[clang] adding explicit(bool) from c++2a

this patch adds support for the explicit bool specifier.

Changes:
- The parsing for the explicit(bool) specifier was added in ParseDecl.cpp.
- The storage of the explicit specifier was changed. the explicit specifier was stored as a boolean value in the FunctionDeclBitfields and in the DeclSpec class. now it is stored as a PointerIntPair<Expr*, 2> with a flag and a potential expression in CXXConstructorDecl, CXXDeductionGuideDecl, CXXConversionDecl and in the DeclSpec class.
- Following the AST change, Serialization, ASTMatchers, ASTComparator and ASTPrinter were adapted.
- Template instantiation was adapted to instantiate the potential expressions of the explicit(bool) specifier When instantiating their associated declaration.
- The Add*Candidate functions were adapted, they now take a Boolean indicating if the context allowing explicit constructor or conversion function and this boolean is used to remove invalid overloads that required template instantiation to be detected.
- Test for Semantic and Serialization were added.

This patch is not yet complete. I still need to check that interaction with CTAD and deduction guides is correct. and add more tests for AST operations. But I wanted first feedback.
Perhaps this patch should be spited in smaller patches, but making each patch testable as a standalone may be tricky.

Patch by Tyker

Differential Revision: https://reviews.llvm.org/D60934

llvm-svn: 359949

clang/include/clang/AST/Decl.h

@@ -2369,16 +2369,6 @@ class FunctionDecl : public DeclaratorDecl,
   /// that was defined in the class body.
   bool isInlined() const { return FunctionDeclBits.IsInline; }
 
-  /// Whether this function is marked as explicit explicitly.
-  bool isExplicitSpecified() const {
-    return FunctionDeclBits.IsExplicitSpecified;
-  }
-
-  /// State that this function is marked as explicit explicitly.
-  void setExplicitSpecified(bool ExpSpec = true) {
-    FunctionDeclBits.IsExplicitSpecified = ExpSpec;
-  }
-
   bool isInlineDefinitionExternallyVisible() const;
 
   bool isMSExternInline() const;

clang/include/clang/AST/DeclBase.h

@@ -1472,10 +1472,6 @@ class DeclContext {
     uint64_t IsInline : 1;
     uint64_t IsInlineSpecified : 1;
 
-    /// This is shared by CXXConstructorDecl,
-    /// CXXConversionDecl, and CXXDeductionGuideDecl.
-    uint64_t IsExplicitSpecified : 1;
-
     uint64_t IsVirtualAsWritten : 1;
     uint64_t IsPure : 1;
     uint64_t HasInheritedPrototype : 1;
@@ -1523,7 +1519,7 @@ class DeclContext {
   };
 
   /// Number of non-inherited bits in FunctionDeclBitfields.
-  enum { NumFunctionDeclBits = 25 };
+  enum { NumFunctionDeclBits = 24 };
 
   /// Stores the bits used by CXXConstructorDecl. If modified
   /// NumCXXConstructorDeclBits and the accessor
@@ -1535,17 +1531,25 @@ class DeclContext {
     /// For the bits in FunctionDeclBitfields.
     uint64_t : NumFunctionDeclBits;
 
-    /// 25 bits to fit in the remaining availible space.
+    /// 24 bits to fit in the remaining available space.
     /// Note that this makes CXXConstructorDeclBitfields take
     /// exactly 64 bits and thus the width of NumCtorInitializers
     /// will need to be shrunk if some bit is added to NumDeclContextBitfields,
     /// NumFunctionDeclBitfields or CXXConstructorDeclBitfields.
-    uint64_t NumCtorInitializers : 25;
+    uint64_t NumCtorInitializers : 24;
     uint64_t IsInheritingConstructor : 1;
+
+    /// Whether this constructor has a trail-allocated explicit specifier.
+    uint64_t HasTrailingExplicitSpecifier : 1;
+    /// If this constructor does't have a trail-allocated explicit specifier.
+    /// Whether this constructor is explicit specified.
+    uint64_t IsSimpleExplicit : 1;
   };
 
   /// Number of non-inherited bits in CXXConstructorDeclBitfields.
-  enum { NumCXXConstructorDeclBits = 26 };
+  enum {
+    NumCXXConstructorDeclBits = 64 - NumDeclContextBits - NumFunctionDeclBits
+  };
 
