Add -Wunused-local-typedef, a warning that finds unused local typedefs.

The warning warns on TypedefNameDecls -- typedefs and C++11 using aliases --
that are !isReferenced(). Since the isReferenced() bit on TypedefNameDecls
wasn't used for anything before this warning it wasn't always set correctly,
so this patch also adds a few missing MarkAnyDeclReferenced() calls in
various places for TypedefNameDecls.

This is made a bit complicated due to local typedefs possibly being used only
after their local scope has closed. Consider:

    template <class T>
    void template_fun(T t) {
      typename T::Foo s3foo;  // YYY
      (void)s3foo;
    }
    void template_fun_user() {
      struct Local {
        typedef int Foo;  // XXX
      } p;
      template_fun(p);
    }

Here the typedef in XXX is only used at end-of-translation unit, when YYY in
template_fun() gets instantiated. To handle this, typedefs that are unused when
their scope exits are added to a set of potentially unused typedefs, and that
set gets checked at end-of-TU. Typedefs that are still unused at that point then
get warned on. There's also serialization code for this set, so that the
warning works with precompiled headers and modules. For modules, the warning
is emitted when the module is built, for precompiled headers each time the
header gets used.

Finally, consider a function using C++14 auto return types to return a local
type defined in a header:

    auto f() {
      struct S { typedef int a; };
      return S();
    }

Here, the typedef escapes its local scope and could be used by only some
translation units including the header. To not warn on this, add a
RecursiveASTVisitor that marks all delcs on local types returned from auto
functions as referenced. (Except if it's a function with internal linkage, or
the decls are private and the local type has no friends -- in these cases, it
_is_ safe to warn.)

Several of the included testcases (most of the interesting ones) were provided
by Richard Smith.

(gcc's spelling -Wunused-local-typedefs is supported as an alias for this
warning.)

llvm-svn: 217298

clang/include/clang/Basic/DiagnosticGroups.td

@@ -402,6 +402,7 @@ def UnusedValue : DiagGroup<"unused-value", [UnusedComparison, UnusedResult]>;
 def UnusedConstVariable : DiagGroup<"unused-const-variable">;
 def UnusedVariable : DiagGroup<"unused-variable",
                                [UnusedConstVariable]>;
+def UnusedLocalTypedef : DiagGroup<"unused-local-typedef">;
 def UnusedPropertyIvar :  DiagGroup<"unused-property-ivar">;
 def UsedButMarkedUnused : DiagGroup<"used-but-marked-unused">;
 def UserDefinedLiterals : DiagGroup<"user-defined-literals">;
@@ -526,7 +527,7 @@ def Unused : DiagGroup<"unused",
                        [UnusedArgument, UnusedFunction, UnusedLabel,
                         // UnusedParameter, (matches GCC's behavior)
                         // UnusedMemberFunction, (clean-up llvm before enabling)
-                        UnusedPrivateField,
+                        UnusedPrivateField, UnusedLocalTypedef,
                         UnusedValue, UnusedVariable, UnusedPropertyIvar]>,
                         DiagCategory<"Unused Entity Issue">;
 
@@ -622,6 +623,8 @@ def : DiagGroup<"int-conversions",
                 [IntConversion]>; // -Wint-conversions = -Wint-conversion
 def : DiagGroup<"vector-conversions",
                 [VectorConversion]>; // -Wvector-conversions = -Wvector-conversion
+def : DiagGroup<"unused-local-typedefs", [UnusedLocalTypedef]>;
+                // -Wunused-local-typedefs = -Wunused-local-typedef
 
 // A warning group for warnings that we want to have on by default in clang,
 // but which aren't on by default in GCC.

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -175,6 +175,9 @@ def warn_unused_parameter : Warning<"unused parameter %0">,
   InGroup<UnusedParameter>, DefaultIgnore;
 def warn_unused_variable : Warning<"unused variable %0">,
   InGroup<UnusedVariable>, DefaultIgnore;
+def warn_unused_local_typedef : Warning<
+  "unused %select{typedef|type alias}0 %1">,
+  InGroup<UnusedLocalTypedef>, DefaultIgnore;
 def warn_unused_property_backing_ivar : 
   Warning<"ivar %0 which backs the property is not "
   "referenced in this property's accessor">,

clang/include/clang/Sema/ExternalSemaSource.h

@@ -20,6 +20,10 @@
 #include "llvm/ADT/MapVector.h"
 #include <utility>
 
+namespace llvm {
+template <class T, unsigned n> class SmallSetVector;
+}
+
 namespace clang {
 
 class CXXConstructorDecl;
@@ -132,6 +136,15 @@ public:
   /// introduce the same declarations repeatedly.
   virtual void ReadDynamicClasses(SmallVectorImpl<CXXRecordDecl *> &Decls) {}
 
