Re-apply "Deferred Concept Instantiation Implementation""

This reverts commit d4d47e5.

This fixes the lldb crash that was observed by ensuring that our
friend-'template contains reference to' TreeTransform properly handles a
TemplateDecl.

Author: Erich Keane

clang/docs/ReleaseNotes.rst

@@ -451,10 +451,11 @@ C++20 Feature Support
 - No longer attempt to evaluate a consteval UDL function call at runtime when
   it is called through a template instantiation. This fixes
   `Issue 54578 <https://github.com/llvm/llvm-project/issues/54578>`_.
-
-- Implemented ``__builtin_source_location()``, which enables library support
-  for ``std::source_location``.
-
+- Implemented `__builtin_source_location()` which enables library support for std::source_location.
+- Clang now correctly delays the instantiation of function constraints until
+  the time of checking, which should now allow the libstdc++ ranges implementation
+  to work for at least trivial examples.  This fixes
+  `Issue 44178 <https://github.com/llvm/llvm-project/issues/44178>`_.
 - The mangling scheme for C++20 modules has incompatibly changed. The
   initial mangling was discovered not to be reversible, and the weak
   ownership design decision did not give the backwards compatibility

clang/include/clang/AST/Decl.h

@@ -1890,7 +1890,9 @@ class FunctionDecl : public DeclaratorDecl,
     TK_FunctionTemplateSpecialization,
     // A function template specialization that hasn't yet been resolved to a
     // particular specialized function template.
-    TK_DependentFunctionTemplateSpecialization
+    TK_DependentFunctionTemplateSpecialization,
+    // A non templated function which is in a dependent scope.
+    TK_DependentNonTemplate
   };
 
   /// Stashed information about a defaulted function definition whose body has
@@ -1939,20 +1941,21 @@ class FunctionDecl : public DeclaratorDecl,
   /// The template or declaration that this declaration
   /// describes or was instantiated from, respectively.
   ///
-  /// For non-templates, this value will be NULL. For function
-  /// declarations that describe a function template, this will be a
-  /// pointer to a FunctionTemplateDecl. For member functions
-  /// of class template specializations, this will be a MemberSpecializationInfo
-  /// pointer containing information about the specialization.
-  /// For function template specializations, this will be a
-  /// FunctionTemplateSpecializationInfo, which contains information about
-  /// the template being specialized and the template arguments involved in
-  /// that specialization.
-  llvm::PointerUnion<FunctionTemplateDecl *,
-                     MemberSpecializationInfo *,
+  /// For non-templates this value will be NULL, unless this non-template
+  /// function declaration was declared directly inside of a function template,
+  /// in which case this will have a pointer to a FunctionDecl, stored in the
+  /// NamedDecl. For function declarations that describe a function template,
+  /// this will be a pointer to a FunctionTemplateDecl, stored in the NamedDecl.
+  /// For member functions of class template specializations, this will be a
+  /// MemberSpecializationInfo pointer containing information about the
+  /// specialization. For function template specializations, this will be a
+  /// FunctionTemplateSpecializationInfo, which contains information about the
+  /// template being specialized and the template arguments involved in that
+  /// specialization.
+  llvm::PointerUnion<NamedDecl *, MemberSpecializationInfo *,
                      FunctionTemplateSpecializationInfo *,
                      DependentFunctionTemplateSpecializationInfo *>
-    TemplateOrSpecialization;
+      TemplateOrSpecialization;
 
   /// Provides source/type location info for the declaration name embedded in
   /// the DeclaratorDecl base class.
@@ -2695,6 +2698,11 @@ class FunctionDecl : public DeclaratorDecl,
     setInstantiationOfMemberFunction(getASTContext(), FD, TSK);
   }
 
+  /// Specify that this function declaration was instantiated from FunctionDecl
+  /// FD. This is only used if this is a function declaration declared locally
+  /// inside of a function template.
+  void setInstantiatedFromDecl(FunctionDecl *FD);
+
   /// Retrieves the function template that is described by this
   /// function declaration.
   ///
@@ -2709,6 +2717,8 @@ class FunctionDecl : public DeclaratorDecl,
   /// FunctionTemplateDecl from a FunctionDecl.
   FunctionTemplateDecl *getDescribedFunctionTemplate() const;
 
