core.warnambiguousrefs: warns when "name" is used and both "name" branch and tag exists.

Signed-off-by: Junio C Hamano <junkio@cox.net>

cache.h

@@ -165,6 +165,7 @@ extern void rollback_index_file(struct cache_file *);
 extern int trust_executable_bit;
 extern int assume_unchanged;
 extern int only_use_symrefs;
+extern int warn_ambiguous_refs;
 extern int diff_rename_limit_default;
 extern int shared_repository;
 extern const char *apply_default_whitespace;

config.c

@@ -232,6 +232,11 @@ int git_default_config(const char *var, const char *value)
 		return 0;
 	}
 
+	if (!strcmp(var, "core.warnambiguousrefs")) {
+		warn_ambiguous_refs = git_config_bool(var, value);
+		return 0;
+	}
+
 	if (!strcmp(var, "user.name")) {
 		strncpy(git_default_name, value, sizeof(git_default_name));
 		return 0;

environment.c

@@ -14,6 +14,7 @@ char git_default_name[MAX_GITNAME];
 int trust_executable_bit = 1;
 int assume_unchanged = 0;
 int only_use_symrefs = 0;
+int warn_ambiguous_refs = 0;
 int repository_format_version = 0;
 char git_commit_encoding[MAX_ENCODING_LENGTH] = "utf-8";
 int shared_repository = 0;

sha1_name.c

@@ -240,9 +240,13 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 		"refs",
 		"refs/tags",
 		"refs/heads",
+		"refs/remotes",
 		NULL
 	};
 	const char **p;
+	const char *warning = "warning: refname '%.*s' is ambiguous.\n";
+	char *pathname;
+	int already_found = 0;
 
 	if (len == 40 && !get_sha1_hex(str, sha1))
 		return 0;
@@ -252,10 +256,23 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 		return -1;
 
 	for (p = prefix; *p; p++) {
-		char *pathname = git_path("%s/%.*s", *p, len, str);
-		if (!read_ref(pathname, sha1))
-			return 0;
+		unsigned char sha1_from_ref[20];
+		unsigned char *this_result =
+			already_found ? sha1_from_ref : sha1;
+		pathname = git_path("%s/%.*s", *p, len, str);
+		if (!read_ref(pathname, this_result)) {
+			if (warn_ambiguous_refs) {
+				if (already_found &&
+				    !memcmp(sha1, sha1_from_ref, 20))
+					fprintf(stderr, warning, len, str);
+				already_found++;
+			}
+			else
+				return 0;
+		}
 	}
+	if (already_found)
+		return 0;
 	return -1;
 }