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:
> > > 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.
https://reviews.llvm.org/D42730
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