diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 716761c4ba5b..1402304d7e00 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -376,6 +376,8 @@ Improvements to Clang's diagnostics
 
 - Clang now diagnoses when a ``requires`` expression has a local parameter of void type, aligning with the function parameter (#GH109831).
 
+- Clang now emits a diagnostic note at the class declaration when the method definition does not match any declaration (#GH110638).
+
 Improvements to Clang's time-trace
 ----------------------------------
 
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 0e536f71a2f7..e4c45cbc09e0 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -9086,9 +9086,14 @@ static NamedDecl *DiagnoseInvalidRedeclaration(
   SemaRef.Diag(NewFD->getLocation(), DiagMsg)
       << Name << NewDC << IsDefinition << NewFD->getLocation();
 
-  bool NewFDisConst = false;
-  if (CXXMethodDecl *NewMD = dyn_cast<CXXMethodDecl>(NewFD))
-    NewFDisConst = NewMD->isConst();
+  CXXMethodDecl *NewMD = dyn_cast<CXXMethodDecl>(NewFD);
+  if (NewMD && DiagMsg == diag::err_member_decl_does_not_match) {
+    CXXRecordDecl *RD = NewMD->getParent();
+    SemaRef.Diag(RD->getLocation(), diag::note_defined_here)
+        << RD->getName() << RD->getLocation();
+  }
+
+  bool NewFDisConst = NewMD && NewMD->isConst();
 
   for (SmallVectorImpl<std::pair<FunctionDecl *, unsigned> >::iterator
        NearMatch = NearMatches.begin(), NearMatchEnd = NearMatches.end();
diff --git a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p1.cpp b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p1.cpp
index 9e890204c78b..752451f3d974 100644
--- a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p1.cpp
+++ b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p1.cpp
@@ -164,11 +164,12 @@ namespace {
 
 #if __cplusplus < 201402L
 namespace ImplicitConstexprDef {
-  struct A {
+  struct A { // #defined-here
     void f(); // expected-note {{member declaration does not match because it is not const qualified}}
   };
 
   constexpr void A::f() { } // expected-warning {{'constexpr' non-static member function will not be implicitly 'const' in C++14; add 'const' to avoid a change in behavior}}
                             // expected-error@-1 {{out-of-line definition of 'f' does not match any declaration in 'ImplicitConstexprDef::A'}}
+                            // expected-note@#defined-here {{defined here}}
 }
 #endif
diff --git a/clang/test/CXX/dcl.decl/dcl.meaning/dcl.fct/p8.cpp b/clang/test/CXX/dcl.decl/dcl.meaning/dcl.fct/p8.cpp
index 0454412229fa..32ad25e2b705 100644
--- a/clang/test/CXX/dcl.decl/dcl.meaning/dcl.fct/p8.cpp
+++ b/clang/test/CXX/dcl.decl/dcl.meaning/dcl.fct/p8.cpp
@@ -1,8 +1,9 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s
 
-struct A { };
+struct A { }; // #defined-here
 A::A (enum { e1 }) {} // expected-error{{cannot be defined in a parameter}}
 void A::f(enum { e2 }) {} // expected-error{{cannot be defined in a parameter}}
 
 enum { e3 } A::g() { } // expected-error{{cannot be defined in the result type}} \
 // expected-error{{out-of-line definition}}
+// expected-note@#defined-here{{defined here}}
diff --git a/clang/test/CXX/dcl/dcl.fct/p17.cpp b/clang/test/CXX/dcl/dcl.fct/p17.cpp
index d7487233f5d5..4a81875cb4f8 100644
--- a/clang/test/CXX/dcl/dcl.fct/p17.cpp
+++ b/clang/test/CXX/dcl/dcl.fct/p17.cpp
@@ -96,7 +96,7 @@ namespace unconstrained {
   // expected-error@-1{{no matching}}
 
   template<typename T>
-  struct S {
+  struct S { // #defined-here
     constexpr auto f1(auto x, T t) -> decltype(x + t);
 
     template<typename U>
@@ -110,6 +110,7 @@ namespace unconstrained {
   template<typename U>
   constexpr auto S<T>::f2(auto x, U u, T t) -> decltype(x + u + t) { return x + u + t; }
   // expected-error@-1 {{out-of-line definition of 'f2' does not match any declaration in 'S<T>'}}
+  // expected-note@#defined-here {{S defined here}}
 
