Recently I had a scenario where I had:
1. A class C with many members m_1...m_n of the same type T
2. T's default constructor was deleted
3. I accidentally omitted an explicitly constructed member in the
initializer list C() : m_1(foo), m_2(bar), ... { }
Clang told me that T's default constructor was deleted, and told me that
the call to T() was in C() (which it implicitly was), but didn't tell me
which member was being default constructed.
It was difficult to fix this problem because I had no easy way to list
all the members of type T in C and C's superclasses which would have let
me find which member was missing,
clang/test/CXX/class/class.init/p1.cpp is a simplified version of this
problem (a2 is missing from the initializer list of B)
39879e4f40