   /// Stores the bits used by ObjCMethodDecl.
   /// If modified NumObjCMethodDeclBits and the accessor

clang/include/clang/AST/DeclCXX.h

@@ -1990,6 +1990,50 @@ class CXXRecordDecl : public RecordDecl {
   }
 };
 
+/// Store information needed for an explicit specifier.
+/// used by CXXDeductionGuideDecl, CXXConstructorDecl and CXXConversionDecl.
+class ExplicitSpecifier {
+  llvm::PointerIntPair<Expr *, 2, ExplicitSpecKind> ExplicitSpec{
+      nullptr, ExplicitSpecKind::ResolvedFalse};
+
+public:
+  ExplicitSpecifier() = default;
+  ExplicitSpecifier(Expr *Expression, ExplicitSpecKind Kind)
+      : ExplicitSpec(Expression, Kind) {}
+  ExplicitSpecKind getKind() const { return ExplicitSpec.getInt(); }
+  const Expr *getExpr() const { return ExplicitSpec.getPointer(); }
+  Expr *getExpr() { return ExplicitSpec.getPointer(); }
+
+  /// Return true if the ExplicitSpecifier isn't defaulted.
+  bool isSpecified() const {
+    return ExplicitSpec.getInt() != ExplicitSpecKind::ResolvedFalse ||
+           ExplicitSpec.getPointer();
+  }
+
+  /// Check for Equivalence of explicit specifiers.
+  /// Return True if the explicit specifier are equivalent false otherwise.
+  bool isEquivalent(const ExplicitSpecifier Other) const;
+  /// Return true if the explicit specifier is already resolved to be explicit.
+  bool isExplicit() const {
+    return ExplicitSpec.getInt() == ExplicitSpecKind::ResolvedTrue;
+  }
+  /// Return true if the ExplicitSpecifier isn't valid.
+  /// This state occurs after a substitution failures.
+  bool isInvalid() const {
+    return ExplicitSpec.getInt() == ExplicitSpecKind::Unresolved &&
+           !ExplicitSpec.getPointer();
+  }
+  void setKind(ExplicitSpecKind Kind) { ExplicitSpec.setInt(Kind); }
+  void setExpr(Expr *E) { ExplicitSpec.setPointer(E); }
+  // getFromDecl - retrieve the explicit specifier in the given declaration.
+  // if the given declaration has no explicit. the returned explicit specifier
+  // is defaulted. .isSpecified() will be false.
+  static ExplicitSpecifier getFromDecl(FunctionDecl *Function);
+  static ExplicitSpecifier Invalid() {
+    return ExplicitSpecifier(nullptr, ExplicitSpecKind::Unresolved);
+  }
+};
+
 /// Represents a C++ deduction guide declaration.
 ///
 /// \code
@@ -2005,31 +2049,36 @@ class CXXDeductionGuideDecl : public FunctionDecl {
 
 private:
   CXXDeductionGuideDecl(ASTContext &C, DeclContext *DC, SourceLocation StartLoc,
-                        bool IsExplicit, const DeclarationNameInfo &NameInfo,
-                        QualType T, TypeSourceInfo *TInfo,
-                        SourceLocation EndLocation)
+                        ExplicitSpecifier ES,
+                        const DeclarationNameInfo &NameInfo, QualType T,
+                        TypeSourceInfo *TInfo, SourceLocation EndLocation)
       : FunctionDecl(CXXDeductionGuide, C, DC, StartLoc, NameInfo, T, TInfo,
-                     SC_None, false, false) {
+                     SC_None, false, false),
+        ExplicitSpec(ES) {
     if (EndLocation.isValid())
       setRangeEnd(EndLocation);
-    setExplicitSpecified(IsExplicit);
     setIsCopyDeductionCandidate(false);
   }
 
+  ExplicitSpecifier ExplicitSpec;
+  void setExplicitSpecifier(ExplicitSpecifier ES) { ExplicitSpec = ES; }
+
 public:
   friend class ASTDeclReader;
   friend class ASTDeclWriter;
 
