[clang][Sema] Diagnose exceptions only in non-dependent context in discarded try/catch/throw blocks

Resolves #138939

When enabling `--fno-exceptions` flag, discarded statements containing
`try/catch/throw` in an independent context can be avoided from being
rejected.

Author: Rajveer100

clang/lib/Sema/SemaExprCXX.cpp

@@ -854,7 +854,8 @@ ExprResult Sema::BuildCXXThrow(SourceLocation OpLoc, Expr *Ex,
   // Don't report an error if 'throw' is used in system headers or in an OpenMP
   // target region compiled for a GPU architecture.
   if (!IsOpenMPGPUTarget && !getLangOpts().CXXExceptions &&
-      !getSourceManager().isInSystemHeader(OpLoc) && !getLangOpts().CUDA) {
+      !getSourceManager().isInSystemHeader(OpLoc) && !getLangOpts().CUDA &&
+      !CurContext->isDependentContext()) {
     // Delay error emission for the OpenMP device code.
     targetDiag(OpLoc, diag::err_exceptions_disabled) << "throw";
   }

clang/lib/Sema/SemaStmt.cpp

@@ -4305,7 +4305,8 @@ StmtResult Sema::ActOnCXXTryBlock(SourceLocation TryLoc, Stmt *TryBlock,
   // Don't report an error if 'try' is used in system headers or in an OpenMP
   // target region compiled for a GPU architecture.
   if (!IsOpenMPGPUTarget && !getLangOpts().CXXExceptions &&
-      !getSourceManager().isInSystemHeader(TryLoc) && !getLangOpts().CUDA) {
+      !getSourceManager().isInSystemHeader(TryLoc) && !getLangOpts().CUDA &&
+      !CurContext->isDependentContext()) {
     // Delay error emission for the OpenMP device code.
     targetDiag(TryLoc, diag::err_exceptions_disabled) << "try";
   }

clang/test/SemaCXX/no-exceptions.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -verify %s
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++20 %s
 
 // Various tests for -fno-exceptions
 
@@ -32,3 +32,28 @@ void g() {
 }
 
 }
+
+namespace test2 {
+template <auto enable> void foo(auto &&Fnc) {
+  if constexpr (enable)
+    try {
+      Fnc();
+    } catch (...) {
+    }
+  else
+    Fnc();
+}
+
+void bar1() {
+  foo<false>([] {});
+}
+
+template <typename T> void foo() {
+  try {
+  } catch (...) {
+  }
+  throw 1;
+}
+void bar2() { foo<int>(); }
+
+}