bug#60464: 29.0.60; Regression - pcomplete-arg fails with argument 'last

[Gregory Heytings]

After working a bit more on this bug, I concluded that what Stefan 
initially suggested, to use the string representation of the value, is 
safer than trying to extract the string corresponding to the argument that 
the user typed in from the command line.

But that's not the end of the story.  The problem is that, IIUC, in 
Eshell, in a directory with .el files and without .EL files:

(1) ls *.el TAB should display all these files in *Completions*

(2) ls *.EL TAB should say "No match"

(3) ls *.el SPC TAB should display all files (not just the .el ones) in 
*Completions*

(4) ls *.EL SPC TAB should display all files (not just the .el ones) in 
*Completions*

IOW, sometimes pcomplete-arg should in fact return a list and not a single 
string value, because that's what Eshell expects (case (1) above), and 
sometimes it shouldn't.  According to my tests, a non-string value can be 
returned if and only if index is 'last'.  Hopefully, this is also what 
other users of pcomplete expect.

Can you please test the attached patch as extensively as possible, and 
report if you see regressions?

Jim, can you also try the patch and report if you see regressions?

Stefan and Eli, does that patch look right to you?

Thanks.

Further-improvement-for-non-string-values-in-pcomple.patch
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