+  /// \brief Read the set of potentially unused typedefs known to the source.
+  ///
+  /// The external source should append its own potentially unused local
+  /// typedefs to the given vector of declarations. Note that this routine may
+  /// be invoked multiple times; the external source should take care not to
+  /// introduce the same declarations repeatedly.
+  virtual void ReadUnusedLocalTypedefNameCandidates(
+      llvm::SmallSetVector<const TypedefNameDecl *, 4> &Decls) {};
+
   /// \brief Read the set of locally-scoped external declarations known to the
   /// external Sema source.
   ///

clang/include/clang/Sema/MultiplexExternalSemaSource.h

@@ -282,6 +282,15 @@ public:
   /// introduce the same declarations repeatedly.
   void ReadDynamicClasses(SmallVectorImpl<CXXRecordDecl*> &Decls) override;
 
+  /// \brief Read the set of potentially unused typedefs known to the source.
+  ///
+  /// The external source should append its own potentially unused local
+  /// typedefs to the given vector of declarations. Note that this routine may
+  /// be invoked multiple times; the external source should take care not to
+  /// introduce the same declarations repeatedly.
+  void ReadUnusedLocalTypedefNameCandidates(
+      llvm::SmallSetVector<const TypedefNameDecl *, 4> &Decls) override;
+
   /// \brief Read the set of locally-scoped extern "C" declarations known to the
   /// external Sema source.
   ///

clang/include/clang/Sema/Sema.h

@@ -389,6 +389,10 @@ public:
   /// \brief Set containing all declared private fields that are not used.
   NamedDeclSetType UnusedPrivateFields;
 
+  /// \brief Set containing all typedefs that are likely unused.
+  llvm::SmallSetVector<const TypedefNameDecl *, 4>
+      UnusedLocalTypedefNameCandidates;
+
   typedef llvm::SmallPtrSet<const CXXRecordDecl*, 8> RecordDeclSetTy;
 
   /// PureVirtualClassDiagSet - a set of class declarations which we have
@@ -1048,6 +1052,8 @@ public:
   /// \brief Retrieve the module loader associated with the preprocessor.
   ModuleLoader &getModuleLoader() const;
 
+  void emitAndClearUnusedLocalTypedefWarnings();
+
   void ActOnEndOfTranslationUnit();
 
   void CheckDelegatingCtorCycles();
@@ -3209,6 +3215,7 @@ public:
   /// DiagnoseUnusedExprResult - If the statement passed in is an expression
   /// whose result is unused, warn.
   void DiagnoseUnusedExprResult(const Stmt *S);
+  void DiagnoseUnusedNestedTypedefs(const RecordDecl *D);
   void DiagnoseUnusedDecl(const NamedDecl *ND);
 
   /// Emit \p DiagID if statement located on \p StmtLoc has a suspicious null

clang/include/clang/Serialization/ASTBitCodes.h

@@ -545,7 +545,10 @@ namespace clang {
       LATE_PARSED_TEMPLATE = 50,
 
       /// \brief Record code for \#pragma optimize options.
-      OPTIMIZE_PRAGMA_OPTIONS = 51
+      OPTIMIZE_PRAGMA_OPTIONS = 51,
+
+      /// \brief Record code for potentially unused local typedef names.
+      UNUSED_LOCAL_TYPEDEF_NAME_CANDIDATES = 52,
     };
 
     /// \brief Record types used within a source manager block.

clang/include/clang/Serialization/ASTReader.h

@@ -759,6 +759,11 @@ private:
   /// at the end of the TU, in which case it directs CodeGen to emit the VTable.
   SmallVector<uint64_t, 16> DynamicClasses;
 
+  /// \brief The IDs of all potentially unused typedef names in the chain.
+  ///
+  /// Sema tracks these to emit warnings.
+  SmallVector<uint64_t, 16> UnusedLocalTypedefNameCandidates;
+
   /// \brief The IDs of the declarations Sema stores directly.
   ///
   /// Sema tracks a few important decls, such as namespace std, directly.
@@ -1789,6 +1794,9 @@ public:
 
   void ReadDynamicClasses(SmallVectorImpl<CXXRecordDecl *> &Decls) override;
 
+  void ReadUnusedLocalTypedefNameCandidates(
+      llvm::SmallSetVector<const TypedefNameDecl *, 4> &Decls) override;
+
   void ReadLocallyScopedExternCDecls(
                                   SmallVectorImpl<NamedDecl *> &Decls) override;
 

clang/lib/Sema/MultiplexExternalSemaSource.cpp

@@ -242,6 +242,12 @@ void MultiplexExternalSemaSource::ReadDynamicClasses(
     Sources[i]->ReadDynamicClasses(Decls);
 }
 