+  FunctionDecl *getInstantiatedFromDecl() const;
+
   void setDescribedFunctionTemplate(FunctionTemplateDecl *Template);
 
   /// Determine whether this function is a function template

clang/include/clang/AST/DeclBase.h

@@ -920,10 +920,10 @@ class alignas(8) Decl {
 
   /// If this decl is defined inside a function/method/block it returns
   /// the corresponding DeclContext, otherwise it returns null.
-  const DeclContext *getParentFunctionOrMethod() const;
-  DeclContext *getParentFunctionOrMethod() {
-    return const_cast<DeclContext*>(
-                    const_cast<const Decl*>(this)->getParentFunctionOrMethod());
+  const DeclContext *getParentFunctionOrMethod(bool Lexical = false) const;
+  DeclContext *getParentFunctionOrMethod(bool Lexical = false) {
+    return const_cast<DeclContext *>(
+        const_cast<const Decl *>(this)->getParentFunctionOrMethod(Lexical));
   }
 
   /// Retrieves the "canonical" declaration of the given declaration.

clang/include/clang/Sema/Sema.h

@@ -3622,6 +3622,11 @@ class Sema final {
                   bool ConsiderCudaAttrs = true,
                   bool ConsiderRequiresClauses = true);
 
+  // Calculates whether the expression Constraint depends on an enclosing
+  // template, for the purposes of [temp.friend] p9.
+  bool ConstraintExpressionDependsOnEnclosingTemplate(unsigned TemplateDepth,
+                                                      const Expr *Constraint);
+
   enum class AllowedExplicit {
     /// Allow no explicit functions to be used.
     None,
@@ -7091,6 +7096,21 @@ class Sema final {
       LocalInstantiationScope &Scope,
       const MultiLevelTemplateArgumentList &TemplateArgs);
 
+  /// used by SetupConstraintCheckingTemplateArgumentsAndScope to recursively(in
+  /// the case of lambdas) set up the LocalInstantiationScope of the current
+  /// function.
+  bool SetupConstraintScope(
+      FunctionDecl *FD, llvm::Optional<ArrayRef<TemplateArgument>> TemplateArgs,
+      MultiLevelTemplateArgumentList MLTAL, LocalInstantiationScope &Scope);
+
+  /// Used during constraint checking, sets up the constraint template arguemnt
+  /// lists, and calls SetupConstraintScope to set up the
+  /// LocalInstantiationScope to have the proper set of ParVarDecls configured.
+  llvm::Optional<MultiLevelTemplateArgumentList>
+  SetupConstraintCheckingTemplateArgumentsAndScope(
+      FunctionDecl *FD, llvm::Optional<ArrayRef<TemplateArgument>> TemplateArgs,
+      LocalInstantiationScope &Scope);
+
 public:
   const NormalizedConstraint *
   getNormalizedAssociatedConstraints(
@@ -7121,8 +7141,10 @@ class Sema final {
   /// check (either a concept or a constrained entity).
   /// \param ConstraintExprs a list of constraint expressions, treated as if
   /// they were 'AND'ed together.
-  /// \param TemplateArgs the list of template arguments to substitute into the
-  /// constraint expression.
+  /// \param TemplateArgList the multi-level list of template arguments to
+  /// substitute into the constraint expression. This should be relative to the
+  /// top-level (hence multi-level), since we need to instantiate fully at the
+  /// time of checking.
   /// \param TemplateIDRange The source range of the template id that
   /// caused the constraints check.
   /// \param Satisfaction if true is returned, will contain details of the
@@ -7132,7 +7154,40 @@ class Sema final {
   /// false otherwise.
   bool CheckConstraintSatisfaction(
       const NamedDecl *Template, ArrayRef<const Expr *> ConstraintExprs,
-      ArrayRef<TemplateArgument> TemplateArgs,
+      const MultiLevelTemplateArgumentList &TemplateArgList,
+      SourceRange TemplateIDRange, ConstraintSatisfaction &Satisfaction) {
+    llvm::SmallVector<Expr *, 4> Converted;
+    return CheckConstraintSatisfaction(Template, ConstraintExprs, Converted,
+                                       TemplateArgList, TemplateIDRange,
+                                       Satisfaction);
+  }
+
+  /// \brief Check whether the given list of constraint expressions are
+  /// satisfied (as if in a 'conjunction') given template arguments.
+  /// Additionally, takes an empty list of Expressions which is populated with
+  /// the instantiated versions of the ConstraintExprs.
+  /// \param Template the template-like entity that triggered the constraints
+  /// check (either a concept or a constrained entity).
+  /// \param ConstraintExprs a list of constraint expressions, treated as if
+  /// they were 'AND'ed together.
+  /// \param ConvertedConstraints a out parameter that will get populated with
+  /// the instantiated version of the ConstraintExprs if we successfully checked
+  /// satisfaction.
+  /// \param TemplateArgList the multi-level list of template arguments to
+  /// substitute into the constraint expression. This should be relative to the
+  /// top-level (hence multi-level), since we need to instantiate fully at the
+  /// time of checking.
+  /// \param TemplateIDRange The source range of the template id that
+  /// caused the constraints check.
+  /// \param Satisfaction if true is returned, will contain details of the
+  /// satisfaction, with enough information to diagnose an unsatisfied
+  /// expression.
+  /// \returns true if an error occurred and satisfaction could not be checked,
+  /// false otherwise.
+  bool CheckConstraintSatisfaction(
+      const NamedDecl *Template, ArrayRef<const Expr *> ConstraintExprs,
+      llvm::SmallVectorImpl<Expr *> &ConvertedConstraints,
+      const MultiLevelTemplateArgumentList &TemplateArgList,
       SourceRange TemplateIDRange, ConstraintSatisfaction &Satisfaction);
 
