[libc++][Clang] Added explanation why is_constructible evaluated to false. Updated the diagnostics checks in libc++ tests. (#144220)

Added explanation why a is constructible evaluated to false. Also fixed
problem with ExtractTypeTraitFromExpression. In case std::is_xxx_v<>
with variadic pack it tries to get template argument, but fails in
expression Arg.getAsType() due to Arg.getKind() ==
TemplateArgument::ArgKind::Pack, but not
TemplateArgument::ArgKind::Type.
Reverts #144127
Fixies
https://github.com/llvm/llvm-project/pull/143309#issuecomment-2970012054

2 files changed, 3 insertions, 0 deletions

diff --git a/libcxx/test/std/utilities/function.objects/func.bind.partial/bind_back.verify.cpp b/libcxx/test/std/utilities/function.objects/func.bind.partial/bind_back.verify.cpp
index eb100c1..6a63b65 100644
--- a/libcxx/test/std/utilities/function.objects/func.bind.partial/bind_back.verify.cpp
+++ b/libcxx/test/std/utilities/function.objects/func.bind.partial/bind_back.verify.cpp
@@ -69,6 +69,8 @@ void test() {
     auto f = std::bind_back([](const Arg&) {}, x);
     // expected-error-re@*:* {{static assertion failed{{.*}}bind_back requires all decay_t<Args> to be constructible from respective Args}}
     // expected-error@*:* {{no matching constructor for initialization}}
+    // expected-error@*:* 0-1{{call to deleted constructor of 'F'}}
+    // expected-error@*:* 0-1{{call to deleted constructor of 'Arg'}}
   }
 
   { // Mandates: (is_move_constructible_v<decay_t<Args>> && ...)
diff --git a/libcxx/test/std/utilities/function.objects/func.bind_front/bind_front.verify.cpp b/libcxx/test/std/utilities/function.objects/func.bind_front/bind_front.verify.cpp
index 5100259..27a1fba 100644
--- a/libcxx/test/std/utilities/function.objects/func.bind_front/bind_front.verify.cpp
+++ b/libcxx/test/std/utilities/function.objects/func.bind_front/bind_front.verify.cpp
@@ -42,4 +42,5 @@ void f() {
     auto d = std::bind_front(do_nothing, n); // expected-error {{no matching function for call to 'bind_front'}}
 
     auto t = std::bind_front(testNotMoveConst, NotMoveConst(0)); // expected-error {{no matching function for call to 'bind_front'}}
+    // expected-error@*:* 0-1{{call to deleted constructor of 'NotMoveConst'}}
 }