   template<typename T>
   template<typename U>
diff --git a/clang/test/CXX/drs/cwg22xx.cpp b/clang/test/CXX/drs/cwg22xx.cpp
index 797c3ed8546e..0614d4f34ad5 100644
--- a/clang/test/CXX/drs/cwg22xx.cpp
+++ b/clang/test/CXX/drs/cwg22xx.cpp
@@ -102,12 +102,13 @@ namespace MultilevelSpecialization {
   // default argument -- how far back do we look when determining whether a
   // parameter was expanded from a pack?
   //   -- zygoloid 2020-06-02
-  template<typename ...T> struct B {
+  template<typename ...T> struct B { // #cwg2233-B
     template <T... V> void f(int i = 0, int (&... arr)[V]);
   };
   template<> template<int a, int b>
     void B<int, int>::f(int i, int (&arr1)[a], int (&arr2)[b]) {}
     // since-cxx11-error@-1 {{out-of-line definition of 'f' does not match any declaration in 'cwg2233::MultilevelSpecialization::B<int, int>'}}
+    //   since-cxx11-note@#cwg2233-B {{defined here}}
   template<> template<>
     void B<int, int>::f<1, 1>(int i, int (&arr1a)[1], int (&arr2a)[1]) {}
 }
diff --git a/clang/test/CXX/drs/cwg3xx.cpp b/clang/test/CXX/drs/cwg3xx.cpp
index 7157feed3f76..f20054c3701b 100644
--- a/clang/test/CXX/drs/cwg3xx.cpp
+++ b/clang/test/CXX/drs/cwg3xx.cpp
@@ -597,9 +597,10 @@ namespace cwg336 { // cwg336: yes
         void mf2();
       };
     };
-    template<> template<class X> class A<int>::B {};
+    template<> template<class X> class A<int>::B {}; // #cwg336-B
     template<> template<> template<class T> void A<int>::B<double>::mf1(T t) {}
     // expected-error@-1 {{out-of-line definition of 'mf1' does not match any declaration in 'cwg336::Pre::A<int>::B<double>'}}
+    //   expected-note@#cwg336-B {{defined here}}
     template<class Y> template<> void A<Y>::B<double>::mf2() {}
     // expected-error@-1 {{nested name specifier 'A<Y>::B<double>::' for declaration does not refer into a class, class template or class template partial specialization}}
   }
@@ -758,7 +759,7 @@ namespace cwg347 { // cwg347: yes
     void g();
   };
 
-  struct derived : base {};
+  struct derived : base {}; // #cwg347-derived
 
   struct derived::nested {};
   // expected-error@-1 {{no struct named 'nested' in 'cwg347::derived'}}
@@ -766,8 +767,10 @@ namespace cwg347 { // cwg347: yes
   // expected-error@-1 {{no member named 'n' in 'cwg347::derived'}}
   void derived::f() {}
   // expected-error@-1 {{out-of-line definition of 'f' does not match any declaration in 'cwg347::derived'}}
+  //   expected-note@#cwg347-derived {{defined here}}
   void derived::g() {}
   // expected-error@-1 {{out-of-line definition of 'g' does not match any declaration in 'cwg347::derived'}}
+  //   expected-note@#cwg347-derived {{defined here}}
 }
 
 // cwg348: na
@@ -1009,18 +1012,20 @@ namespace cwg355 { struct ::cwg355_S s; }
 // cwg356: na
 
 namespace cwg357 { // cwg357: yes
-  template<typename T> struct A {
+  template<typename T> struct A { // #cwg357-A
     void f() const; // #cwg357-f
   };
   template<typename T> void A<T>::f() {}
   // expected-error@-1 {{out-of-line definition of 'f' does not match any declaration in 'A<T>'}}
+  //   expected-note@#cwg357-A {{defined here}}
   //   expected-note@#cwg357-f {{member declaration does not match because it is const qualified}}
 
