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Re: Allow [[deprecated]] on call site to disable deprecated warning

From: Avi Kivity <avi_at_[hidden]>
Date: Sun, 7 Feb 2021 16:07:38 +0200
On 07/02/2021 15.55, Marcin Jaczewski wrote:
> niedz., 7 lut 2021 o 14:46 Avi Kivity via Std-Proposals
> <std-proposals_at_[hidden]> napisaƂ(a):
>> On 07/02/2021 13.37, Andrey Semashev via Std-Proposals wrote:
>>> On February 7, 2021 1:22:41 PM Avi Kivity via Std-Proposals
>>> <std-proposals_at_[hidden]> wrote:
>>>> On 28/01/2021 13.34, Ville Voutilainen via Std-Proposals wrote:
>>>>> On Thu, 28 Jan 2021 at 13:06, Dominic Fandrey via Std-Proposals
>>>>> <std-proposals_at_[hidden]> wrote:
>>>>>> I recently ran into this issue:
>>>>>> 1. Marked a set of legacy methods [[deprecated]]
>>>>>> 2. Unit tests no longer compile (we run -Wall -Werror of course)
>>>>>> Of course I don't want to get rid of the unit tests before I get
>>>>>> rid of the
>>>>>> functions. So I was faced with two choices:
>>>>>> 1. Create #ifdef #pragma soup for all 3 compilers that we use
>>>>>> 2. Remove [[deprecated]]
>>>>>> The #ifdef #pragma soup needs to be updated every time a compiler
>>>>>> is added,
>>>>>> and it bloats the code and makes unit tests more difficult to read.
>>>>>> So I
>>>>>> went for option 2. As long as I cannot ignore [[deprecated]] in a
>>>>>> portable
>>>>>> manner I cannot use it.
>>>>>> So my suggestion is:
>>>>>> ```
>>>>>> [[deprecated("use: std::optional<std::size_t> size()")]]int
>>>>>> size(std::size_t & size);
>>>>>> bool test_size() {
>>>>>> std::size_t s{0};
>>>>>> return 0 == [[deprecated]]size(s) && s != 0;
>>>>>> }
>>>>> Create your own MY_DEPRECATED macro, make it expand to actual
>>>>> deprecation normally, but not in unit tests,
>>>>> compile the unit tests with -DMY_SOMETHING that disables deprecations.
>>>>> Or just add a #define into
>>>>> your unit tests.
>>>> Doesn't that break with modules?
>>>> We should not be suggesting solutions that involve the preprocessor
>>>> in 2021.
>>> I don't think that preprocessor is deprecated or its proper use should
>>> be judged or anything. A preprocessor based solution is fine if this
>>> tool is best fit for the job.
>> It does not work with modules. If I have a module that has a
>> [[deprecated]] declaration, no amount of preprocessor tricks in the
>> importing code will affect that declaration.
> But if you control implementation adding `MY_DEPRECATED` and you
> control the build of all modules (aka `-D???` compiler switch) then
> this will work.

It doesn't work. It disables the warning for all call sites, not just
the call site of the unit test.

Without modules, it works, because a header file is evaluated
independently in each translation unit. With modules, a declaration is
exactly the same in all call sites.

> Of course you can't affect macros of module from other module as this
> was one of the main goals of the model proposal.
> But this is not this case. Only problem would be that you will need to
> make a clear build of all modules when you change flags of
> compilation.

So, to unit test something I need to recompile everything?

Compile times are long enough already, and people like to test the code
that runs in production, not code that was specially compiled for the test.

Received on 2021-02-07 08:07:44