[clang][Sema] deleted overriding function can have lax except spec

clang/docs/ReleaseNotes.rst

@@ -194,6 +194,9 @@ C++2c Feature Support
 Resolutions to C++ Defect Reports
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
+- Implemented `CWG1351 <https://cplusplus.github.io/CWG/issues/1351.html>`_ which allows lax exception specifications on
+  overriding functions that are explicitly defined to be deleted.
+
 C Language Changes
 ------------------
 - ``structs``, ``unions``, and ``arrays`` that are const may now be used as

clang/lib/Sema/SemaExceptionSpec.cpp

@@ -979,6 +979,11 @@ bool Sema::CheckOverridingFunctionExceptionSpec(const CXXMethodDecl *New,
   if (isa<CXXDestructorDecl>(New) && New->getParent()->isDependentType())
     return false;
 
+  // CWG1351: if the overriding function is defined as deleted, we don't need
+  // this check.
+  if (New->isDeleted())
+    return false;
+
   // If the old exception specification hasn't been parsed yet, or the new
   // exception specification can't be computed yet, remember that we need to
   // perform this check when we get to the end of the outermost

clang/test/CXX/drs/dr13xx.cpp

@@ -379,6 +379,18 @@ namespace dr1347 { // dr1347: 3.1
 #endif
 }
 
+namespace dr1351 { // dr1351: 1
+#if __cplusplus >= 201103L
+  struct Base {
+    virtual void method() noexcept = delete;
+  };
+
+  struct Derived : Base {
+    void method() override = delete;
+  };
+#endif
+}
+
 namespace dr1358 { // dr1358: 3.1
 #if __cplusplus >= 201103L
   struct Lit { constexpr operator int() const { return 0; } };
@@ -425,7 +437,7 @@ namespace dr1359 { // dr1359: 3.5
   union B { constexpr B() = default; int a; }; // #dr1359-B
   // cxx11-17-error@-1 {{defaulted definition of default constructor is not constexpr}}
   union C { constexpr C() = default; int a, b; }; // #dr1359-C
-  // cxx11-17-error@-1 {{defaulted definition of default constructor is not constexpr}} 
+  // cxx11-17-error@-1 {{defaulted definition of default constructor is not constexpr}}
   struct X { constexpr X() = default; union {}; };
   // since-cxx11-error@-1 {{declaration does not declare anything}}
   struct Y { constexpr Y() = default; union { int a; }; }; // #dr1359-Y
@@ -645,7 +657,7 @@ struct A {
 } // namespace dr1397
 
 namespace dr1399 { // dr1399: dup 1388
-  template<typename ...T> void f(T..., int, T...) {} // #dr1399-f 
+  template<typename ...T> void f(T..., int, T...) {} // #dr1399-f
   // cxx98-error@-1 {{variadic templates are a C++11 extension}}
   void g() {
     f(0);

clang/test/CXX/except/except.spec/p5-virtual.cpp

@@ -45,6 +45,8 @@ struct Base
   virtual void f15();
   virtual void f16();
 
+  virtual void f17() noexcept = delete;
+
   virtual void g1() throw(); // expected-note {{overridden virtual function is here}}
   virtual void g2() throw(int); // expected-note {{overridden virtual function is here}}
   virtual void g3() throw(A); // expected-note {{overridden virtual function is here}}
@@ -81,6 +83,8 @@ struct Derived : Base
   virtual void f15() noexcept;
   virtual void f16() throw();
 
+  virtual void f17() = delete;
+
   virtual void g1() throw(int); // expected-error {{exception specification of overriding function is more lax}}
   virtual void g2(); // expected-error {{exception specification of overriding function is more lax}}
   virtual void g3() throw(D); // expected-error {{exception specification of overriding function is more lax}}