-  struct B {
+  struct B { // #cwg357-B
     template<typename T> void f();
   };
   template<typename T> void B::f() const {}
   // expected-error@-1 {{out-of-line definition of 'f' does not match any declaration in 'cwg357::B'}}
+  //   expected-note@#cwg357-B {{defined here}}
 }
 
 namespace cwg358 { // cwg358: yes
diff --git a/clang/test/CXX/special/class.inhctor/p8.cpp b/clang/test/CXX/special/class.inhctor/p8.cpp
index 58c01d2b912d..dbc357c1a8d4 100644
--- a/clang/test/CXX/special/class.inhctor/p8.cpp
+++ b/clang/test/CXX/special/class.inhctor/p8.cpp
@@ -24,9 +24,10 @@ struct C {
   template<typename T> constexpr C(T t) : v(t) {}
   int v;
 };
-struct D : C {
+struct D : C { // #defined-here
   using C::C;
 };
 static_assert(D(123).v == 123, "");
 
 template<typename T> constexpr D::D(T t) : C(t) {} // expected-error {{does not match any declaration in 'D'}}
+                                                   // expected-note@#defined-here {{defined here}}
diff --git a/clang/test/CXX/temp/temp.constr/temp.constr.decl/func-template-decl.cpp b/clang/test/CXX/temp/temp.constr/temp.constr.decl/func-template-decl.cpp
index 30fbec64eea7..9a8148bdf625 100644
--- a/clang/test/CXX/temp/temp.constr/temp.constr.decl/func-template-decl.cpp
+++ b/clang/test/CXX/temp/temp.constr/temp.constr.decl/func-template-decl.cpp
@@ -47,7 +47,7 @@ int AA::A() { return sizeof(T); }
 namespace diag {
 
 template <unsigned N>
-struct TA {
+struct TA { // #defined-here
   template <template <unsigned> class TT> requires TT<N>::happy
   int A();
 };
@@ -55,5 +55,6 @@ struct TA {
 template <unsigned N>
 template <template <unsigned> class TT> int TA<N>::A() { return sizeof(TT<N>); }
 // expected-error@-1{{out-of-line definition of 'A' does not match any declaration in 'TA<N>'}}
+// expected-note@#defined-here{{defined here}}
 
 } // end namespace diag
diff --git a/clang/test/CXX/temp/temp.res/temp.local/p8.cpp b/clang/test/CXX/temp/temp.res/temp.local/p8.cpp
index 56599985da06..f503b4f15dd3 100644
--- a/clang/test/CXX/temp/temp.res/temp.local/p8.cpp
+++ b/clang/test/CXX/temp/temp.res/temp.local/p8.cpp
@@ -69,7 +69,7 @@ namespace SearchClassBetweenTemplateParameterLists {
 
   template<typename T> struct A {
     using AA = void;
-    template<typename U> struct B {
+    template<typename U> struct B { // #defined-here
       using BB = void;
       void f(U);
       void g(U);
@@ -127,19 +127,19 @@ namespace SearchClassBetweenTemplateParameterLists {
   template<typename T> template<typename BB>
   void A<T>::B<BB>::g(BB) { // expected-error {{does not match}}
     BB bb; // expected-error {{incomplete type}}
-  }
+  } // expected-note@#defined-here {{defined here}}
 
   // error, 'AA' found in (4)
   template<typename AA> template<typename U>
   void A<AA>::B<U>::h(AA) { // expected-error {{does not match}}
     AA aa; // expected-error {{incomplete type}}
-  }
+  } // expected-note@#defined-here {{defined here}}
 
   // error, 'BB' found in (2)
   template<typename BB> template<typename U>
   void A<BB>::B<U>::i(BB) { // expected-error {{does not match}}
     BB bb; // expected-error {{incomplete type}}
-  }
+  } // expected-note@#defined-here {{defined here}}
 
   // OK, 'BB' found in (1)
   template<typename T> template<typename U> template<typename BB>
@@ -151,7 +151,7 @@ namespace SearchClassBetweenTemplateParameterLists {
   template<typename T> template<typename BB> template<typename V>
   void A<T>::B<BB>::k(V) { // expected-error {{does not match}}
     BB bb; // expected-error {{incomplete type}}
-  }
+  } // expected-note@#defined-here {{defined here}}
 
   int CC;
   template <typename> struct C;
diff --git a/clang/test/CXX/temp/temp.spec/temp.expl.spec/p12.cpp b/clang/test/CXX/temp/temp.spec/temp.expl.spec/p12.cpp
index 2a5748908369..9717fbf419b0 100644
--- a/clang/test/CXX/temp/temp.spec/temp.expl.spec/p12.cpp
+++ b/clang/test/CXX/temp/temp.spec/temp.expl.spec/p12.cpp
@@ -31,7 +31,7 @@ constexpr void A::f1<long>(); // since-cxx14-error {{no function template matche
 // members of a class template explicitly specialized for an implicitly
 // instantiated specialization of that template.
 template<typename T>
-struct B {
+struct B { // #defined-here
   void g0(); // since-cxx14-note {{previous declaration is here}}
              // cxx11-note@-1 {{member declaration does not match because it is not const qualified}}
 