   /// \brief Check whether the given non-dependent constraint expression is
@@ -7168,9 +7223,9 @@ class Sema final {
   ///
   /// \returns true if the constrains are not satisfied or could not be checked
   /// for satisfaction, false if the constraints are satisfied.
-  bool EnsureTemplateArgumentListConstraints(TemplateDecl *Template,
-                                       ArrayRef<TemplateArgument> TemplateArgs,
-                                             SourceRange TemplateIDRange);
+  bool EnsureTemplateArgumentListConstraints(
+      TemplateDecl *Template, MultiLevelTemplateArgumentList TemplateArgs,
+      SourceRange TemplateIDRange);
 
   /// \brief Emit diagnostics explaining why a constraint expression was deemed
   /// unsatisfied.
@@ -8904,7 +8959,8 @@ class Sema final {
 
   MultiLevelTemplateArgumentList getTemplateInstantiationArgs(
       const NamedDecl *D, const TemplateArgumentList *Innermost = nullptr,
-      bool RelativeToPrimary = false, const FunctionDecl *Pattern = nullptr);
+      bool RelativeToPrimary = false, const FunctionDecl *Pattern = nullptr,
+      bool LookBeyondLambda = false, bool IncludeContainingStruct = false);
 
   /// A context in which code is being synthesized (where a source location
   /// alone is not sufficient to identify the context). This covers template
@@ -9637,6 +9693,11 @@ class Sema final {
                       ExtParameterInfoBuilder &ParamInfos);
   ExprResult SubstExpr(Expr *E,
                        const MultiLevelTemplateArgumentList &TemplateArgs);
+  // Unlike the above, this evaluates constraints, which should only happen at
+  // 'constraint checking' time.
+  ExprResult
+  SubstConstraintExpr(Expr *E,
+                      const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// Substitute the given template arguments into a list of
   /// expressions, expanding pack expansions if required.
@@ -9660,13 +9721,14 @@ class Sema final {
 
   TemplateParameterList *
   SubstTemplateParams(TemplateParameterList *Params, DeclContext *Owner,
-                      const MultiLevelTemplateArgumentList &TemplateArgs);
+                      const MultiLevelTemplateArgumentList &TemplateArgs,
+                      bool InstantiateConstraints = false);
 
   bool
   SubstTemplateArguments(ArrayRef<TemplateArgumentLoc> Args,
                          const MultiLevelTemplateArgumentList &TemplateArgs,
-                         TemplateArgumentListInfo &Outputs);
-
+                         TemplateArgumentListInfo &Outputs,
+                         bool InstantiateConstraints = false);
 
