Better error message when missing args to pdb command

[hauntsaninja]

Current behaviour:

λ ./python.exe -c 'breakpoint()'
> <string>(1)<module>()
-> breakpoint()
(Pdb) source
*** SyntaxError: invalid syntax

Proposed behaviour:

./python.exe -c 'breakpoint()'
> <string>(1)<module>()
-> breakpoint()
(Pdb) source
*** Missing arg!

Linked PRs

• gh-126944: Better error for missing arg in pdb #126945
• gh-126944: Show explicit errors when required arguments of pdb commands are missing #130240