[PATCH v2 2/2] config: provide extra detail about worktree config

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <dstolee@microsoft.com>

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.

This warning is specifically placed inside an existing error message
for 'git config --worktree' that already fails if the repository format
version is not 1.

Reported-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 builtin/config.c           |  5 +++--
 t/t2404-worktree-config.sh | 12 ++++++++++++
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/builtin/config.c b/builtin/config.c
index ee4aef6a35..2cdc293ae5 100644
--- a/builtin/config.c
+++ b/builtin/config.c
@@ -678,8 +678,9 @@ int cmd_config(int argc, const char **argv, const char *prefix)
 		else if (worktrees[0] && worktrees[1])
 			die(_("--worktree cannot be used with multiple "
 			      "working trees unless the config\n"
-			      "extension worktreeConfig is enabled. "
-			      "Please read \"CONFIGURATION FILE\"\n"
+			      "extension worktreeConfig is enabled "
+			      "and core.repositoryFormatVersion is at least\n"
+			      "1. Please read \"CONFIGURATION FILE\""
 			      "section in \"git help worktree\" for details"));
 		else
 			given_config_source.file = git_pathdup("config");
diff --git a/t/t2404-worktree-config.sh b/t/t2404-worktree-config.sh
index 9536d10919..303a2644bd 100755
--- a/t/t2404-worktree-config.sh
+++ b/t/t2404-worktree-config.sh
@@ -77,5 +77,17 @@ test_expect_success 'config.worktree no longer read without extension' '
 	test_cmp_config -C wt1 shared this.is &&
 	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 config --worktree test.one true &&
+	test_cmp_config true test.one &&
+	test_config core.repositoryformatversion 0 &&
+	test_must_fail git config --worktree test.two true 2>err &&
+	test_i18ngrep "extension worktreeConfig is enabled" err &&
+	git config --unset core.repositoryformatversion &&
+	test_must_fail git config --worktree test.three true 2>err &&
+	test_i18ngrep "core.repositoryFormatVersion is at least" err
+'
 
 test_done
-- 
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