[PATCH] D55433: [clang-tidy] Adding a new modernize use nodiscard checker

[MyDeveloperDay via Phabricator via cfe-commits]

MyDeveloperDay marked 3 inline comments as done.
MyDeveloperDay added inline comments.


================
Comment at: test/clang-tidy/modernize-use-nodiscard.cpp:126
+template<class T>
+class Bar
+{
----------------
MyDeveloperDay wrote:
> MyDeveloperDay wrote:
> > JonasToth wrote:
> > > MyDeveloperDay wrote:
> > > > curdeius wrote:
> > > > > JonasToth wrote:
> > > > > > I think the template tests should be improved.
> > > > > > What happens for `T empty()`, `typename T::value_type empty()` and so on. THe same for the parameters for functions/methods (including function templates).
> > > > > > 
> > > > > > Thinking of it, it might be a good idea to ignore functions where the heuristic depends on the template-paramters.
> > > > > It might be a good idea to add a note in the documentation about handling of function templates and functions in class templates.
> > > > I think I need some help to determine if the parameter is a template parameter (specially a const T & or a const_reference)
> > > > 
> > > > I'm trying to remove functions which have any type of Template parameter (at least for now)
> > > > 
> > > > I've modified the hasNonConstReferenceOrPointerArguments matcher to use isTemplateTypeParamType()
> > > > 
> > > > but this doesn't seem to work though an Alias or even just with a const &
> > > > 
> > > > ```
> > > >   return llvm::any_of(Node.parameters(), [](const ParmVarDecl *Par) {
> > > >     QualType ParType = Par->getType();
> > > > 
> > > >     if (ParType->isTemplateTypeParmType())
> > > >       return true;
> > > > 
> > > >     if (ParType->isPointerType() || isNonConstReferenceType(ParType))
> > > >       return true;
> > > > 
> > > >     return false;
> > > >   });
> > > > ```
> > > > 
> > > > mostly the tests cases work for  T and T&  (see below)
> > > > 
> > > > but it does not seem to work for const T&, or const_reference, where it still wants to add the [[nodiscard]]
> > > > 
> > > > Could anyone give me any pointers, or somewhere I can look to learn?  I was thinking I needed to look at the getUnqualifiedDeSugared() but it didn't seem to work the way I expected.
> > > > 
> > > > ```
> > > > template<class T>
> > > > class Bar
> > > > {
> > > >     public:
> > > >     using value_type = T;
> > > >     using reference = value_type&;
> > > >     using const_reference = const value_type&;
> > > > 
> > > >     bool empty() const;
> > > >     // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: function 'empty' should be marked NO_DISCARD [modernize-use-nodiscard]
> > > >     // CHECK-FIXES: NO_DISCARD bool empty() const;
> > > > 
> > > >     // we cannot assume that the template parameter isn't a pointer
> > > >     bool f25(value_type) const;
> > > >     // CHECK-MESSAGES-NOT: warning:
> > > >     // CHECK-FIXES: bool f25(value_type) const;
> > > > 
> > > >     bool f27(reference) const;
> > > >     // CHECK-MESSAGES-NOT: warning:
> > > >     // CHECK-FIXES: bool f27(reference) const
> > > > 
> > > >     typename T::value_type f35() const;
> > > >     // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: function 'f35' should be marked NO_DISCARD [modernize-use-nodiscard]
> > > >     // CHECK-FIXES: NO_DISCARD typename T::value_type f35() const
> > > > 
> > > >     T f34() const;
> > > >     // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: function 'f34' should be marked NO_DISCARD [modernize-use-nodiscard]
> > > >     // CHECK-FIXES: NO_DISCARD T f34() const
> > > > 
> > > >     bool f31(T) const;
> > > >     // CHECK-MESSAGES-NOT: warning:
> > > >     // CHECK-FIXES: bool f31(T) const
> > > > 
> > > >     bool f33(T&) const;
> > > >     // CHECK-MESSAGES-NOT: warning:
> > > >     // CHECK-FIXES: bool f33(T&) const
> > > > 
> > > >     // -------------  FIXME TESTS BELOW FAIL ------------- //
> > > >     bool f26(const_reference) const;
> > > >     // CHECK-MESSAGES-NOT: warning:
> > > >     // CHECK-FIXES: bool f26(const_reference) const;
> > > > 
> > > >     bool f32(const T&) const;
> > > >     // CHECK-MESSAGES-NOT: warning:
> > > >     // CHECK-FIXES: bool f32(const T&) const
> > > > };
> > > > 
> > > > ```
> > > > 
> > > > 
> > > > 
> > > > 
> > > > 
> > > > 
> > > Is this resolved, as you marked it done?
> > Still working on these last 2 cases, they don't seem to be excluded with the isTemplateTypeParmType() call
> > 
> >     // -------------  FIXME TESTS BELOW FAIL ------------- //
> >     bool f26(const_reference) const;
> >     // CHECK-MESSAGES-NOT: warning:
> >     // CHECK-FIXES: bool f26(const_reference) const;
> > 
> >     bool f32(const T&) const;
> >     // CHECK-MESSAGES-NOT: warning:
> >     // CHECK-FIXES: bool f32(const T&) const
> > 
> > Let me fix what I can and I'll send an updated revision
> template arguments are now ignored so these tests are fixed
I found detecting  `typename T::value_type` and  `const_reference`, particularly troublesome, in the end opting for the following, which I wasn't too happy with


```
static bool isAliasedTemplateParamType(const QualType &ParamType) {
  return (ParamType.getCanonicalType().getAsString().find("type-parameter-") !=
          std::string::npos);
}

```
I'm not sure if there is a better way?


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https://reviews.llvm.org/D55433