[Rpm-maint] [rpm-software-management/rpm] Macro Language - tips, best reference ? (Discussion #2094)

[JVDptt]

Aargh !

Why does this work with only RPM  v4.17 (Fedora 36), not with RPM v4.14.3
(Rocky EL8) :

with RPM v4.17:
$ rpm --eval '%define is_enabled() %["%{expr %{%1}}"=="1"?"%2":"%3"]
%global a_var 1
%{warn:%{is_enabled a_var OK NOT_OK}}'
warning: OK
$

with RPM v4.14.3:
$ rpm --eval '%define is_enabled() %["%{expr %{%1}}"=="1"?"%2":"%3"]
%global a_var 1
%{warn %{is_enabled a_var OK NOT_OK}}'
warning:
$


On Wed, 15 Jun 2022 at 18:44, Jason Vas Dias ***@***.***> wrote:

> Best solution found :
>
> $ rpm --eval '%define is_enabled() %["%{expr
> %{%1}}"=="1"?"Enabled":"Disabled"]
> %global a_var 1
> %{warn:%{is_enabled:a_var}}'
> warning: Enabled
> $
>
> Thanks Panu !
>
> But I'm still not quite getting why this breaks it:
> rpm --eval '%define is_enabled()
> %["%{expr:%{%1}}"=="1"?"Enabled":"Disabled"]
>   ie. just adding the colon after expr             ^- here
> makes rpm emit : "error: parse error in expression: %{a_var}".
> Why ? I am calling all other macros with ':' (colons) separating macro
> name from parameters -
> why can't I do that with expr ?
>
> But anyway, problem solved ! Many thanks.
>
> On Tue, 14 Jun 2022 at 08:48, Panu Matilainen ***@***.***>
> wrote:
>
>> Good question 👍
>>
>> A couple of fundamental problems there:
>>
>>    - function-like (aka parametric) macros, such as is_enabled() should
>>    not be %global because with %global, the body is expanded at definition
>>    time and any tests around eg %1 just melt away useless. Use %define
>>    instead, and lot of weirdness goes away. Alternatively you can escape the
>>    %1, but as a general guideline anything but simple constants, %define is
>>    what you usually want. The "always use global" guidelines in various places
>>    are misguided, really.
>>    - the %{?%1} in is_enabled() tests whether that macro got an argument
>>    or not, which is not what you want. Test with an expression instead.
>>
>> For example:
>>
>> [pmatilai🎩︎localhost ~]$ rpm --eval '%["%{?a_var}"=="1"?"yes":"no"]'
>>
>> no
>>
>> [pmatilai🎩︎localhost ~]$ rpm --define "a_var 0" --eval '%["%{?a_var}"=="1"?"yes":"no"]'
>>
>> no
>>
>> [pmatilai🎩︎localhost ~]$ rpm --define "a_var 1" --eval '%["%{?a_var}"=="1"?"yes":"no"]'
>>
>> yes
>>
>>
>> (Whether you use --eval or --define is a matter of style, but it's better
>> to split stuff over multiple --define/--eval uses (they're simply processed
>> in order), makes it easier to handle for us humans.)
>>
>> Turning that into a parametric macro gets you something like this:
>>
>> [pmatilai🎩︎localhost rpm]$ rpm --define '%is_enabled() %["%{?1}"=="1"?"yes":"no"]' --eval '%{is_enabled %a_var}'
>>
>> no
>>
>> [pmatilai🎩︎localhost rpm]$ rpm --define 'a_var 0' --define '%is_enabled() %["%{?1}"=="1"?"yes":"no"]' --eval '%{is_enabled %a_var}'
>>
>> no
>>
>> [pmatilai🎩︎localhost rpm]$ rpm --define 'a_var 1' --define '%is_enabled() %["%{?1}"=="1"?"yes":"no"]' --eval '%{is_enabled %a_var}'
>>
>> yes
>>
>>
>> Note quoting around the %1 argument test: macros always expand to string
>> values, so testing for integer value would only give you errors. The rest
>> kinda depends what exactly you want to do with it.
>>
>> Hope that helps.
>>
>> —
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>>
>


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