+void MultiplexExternalSemaSource::ReadUnusedLocalTypedefNameCandidates(
+    llvm::SmallSetVector<const TypedefNameDecl *, 4> &Decls) {
+  for(size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->ReadUnusedLocalTypedefNameCandidates(Decls);
+}
+
 void MultiplexExternalSemaSource::ReadLocallyScopedExternCDecls(
                                            SmallVectorImpl<NamedDecl*> &Decls) {
   for(size_t i = 0; i < Sources.size(); ++i)

clang/lib/Sema/Sema.cpp

@@ -597,6 +597,19 @@ static bool IsRecordFullyDefined(const CXXRecordDecl *RD,
   return Complete;
 }
 
+void Sema::emitAndClearUnusedLocalTypedefWarnings() {
+  if (ExternalSource)
+    ExternalSource->ReadUnusedLocalTypedefNameCandidates(
+        UnusedLocalTypedefNameCandidates);
+  for (const TypedefNameDecl *TD : UnusedLocalTypedefNameCandidates) {
+    if (TD->isReferenced())
+      continue;
+    Diag(TD->getLocation(), diag::warn_unused_local_typedef)
+        << isa<TypeAliasDecl>(TD) << TD->getDeclName();
+  }
+  UnusedLocalTypedefNameCandidates.clear();
+}
+
 /// ActOnEndOfTranslationUnit - This is called at the very end of the
 /// translation unit when EOF is reached and all but the top-level scope is
 /// popped.
@@ -719,6 +732,10 @@ void Sema::ActOnEndOfTranslationUnit() {
       }
     }
 
+    // Warnings emitted in ActOnEndOfTranslationUnit() should be emitted for
+    // modules when they are built, not every time they are used.
+    emitAndClearUnusedLocalTypedefWarnings();
+
     // Modules don't need any of the checking below.
     TUScope = nullptr;
     return;
@@ -827,6 +844,8 @@ void Sema::ActOnEndOfTranslationUnit() {
     if (ExternalSource)
       ExternalSource->ReadUndefinedButUsed(UndefinedButUsed);
     checkUndefinedButUsed(*this);
+
+    emitAndClearUnusedLocalTypedefWarnings();
   }
 
   if (!Diags.isIgnored(diag::warn_unused_private_field, SourceLocation())) {

clang/lib/Sema/SemaCXXScopeSpec.cpp

@@ -612,6 +612,9 @@ bool Sema::BuildCXXNestedNameSpecifier(Scope *S,
        }
     }
 
+    if (auto *TD = dyn_cast_or_null<TypedefNameDecl>(SD))
+      MarkAnyDeclReferenced(TD->getLocation(), TD, /*OdrUse=*/false);
+
     // If we're just performing this lookup for error-recovery purposes,
     // don't extend the nested-name-specifier. Just return now.
     if (ErrorRecoveryLookup)

clang/lib/Sema/SemaDecl.cpp

@@ -380,6 +380,7 @@ ParsedType Sema::getTypeName(const IdentifierInfo &II, SourceLocation NameLoc,
     DiagnoseUseOfDecl(IIDecl, NameLoc);
 
     T = Context.getTypeDeclType(TD);
+    MarkAnyDeclReferenced(TD->getLocation(), TD, /*OdrUse=*/false);
 
     // NOTE: avoid constructing an ElaboratedType(Loc) if this is a
     // constructor or destructor name (in such a case, the scope specifier
@@ -928,6 +929,7 @@ Corrected:
   NamedDecl *FirstDecl = (*Result.begin())->getUnderlyingDecl();
   if (TypeDecl *Type = dyn_cast<TypeDecl>(FirstDecl)) {
     DiagnoseUseOfDecl(Type, NameLoc);
+    MarkAnyDeclReferenced(Type->getLocation(), Type, /*OdrUse=*/false);
     QualType T = Context.getTypeDeclType(Type);
     if (SS.isNotEmpty())
       return buildNestedType(*this, SS, T, NameLoc);
@@ -1395,10 +1397,22 @@ static bool ShouldDiagnoseUnusedDecl(const NamedDecl *D) {
 
   if (isa<LabelDecl>(D))
     return true;
+
+  // Except for labels, we only care about unused decls that are local to
+  // functions.
+  bool WithinFunction = D->getDeclContext()->isFunctionOrMethod();
+  if (const auto *R = dyn_cast<CXXRecordDecl>(D->getDeclContext()))
+    // For dependent types, the diagnostic is deferred.
+    WithinFunction =
+        WithinFunction || (R->isLocalClass() && !R->isDependentType());
+  if (!WithinFunction)
+    return false;
+
+  if (isa<TypedefNameDecl>(D))
+    return true;
   
