https://bugs.llvm.org/show_bug.cgi?id=50577
Bug ID: 50577
Summary: Partial ordering of function templates accepting
template template parameters sensitive to existence of
parameter list in requires expression
Product: clang
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: C++2a
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected], [email protected]
The following translation unit is accepted by clang unless you define
AMBIGUOUS:
```
template<typename>
struct s {
};
#ifdef AMBIGUOUS
template<typename T>
concept true1 = requires(T) {
requires true;
};
#else
template<typename T>
concept true1 = requires {
requires true;
};
#endif
template<typename T>
concept true2 = requires {
requires true;
};
template<template<typename...> typename Template, typename T> requires
true1<Template<int>> and true2<T>
void f(T) {
}
template<template<typename, auto...> typename Template, typename T> requires
true1<Template<int>>
void f(T) {
}
void g() {
f<s>(0);
}
```
If AMBIGUOUS is defined, it is rejected with the error message
```
source>:35:2: error: call to 'f' is ambiguous
f<s>(0);
^~~~
<source>:27:6: note: candidate function [with Template = s, T = int]
void f(T) {
^
<source>:30:6: note: candidate function [with Template = s, T = int]
void f(T) {
^
1 error generated.
Compiler returned: 1
```
See it live: https://godbolt.org/z/6ecMWxcq6
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