   Decl *SubstDecl(Decl *D, DeclContext *Owner,
                   const MultiLevelTemplateArgumentList &TemplateArgs);
@@ -9758,7 +9820,8 @@ class Sema final {
                     const MultiLevelTemplateArgumentList &TemplateArgs);
 
   bool SubstTypeConstraint(TemplateTypeParmDecl *Inst, const TypeConstraint *TC,
-                           const MultiLevelTemplateArgumentList &TemplateArgs);
+                           const MultiLevelTemplateArgumentList &TemplateArgs,
+                           bool isEvaluatingAConstraint);
 
   bool InstantiateDefaultArgument(SourceLocation CallLoc, FunctionDecl *FD,
                                   ParmVarDecl *Param);

clang/include/clang/Sema/Template.h

@@ -75,6 +75,8 @@ enum class TemplateSubstitutionKind : char {
   class MultiLevelTemplateArgumentList {
     /// The template argument list at a certain template depth
     using ArgList = ArrayRef<TemplateArgument>;
+    using ArgListsIterator = SmallVector<ArgList, 4>::iterator;
+    using ConstArgListsIterator = SmallVector<ArgList, 4>::const_iterator;
 
     /// The template argument lists, stored from the innermost template
     /// argument list (first) to the outermost template argument list (last).
@@ -121,6 +123,12 @@ enum class TemplateSubstitutionKind : char {
       return TemplateArgumentLists.size();
     }
 
+    /// Determine the number of substituted args at 'Depth'.
+    unsigned getNumSubstitutedArgs(unsigned Depth) const {
+      assert(NumRetainedOuterLevels <= Depth && Depth < getNumLevels());
+      return TemplateArgumentLists[getNumLevels() - Depth - 1].size();
+    }
+
     unsigned getNumRetainedOuterLevels() const {
       return NumRetainedOuterLevels;
     }
@@ -158,6 +166,14 @@ enum class TemplateSubstitutionKind : char {
       return !(*this)(Depth, Index).isNull();
     }
 
+    bool isAnyArgInstantiationDependent() const {
+      for (ArgList List : TemplateArgumentLists)
+        for (const TemplateArgument &TA : List)
+          if (TA.isInstantiationDependent())
+            return true;
+      return false;
+    }
+
     /// Clear out a specific template argument.
     void setArgument(unsigned Depth, unsigned Index,
                      TemplateArgument Arg) {
@@ -183,6 +199,14 @@ enum class TemplateSubstitutionKind : char {
       TemplateArgumentLists.push_back(Args);
     }
 
+    /// Replaces the current 'innermost' level with the provided argument list.
+    /// This is useful for type deduction cases where we need to get the entire
+    /// list from the AST, but then add the deduced innermost list.
+    void replaceInnermostTemplateArguments(ArgList Args) {
+      assert(TemplateArgumentLists.size() > 0 && "Replacing in an empty list?");
+      TemplateArgumentLists[0] = Args;
+    }
+
     /// Add an outermost level that we are not substituting. We have no
     /// arguments at this level, and do not remove it from the depth of inner
     /// template parameters that we instantiate.
@@ -197,6 +221,16 @@ enum class TemplateSubstitutionKind : char {
     const ArgList &getInnermost() const {
       return TemplateArgumentLists.front();
     }
+
+    /// Retrieve the outermost template argument list.
+    const ArgList &getOutermost() const { return TemplateArgumentLists.back(); }
+
+    ArgListsIterator begin() { return TemplateArgumentLists.begin(); }
+    ConstArgListsIterator begin() const {
+      return TemplateArgumentLists.begin();
+    }
+    ArgListsIterator end() { return TemplateArgumentLists.end(); }
+    ConstArgListsIterator end() const { return TemplateArgumentLists.end(); }
   };
 
   /// The context in which partial ordering of function templates occurs.
@@ -469,6 +503,7 @@ enum class TemplateSubstitutionKind : char {
     const MultiLevelTemplateArgumentList &TemplateArgs;
     Sema::LateInstantiatedAttrVec* LateAttrs = nullptr;
     LocalInstantiationScope *StartingScope = nullptr;
+    bool EvaluatingAConstraint = false;
 