-  static CXXDeductionGuideDecl *Create(ASTContext &C, DeclContext *DC,
-                                       SourceLocation StartLoc, bool IsExplicit,
-                                       const DeclarationNameInfo &NameInfo,
-                                       QualType T, TypeSourceInfo *TInfo,
-                                       SourceLocation EndLocation);
+  static CXXDeductionGuideDecl *
+  Create(ASTContext &C, DeclContext *DC, SourceLocation StartLoc,
+         ExplicitSpecifier ES, const DeclarationNameInfo &NameInfo, QualType T,
+         TypeSourceInfo *TInfo, SourceLocation EndLocation);
 
   static CXXDeductionGuideDecl *CreateDeserialized(ASTContext &C, unsigned ID);
 
-  /// Whether this deduction guide is explicit.
-  bool isExplicit() const { return isExplicitSpecified(); }
+  ExplicitSpecifier getExplicitSpecifier() { return ExplicitSpec; }
+  const ExplicitSpecifier getExplicitSpecifier() const { return ExplicitSpec; }
+
+  /// Return true if the declartion is already resolved to be explicit.
+  bool isExplicit() const { return ExplicitSpec.isExplicit(); }
 
   /// Get the template for which this guide performs deduction.
   TemplateDecl *getDeducedTemplate() const {
@@ -2498,7 +2547,8 @@ class InheritedConstructor {
 /// \endcode
 class CXXConstructorDecl final
     : public CXXMethodDecl,
-      private llvm::TrailingObjects<CXXConstructorDecl, InheritedConstructor> {
+      private llvm::TrailingObjects<CXXConstructorDecl, InheritedConstructor,
+                                    ExplicitSpecifier> {
   // This class stores some data in DeclContext::CXXConstructorDeclBits
   // to save some space. Use the provided accessors to access it.
 
@@ -2508,28 +2558,74 @@ class CXXConstructorDecl final
   LazyCXXCtorInitializersPtr CtorInitializers;
 
   CXXConstructorDecl(ASTContext &C, CXXRecordDecl *RD, SourceLocation StartLoc,
-                     const DeclarationNameInfo &NameInfo,
-                     QualType T, TypeSourceInfo *TInfo,
-                     bool isExplicitSpecified, bool isInline,
+                     const DeclarationNameInfo &NameInfo, QualType T,
+                     TypeSourceInfo *TInfo, ExplicitSpecifier ES, bool isInline,
                      bool isImplicitlyDeclared, bool isConstexpr,
                      InheritedConstructor Inherited);
 
   void anchor() override;
 
+  size_t numTrailingObjects(OverloadToken<InheritedConstructor>) const {
+    return CXXConstructorDeclBits.IsInheritingConstructor;
+  }
+  size_t numTrailingObjects(OverloadToken<ExplicitSpecifier>) const {
+    return CXXConstructorDeclBits.HasTrailingExplicitSpecifier;
+  }
+
+  ExplicitSpecifier getExplicitSpecifierInternal() const {
+    if (CXXConstructorDeclBits.HasTrailingExplicitSpecifier)
+      return *getCanonicalDecl()->getTrailingObjects<ExplicitSpecifier>();
+    return ExplicitSpecifier(
+        nullptr, getCanonicalDecl()->CXXConstructorDeclBits.IsSimpleExplicit
+                     ? ExplicitSpecKind::ResolvedTrue
+                     : ExplicitSpecKind::ResolvedFalse);
+  }
+
+  void setExplicitSpecifier(ExplicitSpecifier ES) {
+    assert((!ES.getExpr() ||
+            CXXConstructorDeclBits.HasTrailingExplicitSpecifier) &&
+           "cannot set this explicit specifier. no trail-allocated space for "
+           "explicit");
+    if (ES.getExpr())
+      *getCanonicalDecl()->getTrailingObjects<ExplicitSpecifier>() = ES;
+    else
+      CXXConstructorDeclBits.IsSimpleExplicit = ES.isExplicit();
+  }
+
+  enum TraillingAllocKind {
+    TAKInheritsConstructor = 1,
+    TAKHasTailExplicit = 1 << 1,
+  };
+
+  uint64_t getTraillingAllocKind() const {
+    return numTrailingObjects(OverloadToken<InheritedConstructor>()) |
+           (numTrailingObjects(OverloadToken<ExplicitSpecifier>()) << 1);
+  }
+
 public:
   friend class ASTDeclReader;
   friend class ASTDeclWriter;
   friend TrailingObjects;
 
