[clang] [Clang][Sema] Print more static_assert exprs (PR #74852)

[via cfe-commits]

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@@ -0,0 +1,115 @@
+// RUN: %clang_cc1 -std=c++2a -verify %s
+
+struct A {
+  int a, b[3], c;
+  bool operator==(const A&) const = default;
+};
+
+constexpr auto a0 = A{0, 0, 3, 4, 5};
+
+// expected-note at +1 {{evaluates to 'A{0, {0, 3, 4}, 5} == A{1, {2, 3, 4}, 5}'}}
+static_assert(a0 == A{1, {2, 3, 4}, 5}); // expected-error {{failed}}
+
+struct _arr {
+  const int b[3];
+  constexpr bool operator==(const int rhs[3]) const {
+    for (unsigned i = 0; i < sizeof(b) / sizeof(int); i++)
+      if (b[i] != rhs[i])
+        return false;
+    return true;
+  }
+};
+
+// expected-note at +1 {{{evaluates to '_arr{{2, 3, 4}} == (int[3]){0, 3, 4}'}}}
+static_assert(_arr{2, 3, 4} == a0.b); // expected-error {{failed}}
+
+struct B {
+  int a, c; // named the same just to keep things fresh
+  bool operator==(const B&) const = default;
+};
+
+// expected-note at +1 {{evaluates to 'B{7, 6} == B{8, 6}'}}
+static_assert(B{7, 6} == B{8, 6}); // expected-error {{failed}}
+
+typedef int v4si __attribute__((__vector_size__(16)));
+
+struct C: A, B {
+  enum { E1, E2 } e;
+  bool operator==(const C&) const = default;
+};
+
+constexpr auto cc = C{A{1, {2, 3, 4}, 5}, B{7, 6}, C::E1};
+
+// expected-note at +1 {{{evaluates to 'C{{1, {2, 3, 4}, 5}, {7, 6}, 0} == C{{0, {0, 3, 4}, 5}, {5, 0}, 1}'}}}
+static_assert(cc == C{a0, {5}, C::E2}); // expected-error {{failed}}
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sethp wrote:

I hear your frustration there: it's a very goldilocks problem to get the feedback "just right," and not one made easier by the, ah, breadth of individual preferences (and the cartesian product thereof with the standards).

In this case, would it make sense to mirror what clang does with e.g. integer constants, and skip the note if they evaluate identically to as-written? So, we'd avoid noting the redundant info for `static_assert(S{1, 2, 3} == S{1, 2, 3})`, but still emit the result of the `bit_cast` for `static_assert(S{1, 2, 3} == std::bit_cast<S>(0x030201))`?

https://github.com/llvm/llvm-project/pull/74852