Re: [PATCHv2 1/2] gdb/guile: perform tilde expansion when sourcing guile scripts

[Simon Marchi via Gdb-patches <gdb-patches@sourceware.org>]

On 2021-05-05 5:01 p.m., Andrew Burgess wrote:
> Before this patch:
> 
>   (gdb) source ~/script.scm
>   ERROR: In procedure apply-smob/1:
>   ERROR: In procedure primitive-load-path: Unable to find file "~/script.scm" in load path
>   Error while executing Scheme code.
>   (gdb)
> 
> This is because the path is not tilde expanded.  In contrast, when
> sourcing a .py or .gdb script the path is tilde expanded.
> 
> This commit fixes this oversight, and allows the above source command
> to work as expected.
> 
> The tilde expansion is done in guile/scm-safe-call.c rather than at a
> higher level, for example, it might be tempting to add the tilde
> expansion in cli/cli-cmds.c:source_script_from_stream, however, not
> every extension language wants to see a tilde expanded file path.  For
> example, consider Python.  Currently we pass in an unexpanded path and
> we see this behaviour:
> 
>   (gdb) source ~/tmp/xxx.py
>   Traceback (most recent call last):
>     File "~/tmp/xxx.py", line 1, in <module>
>   NameError: name 'undefined' is not defined
> 
> If we performed tilde expansion prior to calling the Python sourcer
> function (gdbpy_source_script), we would instead see:
> 
>   (gdb) source ~/tmp/xxx.py
>   Traceback (most recent call last):
>     File "/home/andrew/tmp/xxx.py", line 1, in <module>
>       undefined
>   NameError: name 'undefined' is not defined
> 
> Notice the path expansion in the second line of the error message, I
> believe this is a change for the worse.

I really don't have a strong opinion, but I don't think this would be a
problematic change.  The tilde-expansion thing is really a shell thing
(and we replicate it in GDB).  But once the paths are processed by
programs such as Python, the tilde usually doesn't have a special
meaning.

If I do:

    $ python3 ~/foo.py

I get:

    Traceback (most recent call last):
      File "/home/simark/foo.py", line 1, in <module>
	blah
    NameError: name 'blah' is not defined

Because the shell did the tilde-expansion before passing the file name
to Python.  If I do:

    $ python3 '~/foo.py'

then I get:

    python3: can't open file '/home/simark/build/binutils-gdb-one-target/gdb/~/foo.py': [Errno 2] No such file or directory

Python shows the tilde version of the path in our error messages just
becore we tell it that's the name of the file, Python doesn't use that
name otherwise (I think).  We could tell it the filename is "potato",
and it would say that the error is in file "potato".

So in a sense, passing the tilde-expanded version would make it look
more like the "regular" Python interpreter.

But like I said, I don't have a strong opinion: in the end this is shown
to the user, they will understand it either way.

Otherwise, the patch LGTM.

Simon