[PATCH] setup: warn about un-enabled extensions

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

When any `extensions.*` setting is configured, we newly ignore it unless
`core.repositoryFormatVersion` is set to a positive value.

This might be quite surprising, e.g. when calling `git config --worktree
[...]` elicits a warning that it requires
`extensions.worktreeConfig = true` when that setting _is_ configured
(but ignored because `core.repositoryFormatVersion` is unset).

Let's warn about this situation specifically, especially because there
might be already setups out there that configured a sparse worktree
using Git v2.27.0 (which does set `extensions.worktreeConfig` but not
`core.repositoryFormatVersion`) and users might want to work in those
setups with Git v2.28.0, too.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
    Warn when extensions.* is ignored
    
    I did actually run into this today. One of my pipelines is configured to
    clone a bare repository, then set up a sparse secondary worktree. This
    used to work, but all of a sudden, the git config --worktree
    core.sparseCheckout true call failed because I'm now using v2.28.0-rc0.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-675%2Fdscho%2Frepo-format-version-advice-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-675/dscho/repo-format-version-advice-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/675

 cache.h                    |  2 +-
 setup.c                    | 16 +++++++++++++++-
 t/t2404-worktree-config.sh | 15 +++++++++++++++
 3 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/cache.h b/cache.h
index 126ec56c7f..da2c71f366 100644
--- a/cache.h
+++ b/cache.h
@@ -1042,7 +1042,7 @@ struct repository_format {
 	int worktree_config;
 	int is_bare;
 	int hash_algo;
-	int has_extensions;
+	int has_extensions, saw_extensions;
 	char *work_tree;
 	struct string_list unknown_extensions;
 };
diff --git a/setup.c b/setup.c
index dbac2eabe8..0f45e2e174 100644
--- a/setup.c
+++ b/setup.c
@@ -489,6 +489,15 @@ static int check_repository_format_gently(const char *gitdir, struct repository_
 	read_repository_format(candidate, sb.buf);
 	strbuf_release(&sb);
 
+	if (candidate->version < 1 &&
+	    (candidate->saw_extensions || candidate->has_extensions))
+		advise(_("extensions.* settings require a positive repository "
+			 "format version greater than zero.\n"
+			 "\n"
+			 "Please use the following call to enable extensions.* "
+			 "config settings:\n"
+			 "\"git config core.repositoryFormatVersion 1\""));
+
 	/*
 	 * For historical use of check_repository_format() in git-init,
 	 * we treat a missing config as a silent "ok", even when nongit_ok
@@ -584,8 +593,13 @@ int read_repository_format(struct repository_format *format, const char *path)
 {
 	clear_repository_format(format);
 	git_config_from_file(check_repo_format, path, format);
-	if (format->version == -1)
+	if (format->version == -1) {
+		int saw_extensions = format->has_extensions;
+
 		clear_repository_format(format);
+
+		format->saw_extensions = saw_extensions;
+	}
 	return format->version;
 }
 
diff --git a/t/t2404-worktree-config.sh b/t/t2404-worktree-config.sh
index 9536d10919..1c08a45177 100755
--- a/t/t2404-worktree-config.sh
+++ b/t/t2404-worktree-config.sh
@@ -78,4 +78,19 @@ test_expect_success 'config.worktree no longer read without extension' '
 	test_cmp_config -C wt2 shared this.is
 '
 
+test_expect_success 'show advice when extensions.* are not enabled' '
+	test_config core.repositoryformatversion 1 &&
+	test_config extensions.worktreeConfig true &&
+	git status 2>err &&
+	test_i18ngrep ! "git config core.repositoryFormatVersion 1" err &&
+
+	test_config core.repositoryformatversion 0 &&
+	git status 2>err &&
+	test_i18ngrep "git config core.repositoryFormatVersion 1" err &&
+
+	git config --unset core.repositoryformatversion &&
+	git status 2>err &&
+	test_i18ngrep "git config core.repositoryFormatVersion 1" err
+'
+
 test_done

base-commit: bd42bbe1a46c0fe486fc33e82969275e27e4dc19
-- 
gitgitgadget