Support $XDG_CONFIG_HOME in module search path

[nsfisis]

Overview

Add support for the $XDG_CONFIG_HOME environment variable in module search path, following the XDG Base Directory Specification.

Related issue: #2966

Changes

Expand $JQ_CONFIG_HOME in module search path like $ORIGIN.

The actual value is resolved as follows:

1. $XDG_CONFIG_HOME/jq if the environment variable $XDG_CONFIG_HOME is set and the directory exists
2. Non-Windows platforms: $HOME/.config/jq if the directory exists
3. $HOME/.jq

In addition, the default module search path is changed:

• ~/.jq → $JQ_CONFIG_HOME (changed)
• $ORIGIN/../lib/jq
• $ORIGIN/../lib

Original Changes

Note

This section describes the original changes before code review.

Expand $XDG_CONFIG_HOME/ in module search path to the value of the environment variable $XDG_CONFIG_HOME like $ORIGIN.

If $XDG_CONFIG_HOME is unset or empty,

• Non-Windows: falls back to $HOME/.config, which is suggested by XDG Base Directory Specification
• Windows: removes the path from search path list

In addition, add $XDG_CONFIG_HOME/jq to the default module search path. Search order is as follows:

• ~/.jq
• $XDG_CONFIG_HOME/jq (added)
• $ORIGIN/../lib/jq
• $ORIGIN/../lib

~/.jq takes priority over $XDG_CONFIG_HOME/jq to keep compatibility.

References

• XDG Base Directory Specification

[wader]

I wonder if it would make more sense to skip search path changes and introduce a get_config_home function etc that do something like this:

• if $XDG_CONFIG_HOME is set and is not empty use $XDG_CONFIG_HOME/jq
• if $HOME/.config/jq exist and is a directory use it
• use $HOME

and use it in load_program?

(note that i skipped thinking about windows here)

[nsfisis]

Thank you for review!

I introduced $JQ_CONFIG_HOME, which is expanded to the resolved config home.

The value is determined as follows:

1. $XDG_CONFIG_HOME/jq if the environment variable is set and the directory exists
2. Non-Windows: $HOME/.config/jq if the directory exists
3. $HOME/.jq (original jq config home)

If a user has $XDG_CONFIG_HOME/jq or ~/.config/jq, the scripts under the directories will be loaded. Otherwise, the ~/.jq directory is loaded as before.

[wader]

Thanks. And i think it makes sense that this should not affect include "~/...", that would be confusing?

What do other maintainers thinks? it seems reasonable that jq should support XDG_CONFIG_HOME somehow