@@ -49,11 +49,13 @@ template<>
 constexpr void B<short>::g0(); // since-cxx14-error {{constexpr declaration of 'g0' follows non-constexpr declaration}}
                                // cxx11-error@-1 {{out-of-line declaration of 'g0' does not match any declaration in 'B<short>'}}
                                // cxx11-warning@-2 {{'constexpr' non-static member function will not be implicitly 'const' in C++14; add 'const'}}
+                               // expected-note@#defined-here {{defined here}}
 
 template<>
 constexpr void B<short>::g1(); // since-cxx14-error {{out-of-line declaration of 'g1' does not match any declaration in 'B<short>'}}
                                // cxx11-error@-1 {{constexpr declaration of 'g1' follows non-constexpr declaration}}
                                // cxx11-warning@-2 {{'constexpr' non-static member function will not be implicitly 'const' in C++14; add 'const'}}
+                               // expected-note@#defined-here {{defined here}}
 
 template<>
 template<typename U>
@@ -66,5 +68,3 @@ template<typename U>
 constexpr void B<long>::h1(); // since-cxx14-error {{out-of-line declaration of 'h1' does not match any declaration in 'B<long>'}}
                               // cxx11-error@-1 {{constexpr declaration of 'h1' follows non-constexpr declaration}}
                               // cxx11-warning@-2 {{'constexpr' non-static member function will not be implicitly 'const' in C++14; add 'const'}}
-
-
diff --git a/clang/test/CXX/temp/temp.spec/temp.expl.spec/p14-23.cpp b/clang/test/CXX/temp/temp.spec/temp.expl.spec/p14-23.cpp
index a023bf84137d..062c2db7db0e 100644
--- a/clang/test/CXX/temp/temp.spec/temp.expl.spec/p14-23.cpp
+++ b/clang/test/CXX/temp/temp.spec/temp.expl.spec/p14-23.cpp
@@ -8,7 +8,7 @@ namespace N0 {
   concept D = I < 8;
 
   template<int I>
-  struct A {
+  struct A { // #defined-here
     constexpr static int f() { return 0; }
     constexpr static int f() requires C<I> && D<I> { return 1; }
     constexpr static int f() requires C<I> { return 2; }
@@ -56,6 +56,7 @@ namespace N0 {
 
   template<>
   constexpr int A<0>::h() { return 2; } // expected-error {{out-of-line definition of 'h' does not match any declaration in 'N0::A<0>'}}
+                                        // expected-note@#defined-here {{defined here}}
 
   static_assert(A<5>::h() == 0);
   static_assert(A<4>::h() == 1);
diff --git a/clang/test/CXX/temp/temp.spec/temp.expl.spec/p18.cpp b/clang/test/CXX/temp/temp.spec/temp.expl.spec/p18.cpp
index 4d175a886087..5351773fafe8 100644
--- a/clang/test/CXX/temp/temp.spec/temp.expl.spec/p18.cpp
+++ b/clang/test/CXX/temp/temp.spec/temp.expl.spec/p18.cpp
@@ -7,13 +7,14 @@ template<class T1> class A {
 }; 
 
 template<> template<class X>
-class A<long>::B { }; 
+class A<long>::B { }; // #defined-here
 
 template<> template<> template<class T>
   void A<int>::B<double>::mf1(T t) { } 
 
 template<> template<> template<class T>
 void A<long>::B<double>::mf1(T t) { } // expected-error{{does not match}}
+                                      // expected-note@#defined-here{{defined here}}
 
 // FIXME: This diagnostic could probably be better.
 template<class Y> template<>
diff --git a/clang/test/FixIt/member-mismatch.cpp b/clang/test/FixIt/member-mismatch.cpp
index 2d2aec2e176b..e9c649d85c5c 100644
--- a/clang/test/FixIt/member-mismatch.cpp
+++ b/clang/test/FixIt/member-mismatch.cpp
@@ -1,12 +1,14 @@
 // RUN: %clang_cc1 -verify %s
 // RUN: not %clang_cc1 -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
 
