static assertion fires from return type when leading constraint is not satisfied

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GCC accepts this code, Clang and MSVC reject it due to failed static assertion in assert.
What does the standard say?
assert
template typename T
constexpr int assert() {
static_assert(sizeof(T) == 1);
return 1;
}

template auto I
using Int = int;

template typename T requires (sizeof(T) == 1)
constexpr auto foo(T) - Int assert T () {
return 1;
}

template typename T requires (sizeof(T) 1)
constexpr auto foo(T a) - Int 1 {
return 2;
}

static_assert(foo('1') == 1);
static_assert(foo(2) == 2);

template typename T
constexpr int assert() {
static_assert(sizeof(T) == 1);
return 1;
}

template auto I
using Int = int;

template typename T requires (sizeof(T) == 1)
constexpr auto foo(T) - Int assert T () {
return 1;
}

template typename T requires (sizeof(T) 1)
constexpr auto foo(T a) - Int 1 {
return 2;
}

static_assert(foo('1') == 1);
static_assert(foo(2) == 2);

Clang output:
source :3:19: error: static assertion failed due to requirement 'sizeof(int) == 1'
3 | static_assert(sizeof(T) == 1);
| ^~~~~~~~~~~~~~
source :11:30: note: in instantiation of function template specialization 'assert int ' requested here
11 | constexpr auto foo(T) - Int assert T () {
| ^
source :21:15: note: while substituting deduced template arguments into function template 'foo' [with T = int]
21 | static_assert(foo(2) == 2);
| ^
source :3:29: note: expression evaluates to '4 == 1'
3 | static_assert(sizeof(T) == 1);

source :3:19: error: static assertion failed due to requirement 'sizeof(int) == 1'
3 | static_assert(sizeof(T) == 1);
| ^~~~~~~~~~~~~~
source :11:30: note: in instantiation of function template specialization 'assert int ' requested here
11 | constexpr auto foo(T) - Int assert T () {
| ^
source :21:15: note: while substituting deduced template arguments into function template 'foo' [with T = int]
21 | static_assert(foo(2) == 2);
| ^
source :3:29: note: expression evaluates to '4 == 1'
3 | static_assert(sizeof(T) == 1);

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