   // White-list anything that isn't a local variable.
-  if (!isa<VarDecl>(D) || isa<ParmVarDecl>(D) || isa<ImplicitParamDecl>(D) ||
-      !D->getDeclContext()->isFunctionOrMethod())
+  if (!isa<VarDecl>(D) || isa<ParmVarDecl>(D) || isa<ImplicitParamDecl>(D))
     return false;
 
   // Types of valid local variables should be complete, so this should succeed.
@@ -1461,11 +1475,30 @@ static void GenerateFixForUnusedDecl(const NamedDecl *D, ASTContext &Ctx,
   return;
 }
 
+void Sema::DiagnoseUnusedNestedTypedefs(const RecordDecl *D) {
+  if (D->getTypeForDecl()->isDependentType())
+    return;
+
+  for (auto *TmpD : D->decls()) {
+    if (const auto *T = dyn_cast<TypedefNameDecl>(TmpD))
+      DiagnoseUnusedDecl(T);
+    else if(const auto *R = dyn_cast<RecordDecl>(TmpD))
+      DiagnoseUnusedNestedTypedefs(R);
+  }
+}
+
 /// DiagnoseUnusedDecl - Emit warnings about declarations that are not used
 /// unless they are marked attr(unused).
 void Sema::DiagnoseUnusedDecl(const NamedDecl *D) {
   if (!ShouldDiagnoseUnusedDecl(D))
     return;
+
+  if (auto *TD = dyn_cast<TypedefNameDecl>(D)) {
+    // typedefs can be referenced later on, so the diagnostics are emitted
+    // at end-of-translation-unit.
+    UnusedLocalTypedefNameCandidates.insert(TD);
+    return;
+  }
   
   FixItHint Hint;
   GenerateFixForUnusedDecl(D, Context, Hint);
@@ -1505,8 +1538,11 @@ void Sema::ActOnPopScope(SourceLocation Loc, Scope *S) {
     if (!D->getDeclName()) continue;
 
     // Diagnose unused variables in this scope.
-    if (!S->hasUnrecoverableErrorOccurred())
+    if (!S->hasUnrecoverableErrorOccurred()) {
       DiagnoseUnusedDecl(D);
+      if (const auto *RD = dyn_cast<RecordDecl>(D))
+        DiagnoseUnusedNestedTypedefs(RD);
+    }
     
     // If this was a forward reference to a label, verify it was defined.
     if (LabelDecl *LD = dyn_cast<LabelDecl>(D))

clang/lib/Sema/SemaStmt.cpp

@@ -19,6 +19,7 @@
 #include "clang/AST/EvaluatedExprVisitor.h"
 #include "clang/AST/ExprCXX.h"
 #include "clang/AST/ExprObjC.h"
+#include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/AST/StmtCXX.h"
 #include "clang/AST/StmtObjC.h"
 #include "clang/AST/TypeLoc.h"
@@ -2710,6 +2711,40 @@ Sema::ActOnCapScopeReturnStmt(SourceLocation ReturnLoc, Expr *RetValExp) {
   return Result;
 }
 
+namespace {
+/// \brief Marks all typedefs in all local classes in a type referenced.
+///
+/// In a function like
+/// auto f() {
+///   struct S { typedef int a; };
+///   return S();
+/// }
+///
+/// the local type escapes and could be referenced in some TUs but not in
+/// others. Pretend that all local typedefs are always referenced, to not warn
+/// on this. This isn't necessary if f has internal linkage, or the typedef
+/// is private.
+class LocalTypedefNameReferencer
+    : public RecursiveASTVisitor<LocalTypedefNameReferencer> {
+public:
+  LocalTypedefNameReferencer(Sema &S) : S(S) {}
+  bool VisitRecordType(const RecordType *RT);
+private:
+  Sema &S;
+};
+bool LocalTypedefNameReferencer::VisitRecordType(const RecordType *RT) {
+  auto *R = dyn_cast<CXXRecordDecl>(RT->getDecl());
+  if (!R || !R->isLocalClass() || !R->isLocalClass()->isExternallyVisible() ||
+      R->isDependentType())
+    return true;
+  for (auto *TmpD : R->decls())
+    if (auto *T = dyn_cast<TypedefNameDecl>(TmpD))
+      if (T->getAccess() != AS_private || R->hasFriends())
+        S.MarkAnyDeclReferenced(T->getLocation(), T, /*OdrUse=*/false);
+  return true;
+}
+}
+
 /// Deduce the return type for a function from a returned expression, per
 /// C++1y [dcl.spec.auto]p6.
 bool Sema::DeduceFunctionTypeFromReturnExpr(FunctionDecl *FD,
@@ -2755,6 +2790,11 @@ bool Sema::DeduceFunctionTypeFromReturnExpr(FunctionDecl *FD,
 
     if (DAR != DAR_Succeeded)
       return true;
+
+    // If a local type is part of the returned type, mark its fields as
+    // referenced.
+    LocalTypedefNameReferencer Referencer(*this);
+    Referencer.TraverseType(RetExpr->getType());
   } else {
     //  In the case of a return with no operand, the initializer is considered
     //  to be void().

