[clang] fix crash on template instantiation of invalid requires expressions

See PR48656.

The implementation of the template instantiation of requires expressions
was incorrectly trying to get the expression from an 'ExprRequirement'
before checking if it was an error state.

Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>

Reviewed By: rsmith

Differential Revision: https://reviews.llvm.org/D107399

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -1934,25 +1934,23 @@ TemplateInstantiator::TransformExprRequirement(concepts::ExprRequirement *Req) {
     return Req;
 
   Sema::SFINAETrap Trap(SemaRef);
-  TemplateDeductionInfo Info(Req->getExpr()->getBeginLoc());
 
   llvm::PointerUnion<Expr *, concepts::Requirement::SubstitutionDiagnostic *>
       TransExpr;
   if (Req->isExprSubstitutionFailure())
     TransExpr = Req->getExprSubstitutionDiagnostic();
   else {
-    Sema::InstantiatingTemplate ExprInst(SemaRef, Req->getExpr()->getBeginLoc(),
-                                         Req, Info,
-                                         Req->getExpr()->getSourceRange());
+    Expr *E = Req->getExpr();
+    TemplateDeductionInfo Info(E->getBeginLoc());
+    Sema::InstantiatingTemplate ExprInst(SemaRef, E->getBeginLoc(), Req, Info,
+                                         E->getSourceRange());
     if (ExprInst.isInvalid())
       return nullptr;
-    ExprResult TransExprRes = TransformExpr(Req->getExpr());
+    ExprResult TransExprRes = TransformExpr(E);
     if (TransExprRes.isInvalid() || Trap.hasErrorOccurred())
-      TransExpr = createSubstDiag(SemaRef, Info,
-          [&] (llvm::raw_ostream& OS) {
-              Req->getExpr()->printPretty(OS, nullptr,
-                                          SemaRef.getPrintingPolicy());
-          });
+      TransExpr = createSubstDiag(SemaRef, Info, [&](llvm::raw_ostream &OS) {
+        E->printPretty(OS, nullptr, SemaRef.getPrintingPolicy());
+      });
     else
       TransExpr = TransExprRes.get();
   }
@@ -1966,6 +1964,7 @@ TemplateInstantiator::TransformExprRequirement(concepts::ExprRequirement *Req) {
   else if (RetReq.isTypeConstraint()) {
     TemplateParameterList *OrigTPL =
         RetReq.getTypeConstraintTemplateParameterList();
+    TemplateDeductionInfo Info(OrigTPL->getTemplateLoc());
     Sema::InstantiatingTemplate TPLInst(SemaRef, OrigTPL->getTemplateLoc(),
                                         Req, Info, OrigTPL->getSourceRange());
     if (TPLInst.isInvalid())

clang/test/CXX/expr/expr.prim/expr.prim.req/type-requirement.cpp

@@ -192,3 +192,29 @@ namespace std_example {
   using c3 = C2_check<has_inner>; // expected-error{{constraints not satisfied for class template 'C2_check' [with T = std_example::has_inner]}}
   using c4 = C3_check<void>; // expected-error{{constraints not satisfied for class template 'C3_check' [with T = void]}}
 }
+
+namespace PR48656 {
+
+template <typename T> concept C = requires { requires requires { T::a; }; };
+// expected-note@-1 {{because 'T::a' would be invalid: no member named 'a' in 'PR48656::T1'}}
+
+template <C...> struct A {};
+// expected-note@-1 {{because 'PR48656::T1' does not satisfy 'C'}}
+
+struct T1 {};
+template struct A<T1>; // expected-error {{constraints not satisfied for class template 'A' [with $0 = <PR48656::T1>]}}
+
+struct T2 { static constexpr bool a = false; };
+template struct A<T2>;
+
+template <typename T> struct T3 {
+  static void m(auto) requires requires { T::fail; } {}
+  // expected-note@-1 {{constraints not satisfied}}
+  // expected-note@-2 {{type 'int' cannot be used prior to '::'}}
+};
+template <typename... Args> void t3(Args... args) { (..., T3<int>::m(args)); }
+// expected-error@-1 {{no matching function for call to 'm'}}
+
+template void t3<int>(int); // expected-note {{requested here}}
+
+} // namespace PR48656

clang/test/CXX/temp/temp.constr/temp.constr.normal/p1.cpp

@@ -91,7 +91,7 @@ struct X {
 template<class T> concept C1 = sizeof(T) != 0;
 template<class T> concept C2 = C1<typename T::template Y<1>::type>;
 
-template<class T> requires C1<T> void t1() = delete;          // expected-note {{candidate function}}
+template<class T> requires C1<T> void t1() {};                // expected-note {{candidate function}}
 template<class T> requires C1<T> && C2<T> void t1() = delete; // expected-note {{candidate function}}
 template void t1<X>();
 void t1() { t1<X>(); } // expected-error {{call to deleted function 't1'}}