   static CXXConstructorDecl *CreateDeserialized(ASTContext &C, unsigned ID,
-                                                bool InheritsConstructor);
+                                                uint64_t AllocKind);
   static CXXConstructorDecl *
   Create(ASTContext &C, CXXRecordDecl *RD, SourceLocation StartLoc,
          const DeclarationNameInfo &NameInfo, QualType T, TypeSourceInfo *TInfo,
-         bool isExplicit, bool isInline, bool isImplicitlyDeclared,
+         ExplicitSpecifier ES, bool isInline, bool isImplicitlyDeclared,
          bool isConstexpr,
          InheritedConstructor Inherited = InheritedConstructor());
 
+  ExplicitSpecifier getExplicitSpecifier() {
+    return getExplicitSpecifierInternal();
+  }
+  const ExplicitSpecifier getExplicitSpecifier() const {
+    return getExplicitSpecifierInternal();
+  }
+
+  /// Return true if the declartion is already resolved to be explicit.
+  bool isExplicit() const { return getExplicitSpecifier().isExplicit(); }
+
   /// Iterates through the member/base initializer list.
   using init_iterator = CXXCtorInitializer **;
 
@@ -2600,11 +2696,6 @@ class CXXConstructorDecl final
     CtorInitializers = Initializers;
   }
 
-  /// Whether this function is explicit.
-  bool isExplicit() const {
-    return getCanonicalDecl()->isExplicitSpecified();
-  }
-
   /// Determine whether this constructor is a delegating constructor.
   bool isDelegatingConstructor() const {
     return (getNumCtorInitializers() == 1) &&
@@ -2783,34 +2874,39 @@ class CXXDestructorDecl : public CXXMethodDecl {
 class CXXConversionDecl : public CXXMethodDecl {
   CXXConversionDecl(ASTContext &C, CXXRecordDecl *RD, SourceLocation StartLoc,
                     const DeclarationNameInfo &NameInfo, QualType T,
-                    TypeSourceInfo *TInfo, bool isInline,
-                    bool isExplicitSpecified, bool isConstexpr,
-                    SourceLocation EndLocation)
+                    TypeSourceInfo *TInfo, bool isInline, ExplicitSpecifier ES,
+                    bool isConstexpr, SourceLocation EndLocation)
       : CXXMethodDecl(CXXConversion, C, RD, StartLoc, NameInfo, T, TInfo,
-                      SC_None, isInline, isConstexpr, EndLocation) {
-    setExplicitSpecified(isExplicitSpecified);
-  }
-
+                      SC_None, isInline, isConstexpr, EndLocation),
+        ExplicitSpec(ES) {}
   void anchor() override;
 
+  ExplicitSpecifier ExplicitSpec;
+
+  void setExplicitSpecifier(ExplicitSpecifier ES) { ExplicitSpec = ES; }
+
 public:
   friend class ASTDeclReader;
   friend class ASTDeclWriter;
 
-  static CXXConversionDecl *Create(ASTContext &C, CXXRecordDecl *RD,
-                                   SourceLocation StartLoc,
-                                   const DeclarationNameInfo &NameInfo,
-                                   QualType T, TypeSourceInfo *TInfo,
-                                   bool isInline, bool isExplicit,
-                                   bool isConstexpr,
-                                   SourceLocation EndLocation);
+  static CXXConversionDecl *
+  Create(ASTContext &C, CXXRecordDecl *RD, SourceLocation StartLoc,
+         const DeclarationNameInfo &NameInfo, QualType T, TypeSourceInfo *TInfo,
+         bool isInline, ExplicitSpecifier ES, bool isConstexpr,
+         SourceLocation EndLocation);
   static CXXConversionDecl *CreateDeserialized(ASTContext &C, unsigned ID);
 
-  /// Whether this function is explicit.
-  bool isExplicit() const {
-    return getCanonicalDecl()->isExplicitSpecified();
+  ExplicitSpecifier getExplicitSpecifier() {
+    return getCanonicalDecl()->ExplicitSpec;
   }
 