     /// A list of out-of-line class template partial
     /// specializations that will need to be instantiated after the
@@ -487,10 +522,12 @@ enum class TemplateSubstitutionKind : char {
 
   public:
     TemplateDeclInstantiator(Sema &SemaRef, DeclContext *Owner,
-                             const MultiLevelTemplateArgumentList &TemplateArgs)
+                             const MultiLevelTemplateArgumentList &TemplateArgs,
+                             bool EvaluatingConstraint = false)
         : SemaRef(SemaRef),
           SubstIndex(SemaRef, SemaRef.ArgumentPackSubstitutionIndex),
-          Owner(Owner), TemplateArgs(TemplateArgs) {}
+          Owner(Owner), TemplateArgs(TemplateArgs),
+          EvaluatingAConstraint(EvaluatingConstraint) {}
 
 // Define all the decl visitors using DeclNodes.inc
 #define DECL(DERIVED, BASE) \

clang/lib/AST/ASTImporter.cpp

@@ -3109,6 +3109,11 @@ Error ASTNodeImporter::ImportTemplateInformation(
   case FunctionDecl::TK_FunctionTemplate:
     return Error::success();
 
+  case FunctionDecl::TK_DependentNonTemplate:
+    if (Expected<FunctionDecl *> InstFDOrErr =
+            import(FromFD->getInstantiatedFromDecl()))
+      ToFD->setInstantiatedFromDecl(*InstFDOrErr);
+    return Error::success();
   case FunctionDecl::TK_MemberSpecialization: {
     TemplateSpecializationKind TSK = FromFD->getTemplateSpecializationKind();
 

clang/lib/AST/Decl.cpp

@@ -3732,8 +3732,12 @@ const IdentifierInfo *FunctionDecl::getLiteralIdentifier() const {
 FunctionDecl::TemplatedKind FunctionDecl::getTemplatedKind() const {
   if (TemplateOrSpecialization.isNull())
     return TK_NonTemplate;
-  if (TemplateOrSpecialization.is<FunctionTemplateDecl *>())
+  if (auto *ND = TemplateOrSpecialization.dyn_cast<NamedDecl *>()) {
+    if (isa<FunctionDecl>(ND))
+      return TK_DependentNonTemplate;
+    assert(isa<FunctionTemplateDecl>(ND) && "No other types it could be?");
     return TK_FunctionTemplate;
+  }
   if (TemplateOrSpecialization.is<MemberSpecializationInfo *>())
     return TK_MemberSpecialization;
   if (TemplateOrSpecialization.is<FunctionTemplateSpecializationInfo *>())
@@ -3774,15 +3778,28 @@ FunctionDecl::setInstantiationOfMemberFunction(ASTContext &C,
 }
 
 FunctionTemplateDecl *FunctionDecl::getDescribedFunctionTemplate() const {
-  return TemplateOrSpecialization.dyn_cast<FunctionTemplateDecl *>();
+  return dyn_cast_or_null<FunctionTemplateDecl>(
+      TemplateOrSpecialization.dyn_cast<NamedDecl *>());
 }
 
-void FunctionDecl::setDescribedFunctionTemplate(FunctionTemplateDecl *Template) {
+void FunctionDecl::setDescribedFunctionTemplate(
+    FunctionTemplateDecl *Template) {
   assert(TemplateOrSpecialization.isNull() &&
          "Member function is already a specialization");
   TemplateOrSpecialization = Template;
 }
 
+void FunctionDecl::setInstantiatedFromDecl(FunctionDecl *FD) {
+  assert(TemplateOrSpecialization.isNull() &&
+         "function is already a specialization");
+  TemplateOrSpecialization = FD;
+}
+
+FunctionDecl *FunctionDecl::getInstantiatedFromDecl() const {
+  return dyn_cast_or_null<FunctionDecl>(
+      TemplateOrSpecialization.dyn_cast<NamedDecl *>());
+}
+
 bool FunctionDecl::isImplicitlyInstantiable() const {
   // If the function is invalid, it can't be implicitly instantiated.
   if (isInvalidDecl())