macOS: precompose startup_info->prefix

The "prefix" was precomposed for macOS in commit 5c327502 (MacOS:
precompose_argv_prefix(), 2021-02-03).

However, this commit forgot to update "startup_info->prefix" after
precomposing.

Move the (possible) precomposition towards the end of
setup_git_directory_gently(), so that precompose_string_if_needed()
can use git_config_get_bool("core.precomposeunicode") correctly.

Keep prefix, startup_info->prefix and GIT_PREFIX_ENVIRONMENT all in sync.

And as a result, the prefix no longer needs to be precomposed in git.c

Reported-by: Dmitry Torilov <d.torilov@gmail.com>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Torsten Bögershausen <tboegi@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git.c

@@ -420,7 +420,7 @@ static int run_builtin(struct cmd_struct *p, int argc, const char **argv)
 			int nongit_ok;
 			prefix = setup_git_directory_gently(&nongit_ok);
 		}
-		prefix = precompose_argv_prefix(argc, argv, prefix);
+		precompose_argv_prefix(argc, argv, NULL);
 		if (use_pager == -1 && p->option & (RUN_SETUP | RUN_SETUP_GENTLY) &&
 		    !(p->option & DELAY_PAGER_CONFIG))
 			use_pager = check_pager_config(p->cmd);

setup.c

@@ -1274,18 +1274,10 @@ const char *setup_git_directory_gently(int *nongit_ok)
 	 * the GIT_PREFIX environment variable must always match. For details
 	 * see Documentation/config/alias.txt.
 	 */
-	if (nongit_ok && *nongit_ok) {
+	if (nongit_ok && *nongit_ok)
 		startup_info->have_repository = 0;
-		startup_info->prefix = NULL;
-		setenv(GIT_PREFIX_ENVIRONMENT, "", 1);
-	} else {
-		startup_info->have_repository = 1;
-		startup_info->prefix = prefix;
-		if (prefix)
-			setenv(GIT_PREFIX_ENVIRONMENT, prefix, 1);
 	else
-			setenv(GIT_PREFIX_ENVIRONMENT, "", 1);
-	}
+		startup_info->have_repository = 1;
 
 	/*
 	 * Not all paths through the setup code will call 'set_git_dir()' (which
@@ -1311,6 +1303,22 @@ const char *setup_git_directory_gently(int *nongit_ok)
 		if (startup_info->have_repository)
 			repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
 	}
+	/*
+	 * Since precompose_string_if_needed() needs to look at
+	 * the core.precomposeunicode configuration, this
+	 * has to happen after the above block that finds
+	 * out where the repository is, i.e. a preparation
+	 * for calling git_config_get_bool().
+	 */
+	if (prefix) {
+		prefix = precompose_string_if_needed(prefix);
+		startup_info->prefix = prefix;
+		setenv(GIT_PREFIX_ENVIRONMENT, prefix, 1);
+	} else {
+		startup_info->prefix = NULL;
+		setenv(GIT_PREFIX_ENVIRONMENT, "", 1);
+	}
+
 
 	strbuf_release(&dir);
 	strbuf_release(&gitdir);