[Clang] Implement CWG2518 - static_assert(false)

This allows `static_assert(false)` to not be ill-formed
in template definitions.

This change is applied as a DR in all C++ modes.

Of notes, a couple of tests were relying of the eager nature
of static_assert

* test/SemaTemplate/instantiation-dependence.cpp
* test/SemaTemplate/instantiate-var-template.cpp

I don't know if the changes to `static_assert`
still allow that sort of tests to be expressed.

Reviewed By: #clang-language-wg, erichkeane, aaron.ballman

Differential Revision: https://reviews.llvm.org/D144285

---

Fixes the build with newer versions of MSVC's STL, reported as
root-project#15321

(cherry picked from commit c767271)

interpreter/llvm-project/clang/docs/ReleaseNotes.rst

@@ -223,6 +223,8 @@ sections with improvements to Clang's support for those languages.
 
 C++ Language Changes
 --------------------
+- Implemented `CWG2518 <https://wg21.link/CWG2518>`_ which allows ``static_assert(false)``
+  to not be ill-formed when its condition is evaluated in the context of a template definition.
 
 C++20 Feature Support
 ^^^^^^^^^^^^^^^^^^^^^

interpreter/llvm-project/clang/lib/Sema/SemaDeclCXX.cpp

@@ -16802,7 +16802,14 @@ Decl *Sema::BuildStaticAssertDeclaration(SourceLocation StaticAssertLoc,
                        FoldKind).isInvalid())
       Failed = true;
 
-    if (!Failed && !Cond) {
+    // CWG2518
+    // [dcl.pre]/p10  If [...] the expression is evaluated in the context of a
+    // template definition, the declaration has no effect.
+    bool InTemplateDefinition =
+        getLangOpts().CPlusPlus && CurContext->isDependentContext();
+
+    if (!Failed && !Cond && !InTemplateDefinition) {
+
       SmallString<256> MsgBuffer;
       llvm::raw_svector_ostream Msg(MsgBuffer);
       if (AssertMessage) {
@@ -16833,7 +16840,8 @@ Decl *Sema::BuildStaticAssertDeclaration(SourceLocation StaticAssertLoc,
         DiagnoseStaticAssertDetails(InnerCond);
       } else {
         Diag(StaticAssertLoc, diag::err_static_assert_failed)
-          << !AssertMessage << Msg.str() << AssertExpr->getSourceRange();
+            << !AssertMessage << Msg.str() << AssertExpr->getSourceRange();
+        PrintContextStack();
       }
       Failed = true;
     }

interpreter/llvm-project/clang/www/cxx_dr_status.html

@@ -14915,7 +14915,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
     <td><a href="https://wg21.link/cwg2518">2518</a></td>
     <td>review</td>
     <td>Conformance requirements and <TT>#error</TT>/<TT>#warning</TT></td>
-    <td align="center">Not resolved</td>
+    <td class="unreleased" align="center">Clang 17</td>
   </tr>
   <tr class="open" id="2519">
     <td><a href="https://wg21.link/cwg2519">2519</a></td>

interpreter/llvm-project/llvm-project.tag

@@ -1 +1 @@
-ROOT-llvm16-20240402-01
+ROOT-llvm16-20240604-01