clang/lib/Sema/SemaStmtAsm.cpp

@@ -467,9 +467,10 @@ bool Sema::LookupInlineAsmField(StringRef Base, StringRef Member,
   NamedDecl *FoundDecl = BaseResult.getFoundDecl();
   if (VarDecl *VD = dyn_cast<VarDecl>(FoundDecl))
     RT = VD->getType()->getAs<RecordType>();
-  else if (TypedefNameDecl *TD = dyn_cast<TypedefNameDecl>(FoundDecl))
+  else if (TypedefNameDecl *TD = dyn_cast<TypedefNameDecl>(FoundDecl)) {
+    MarkAnyDeclReferenced(TD->getLocation(), TD, /*OdrUse=*/false);
     RT = TD->getUnderlyingType()->getAs<RecordType>();
-  else if (TypeDecl *TD = dyn_cast<TypeDecl>(FoundDecl))
+  } else if (TypeDecl *TD = dyn_cast<TypeDecl>(FoundDecl))
     RT = TD->getTypeForDecl()->getAs<RecordType>();
   if (!RT)
     return true;

clang/lib/Sema/SemaTemplate.cpp

@@ -7945,6 +7945,7 @@ Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
     if (TypeDecl *Type = dyn_cast<TypeDecl>(Result.getFoundDecl())) {
       // We found a type. Build an ElaboratedType, since the
       // typename-specifier was just sugar.
+      MarkAnyDeclReferenced(Type->getLocation(), Type, /*OdrUse=*/false);
       return Context.getElaboratedType(ETK_Typename, 
                                        QualifierLoc.getNestedNameSpecifier(),
                                        Context.getTypeDeclType(Type));

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -1200,6 +1200,9 @@ Decl *TemplateDeclInstantiator::VisitCXXRecordDecl(CXXRecordDecl *D) {
     SemaRef.InstantiateClassMembers(D->getLocation(), Record, TemplateArgs,
                                     TSK_ImplicitInstantiation);
   }
+
+  SemaRef.DiagnoseUnusedNestedTypedefs(Record);
+
   return Record;
 }
 
@@ -3653,7 +3656,7 @@ void Sema::BuildVariableInstantiation(
   // Diagnose unused local variables with dependent types, where the diagnostic
   // will have been deferred.
   if (!NewVar->isInvalidDecl() &&
-      NewVar->getDeclContext()->isFunctionOrMethod() && !NewVar->isUsed() &&
+      NewVar->getDeclContext()->isFunctionOrMethod() &&
       OldVar->getType()->isDependentType())
     DiagnoseUnusedDecl(NewVar);
 }

clang/lib/Serialization/ASTReader.cpp

@@ -3285,6 +3285,12 @@ ASTReader::ReadASTBlock(ModuleFile &F, unsigned ClientLoadCapabilities) {
       }
       OptimizeOffPragmaLocation = ReadSourceLocation(F, Record[0]);
       break;
+
+    case UNUSED_LOCAL_TYPEDEF_NAME_CANDIDATES:
+      for (unsigned I = 0, N = Record.size(); I != N; ++I)
+        UnusedLocalTypedefNameCandidates.push_back(
+            getGlobalDeclID(F, Record[I]));
+      break;
     }
   }
 }
@@ -7196,6 +7202,18 @@ void ASTReader::ReadDynamicClasses(SmallVectorImpl<CXXRecordDecl *> &Decls) {
   DynamicClasses.clear();
 }
 
+void ASTReader::ReadUnusedLocalTypedefNameCandidates(
+    llvm::SmallSetVector<const TypedefNameDecl *, 4> &Decls) {
+  for (unsigned I = 0, N = UnusedLocalTypedefNameCandidates.size(); I != N;
+       ++I) {
+    TypedefNameDecl *D = dyn_cast_or_null<TypedefNameDecl>(
+        GetDecl(UnusedLocalTypedefNameCandidates[I]));
+    if (D)
+      Decls.insert(D);
+  }
+  UnusedLocalTypedefNameCandidates.clear();
+}
+
 void 
 ASTReader::ReadLocallyScopedExternCDecls(SmallVectorImpl<NamedDecl *> &Decls) {
   for (unsigned I = 0, N = LocallyScopedExternCDecls.size(); I != N; ++I) {

clang/lib/Serialization/ASTWriter.cpp

@@ -4284,6 +4284,11 @@ void ASTWriter::WriteASTCore(Sema &SemaRef,
     }
   }
 
+  // Build a record containing all of the UnusedLocalTypedefNameCandidates.
+  RecordData UnusedLocalTypedefNameCandidates;
+  for (const TypedefNameDecl *TD : SemaRef.UnusedLocalTypedefNameCandidates)
+    AddDeclRef(TD, UnusedLocalTypedefNameCandidates);
+
   // Build a record containing all of dynamic classes declarations.
   RecordData DynamicClasses;
   AddLazyVectorDecls(*this, SemaRef.DynamicClasses, DynamicClasses);
@@ -4561,6 +4566,11 @@ void ASTWriter::WriteASTCore(Sema &SemaRef,
   if (!DynamicClasses.empty())
     Stream.EmitRecord(DYNAMIC_CLASSES, DynamicClasses);
 
