[Concepts] Class template associated constraints

Summary:
This adds associated constraints as a property of class templates.
An error is produced if redeclarations are not similarly constrained.

Reviewers: rsmith, faisalv, aaron.ballman

Reviewed By: rsmith

Subscribers: cfe-commits, nwilson

Differential Revision: https://reviews.llvm.org/D25674

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@294697 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 64 insertions, 4 deletions

diff --git a/lib/AST/DeclTemplate.cpp b/lib/AST/DeclTemplate.cpp
index a5fbb0a3ba..22f6e18d56 100644
--- a/lib/AST/DeclTemplate.cpp
+++ b/lib/AST/DeclTemplate.cpp
@@ -297,10 +297,18 @@ ClassTemplateDecl *ClassTemplateDecl::Create(ASTContext &C,
                                              SourceLocation L,
                                              DeclarationName Name,
                                              TemplateParameterList *Params,
-                                             NamedDecl *Decl) {
+                                             NamedDecl *Decl,
+                                             Expr *AssociatedConstraints) {
   AdoptTemplateParameterList(Params, cast<DeclContext>(Decl));
-  ClassTemplateDecl *New = new (C, DC) ClassTemplateDecl(C, DC, L, Name,
-                                                         Params, Decl);
+
+  if (!AssociatedConstraints) {
+    return new (C, DC) ClassTemplateDecl(C, DC, L, Name, Params, Decl);
+  }
+
+  ConstrainedTemplateDeclInfo *const CTDI = new (C) ConstrainedTemplateDeclInfo;
+  ClassTemplateDecl *const New =
+      new (C, DC) ClassTemplateDecl(CTDI, C, DC, L, Name, Params, Decl);
+  New->setAssociatedConstraints(AssociatedConstraints);
   return New;
 }
 
diff --git a/lib/Sema/SemaTemplate.cpp b/lib/Sema/SemaTemplate.cpp
index d0ed17cc49..9d9d1270bf 100644
--- a/lib/Sema/SemaTemplate.cpp
+++ b/lib/Sema/SemaTemplate.cpp
@@ -45,6 +45,26 @@ clang::getTemplateParamsRange(TemplateParameterList const * const *Ps,
   return SourceRange(Ps[0]->getTemplateLoc(), Ps[N-1]->getRAngleLoc());
 }
 
+namespace clang {
+/// \brief [temp.constr.decl]p2: A template's associated constraints are
+/// defined as a single constraint-expression derived from the introduced
+/// constraint-expressions [ ... ].
+///
+/// \param Params The template parameter list and optional requires-clause.
+///
+/// \param FD The underlying templated function declaration for a function
+/// template.
+static Expr *formAssociatedConstraints(TemplateParameterList *Params,
+                                       FunctionDecl *FD);
+}
+
+static Expr *clang::formAssociatedConstraints(TemplateParameterList *Params,
+                                              FunctionDecl *FD) {
+  // FIXME: Concepts: collect additional introduced constraint-expressions
+  assert(!FD && "Cannot collect constraints from function declaration yet.");
+  return Params->getRequiresClause();
+}
+
 /// \brief Determine whether the declaration found is acceptable as the name
 /// of a template and, if so, return that template declaration. Otherwise,
 /// returns NULL.
@@ -1137,6 +1157,9 @@ Sema::CheckClassTemplate(Scope *S, unsigned TagSpec, TagUseKind TUK,
     }
   }
 
+  // TODO Memory management; associated constraints are not always stored.
+  Expr *const CurAC = formAssociatedConstraints(TemplateParams, nullptr);
+
   if (PrevClassTemplate) {
     // Ensure that the template parameter lists are compatible. Skip this check
     // for a friend in a dependent context: the template parameter list itself
@@ -1148,6 +1171,29 @@ Sema::CheckClassTemplate(Scope *S, unsigned TagSpec, TagUseKind TUK,
                                         TPL_TemplateMatch))
       return true;
 
+    // Check for matching associated constraints on redeclarations.
+    const Expr *const PrevAC = PrevClassTemplate->getAssociatedConstraints();
+    const bool RedeclACMismatch = [&] {
+      if (!(CurAC || PrevAC))
+        return false; // Nothing to check; no mismatch.
+      if (CurAC && PrevAC) {
+        llvm::FoldingSetNodeID CurACInfo, PrevACInfo;
+        CurAC->Profile(CurACInfo, Context, /*Canonical=*/true);
+        PrevAC->Profile(PrevACInfo, Context, /*Canonical=*/true);
+        if (CurACInfo == PrevACInfo)
+          return false; // All good; no mismatch.
+      }
+      return true;
+    }();
+
+    if (RedeclACMismatch) {
+      Diag(CurAC ? CurAC->getLocStart() : NameLoc,
+           diag::err_template_different_associated_constraints);
+      Diag(PrevAC ? PrevAC->getLocStart() : PrevClassTemplate->getLocation(),
+           diag::note_template_prev_declaration) << /*declaration*/0;
+      return true;
+    }
+
     // C++ [temp.class]p4:
     //   In a redeclaration, partial specialization, explicit
     //   specialization or explicit instantiation of a class template,
@@ -1250,10 +1296,15 @@ Sema::CheckClassTemplate(Scope *S, unsigned TagSpec, TagUseKind TUK,
     AddMsStructLayoutForRecord(NewClass);
   }
 
+  // Attach the associated constraints when the declaration will not be part of
+  // a decl chain.
+  Expr *const ACtoAttach =
+      PrevClassTemplate && ShouldAddRedecl ? nullptr : CurAC;
+
   ClassTemplateDecl *NewTemplate
     = ClassTemplateDecl::Create(Context, SemanticContext, NameLoc,
                                 DeclarationName(Name), TemplateParams,
-                                NewClass);
+                                NewClass, ACtoAttach);
 
   if (ShouldAddRedecl)
     NewTemplate->setPreviousDecl(PrevClassTemplate);
diff --git a/lib/Serialization/ASTReaderDecl.cpp b/lib/Serialization/ASTReaderDecl.cpp
index 5638cdfde5..6da820f09a 100644
--- a/lib/Serialization/ASTReaderDecl.cpp
+++ b/lib/Serialization/ASTReaderDecl.cpp
@@ -1876,6 +1876,7 @@ DeclID ASTDeclReader::VisitTemplateDecl(TemplateDecl *D) {
   DeclID PatternID = ReadDeclID();
   NamedDecl *TemplatedDecl = cast_or_null<NamedDecl>(Reader.GetDecl(PatternID));
   TemplateParameterList *TemplateParams = Record.readTemplateParameterList();
+  // FIXME handle associated constraints
   D->init(TemplatedDecl, TemplateParams);
 
   return PatternID;