-class Foo {
+class Foo { // #defined-here
   int get() const; // expected-note {{because it is const qualified}}
   void set(int); // expected-note {{because it is not const qualified}}
 };
 
 // CHECK: fix-it:"{{.*}}":{[[@LINE+1]]:15-[[@LINE+1]]:15}:" const"
 int Foo::get() {} // expected-error {{does not match any declaration}}
+                  // expected-note@#defined-here {{defined here}}
 // CHECK: fix-it:"{{.*}}":{[[@LINE+1]]:20-[[@LINE+1]]:26}:""
 void Foo::set(int) const {} // expected-error {{does not match any declaration}}
+                            // expected-note@#defined-here {{defined here}}
diff --git a/clang/test/Parser/cxx-class.cpp b/clang/test/Parser/cxx-class.cpp
index c90c7e030a8b..a6757f39146a 100644
--- a/clang/test/Parser/cxx-class.cpp
+++ b/clang/test/Parser/cxx-class.cpp
@@ -100,9 +100,10 @@ class F {
 #endif
 
 namespace ctor_error {
-  class Foo {};
+  class Foo {}; // #defined-here
   // By [class.qual]p2, this is a constructor declaration.
   Foo::Foo (F) = F(); // expected-error{{does not match any declaration in 'ctor_error::Foo'}}
+                      // expected-note@#defined-here{{defined here}}
 
   class Ctor { // expected-note{{not complete until the closing '}'}}
     Ctor(f)(int); // ok
diff --git a/clang/test/SemaCXX/attr-target-mv.cpp b/clang/test/SemaCXX/attr-target-mv.cpp
index 5b2f0fc825f3..b8db6d371bd5 100644
--- a/clang/test/SemaCXX/attr-target-mv.cpp
+++ b/clang/test/SemaCXX/attr-target-mv.cpp
@@ -180,14 +180,15 @@ void constexpr_test() {
   static_assert(foo() == 2, "Should call 'default' in a constexpr context");
 }
 
-struct BadOutOfLine {
+struct BadOutOfLine { // #defined-here
   int __attribute__((target("sse4.2"))) foo(int);
   int __attribute__((target("default"))) foo(int);
 };
 
 int __attribute__((target("sse4.2"))) BadOutOfLine::foo(int) { return 0; }
 int __attribute__((target("default"))) BadOutOfLine::foo(int) { return 1; }
-// expected-error@+3 {{out-of-line definition of 'foo' does not match any declaration in 'BadOutOfLine'}}
-// expected-note@-3 {{member declaration nearly matches}}
-// expected-note@-3 {{member declaration nearly matches}}
+// expected-error@+4 {{out-of-line definition of 'foo' does not match any declaration in 'BadOutOfLine'}}
+// expected-note@#defined-here {{defined here}}
+// expected-note@-4 {{member declaration nearly matches}}
+// expected-note@-4 {{member declaration nearly matches}}
 int __attribute__((target("arch=atom"))) BadOutOfLine::foo(int) { return 1; }
diff --git a/clang/test/SemaCXX/attr-target-version.cpp b/clang/test/SemaCXX/attr-target-version.cpp
index b3385f043590..14460756db17 100644
--- a/clang/test/SemaCXX/attr-target-version.cpp
+++ b/clang/test/SemaCXX/attr-target-version.cpp
@@ -97,13 +97,14 @@ using ::Decl;
 __attribute__((target_version("jscvt"))) void Decl();
 } // namespace Nms
 
