Question about `platforms` and `${os.platform}`

[Jason Liu]

On Sat, Dec 11, 2021 at 5:20 PM Ryan Schmidt <ryandesign at macports.org>
wrote:

>
>
> On Dec 10, 2021, at 15:07, Jason Liu wrote:
>
>>
>> A conversation in one of my PRs has brought up an interesting question
>> that I've been wondering about for a long time. In Portfiles, whenever I've
>> had a test for `${os.major} <= xx`, I've typically always added an
>> additional check for darwin in the front, i.e.:
>>
>> if {${os.platform} eq "darwin" && ${os.major} <= xx} {
>>
>> I've done it that way because I basically copied what I saw from other
>> Portfiles, and because I get gently admonished by the committers when I
>> forget to.
>
>
> Yes, please always do that.


Then would it be easier (or even kosher) to simply wrap the majority of the
Portfile inside of a single

if {${os.platform} eq "darwin"} {

and be done with it, instead of needing to add one each and every time I
have a conditional involving `${os.major}`?

I was under the impression that the `platforms darwin` line means that the
>> entire Portfile is supposed to be valid only for `${os.platform} eq
>> "darwin"`, no? (In other words, my understanding is that a line such as
>> `platforms darwin freebsd openbsd` is meant to signify that "this Portfile
>> is supposed to be valid for the listed platforms".) If that's not the case,
>> then what is the purpose of `platforms darwin`?
>
>
> The platforms line is not used by MacPorts in any way at this time, other
> than to display it in the output of "port info". There is a ticket about
> possibly using it in the future as a way to indicate which OS versions the
> port is compatible with, but I don't think that got beyond the idea phase.
>

That seems like a pity, and a bit of a waste, considering that platforms is
being included in each and every Portfile.

-- 
Jason Liu


On Sat, Dec 11, 2021 at 5:20 PM Ryan Schmidt <ryandesign at macports.org>
wrote:

>
>
> On Dec 10, 2021, at 15:07, Jason Liu wrote:
>
> > A conversation in one of my PRs has brought up an interesting question
> that I've been wondering about for a long time. In Portfiles, whenever I've
> had a test for `${os.major} <= xx`, I've typically always added an
> additional check for darwin in the front, i.e.:
> >
> > if {${os.platform} eq "darwin" && ${os.major} <= xx} {
> >
> > I've done it that way because I basically copied what I saw from other
> Portfiles, and because I get gently admonished by the committers when I
> forget to.
>
> Yes, please always do that.
>
>
> > But I've also always wondered why it's necessary.
>
> Your Portfile could be parsed or accessed by non-Darwin operating systems.
> For example, before we took over server hosting duties in 2016, all of the
> server VMs including the one that generated the PortIndex files (except the
> actual macOS build machines) were running Linux; perhaps some day we will
> once again want to try using a server OS other than macOS for this task.
> There are even some users using Linux to test various things in MacPorts.
> We don't really expect many ports to be installable on other operating
> systems or for maintainers to test anything on other operating systems, but
> just take 2 seconds when you're writing an OS version conditional to think
> about what you're trying to express, and then express it, including
> checking os.platform. Typical forms include the one you mentioned:
>
> if {${os.platform} eq "darwin" && ${os.major} <= xx}
>
> (<, <=, ==, >=, >)
>
> And the other one:
>
> if {${os.platform} ne "darwin" || ${os.major} <= xx}
>
> (<, <=, ==, >=, >)
>
> Usually the decision about which to use comes down to whether the thing
> you're doing is Mac-specific or not. For example, if you were writing a
> conditional to use the Security framework on recent macOS and openssl on
> older macOS, what should happen if perchance the port is used on non-macOS?
> In this case, the answer is that frameworks are a Mac thing, so you would
> want to use openssl for non-macOS.
>
>
> > I was under the impression that the `platforms darwin` line means that
> the entire Portfile is supposed to be valid only for `${os.platform} eq
> "darwin"`, no? (In other words, my understanding is that a line such as
> `platforms darwin freebsd openbsd` is meant to signify that "this Portfile
> is supposed to be valid for the listed platforms".) If that's not the case,
> then what is the purpose of `platforms darwin`?
>
> The platforms line is not used by MacPorts in any way at this time, other
> than to display it in the output of "port info". There is a ticket about
> possibly using it in the future as a way to indicate which OS versions the
> port is compatible with, but I don't think that got beyond the idea phase.
>
>
>
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