_header_patterns(struct grep_opt *opt)
 	for (p = opt->header_list; p; p = p->next) {
 		if (p->token != GREP_PATTERN_HEAD)
 			die("bug: a non-header pattern in grep header list.");
-		if (p->field < 0 || GREP_HEADER_FIELD_MAX <= p->field)
+		if (p->field < GREP_HEADER_FIELD_MIN ||
+		    GREP_HEADER_FIELD_MAX <= p->field)
 			die("bug: unknown header field %d", p->field);
 		compile_regexp(p, opt);
 	}
diff --git a/grep.h b/grep.h
index 8fc854f..e4a1df5 100644
--- a/grep.h
+++ b/grep.h
@@ -28,7 +28,8 @@ enum grep_context {
 };

 enum grep_header_field {
-	GREP_HEADER_AUTHOR = 0,
+	GREP_HEADER_FIELD_MIN = 0,
+	GREP_HEADER_AUTHOR = GREP_HEADER_FIELD_MIN,
 	GREP_HEADER_COMMITTER,
 	GREP_HEADER_REFLOG,

--
1.8.1.1.435.g20d29be.dirty