[PATCH 2/8] t7900: do not let `$HOME/.gitconfig` interfere with XDG tests

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

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

The XDG config tests for `git maintenance register/unregister`
create a fresh `$XDG_CONFIG_HOME/git/config` and expect git to use
that location. However, if `$HOME/.gitconfig` exists (which may
happen when test-lib.sh writes global config, e.g. to set
`safe.bareRepository`), git prefers `$HOME/.gitconfig` over the XDG
location, and the `maintenance.repo` entry ends up in the wrong
file.

This is an inherent consequence of setting global config in
test-lib.sh rather than adjusting individual tests: writing any
entry to `$HOME/.gitconfig` has side effects beyond the intended
setting, because the mere existence of that file changes which
global config location git prefers for all subsequent writes.
Individual per-test adjustments would not have this interaction.

Fix this by overriding `HOME` to a non-existent directory inside the
subshells that test XDG behavior. Since these subshells already
override `XDG_CONFIG_HOME`, they do not need `$HOME/.gitconfig` at
all, and the subshell scoping ensures the original `HOME` is
restored automatically.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 t/t7900-maintenance.sh | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 4700beacc1..4358df0424 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -101,8 +101,12 @@ test_expect_success "maintenance.autoDetach overrides gc.autoDetach" '
 test_expect_success 'register uses XDG_CONFIG_HOME config if it exists' '
 	test_when_finished rm -r .config/git/config &&
 	(
+		# Override HOME so that .gitconfig (which test-lib.sh may
+		# have created, e.g. to set safe.bareRepository) does not
+		# take precedence over the XDG location.
+		HOME=$PWD/must-not-exist &&
 		XDG_CONFIG_HOME=.config &&
-		export XDG_CONFIG_HOME &&
+		export HOME XDG_CONFIG_HOME &&
 		mkdir -p $XDG_CONFIG_HOME/git &&
 		>$XDG_CONFIG_HOME/git/config &&
 		git maintenance register &&
@@ -124,8 +128,12 @@ test_expect_success 'register does not need XDG_CONFIG_HOME config to exist' '
 test_expect_success 'unregister uses XDG_CONFIG_HOME config if it exists' '
 	test_when_finished rm -r .config/git/config &&
 	(
+		# Override HOME so that .gitconfig (which test-lib.sh may
+		# have created, e.g. to set safe.bareRepository) does not
+		# take precedence over the XDG location.
+		HOME=$PWD/must-not-exist &&
 		XDG_CONFIG_HOME=.config &&
-		export XDG_CONFIG_HOME &&
+		export HOME XDG_CONFIG_HOME &&
 		mkdir -p $XDG_CONFIG_HOME/git &&
 		>$XDG_CONFIG_HOME/git/config &&
 		git maintenance register &&
-- 
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