aaron.ballman added inline comments.
================
Comment at: clang-tidy/modernize/DeprecatedFunctionalCheck.cpp:48-54
+ } else if (const auto *const Call =
+ Result.Nodes.getNodeAs<CallExpr>("ptr_fun_call")) {
+ diag(Call->getLocStart(), Message) << "'std::ptr_fun'";
+ } else if (const auto *const Call =
+ Result.Nodes.getNodeAs<CallExpr>("mem_fun_call")) {
+ diag(Call->getLocStart(), Message) << "'std::mem_fun'";
+ }
----------------
alexfh wrote:
> aaron.ballman wrote:
> > alexfh wrote:
> > > aaron.ballman wrote:
> > > > alexfh wrote:
> > > > > alexfh wrote:
> > > > > > aaron.ballman wrote:
> > > > > > > massberg wrote:
> > > > > > > > aaron.ballman wrote:
> > > > > > > > > I think that this code should be generalized (same with the
> > > > > > > > > matchers) so that you match on `hasAnyName()` for the
> > > > > > > > > function calls and use `CallExpr::getCalleeDecl()` to get the
> > > > > > > > > declaration. e.g.,
> > > > > > > > > ```
> > > > > > > > > if (const auto *Call =
> > > > > > > > > Result.Nodes.getNodeAs<CallExpr>("blech")) {
> > > > > > > > > if (const Decl *Callee = Call->getCalleeDecl())
> > > > > > > > > diag(Call->getLocStart(), Message) << Calleee;
> > > > > > > > > }
> > > > > > > > > ```
> > > > > > > > > This way you can add more named without having to add extra
> > > > > > > > > logic for the diagnostics.
> > > > > > > > I generalized the code and the matcher.
> > > > > > > > When we use
> > > > > > > > ```
> > > > > > > > << cast<NamedDecl>(Callee);
> > > > > > > > ```
> > > > > > > > we get the template arguments in the name , e.g. `ptr_fun<int,
> > > > > > > > int>`, so I chose to use `getQualifiedNameAsString`.
> > > > > > > > If there is there a better way to get the function name without
> > > > > > > > template arguments I appreciate any suggestions.
> > > > > > > >
> > > > > > > >
> > > > > > > Nope, in that case, your code is correct. However, we generally
> > > > > > > provide the template arguments in diagnostics. I see @alexfh was
> > > > > > > asking for them to be removed as not being useful, but I'm not
> > > > > > > certain I agree with his rationale. Yes, all instances are
> > > > > > > deprecated and thus the template arguments don't discern between
> > > > > > > good and bad cases, but showing the template arguments is also
> > > > > > > consistent with the other diagnostics we emit. For instance,
> > > > > > > other "deprecated" diagnostics also emit the template arguments.
> > > > > > > I'm not certain we should be inconsistent with the way we produce
> > > > > > > diagnostics, but I'll defer to Alex if he still feels strongly
> > > > > > > about leaving them off here.
> > > > > > Indeed, -Wdeprecated-declarations warnings print template
> > > > > > arguments. Moreover, they seem to be issued only on instantiations,
> > > > > > see https://godbolt.org/g/W563gw.
> > > > > >
> > > > > > But I have a number of concerns with template arguments in the
> > > > > > deprecation warnings:
> > > > > >
> > > > > > 1. The note attached to the warning lies. Consider a warning from
> > > > > > the test above:
> > > > > > ...
> > > > > > <source>:11:1: warning: 'B<int>' is deprecated: bbb
> > > > > > [-Wdeprecated-declarations]
> > > > > > B<int> e;
> > > > > > ^
> > > > > > <source>:7:10: note: 'B<int>' has been explicitly marked
> > > > > > deprecated here
> > > > > > struct [[deprecated("bbb")]] B {};
> > > > > >
> > > > > > But `B<int>` hasn't been explicitly marked deprecated, only the
> > > > > > template definition of `B` has been. Template arguments are
> > > > > > important in the case of the explicit template specialization
> > > > > > `A<int>` in the same example, but not in cases where the template
> > > > > > definition was marked deprecated, since template arguments only add
> > > > > > noise and no useful information there.
> > > > > > 2. Warnings can easily become unreadable:
> > > > > > https://godbolt.org/g/AFdznH
> > > > > > 3. Certain coding patterns can result in numerous deprecation
> > > > > > warnings differing only in template arguments:
> > > > > > https://godbolt.org/g/U2JCbG. Clang-tidy can deduplicate warnings,
> > > > > > if they have identical text and location, but adding template
> > > > > > arguments to the message will prevent deduplication. I've seen a
> > > > > > case where thousands of deprecation warnings were generated for a
> > > > > > single line in a widely used header.
> > > > > >
> > > > > > So yes, I feel strongly about leaving off template arguments in
> > > > > > case the whole template was marked deprecated. I think it would be
> > > > > > the right thing to do for the -Wdeprecated-declarations diagnostic
> > > > > > as well.
> > > > > s/leaving off/leaving out/
> > > > > The note attached to the warning lies.
> > > >
> > > > No it doesn't? The attribute is inherited from the primary template
> > > > unless your explicit specialization *removes* the attribute.
