aaron.ballman added inline comments.
================
Comment at: test/clang-tidy/misc-definitions-in-headers.hpp:180
+class CE {
+ constexpr static int i = 5; // OK: constexpr definition.
+};
----------------
xazax.hun wrote:
> hokein wrote:
> > hokein wrote:
> > > aaron.ballman wrote:
> > > > This is not as safe as you might think. As-is, this is fine, however,
> > > > if the class is given an inline function where that variable is
> > > > odr-used, you will get an ODR violation.
> > > >
> > > > I think it's mildly better to err on the side of safety here and
> > > > diagnose.
> > > I think the current code (Line `97` in `DefinitionsInHeadersCheck.cpp`)
> > > has already guaranteed this case. Can you try to run it without your
> > > change in the `DefinitionsInHeadersCheck.cpp`?
> > >
> > > I think it still makes sense to add `constexpr` test cases.
> > >
> > >
> > In C++17, `constexpr static int i` is an inline variable, which is fine to
> > define in C++ header -- because `inline` specifier provides a facility
> > allowing definitions (functions/variables) in header that is included in
> > multiple TUs. Additionally, one of the `inline variable` motivations is to
> > support the development of header-only libraries, you can find discussions
> > in http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4424.pdf.
> >
> > Therefore, I'm +1 ignore the inline variables (the same as inline
> > functions).
> Unfortunately, the test will fail without this modification, but I modified
> it to ignore inline variables, which is a way better approach indeed.
The paper you cited was a feature not a defect, so prior to the paper's
adoption in C++17, the behavior is that the constexpr variable may trigger an
ODR violation, which is why I was saying this should be diagnosed rather than
ignored. There was real-world motivation for that paper.
Repository:
rL LLVM
https://reviews.llvm.org/D34449
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