+  const ExplicitSpecifier getExplicitSpecifier() const {
+    return getCanonicalDecl()->ExplicitSpec;
+  }
+
+  /// Return true if the declartion is already resolved to be explicit.
+  bool isExplicit() const { return getExplicitSpecifier().isExplicit(); }
+
   /// Returns the type that this conversion function is converting to.
   QualType getConversionType() const {
     return getType()->getAs<FunctionType>()->getReturnType();

clang/include/clang/ASTMatchers/ASTMatchers.h

@@ -6171,6 +6171,9 @@ AST_MATCHER(CXXConstructorDecl, isDelegatingConstructor) {
 AST_POLYMORPHIC_MATCHER(isExplicit,
                         AST_POLYMORPHIC_SUPPORTED_TYPES(CXXConstructorDecl,
                                                         CXXConversionDecl)) {
+  // FIXME : it's not clear whether this should match a dependent
+  //         explicit(....). this matcher should also be able to match
+  //         CXXDeductionGuideDecl with explicit specifier.
   return Node.isExplicit();
 }
 

clang/include/clang/Basic/DiagnosticCommonKinds.td

@@ -150,6 +150,8 @@ def ext_warn_duplicate_declspec : ExtWarn<"%sub{duplicate_declspec}0">,
 def warn_duplicate_declspec : Warning<"%sub{duplicate_declspec}0">,
   InGroup<DuplicateDeclSpecifier>;
 
+def err_duplicate_declspec : Error<"%sub{duplicate_declspec}0">;
+
 def err_friend_decl_spec : Error<"'%0' is invalid in friend declarations">;
 
 def err_invalid_member_in_interface : Error<

clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -33,6 +33,10 @@ def err_asm_goto_not_supported_yet : Error<
 
 let CategoryName = "Parse Issue" in {
 
+def warn_cxx2a_compat_explicit_bool : Warning<
+  "this expression will be parsed as explicit(bool) in C++2a">,
+  InGroup<CXX2aCompat>, DefaultIgnore;
+
 def ext_empty_translation_unit : Extension<
   "ISO C requires a translation unit to contain at least one declaration">,
   InGroup<DiagGroup<"empty-translation-unit">>;

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -83,11 +83,11 @@ def err_typecheck_converted_constant_expression_indirect : Error<
   "bind reference to a temporary">;
 def err_expr_not_cce : Error<
   "%select{case value|enumerator value|non-type template argument|"
-  "array size|constexpr if condition}0 "
+  "array size|constexpr if condition|explicit specifier argument}0 "
   "is not a constant expression">;
 def ext_cce_narrowing : ExtWarn<
   "%select{case value|enumerator value|non-type template argument|"
-  "array size|constexpr if condition}0 "
+  "array size|constexpr if condition|explicit specifier argument}0 "
   "%select{cannot be narrowed from type %2 to %3|"
   "evaluates to %2, which cannot be narrowed to type %3}1">,
   InGroup<CXX11Narrowing>, DefaultError, SFINAEFailure;
@@ -2115,9 +2115,8 @@ def err_deduction_guide_wrong_scope : Error<
   "deduction guide must be declared in the same scope as template %q0">;
 def err_deduction_guide_defines_function : Error<
   "deduction guide cannot have a function definition">;
-def err_deduction_guide_explicit_mismatch : Error<
-  "deduction guide is %select{not |}0declared 'explicit' but "
-  "previous declaration was%select{ not|}0">;
+def err_deduction_guide_redeclared : Error<
+  "redeclaration of deduction guide">;
 def err_deduction_guide_specialized : Error<"deduction guide cannot be "
   "%select{explicitly instantiated|explicitly specialized}0">;
 def err_deduction_guide_template_not_deducible : Error<
@@ -3640,6 +3639,10 @@ def note_ovl_candidate : Note<
     "| has different qualifiers (expected %5 but found %6)"
     "| has different exception specification}4">;
 
+def note_ovl_candidate_explicit_forbidden : Note<
+    "candidate %0 ignored: cannot be explicit">;
+def note_explicit_bool_resolved_to_true : Note<
+    "explicit(bool) specifier resolved to true">;
 def note_ovl_candidate_inherited_constructor : Note<
     "constructor from base class %0 inherited here">;
 def note_ovl_candidate_inherited_constructor_slice : Note<