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

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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}}
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sethp wrote:

this also doesn't quite work as advertised, either. The closest I could come was something like:

```
constexpr int v[3] = {0, 3, 4};
static_assert(_arr{{2, 3, 4}} == v);
// ->
constexpr int v[3] = {0};
static_assert(_arr{{2}} == v);
```

Because anything else and the evaluator complained about invalid `constexpr` subexpressions in:

```
In call to '_arr{{2}}.operator==(&(int[3]){0}[0])'
```

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