How is P0522R0 breaking code?

Question

Today I was reading the C++17 support page of clang. I\'ve notice something odd. The feature Matching template template parameters to compatible arguments (P0522R0)

Answer 1

A more common scenario is when some code wants to inspect the template arguments with a set of partial specializations, e.g.:

template struct Foo;

template class X, class T> 
struct Foo> { /* ... */ };

template class X, class T, class U> 
struct Foo> { /* ... */ };

// etc., etc.

Foo> is now ill-formed without an appropriate partial ordering fix.