-class Out {
+class Out { // #defined-here
   int __attribute__((target_version("bti"))) func(void);
   int __attribute__((target_version("ssbs2"))) func(void);
 };
 int __attribute__((target_version("bti"))) Out::func(void) { return 1; }
 int __attribute__((target_version("ssbs2"))) Out::func(void) { return 2; }
-// expected-error@+3 {{out-of-line definition of 'func' does not match any declaration in 'Out'}}
-// expected-note@-3 {{member declaration nearly matches}}
-// expected-note@-3 {{member declaration nearly matches}}
+// expected-error@+4 {{out-of-line definition of 'func' does not match any declaration in 'Out'}}
+// expected-note@-2 {{member declaration nearly matches}}
+// expected-note@-4 {{member declaration nearly matches}}
+// expected-note@#defined-here {{defined here}}
 int __attribute__((target_version("rng"))) Out::func(void) { return 3; }
diff --git a/clang/test/SemaCXX/enable_if.cpp b/clang/test/SemaCXX/enable_if.cpp
index 5eec02a64334..1c307881e5d4 100644
--- a/clang/test/SemaCXX/enable_if.cpp
+++ b/clang/test/SemaCXX/enable_if.cpp
@@ -5,7 +5,7 @@ int surrogate(int);
 struct Incomplete;  // expected-note{{forward declaration of 'Incomplete'}} \
                     // expected-note {{forward declaration of 'Incomplete'}}
 
-struct X {
+struct X { // expected-note{{defined here}}
   X() = default;  // expected-note{{candidate constructor not viable: requires 0 arguments, but 1 was provided}}
   X(const X&) = default;  // expected-note{{candidate constructor not viable: no known conversion from 'bool' to 'const X' for 1st argument}}
   X(bool b) __attribute__((enable_if(b, "chosen when 'b' is true")));  // expected-note{{candidate disabled: chosen when 'b' is true}}
diff --git a/clang/test/SemaCXX/function-redecl.cpp b/clang/test/SemaCXX/function-redecl.cpp
index 34d2acc75430..8c0e9a880d07 100644
--- a/clang/test/SemaCXX/function-redecl.cpp
+++ b/clang/test/SemaCXX/function-redecl.cpp
@@ -61,7 +61,7 @@ void B::Notypocorrection(int) { // expected-error {{out-of-line definition of 'N
 }
 
 struct X { int f(); };
-struct Y : public X {};
+struct Y : public X {}; // expected-note {{defined here}}
 int Y::f() { return 3; } // expected-error {{out-of-line definition of 'f' does not match any declaration in 'Y'}}
 
 namespace test1 {
@@ -70,7 +70,7 @@ struct Foo {
 };
 }
 
-class Bar {
+class Bar { // expected-note {{defined here}}
   void f(test1::Foo::Inner foo) const; // expected-note {{member declaration does not match because it is const qualified}}
 };
 
@@ -80,7 +80,8 @@ void Bar::f(Foo::Inner foo) { // expected-error {{out-of-line definition of 'f'
   (void)foo;
 }
 
-class Crash {
+class Crash { // expected-note {{defined here}}
+              // expected-note@-1 {{defined here}}
  public:
   void GetCart(int count) const;
 };
@@ -89,7 +90,8 @@ void Crash::cart(int count) const {} // expected-error {{out-of-line definition
 // ...while this one crashed clang
 void Crash::chart(int count) const {} // expected-error {{out-of-line definition of 'chart' does not match any declaration in 'Crash'}}
 
-class TestConst {
+class TestConst { // expected-note {{defined here}}
+                  // expected-note@-1 {{defined here}}
  public:
   int getit() const; // expected-note {{member declaration does not match because it is const qualified}}
   void setit(int); // expected-note {{member declaration does not match because it is not const qualified}}
@@ -102,7 +104,7 @@ int TestConst::getit() { // expected-error {{out-of-line definition of 'getit' d
 void TestConst::setit(int) const { // expected-error {{out-of-line definition of 'setit' does not match any declaration in 'TestConst'}}
 }
 
-struct J { int typo() const; };
+struct J { int typo() const; }; // expected-note {{defined here}}
 int J::typo_() { return 3; } // expected-error {{out-of-line definition of 'typo_' does not match any declaration in 'J'}}
 
 // Ensure we correct the redecl of Foo::isGood to Bar::Foo::isGood and not
@@ -126,7 +128,7 @@ bool Foo::isGood() { // expected-error {{out-of-line definition of 'isGood' does
 void Foo::beEvil() {} // expected-error {{out-of-line definition of 'beEvil' does not match any declaration in namespace 'redecl_typo::Foo'; did you mean 'BeEvil'?}}
 }
 