+  // Write the record containing potentially unused local typedefs.
+  if (!UnusedLocalTypedefNameCandidates.empty())
+    Stream.EmitRecord(UNUSED_LOCAL_TYPEDEF_NAME_CANDIDATES,
+                      UnusedLocalTypedefNameCandidates);
+
   // Write the record containing pending implicit instantiations.
   if (!PendingInstantiations.empty())
     Stream.EmitRecord(PENDING_IMPLICIT_INSTANTIATIONS, PendingInstantiations);

clang/test/Misc/ast-dump-color.cpp

@@ -89,7 +89,7 @@ struct Invalid {
 //CHECK: {{^}}[[Blue]]| `-[[RESET]][[BLUE]]GuardedByAttr[[RESET]][[Yellow]] 0x{{[0-9a-fA-F]*}}[[RESET]] <[[Yellow]]col:29[[RESET]], [[Yellow]]col:43[[RESET]]>{{$}}
 //CHECK: {{^}}[[Blue]]|   `-[[RESET]][[MAGENTA]]DeclRefExpr[[RESET]][[Yellow]] 0x{{[0-9a-fA-F]*}}[[RESET]] <[[Yellow]]col:40[[RESET]]> [[Green]]'class Mutex':'class Mutex'[[RESET]][[Cyan]] lvalue[[RESET]][[Cyan]][[RESET]] [[GREEN]]Var[[RESET]][[Yellow]] 0x{{[0-9a-fA-F]*}}[[RESET]][[CYAN]] 'mu1'[[RESET]] [[Green]]'class Mutex':'class Mutex'[[RESET]]{{$}}
 //CHECK: {{^}}[[Blue]]|-[[RESET]][[GREEN]]CXXRecordDecl[[RESET]][[Yellow]] 0x{{[0-9a-fA-F]*}}[[RESET]] <[[Yellow]]line:28:1[[RESET]], [[Yellow]]line:30:1[[RESET]]> [[Yellow]]line:28:8[[RESET]] struct[[CYAN]] Invalid[[RESET]] definition
-//CHECK: {{^}}[[Blue]]| |-[[RESET]][[GREEN]]CXXRecordDecl[[RESET]][[Yellow]] 0x{{[0-9a-fA-F]*}}[[RESET]] <[[Yellow]]col:1[[RESET]], [[Yellow]]col:8[[RESET]]> [[Yellow]]col:8[[RESET]] implicit struct[[CYAN]] Invalid[[RESET]]
+//CHECK: {{^}}[[Blue]]| |-[[RESET]][[GREEN]]CXXRecordDecl[[RESET]][[Yellow]] 0x{{[0-9a-fA-F]*}}[[RESET]] <[[Yellow]]col:1[[RESET]], [[Yellow]]col:8[[RESET]]> [[Yellow]]col:8[[RESET]] implicit referenced struct[[CYAN]] Invalid[[RESET]]
 //CHECK: {{^}}[[Blue]]| |-[[RESET]][[GREEN]]CXXConstructorDecl[[RESET]][[Yellow]] 0x{{[0-9a-fA-F]*}}[[RESET]] <[[Yellow]]line:29:3[[RESET]], [[Yellow]]col:42[[RESET]]> [[Yellow]]col:29[[RESET]] invalid[[CYAN]] Invalid[[RESET]] [[Green]]'void (int)'[[RESET]]
 //CHECK: {{^}}[[Blue]]| | |-[[RESET]][[GREEN]]ParmVarDecl[[RESET]][[Yellow]] 0x{{[0-9a-fA-F]*}}[[RESET]] <[[Yellow]]col:37[[RESET]], [[Yellow]]<invalid sloc>[[RESET]]> [[Yellow]]col:42[[RESET]] invalid [[Green]]'int'[[RESET]]
 //CHECK: {{^}}[[Blue]]| | `-[[RESET]][[BLUE]]NoInlineAttr[[RESET]][[Yellow]] 0x{{[0-9a-fA-F]*}}[[RESET]] <[[Yellow]]col:18[[RESET]]>

