config: read both home and xdg files for --global

[delilahw]

Hi,

Here is my reroll.

As reported in [1]: `$HOME/.gitconfig` and `$XDG_CONFIG_HOME/git/config` are both valid global config locations, but `git config list --global` only includes the former in its output.

Suppose we have this config in `$HOME/.gitconfig`:

[home]
    config = true

And this config in `$XDG_CONFIG_HOME/git/config`:

[xdg]
    config = true

Then, to reproduce the issue that `--global` only shows the home config:

$ git config list --global --show-scope --show-origin
global  file:/Users/delilah/.gitconfig    home.config=true

Git correctly applies the XDG config in its effective configuration, but it doesn't show up when `--global` is specified. We can confirm this by checking the output without the `--global` flag:

$ git config list --show-scope --show-origin
global  file:/Users/delilah/.config/git/config    xdg.config=true
global  file:/Users/delilah/.gitconfig            home.config=true

The expected behaviour is both configs should be shown when `--global` is specified, so we'd expect its output to look the same as above. This was confirmed in [2], which quoted the `git config` documentation:

> OPTIONS
>     --global::
>         For writing options: write to global `~/.gitconfig` file
>         rather than the repository `.git/config`, write to
>         `$XDG_CONFIG_HOME/git/config` file if this file exists and the
>         `~/.gitconfig` file doesn't.
>
>         For reading options: read only from global `~/.gitconfig` and from
>         `$XDG_CONFIG_HOME/git/config` rather than from all available files.

The first patch fixes forward slash normalisation on Windows paths. The second patch adds a flag for error handling when reading configuration files. The third patch implements the fix to include both config files when `--global` is specified.

Changes in v2:

• Perform forward slash conversion in `xdg_config_home_for()` rather than the widely used `cleanup_path()`, which could've broken callers that do not expect normalized slashes.
• Squash patches 2-4, such that implementation and tests are in the same patch rather than two sequential patches.
• Reorder patches to prevent a regression from being intentionally introduced and then fixed in a later patch.
• Refactor changes to `do_git_config_sequence()` (originally in v1 patch 4) to use a function for better readability.

[1]: https://lore.kernel.org/git/CAFA9we-QLQRzJdGMMCPatmfrk1oHeiUu9msMRXXk1MLE5HRxBQ@mail.gmail.com/
[2]: https://lore.kernel.org/git/xmqqmt5lezi3.fsf@gitster.g/
[3]: #1938

Thank you all for your time!
Delilah

cc: Delilah Ashley Wu delilahwu@microsoft.com
cc: Derrick Stolee stolee@gmail.com
cc: Johannes Schindelin johannes.schindelin@gmx.de
cc: Junio C Hamano gitster@pobox.com
cc: Patrick Steinhardt ps@pks.im
cc: Kristoffer Haugsbakk kristofferhaugsbakk@fastmail.com

[gitgitgadget]

There is an issue in commit 4c0da9e:
path: use forward slashes in XDG config on Windows

• Commit not signed off

[delilahw]

NB: i won't be submitting this via gitgitgadget anymore because I'd like the subject to contain v2 (superseding #1938). planning to use b4 instead.

[dscho]

NB: i won't be submitting this via gitgitgadget anymore because I'd like the subject to contain v2 (superseding #1938). planning to use b4 instead.

If you wanted to use GitGitGadget and have a v2, you would need to reopen the original PR and force-push there, then /submit there.

[delilahw]

If you wanted to use GitGitGadget and have a v2, you would need to reopen the original PR and force-push there, then /submit there.

thanks for the suggestion @dscho !! i did something weird with my branch and it wouldn't let me reopen the original PR after force pushing, which is why i opened this new PR. but i've setup b4 in the meantime and keen to try it out hehe

[gitgitgadget]

There is an issue in commit 4f4ffa4:
path: use forward slashes in XDG config on Windows

• Lines in the body of the commit messages should be wrapped between 60 and 76 characters.
  Indented lines, and lines without whitespace, are exempt