Re: wrong behaviour when unsetting/setting some variables

On 29/02/2024 18:45, Martijn Dekker wrote:
> Op 29-02-2024 om 18:07 schreef Harald van Dijk:
>> On 29/02/2024 17:41, Martijn Dekker wrote:
>>> Op 28-02-2024 om 00:56 schreef Harald van Dijk:
>>>> However, trying to fix this I come across a corner case where it is 
>>>> not clear to me what the intended behaviour is.
>>>>
>>>>    set -a; readonly foo=bar; export # some shells export, not all
>>>
>>> IMO, the shell should export it in that case; POSIXly, 'set -a' 
>>> should cause the variable to be exported whenever a value is 
>>> effectively assigned to it (whether this is by a "true" shell 
>>> assignment, an assignment-argument, an expansion like ${foo=bar} or 
>>> ${foo:=bar}, indirectly by 'read' or 'getopts', or maybe other cases 
>>> I'm not thinking of).
>>
>> Spec-wise, the thing that troubles me is that the option is specified as
>>
>>  > When this option is on, the export attribute shall be set for each
>>  > variable to which an assignment is performed; see XBD Variable
>>  > Assignment.
>>
>> where XBD Variable Assignment is only about the assignment syntax of 
>> the shell, not other syntax or other commands even if they also cause 
>> variables to become assigned.
> 
> Yeah, that's confusing (and IMO should be fixed in the spec), but that 
> same paragraph goes on to mention 'getopts' and 'read' as examples of 
> utilities that perform assignments. In other words, though 'read var' is 
> no XBD "Variable Assignment" assignment, it's stated explicitly that 
> 'var', on which 'read' performs an assignment, should gain the export 
> attribute.

Good point, though by special-casing getopts and read, it kind of 
implies that it does not apply to other commands and utilities.

Anyway, now that I think we are on the same page about what shells 
*should* do: in dash, a quick search suggests this should be the following:

* Substitutions may perform assignment (the ones you mentioned, plus
   $((...)) arithmetic)
* The for command performs assignments to the loop variable.
* The cd command sets PWD and OLDPWD.
* The getopts command does not merely assign to the specified variable,
   also to OPTARG and OPTIND.
* The local and readonly commands perform assignments to specified
   variables.
* Every command causes a value to be assigned to LINENO.
* Every simple command causes a value to be assigned to _.

The way I implemented LINENO, the implicit export does not work for 
that, and for consistency, it should, even if no one is going to be 
relying on that. I have not gone over the other ones to check if they 
are all handled correctly.

Cheers,
Harald van Dijk