[PATCH] D153536: [Clang] Implement P2169 A nice placeholder with no name

[Corentin Jabot via Phabricator via cfe-commits]

cor3ntin added inline comments.


================
Comment at: clang/test/SemaCXX/cxx2c-placeholder-vars.cpp:2
+// RUN: %clang -cc1 -fsyntax-only -verify -std=c++2c -Wunused-parameter -Wunused %s
+
+void static_var() {
----------------
hubert.reinterpretcast wrote:
> hubert.reinterpretcast wrote:
> > hubert.reinterpretcast wrote:
> > > hubert.reinterpretcast wrote:
> > > > Can we have tests for:
> > > > ```
> > > > struct { int _, _; } a = { ._ = 0 };
> > > > ```
> > > > 
> > > > and
> > > > 
> > > > ```
> > > > struct A {
> > > >   A();
> > > >   int _, _;
> > > > };
> > > > 
> > > > A::A() : _(0) {}
> > > > ```
> > > Codegen test for
> > > ```
> > > static union { int _ = 42; };
> > > int &ref = _;
> > > int foo() { return 13; }
> > > static union { int _ = foo(); };
> > > int main(void) { return ref; }
> > > ```
> > > might be interesting.
> > > 
> > > I suspect that this case was missed in the committee discussion of the paper @cor3ntin.
> > Less controversial tests to consider:
> > ```
> > struct A {
> >   int _;
> >   union { int _; };
> > };
> > struct B { union { int _, _; }; };
> > ```
> > 
> In a similar vein, a codegen test for:
> ```
> struct A { A(); };
> inline void f [[gnu::used]]() {
>   static union { A _{}; };
>   static union { A _{}; };
> }
> ```
> 
> Perhaps not intended to be allowed though (premise was no symbols with "linkage"?)
What's interesting about 

```
static union { int _ = 42; };
int &ref = _;
int foo() { return 13; }
static union { int _ = foo(); };
int main(void) { return ref; }
```
?
It's already supported by clang https://godbolt.org/z/6j89EdnEo


I'm adding the other tests (and fixing the associated bugs, of which there were a few...)



================
Comment at: clang/test/SemaCXX/cxx2c-placeholder-vars.cpp:2
+// RUN: %clang -cc1 -fsyntax-only -verify -std=c++2c -Wunused-parameter -Wunused %s
+
+void static_var() {
----------------
cor3ntin wrote:
> hubert.reinterpretcast wrote:
> > hubert.reinterpretcast wrote:
> > > hubert.reinterpretcast wrote:
> > > > hubert.reinterpretcast wrote:
> > > > > Can we have tests for:
> > > > > ```
> > > > > struct { int _, _; } a = { ._ = 0 };
> > > > > ```
> > > > > 
> > > > > and
> > > > > 
> > > > > ```
> > > > > struct A {
> > > > >   A();
> > > > >   int _, _;
> > > > > };
> > > > > 
> > > > > A::A() : _(0) {}
> > > > > ```
> > > > Codegen test for
> > > > ```
> > > > static union { int _ = 42; };
> > > > int &ref = _;
> > > > int foo() { return 13; }
> > > > static union { int _ = foo(); };
> > > > int main(void) { return ref; }
> > > > ```
> > > > might be interesting.
> > > > 
> > > > I suspect that this case was missed in the committee discussion of the paper @cor3ntin.
> > > Less controversial tests to consider:
> > > ```
> > > struct A {
> > >   int _;
> > >   union { int _; };
> > > };
> > > struct B { union { int _, _; }; };
> > > ```
> > > 
> > In a similar vein, a codegen test for:
> > ```
> > struct A { A(); };
> > inline void f [[gnu::used]]() {
> >   static union { A _{}; };
> >   static union { A _{}; };
> > }
> > ```
> > 
> > Perhaps not intended to be allowed though (premise was no symbols with "linkage"?)
> What's interesting about 
> 
> ```
> static union { int _ = 42; };
> int &ref = _;
> int foo() { return 13; }
> static union { int _ = foo(); };
> int main(void) { return ref; }
> ```
> ?
> It's already supported by clang https://godbolt.org/z/6j89EdnEo
> 
> 
> I'm adding the other tests (and fixing the associated bugs, of which there were a few...)
> 
> Perhaps not intended to be allowed though (premise was no symbols with "linkage"?)


Yes, this should be ill-formed, anything where we would have to mangle  multiple `_` should be ill-formed.
I do believe that's covered though, `_` does not have storage duration.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D153536/new/

https://reviews.llvm.org/D153536