-struct CVQualFun {
+struct CVQualFun { // expected-note {{defined here}}
   void func(int a, int &b); // expected-note {{type of 2nd parameter of member declaration does not match definition ('int &' vs 'int')}}
 };
 
diff --git a/clang/test/SemaCXX/lambda-unevaluated.cpp b/clang/test/SemaCXX/lambda-unevaluated.cpp
index 39ee89bc797f..a9bcab58464e 100644
--- a/clang/test/SemaCXX/lambda-unevaluated.cpp
+++ b/clang/test/SemaCXX/lambda-unevaluated.cpp
@@ -70,21 +70,23 @@ void use_g() { g<6>(&"hello"); } // expected-error {{ambiguous}}
 namespace GH51416 {
 
 template <class T>
-struct A {
+struct A { // #defined-here-A
   void spam(decltype([] {}));
 };
 
 template <class T>
 void A<T>::spam(decltype([] {})) // expected-error{{out-of-line definition of 'spam' does not match}}
+                                 // expected-note@#defined-here-A{{defined here}}
 {}
 
-struct B {
+struct B { // #defined-here-B
   template <class T>
   void spam(decltype([] {}));
 };
 
 template <class T>
 void B::spam(decltype([] {})) {} // expected-error{{out-of-line definition of 'spam' does not match}}
+                                 // expected-note@#defined-here-B{{defined here}}
 
 } // namespace GH51416
 
diff --git a/clang/test/SemaCXX/nested-name-spec.cpp b/clang/test/SemaCXX/nested-name-spec.cpp
index 920ef42bc156..981152dda23f 100644
--- a/clang/test/SemaCXX/nested-name-spec.cpp
+++ b/clang/test/SemaCXX/nested-name-spec.cpp
@@ -25,7 +25,7 @@ int A::C::cx = 17;
 
 static int A::C::cx2 = 17; // expected-error{{'static' can}}
 
-class C2 {
+class C2 { // #defined-here-C2
   void m(); // expected-note{{member declaration does not match because it is not const qualified}}
 
   void f(const int& parm); // expected-note{{type of 1st parameter of member declaration does not match definition ('const int &' vs 'int')}}
@@ -36,8 +36,10 @@ class C2 {
 };
 
 void C2::m() const { } // expected-error{{out-of-line definition of 'm' does not match any declaration in 'C2'}}
+                       // expected-note@#defined-here-C2{{defined here}}
 
 void C2::f(int) { } // expected-error{{out-of-line definition of 'f' does not match any declaration in 'C2'}}
+                    // expected-note@#defined-here-C2{{defined here}}
 
 void C2::m() {
   x = 0;
@@ -122,12 +124,13 @@ namespace E {
 }
 
 
-class Operators {
+class Operators { // #defined-here-Operators
   Operators operator+(const Operators&) const; // expected-note{{member declaration does not match because it is const qualified}}
   operator bool();
 };
 
 Operators Operators::operator+(const Operators&) { // expected-error{{out-of-line definition of 'operator+' does not match any declaration in 'Operators'}}
+                                                   // expected-note@#defined-here-Operators{{defined here}}
   Operators ops;
   return ops;
 }
@@ -149,9 +152,10 @@ void A::f() {} // expected-error-re{{out-of-line definition of 'f' does not matc
 
 void A::g(const int&) { } // expected-error{{out-of-line definition of 'g' does not match any declaration in namespace 'A'}}
 
-struct Struct { };
+struct Struct { }; // #defined-here-Struct
 
 void Struct::f() { } // expected-error{{out-of-line definition of 'f' does not match any declaration in 'Struct'}}
+                     // expected-note@#defined-here-Struct{{defined here}}
 
 void global_func(int);
 void global_func2(int);
diff --git a/clang/test/SemaCXX/out-of-line-def-mismatch.cpp b/clang/test/SemaCXX/out-of-line-def-mismatch.cpp
index a4e130d23435..1ce1cc0c7dfc 100644
--- a/clang/test/SemaCXX/out-of-line-def-mismatch.cpp
+++ b/clang/test/SemaCXX/out-of-line-def-mismatch.cpp
@@ -6,7 +6,11 @@ namespace N2 {
   namespace N1 {
     class C1 {};
 
