[PATCH] D63134: [clang] improving diagnotics for invalid constexpr defaulted special membres

[Tyker via Phabricator via cfe-commits]

Tyker created this revision.
Tyker added a reviewer: rsmith.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

this patch improves diagnostic for invalid constexpr defaulted special members by adding notes explaining why the special member cannot be constexpr.

example
input:

  01 struct B {};
  02 
  03 struct C : virtual B {
  04 };
  05 
  06 struct D {
  07   C c;
  08 };
  09 
  10 struct A : D {
  11   constexpr A() = default;
  12 };
  13 
  14 union U {
  15   A a;
  16   int b;
  17   constexpr U() = default;
  18 };
  19 
  20 struct E {
  21   ~E() {}
  22 };
  23 
  24 struct F {
  25   E e;
  26   constexpr F& operator=(const F&) =default;
  27 };

output with patch:

  test.cpp:11:3: error: defaulted definition of default constructor is not constexpr because:
    constexpr A() = default;
    ^
  test.cpp:10:12: note: base class 'D' of 'A' has a non-constexpr implicit default constructor
  struct A : D {
             ^
  test.cpp:7:5: note: non-static data member 'c' of 'D' has a non-constexpr implicit default constructor
    C c;
      ^
  test.cpp:3:12: note: 'C' inherits virtually from 'B'
  struct C : virtual B {
             ^
  test.cpp:17:3: error: defaulted definition of default constructor is not constexpr because:
    constexpr U() = default;
    ^
  note: unions require exactly one non-static data member initializer to have a constexpr default constructor
  test.cpp:26:3: error: defaulted definition of copy assignment operator is not constexpr because:
    constexpr F& operator=(const F&) =default;
    ^
  note: 'F' is not a literal type
  3 errors generated.

I didn't adapt exitsing tests yet because the diagnostics emitted are likely be adapted during review.


Repository:
  rC Clang

https://reviews.llvm.org/D63134

Files:
  clang/include/clang/Basic/DiagnosticSemaKinds.td
  clang/lib/Sema/SemaDeclCXX.cpp

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