[clang] Reset track of immediate function context when entering new function

Due to not resetting that, clang still thinks that it is in immediate
function context even if it already entered non-consteval function.
This caused consteval functions reaching codegen in some cases.

Fixes #61142

Reviewed By: cor3ntin, aaron.ballman

Differential Revision: https://reviews.llvm.org/D147531

Author: Fznamznon

clang/docs/ReleaseNotes.rst

@@ -279,6 +279,9 @@ Bug Fixes in This Version
 - Fix crash when generating code coverage information for `PseudoObjectExpr` in 
   Clang AST.
   (`#45481 <https://github.com/llvm/llvm-project/issues/45481>`_)
+- Fix the assertion hit when a template consteval function appears in a nested
+  consteval/constexpr call chain.
+  (`#61142 <https://github.com/llvm/llvm-project/issues/61142>`_)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaDecl.cpp

@@ -15180,6 +15180,15 @@ Decl *Sema::ActOnStartOfFunctionDef(Scope *FnBodyScope, Decl *D,
         FD->isConsteval() ? ExpressionEvaluationContext::ImmediateFunctionContext
                           : ExprEvalContexts.back().Context);
 
+  // Each ExpressionEvaluationContextRecord also keeps track of whether the
+  // context is nested in an immediate function context, so smaller contexts
+  // that appear inside immediate functions (like variable initializers) are
+  // considered to be inside an immediate function context even though by
+  // themselves they are not immediate function contexts. But when a new
+  // function is entered, we need to reset this tracking, since the entered
+  // function might be not an immediate function.
+  ExprEvalContexts.back().InImmediateFunctionContext = FD->isConsteval();
+
   // Check for defining attributes before the check for redefinition.
   if (const auto *Attr = FD->getAttr<AliasAttr>()) {
     Diag(Attr->getLocation(), diag::err_alias_is_definition) << FD << 0;

clang/test/CodeGenCXX/cxx20-consteval-crash.cpp

@@ -116,3 +116,27 @@ void method() {
 }
 
 } // namespace GH60166
+
+namespace GH61142 {
+
+template <typename T>
+struct Test {
+  constexpr static void bar() {
+    foo();
+  }
+  consteval static void foo() {};
+};
+
+consteval void a() {
+  Test<int>::bar();
+}
+
+void b() {
+  Test<int>::bar();
+}
+
+// Make sure consteval function is not emitted.
+// CHECK-NOT: call {{.*}}foo{{.*}}()
+// CHECK-NOT: define {{.*}}foo{{.*}}()
+
+} // namespace GH61142