variables not expanded after xargs

[jidanni]

$ $BRO<TAB> #makes $BROWSER. Good!
$ xargs $BRO<TAB> #just beeps. Bad.

[jidanni]

As of 2019 why does this
$ cat $BR<TAB>OWSER
expand, but this
$ xargs $BR<BROWSER>OWSER doesn't?
Please make them both work.

[jidanni]

Normally I can expand $BROWSER
$ $BROW<TAB>
but not in this case:
$ bla bla bla | xargs $BROW<TAB>

[scop]

This would fix it

diff --git a/bash_completion b/bash_completion
index 1d2d2d0b..b8957333 100644
--- a/bash_completion
+++ b/bash_completion
@@ -1820,4 +1823,5 @@ _command_offset()
 
     if [[ $COMP_CWORD -eq 0 ]]; then
+        _variables && return
         local IFS=$'\n'
         compopt -o filenames

There are more places than this where we complete with command names, but we don't complete variable names in any of them based on a quick look. Not entirely sure why. On the other hand a correct completion would depend on exactly what the variable is pointing to; e.g. it should behave differently if it expands to a dir (no space added) or a command (space added) and not even complete variable names that don't expand to either.
But perhaps it would be an improvement just to simply complete the variable names like in this diff. Thoughts?

[jidanni]

Well all I know is the user has already typed in a "$" and a few more letters, before hitting TAB.
And files on Unix don't often start with $, and if they did occasionally. the user could type ./$ or \$ or ./\$ etc. Therefore just expand variables when ever encountering $.

[scop]

Didn't mean that, but rather variables like $HOME, $TMPDIR, etc.

[jidanni]

All I know is that if I do
$ xyz=abc
I expect $x<TAB> will expand to $xyz in all cases, except when inside ' ... '.

[scop]

I'm fairly certain that there is also an expectation whether the completion should add a space after completing the variable or not. But meh, as said, completing the variable in this particular case could be an improvement in the first place, space or not.

[jidanni]

Yup, needs a space after it too.

[scop]

...except when you're completing let's say $HOME or $TMPDIR, or anything that is a directory, then the space is incorrect.

[jidanni]

Hmm, OK. Perhaps detect slashes. And if it is a URL then just like directories, as the user probably wants to put something on the end too...(?)

[scop]

URL completion is out of scope for completion of command names, no URL will complete to a valid one. But as you see, there's more to it than it looks on the surface.

[jidanni]

In this bug I am only talking about expanding the names of variables, not their values. OK let's just always put a space after all of them. No more need to make judgments about which names they use or what their values are.