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:
> > > > > 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.
> > That's why I was pushing for this to be a diagnostics engine-level decision
>
> Diagnostic engine doesn't have enough information on how to distinguish cases
> where the template parameters in the message are useful and where they
> aren't. Specifically, for the deprecation warnings this depends on what is
> explicitly marked with the [[deprecated]] attribute (primary template vs.
> explicit template instantiation - if this even makes sense to do at all). For
> other warnings the logic will be different. For this check there don't seem
> to be any cases where the template arguments would be useful in the message
> (and I would be surprised, if one of the future C++ standards declared only
> certain instantiations of template classes in STL deprecated, but it it does,
> we can reconsider this decision).
> Diagnostic engine doesn't have enough information on how to distinguish cases
> where the template parameters in the message are useful and where they
> aren't. Specifically, for the deprecation warnings this depends on what is
> explicitly marked with the [[deprecated]] attribute (primary template vs.
> explicit template instantiation - if this even makes sense to do at all).
By "explicit template instantiation", do you mean explicit specialization? If
so, that definitely makes sense (it's even called out in the standard).
> For other warnings the logic will be different. For this check there don't
> seem to be any cases where the template arguments would be useful in the
> message (and I would be surprised, if one of the future C++ standards
> declared only certain instantiations of template classes in STL deprecated,
> but it it does, we can reconsider this decision).
`std::vector<bool>` immediately comes to mind where it's reasonable to want to
deprecate the specialization and not the primary template (and the C++
committee might someday decide to do exactly that).
https://reviews.llvm.org/D42730
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