It's possible for weirdness to happen if curbuf is modified while
sourcing from it via :source (with no arguments). For example:
- Deleting lines from or wiping curbuf can cause internal error E315 to
be thrown from ml_get.
- Changing the curbuf to another buffer while sourcing can cause lines
from the new curbuf to then be sourced instead.
Problem:
Anonymous :source (no args) and nvim_exec() don't support Vimscript line continuations.
Solution:
Factor out the concat logic into concat_continued_line() and a
CONCAT_CONTINUED_LINES macro for simple concatenations where lines are
fetched individually.
Closes#14807
It's happening because do_source is only expected to return FAIL when it
was unable to open file . But `nlua_exec_file` returns fail for parsing
and execution error too . Those errors are emitted through `nlua_error`.
So now return value of nlua_exec_file is ignored like do_cmdline. It now
only returns fail when it was unable to open file that check is done
before calling nlua_exec_file or do_cmdline. Errors in nlua_exec_file
are still directly emitted through nlua_error like before.
