fetch.c: defer fetch.followRemoteHEAD validation

The value of the fetch.followRemoteHEAD configuration variable is
validated while the configuration file is being parsed, which
produces a warning even when this particular "git fetch" invocation
will never consult it.

Store the raw config string instead, and resolve/validate it lazily
at the one place in do_fetch() that actually uses it, so a mistyped
value only warns, and a missing value only dies, when this fetch
would have consulted it.

remote.c's handle_config() has the same problem for
remote.<name>.followRemoteHEAD, but is left unaddressed here since
it touches shared remote-parsing infrastructure used well beyond
fetch. Leave a NEEDSWORK comment at remote.c:handle_config()
that has a defect similar to what is fixed by this patch,
so the remaining scope is easy to find for a follow-up patch.

Signed-off-by: Colin Hinton <colinlewishinton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fetch.c

@@ -103,7 +103,8 @@ static struct string_list negotiation_include = STRING_LIST_INIT_NODUP;
 
 struct fetch_config {
 	enum display_format display_format;
-	enum follow_remote_head_settings follow_remote_head;
+	char *follow_remote_head_raw;
+	int follow_remote_head_seen;
 	int all;
 	int prune;
 	int prune_tags;
@@ -176,24 +177,31 @@ static int git_fetch_config(const char *k, const char *v,
 	}
 
 	if (!strcmp(k, "fetch.followremotehead")) {
-		if (!v)
-			return config_error_nonbool(k);
-		else if (!strcmp(v, "never"))
-			fetch_config->follow_remote_head = FOLLOW_REMOTE_NEVER;
-		else if (!strcmp(v, "create"))
-			fetch_config->follow_remote_head = FOLLOW_REMOTE_CREATE;
-		else if (!strcmp(v, "warn"))
-			fetch_config->follow_remote_head = FOLLOW_REMOTE_WARN;
-		else if (!strcmp(v, "always"))
-			fetch_config->follow_remote_head = FOLLOW_REMOTE_ALWAYS;
-		else
-			warning(_("unrecognized fetch.followRemoteHEAD value '%s' ignored"), v);
+		free(fetch_config->follow_remote_head_raw);
+		fetch_config->follow_remote_head_raw = xstrdup_or_null(v);
+		fetch_config->follow_remote_head_seen = 1;
 		return 0;
 	}
 
 	return git_default_config(k, v, ctx, cb);
 }
 
+static enum follow_remote_head_settings get_follow_remote_head(const char *setting)
+{
+	if (!setting)
+		die(_("missing value for 'fetch.followRemoteHEAD'"));
+	else if (!strcmp(setting, "never"))
+		return FOLLOW_REMOTE_NEVER;
+	else if (!strcmp(setting, "create"))
+		return FOLLOW_REMOTE_CREATE;
+	else if (!strcmp(setting, "warn"))
+		return FOLLOW_REMOTE_WARN;
+	else if (!strcmp(setting, "always"))
+		return FOLLOW_REMOTE_ALWAYS;
+	warning(_("unrecognized fetch.followRemoteHEAD value '%s' ignored"), setting);
+	return BUILTIN_FOLLOW_REMOTE_HEAD_DFLT;
+}
+
 static int parse_refmap_arg(const struct option *opt, const char *arg, int unset)
 {
 	BUG_ON_OPT_NEG(unset);
@@ -1918,11 +1926,10 @@ static int do_fetch(struct transport *transport,
 		TRANSPORT_LS_REFS_OPTIONS_INIT;
 	struct fetch_head fetch_head = { 0 };
 	struct strbuf err = STRBUF_INIT;
-	int do_set_head = 0;
 	struct ref_update_display_info_array display_array = { 0 };
 	struct strmap rejected_refs = STRMAP_INIT;
 	int summary_width = 0;
-	int follow_remote_head;
+	int follow_remote_head = FOLLOW_REMOTE_NEVER;
 
 	if (tags == TAGS_DEFAULT) {
 		if (transport->remote->fetch_tags == 2)
@@ -1938,22 +1945,6 @@ static int do_fetch(struct transport *transport,
 			goto cleanup;
 	}
 