clang/test/Modules/Inputs/module.map

@@ -292,6 +292,10 @@ module warning {
   header "warning.h"
 }
 
+module warn_unused_local_typedef {
+  header "warn-unused-local-typedef.h"
+}
+
 module initializer_list {
   header "initializer_list"
 }

clang/test/Modules/Inputs/warn-unused-local-typedef.h

@@ -0,0 +1 @@
+inline void myfun() { typedef int a; }

clang/test/Modules/warn-unused-local-typedef.cpp

@@ -0,0 +1,9 @@
+// RUN: rm -rf %t
+// RUN: %clang -Wunused-local-typedef -c -x objective-c++ -fcxx-modules -fmodules -fmodules-cache-path=%t -I %S/Inputs %s 2>&1 | FileCheck %s -check-prefix=CHECK_1
+// RUN: %clang -Wunused-local-typedef -c -x objective-c++ -fcxx-modules -fmodules -fmodules-cache-path=%t -I %S/Inputs %s 2>&1 | FileCheck %s -check-prefix=CHECK_2 -allow-empty
+
+// For modules, the warning should only fire the first time, when the module is
+// built.
+// CHECK_1: warning: unused typedef
+// CHECK_2-NOT: warning: unused typedef
+@import warn_unused_local_typedef;

clang/test/SemaCXX/implicit-exception-spec.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -fcxx-exceptions -verify -std=c++11 -Wall %s
+// RUN: %clang_cc1 -fsyntax-only -fcxx-exceptions -verify -std=c++11 -Wall -Wno-unused-local-typedefs %s
 
 template<bool b> struct ExceptionIf { static int f(); };
 template<> struct ExceptionIf<false> { typedef int f; };

clang/test/SemaCXX/warn-unused-filescoped.cpp

@@ -1,5 +1,5 @@
-// RUN: %clang_cc1 -fsyntax-only -verify -Wunused -Wunused-member-function -Wno-c++11-extensions -std=c++98 %s
-// RUN: %clang_cc1 -fsyntax-only -verify -Wunused -Wunused-member-function -std=c++11 %s
+// RUN: %clang_cc1 -fsyntax-only -verify -Wunused -Wunused-member-function -Wno-unused-local-typedefs -Wno-c++11-extensions -std=c++98 %s
+// RUN: %clang_cc1 -fsyntax-only -verify -Wunused -Wunused-member-function -Wno-unused-local-typedefs -std=c++11 %s
 
 #ifdef HEADER
 

clang/test/SemaCXX/warn-unused-local-typedef-serialize.cpp

@@ -0,0 +1,11 @@
+// RUN: %clang -x c++-header -c -Wunused-local-typedef %s -o %t.gch -Werror
+// RUN: %clang -DBE_THE_SOURCE -c -Wunused-local-typedef -include %t %s 2>&1 | FileCheck %s
+// RUN: %clang -DBE_THE_SOURCE -c -Wunused-local-typedef -include %t %s 2>&1 | FileCheck %s
+
+#ifndef BE_THE_SOURCE
+inline void myfun() {
+// The warning should fire every time the pch file is used, not when it's built.
+// CHECK: warning: unused typedef
+  typedef int a;
+}
+#endif