> > > > https://godbolt.org/g/ZuXZds
> > > >
> > > > > Warnings can easily become unreadable
> > > >
> > > > This is true of all template diagnostics and isn't specific to
> > > > clang-tidy's treatment of them.
> > > >
> > > > > I've seen a case where thousands of deprecation warnings were
> > > > > generated for a single line in a widely used header.
> > > >
> > > > This sounds more worrying, but at the same time, your link behaving by
> > > > design and doing what I would want it to do. The presence of the
> > > > deprecated primary template isn't what gets diagnosed, it's the *uses*
> > > > of the deprecated entity. This is called out explicitly in
> > > > [dcl.attr.deprecated]p4.
> > > >
> > > > > So yes, I feel strongly about leaving off template arguments in case
> > > > > the whole template was marked deprecated. I think it would be the
> > > > > right thing to do for the -Wdeprecated-declarations diagnostic as
> > > > > well.
> > > >
> > > > I would be strongly opposed to that change to -Wdeprecated-declarations.
> > > >
> > > > We may be at an impasse here, but my viewpoint is unchanged -- I think
> > > > removing the template arguments is inconsistent with other diagnostics.
> > > > I'll defer to you on this, but I think it's a mistake and definitely do
> > > > not want to see it used as precedent.
> > > Let's try to look at this from a different angle: are there benefits
> > > (apart from consistency) of including template arguments to deprecation
> > > warnings where the primary template is deprecated rather than a
> > > specialization? Could you provide an example of a case where template
> > > arguments are making the warning easier to understand or to act upon?
> > >
> > > > The presence of the deprecated primary template isn't what gets
> > > > diagnosed, it's the *uses* of the deprecated entity. This is called out
> > > > explicitly in [dcl.attr.deprecated]p4.
> > > Sure, I'm not proposing to change _where_ the warnings are produced, I
> > > just want the warnings to be free of unnecessary information that
> > > unnecessarily makes the warning messages different. In the example I
> > > provided (https://godbolt.org/g/U2JCbG) the program only refers to the
> > > deprecated entity (class Q) once after it's declared (`Q<T>` in `class S
> > > : Q<T> {};`). IMO knowing the specific value of `T` doesn't give the user
> > > any useful information in this case. This only makes the message less
> > > readable and gets in the way of any efforts to deduplicate the warnings.
> > > Am I missing something?
> > > Let's try to look at this from a different angle: are there benefits
> > > (apart from consistency) of including template arguments to deprecation
> > > warnings where the primary template is deprecated rather than a
> > > specialization? Could you provide an example of a case where template
> > > arguments are making the warning easier to understand or to act upon?
> >
> > My concern is that we elide the template args in *all* cases, not just
> > primary vs specialization. Knowing the template args is quite important in
> > these cases:
> > ```
> > // Primary template isn't deprecated.
> > template<typename T>
> > struct A {};
> >
> > // Specialization is deprecated.
> > template<>
> > struct [[deprecated("aaa")]] A<int> {};
> >
> > // Primary template is deprecated.
> > template<typename T>
> > struct [[deprecated("bbb")]] B {};
> >
> > // Specialization is not deprecated.
> > template<>
> > struct B<int> {};
> > ```
> > However, I agree that in the case where the primary template is deprecated
> > and no specializations differ, the template args don't help all that much.
> >
> > Also, I don't think we should be so quick to write off consistency. I've
> > seen projects parse compiler output before; consistency turns out to be
> > important in weird ways. ;-)
> >
> > > Am I missing something?
> >
> > I think our definition of "unnecessary" is what differs. I consider the
> > template arguments of an instantiation to be necessary as they are part of
> > the type definition. Some types in a template set may be deprecated while
> > others may not be -- losing the template arguments in *all* cases means
> > important information is not conveyed to the user.
> >
> > If we decide we want to change the way we output template diagnostics in
> > the presence of *no* specializations, that's a different discussion.
> > However, the code (as it is) is stripping the template arguments in all
> > cases.
> > My concern is that we elide the template args in *all* cases, not just
> > primary vs specialization.
> > ...
> > However, I agree that in the case where the primary template is deprecated
> > and no specializations differ, the template args don't help all that much.
>
> IIUC, this is the case for all types this check deals with. If it ever
> touches template types that are only deprecated for some sets of template
> arguments, we should make sure it outputs template arguments, since they
> become important.
>
> > Also, I don't think we should be so quick to write off consistency. I've
> > seen projects parse compiler output before;
>
> I'm pretty sure removing template arguments in this check won't break any
> existing projects that parse compiler output ;)
>
> As for consistency with the -Wdeprecated-declarations diagnostic, I could
> have a look at the feasibility of removing template arguments for the cases
> where there's no explicit template specialization.
> IIUC, this is the case for all types this check deals with. If it ever
> touches template types that are only deprecated for some sets of template
> arguments, we should make sure it outputs template arguments, since they
> become important.
That's why I was pushing for this to be a diagnostics engine-level decision --
then we don't have to "remember" to add functionality back in sometime in the
future and all checks (including clang) behave consistently without extra
intervention.
> I'm pretty sure removing template arguments in this check won't break any
> existing projects that parse compiler output ;)
I'm not as confident as you on this point. ;-) However, I don't think that use
case should be an overly strong consideration here, either.
https://reviews.llvm.org/D42730
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