open unexpectedly creates temporary files with undefined variables sometimes #22385
Comments
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Could you provide some TODO-ed unit tests that will currently fail but will pass if this problem is corrected? Thanks. |
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Like this? blead...mauke:perl5:open-undef-todo-tests |
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pp_aelem and pp_alemfast return &PL_sv_undef for non-lvalue array lookups, so the check PerlIO_openn() does for For the CORE::open() call:
I'm not fond of this kind of magical "only-this-SV"-ness, though making it work for any undefined SV might cause other problems (eg. code that expects the open to fail for generic undef values). I don't see a simple fix. |
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I have a couple of (ignorance-based¹) possible solutions:
¹ meaning I don't know how to actually implement them, which always makes it easier to say "just do X!" |
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While CORE::open() doesn't display this misbehaviour for the subscripting ops, it does display it for other OPs that return I considered some of these options. Realize that both the normal open() op and CORE::open() end up being handled by pp_open, and the OP_OPEN generated by coresub_op() has generally default flags, so it wouldn't have a We could invert that flag, so Also the So not simple, and doesn't fully fix it anyway. |
Passing undef as the filename to open should create a temporary file.
Previously, this was implemented as a simple `if (arg == &PL_sv_undef)`
check. However, other operations (such as accessing non-existent
array/hash elements) also return `&PL_sv_undef` directly, which `open`
would then silently interpret as directions to create a temp file.
Solution: Check (at compile time) whether the filename argument is an
`OP_UNDEF`, and if so, set the `OPf_SPECIAL` flag on `OP_OPEN`. At
runtime, if `&PL_sv_undef` is passed but `OPf_SPECIAL` is not set,
replace it by a new mortal SV, which is treated as a regular filename
(that happens to be undef) by PerlIO.
(For runtime calls via `&CORE::open`, we cannot distinguish between
`undef` and `delete $hash{nosuchkey}` as arguments, so to keep the
`undef` case working, we always set `OPf_SPECIAL` in the generated core
sub for `open`.)
This functionality probably should be a private op flag (something like
`OPpUNDEF_MEANS_TEMPFILE`?), but as far as I can tell, all possible
private bits are already taken in `OP_OPEN`.
Fixes Perl#22385.
Passing undef as the filename to open should create a temporary file.
Previously, this was implemented as a simple `if (arg == &PL_sv_undef)`
check. However, other operations (such as accessing non-existent
array/hash elements) also return `&PL_sv_undef` directly, which `open`
would then silently interpret as directions to create a temp file.
Solution: Check (at compile time) whether the filename argument is an
`OP_UNDEF`, and if so, set the `OPf_SPECIAL` flag on `OP_OPEN`. At
runtime, if `&PL_sv_undef` is passed but `OPf_SPECIAL` is not set,
replace it by a new mortal SV, which is treated as a regular filename
(that happens to be undef) by PerlIO.
(For runtime calls via `&CORE::open`, we cannot distinguish between
`undef` and `delete $hash{nosuchkey}` as arguments, so to keep the
`undef` case working, we always set `OPf_SPECIAL` in the generated core
sub for `open`.)
This functionality probably should be a private op flag (something like
`OPpUNDEF_MEANS_TEMPFILE`?), but as far as I can tell, all possible
private bits are already taken in `OP_OPEN`.
Fixes Perl#22385.
Description
perldoc -f open:This feature was added in 5.8.0 and is intended to only trigger when a literal
undefis passed as the filename. It does not happen if a variable whose contents areundefis used:Steps to Reproduce
However, if you use an array or hash element that doesn't exist at all (as opposed to existing but containing
undef), the special behavior kicks in andopensilently succeeds, creating a temp file:Even this behavior is not entirely consistent, however. If you use a runtime call to
&CORE::open, it starts failing again (but with duplicate warning messages for some reason):Expected behavior
A call to
openthat does not pass a literalundef, but an element of an array or hash, should complain about the undefined value and fail. Basically like the&CORE::openversion, but there I'd expect to see only one copy of the warning.Perl configuration
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