clang/test/SemaCXX/warn-unused-local-typedef.cpp

@@ -0,0 +1,231 @@
+// RUN: %clang_cc1 -fsyntax-only -Wunused-local-typedef -verify -std=c++1y -fasm-blocks %s
+
+struct S {
+  typedef int Foo;  // no diag
+};
+
+namespace N {
+  typedef int Foo;  // no diag
+  typedef int Foo2;  // no diag
+}
+
+template <class T> class Vec {};
+
+typedef int global_foo;  // no diag
+
+void f() {
+  typedef int foo0;  // expected-warning {{unused typedef 'foo0'}}
+  using foo0alias = int ;  // expected-warning {{unused type alias 'foo0alias'}}
+
+  typedef int foo1 __attribute__((unused));  // no diag
+
+  typedef int foo2;
+  {
+    typedef int foo2;  // expected-warning {{unused typedef 'foo2'}}
+  }
+  typedef foo2 foo3; // expected-warning {{unused typedef 'foo3'}}
+
+  typedef int foo2_2;  // expected-warning {{unused typedef 'foo2_2'}}
+  {
+    typedef int foo2_2;
+    typedef foo2_2 foo3_2; // expected-warning {{unused typedef 'foo3_2'}}
+  }
+
+  typedef int foo4;
+  foo4 the_thing;
+
+  typedef int* foo5;
+  typedef foo5* foo6;  // no diag
+  foo6 *myptr;
+
+  struct S2 {
+    typedef int Foo; // no diag
+    typedef int Foo2; // expected-warning {{unused typedef 'Foo2'}}
+
+    struct Deeper {
+      typedef int DeepFoo;  // expected-warning {{unused typedef 'DeepFoo'}}
+    };
+  };
+
+  S2::Foo s2foo;
+
+  typedef struct {} foostruct; // expected-warning {{unused typedef 'foostruct'}}
+
+  typedef struct {} foostruct2; // no diag
+  foostruct2 fs2;
+
+  typedef int vecint;  // no diag
+  Vec<vecint> v;
+
+  N::Foo nfoo;
+
+  typedef int ConstExprInt;
+  static constexpr int a = (ConstExprInt)4;
+}
+
+int printf(char const *, ...);
+
+void test() {
+  typedef signed long int superint; // no diag
+  printf("%f", (superint) 42);
+
+  typedef signed long int superint2; // no diag
+  printf("%f", static_cast<superint2>(42));
+
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wunused-local-typedef"
+  typedef int trungl_bot_was_here; // no diag
+#pragma clang diagnostic pop
+
+  typedef int foo; // expected-warning {{unused typedef 'foo'}}
+}
+
+template <class T>
+void template_fun(T t) {
+  typedef int foo; // expected-warning {{unused typedef 'foo'}}
+  typedef int bar; // no-diag
+  bar asdf;
+
+  struct S2 {
+    typedef int Foo; // no diag
+
+    typedef int Foo2; // expected-warning {{unused typedef 'Foo2'}}
+
+    typedef int Foo3; // no diag
+  };
+
+  typename S2::Foo s2foo;
+  typename T::Foo s3foo;
+
+  typedef typename S2::Foo3 TTSF;  // expected-warning {{unused typedef 'TTSF'}}
+}
+void template_fun_user() {
+  struct Local {
+    typedef int Foo; // no-diag
+    typedef int Bar; // expected-warning {{unused typedef 'Bar'}}
+  } p;
+  template_fun(p);
+}
+
+void typedef_in_nested_name() {
+  typedef struct {
+    typedef int Foo;
+  } A;
+  A::Foo adsf;
+
+  using A2 = struct {
+    typedef int Foo;
+  };
+  A2::Foo adsf2;
+}
+
+void use_in_asm() {
+  typedef struct {
+    int a;
+    int b;
+  } A;
+  __asm mov eax, [eax].A.b
+
+  using Alias = struct {
+    int a;
+    int b;
+  };
+  __asm mov eax, [eax].Alias.b
+}
+
+auto sneaky() {
+  struct S {
+    // Local typedefs can be used after the scope they were in has closed:
+    typedef int t;
+
+    // Even if they aren't, this could be an inline function that could be used
+    // in another TU, so this shouldn't warn either:
+    typedef int s;
+
+  private:
+    typedef int p; // expected-warning{{unused typedef 'p'}}
+  };
+  return S();
+}
+auto x = sneaky();
+decltype(x)::t y;
+
+static auto static_sneaky() {
+  struct S {
+    typedef int t;
+    // This function has internal linkage, so we can warn:
+    typedef int s; // expected-warning {{unused typedef 's'}}
+  };
+  return S();
+}
+auto sx = static_sneaky();
+decltype(sx)::t sy;
+
+auto sneaky_with_friends() {
+  struct S {
+  private:
+    friend class G;
+    // Can't warn if we have friends:
+    typedef int p;
+  };
+  return S();
+}
+
+namespace {
+auto nstatic_sneaky() {
+  struct S {
+    typedef int t;
+    // This function has internal linkage, so we can warn:
+    typedef int s; // expected-warning {{unused typedef 's'}}
+  };
+  return S();
+}
+auto nsx = nstatic_sneaky();
+decltype(nsx)::t nsy;
+}
+
+// Like sneaky(), but returning pointer to local type
+template<typename T>
+struct remove_reference { typedef T type; };
+template<typename T> struct remove_reference<T&> { typedef T type; };
+auto pointer_sneaky() {
+  struct S {
+    typedef int t;
+    typedef int s;
+  };
+  return (S*)nullptr;
+}
+remove_reference<decltype(*pointer_sneaky())>::type::t py;
+
+// Like sneaky(), but returning templated struct referencing local type.
+template <class T> struct container { int a; T t; };
+auto template_sneaky() {
+  struct S {
+    typedef int t;
+    typedef int s;
+  };
+  return container<S>();
+}
+auto tx = template_sneaky();
+decltype(tx.t)::t ty;
+
+// Like sneaky(), but doing its sneakiness by returning a member function
+// pointer.
+auto sneaky_memfun() {
+  struct S {
+    typedef int type;
+    int n;
+  };
+  return &S::n;
+}
+
+template <class T> void sneaky_memfun_g(int T::*p) {
+  typename T::type X;
+}
+
+void sneaky_memfun_h() {
+  sneaky_memfun_g(sneaky_memfun());
+}
+
+// This should not disable any warnings:
+#pragma clang diagnostic ignored "-Wunused-local-typedef"