config: test home and xdg files in list --global

The `git config list --global` output includes `$HOME/.gitconfig` (home
config), but ignores `$XDG_CONFIG_HOME/git/config` (XDG config). It
should include both files.

Modify tests to check the following and expect a failure:
  - `git config list --global` should include contents from both the
     home and XDG config locations (assuming they are readable), not
     just the former.

  - `--show-origin` should print correct paths to both config files,
    assuming they exist.

Also, add tests to ensure subsequent patches do not introduce
regressions to `git config list`. Specifically, check that:
  - The home config should take precedence over the XDG config.

  - Without `--global`, it should not bail on unreadable/non-existent
    global config files.

  - With `--global`, it should bail when both `$HOME/.gitconfig` and
    `$XDG_CONFIG_HOME/git/config` are unreadable. It should not bail if
    at least one of them is readable.

The next patch, config: read global scope via config_sequence, will
implement a fix to include both config files when `--global` is
specified.

Reported-by: Jade Lovelace <lists@jade.fyi>
Helped-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Delilah Ashley Wu <delilahwu@microsoft.com>
Reviewed-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: delilahw

t/t1300-config.sh

@@ -2367,6 +2367,71 @@ test_expect_success '--show-scope with --default' '
 	test_cmp expect actual
 '
 
+test_expect_success 'list with nonexistent global config' '
+	rm -rf "$HOME"/.gitconfig "$HOME"/.config/git/config &&
+	git config ${mode_prefix}list --show-scope
+'
+
+test_expect_success 'list --global with nonexistent global config' '
+	rm -rf "$HOME"/.gitconfig "$HOME"/.config/git/config &&
+	test_must_fail git config ${mode_prefix}list --global --show-scope
+'
+
+test_expect_success 'list --global with only home' '
+	rm -rf "$HOME"/.config/git/config &&
+
+	test_when_finished rm -f \"\$HOME\"/.gitconfig &&
+	cat >"$HOME"/.gitconfig <<-EOF &&
+	[home]
+		config = true
+	EOF
+
+	cat >expect <<-EOF &&
+	global	home.config=true
+	EOF
+	git config ${mode_prefix}list --global --show-scope >output &&
+	test_cmp expect output
+'
+
+test_expect_success 'list --global with only xdg' '
+	rm -f "$HOME"/.gitconfig &&
+
+	test_when_finished rm -rf \"\$HOME\"/.config/git &&
+	mkdir -p "$HOME"/.config/git &&
+	cat >"$HOME"/.config/git/config <<-EOF &&
+	[xdg]
+		config = true
+	EOF
+
+	cat >expect <<-EOF &&
+	global	xdg.config=true
+	EOF
+	git config ${mode_prefix}list --global --show-scope >output &&
+	test_cmp expect output
+'
+
+test_expect_success 'list --global with both home and xdg' '
+	test_when_finished rm -f \"\$HOME\"/.gitconfig &&
+	cat >"$HOME"/.gitconfig <<-EOF &&
+	[home]
+		config = true
+	EOF
+
+	test_when_finished rm -rf \"\$HOME\"/.config/git &&
+	mkdir -p "$HOME"/.config/git &&
+	cat >"$HOME"/.config/git/config <<-EOF &&
+	[xdg]
+		config = true
+	EOF
+
+	cat >expect <<-EOF &&
+	global	file:$HOME/.config/git/config	xdg.config=true
+	global	file:$HOME/.gitconfig	home.config=true
+	EOF
+	git config ${mode_prefix}list --global --show-scope --show-origin >output &&
+	! test_cmp expect output
+'
+
 test_expect_success 'override global and system config' '
 	test_when_finished rm -f \"\$HOME\"/.gitconfig &&
 	cat >"$HOME"/.gitconfig <<-EOF &&

t/t1306-xdg-files.sh

@@ -68,9 +68,10 @@ test_expect_success 'read with --list: xdg file exists and ~/.gitconfig exists'
 	>.gitconfig &&
 	echo "[user]" >.gitconfig &&
 	echo "	name = read_gitconfig" >>.gitconfig &&
-	echo user.name=read_gitconfig >expected &&
+	echo user.name=read_config >expected &&
+	echo user.name=read_gitconfig >>expected &&
 	git config --global --list >actual &&
-	test_cmp expected actual
+	! test_cmp expected actual
 '