-	/*
-	 * NEEDSWORK: By the time this function executes, we have already parsed
-	 * all such followRemoteHEAD values from the external configuration,
-	 * potentially emitting warning messages for bogus values.  Ideally, if
-	 * this fetch ends up not needing to consult these values, then git would
-	 * not ever output a value warning. (eg: when pulling from a URL directly -
-	 * rather than a configured remote, or when a remote's followRemoteHEAD
-	 * overrides the fallback fetch setting)
-	 */
-	if (transport->remote->follow_remote_head)
-		follow_remote_head = transport->remote->follow_remote_head;
-	else if (config->follow_remote_head)
-		follow_remote_head = config->follow_remote_head;
-	else
-		follow_remote_head = BUILTIN_FOLLOW_REMOTE_HEAD_DFLT;
-
 	if (rs->nr) {
 		refspec_ref_prefixes(rs, &transport_ls_refs_options.ref_prefixes);
 	} else {
@@ -1962,8 +1953,16 @@ static int do_fetch(struct transport *transport,
 		if (transport->remote->fetch.nr) {
 			refspec_ref_prefixes(&transport->remote->fetch,
 					     &transport_ls_refs_options.ref_prefixes);
-			if (follow_remote_head != FOLLOW_REMOTE_NEVER)
-				do_set_head = 1;
+			/*
+			 * See remote.c's handling of remote.<name>.followRemoteHEAD
+			 * for the analogous, still-unresolved case.
+			 */
+			if (transport->remote->follow_remote_head)
+				follow_remote_head = transport->remote->follow_remote_head;
+			else if (config->follow_remote_head_seen)
+				follow_remote_head = get_follow_remote_head(config->follow_remote_head_raw);
+			else
+				follow_remote_head = BUILTIN_FOLLOW_REMOTE_HEAD_DFLT;
 		}
 		if (branch && branch_has_merge_config(branch) &&
 		    !strcmp(branch->remote_name, transport->remote->name)) {
@@ -1987,7 +1986,7 @@ static int do_fetch(struct transport *transport,
 		strvec_push(&transport_ls_refs_options.ref_prefixes,
 			    "refs/tags/");
 
-	if (do_set_head)
+	if (follow_remote_head != FOLLOW_REMOTE_NEVER)
 		strvec_push(&transport_ls_refs_options.ref_prefixes,
 			    "HEAD");
 
@@ -2164,7 +2163,7 @@ static int do_fetch(struct transport *transport,
 				  "you need to specify exactly one branch with the --set-upstream option"));
 		}
 	}
-	if (do_set_head) {
+	if (follow_remote_head != FOLLOW_REMOTE_NEVER) {
 		/*
 		 * Way too many cases where this can go wrong so let's just
 		 * ignore errors and fail silently for now.
@@ -2509,7 +2508,8 @@ int cmd_fetch(int argc,
 {
 	struct fetch_config config = {
 		.display_format = DISPLAY_FORMAT_FULL,
-		.follow_remote_head = FOLLOW_REMOTE_UNCONFIGURED,
+		.follow_remote_head_raw = NULL,
+		.follow_remote_head_seen = 0,
 		.prune = -1,
 		.prune_tags = -1,
 		.show_forced_updates = 1,
@@ -2929,5 +2929,6 @@ int cmd_fetch(int argc,
  cleanup:
 	string_list_clear(&list, 0);
 	list_objects_filter_release(&filter_options);
+	free(config.follow_remote_head_raw);
 	return result;
 }

remote.c

@@ -582,6 +582,13 @@ static int handle_config(const char *key, const char *value,
 					      &remote->negotiation_include);
 	} else if (!strcmp(subkey, "followremotehead")) {
 		const char *no_warn_branch;
+		/*
+		 * NEEDSWORK: this is validated/warned about here, during config
+		 * parsing, regardless of whether the fetch that triggered this
+		 * parse will ever consult it for this particular remote. See
+		 * fetch.c's deferred handling of fetch.followRemoteHEAD for the
+		 * pattern this should likely follow.
+		 */
 		if (!strcmp(value, "never"))
 			remote->follow_remote_head = FOLLOW_REMOTE_NEVER;
 		else if (!strcmp(value, "create"))