-    struct S2 {
+    struct S2 { // expected-note {{defined here}}
+                // expected-note@-1 {{defined here}}
+                // expected-note@-2 {{defined here}}
+                // expected-note@-3 {{defined here}}
+                // expected-note@-4 {{defined here}}
       void func(S1*); // expected-note {{type of 1st parameter of member declaration does not match definition ('S1 *' (aka 'N2::S1 *') vs 'S1 *' (aka 'N2::N1::S1 *'))}}
       void func(C1&, unsigned, const S1*); // expected-note {{type of 3rd parameter of member declaration does not match definition ('const S1 *' (aka 'const N2::S1 *') vs 'const S1 *' (aka 'const N2::N1::S1 *'))}}
       void func(const S1*, unsigned); //expected-note {{type of 1st parameter of member declaration does not match definition ('const S1 *' vs 'S1')}}
diff --git a/clang/test/SemaCXX/typo-correction.cpp b/clang/test/SemaCXX/typo-correction.cpp
index c262a62f0cb9..45f42c426035 100644
--- a/clang/test/SemaCXX/typo-correction.cpp
+++ b/clang/test/SemaCXX/typo-correction.cpp
@@ -173,6 +173,7 @@ class Parent {
 };
 class Child: public Parent {};
 void Child::add_types(int value) {} // expected-error{{out-of-line definition of 'add_types' does not match any declaration in 'Child'}}
+                                    // expected-note@-2{{defined here}}
 
 // Fix the callback based filtering of typo corrections within
 // Sema::ActOnIdExpression by Parser::ParseCastExpression to allow type names as
diff --git a/clang/test/SemaTemplate/concepts-out-of-line-def.cpp b/clang/test/SemaTemplate/concepts-out-of-line-def.cpp
index 8ca399a0f729..fe8f74928fc3 100644
--- a/clang/test/SemaTemplate/concepts-out-of-line-def.cpp
+++ b/clang/test/SemaTemplate/concepts-out-of-line-def.cpp
@@ -516,7 +516,7 @@ concept something_interesting = requires {
 };
 
 template <class T>
-struct X {
+struct X { // #defined-here
       void foo() requires requires { requires is_not_same_v<T, int>; };
       void bar(decltype(requires { requires is_not_same_v<T, int>; }));
 };
@@ -524,7 +524,8 @@ struct X {
 template <class T>
 void X<T>::foo() requires requires { requires something_interesting<T>; } {}
 // expected-error@-1{{definition of 'foo' does not match any declaration}}
-// expected-note@*{{}}
+// expected-note@#defined-here{{defined here}}
+// expected-note@-8{{member declaration nearly matches}}
 
 template <class T>
 void X<T>::foo() requires requires { requires is_not_same_v<T, int>; } {} // ok
@@ -532,6 +533,7 @@ void X<T>::foo() requires requires { requires is_not_same_v<T, int>; } {} // ok
 template <class T>
 void X<T>::bar(decltype(requires { requires something_interesting<T>; })) {}
 // expected-error@-1{{definition of 'bar' does not match any declaration}}
+// expected-note@#defined-here{{defined here}}
 
 template <class T>
 void X<T>::bar(decltype(requires { requires is_not_same_v<T, int>; })) {}
diff --git a/clang/test/SemaTemplate/recovery-crash.cpp b/clang/test/SemaTemplate/recovery-crash.cpp
index a451d9d108da..88e989aeb406 100644
--- a/clang/test/SemaTemplate/recovery-crash.cpp
+++ b/clang/test/SemaTemplate/recovery-crash.cpp
@@ -47,7 +47,7 @@ namespace PR16225 {
 namespace test1 {
   template <typename> class ArraySlice {};
   class Foo;
-  class NonTemplateClass {
+  class NonTemplateClass { // #defined-here
     void MemberFunction(ArraySlice<Foo>, int);
     template <class T> void MemberFuncTemplate(ArraySlice<T>, int);
   };
@@ -61,7 +61,8 @@ namespace test1 {
     // expected-error@+1 {{member 'UndeclaredMethod' used before its declaration}}
     UndeclaredMethod(resource_data);
   }
-  // expected-error@+2 {{out-of-line definition of 'UndeclaredMethod' does not match any declaration}}
-  // expected-note@+1 {{member is declared here}}
+  // expected-error@+3 {{out-of-line definition of 'UndeclaredMethod' does not match any declaration}}
+  // expected-note@+2 {{member is declared here}}
+  // expected-note@#defined-here {{defined here}}
   void NonTemplateClass::UndeclaredMethod() {}
 }