P0091R3: Implement basic parsing support for C++17 deduction-guides.

We model deduction-guides as functions with a new kind of name that identifies
the template whose deduction they guide; the bulk of this patch is adding the
new name kind. This gives us a clean way to attach an extensible list of guides
to a class template in a way that doesn't require any special handling in AST
files etc (and we're going to need these functions we come to performing
deduction).


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@294266 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 29 insertions, 6 deletions

diff --git a/lib/Parse/ParseDecl.cpp b/lib/Parse/ParseDecl.cpp
index 6da61c689e..9e8823fb4d 100644
--- a/lib/Parse/ParseDecl.cpp
+++ b/lib/Parse/ParseDecl.cpp
@@ -3025,6 +3025,16 @@ void Parser::ParseDeclarationSpecifiers(DeclSpec &DS,
           isConstructorDeclarator(/*Unqualified*/true))
         goto DoneWithDeclSpec;
 
+      // Likewise, if this is a context where the identifier could be a template
+      // name, check whether this is a deduction guide declaration.
+      if (getLangOpts().CPlusPlus1z &&
+          (DSContext == DSC_class || DSContext == DSC_top_level) &&
+          Actions.isDeductionGuideName(getCurScope(), *Tok.getIdentifierInfo(),
+                                       Tok.getLocation()) &&
+          isConstructorDeclarator(/*Unqualified*/ true,
+                                  /*DeductionGuide*/ true))
+        goto DoneWithDeclSpec;
+
       isInvalid = DS.SetTypeSpecType(DeclSpec::TST_typename, Loc, PrevSpec,
                                      DiagID, TypeRep, Policy);
       if (isInvalid)
@@ -4644,7 +4654,7 @@ bool Parser::isDeclarationSpecifier(bool DisambiguatingWithExpression) {
   }
 }
 
-bool Parser::isConstructorDeclarator(bool IsUnqualified) {
+bool Parser::isConstructorDeclarator(bool IsUnqualified, bool DeductionGuide) {
   TentativeParsingAction TPA(*this);
 
   // Parse the C++ scope specifier.
@@ -4732,6 +4742,11 @@ bool Parser::isConstructorDeclarator(bool IsUnqualified) {
 
     case tok::r_paren:
       // C(X   )
+      if (DeductionGuide) {
+        // C(X) -> ... is a deduction guide.
+        IsConstructor = NextToken().is(tok::arrow);
+        break;
+      }
       if (NextToken().is(tok::colon) || NextToken().is(tok::kw_try)) {
         // Assume these were meant to be constructors:
         //   C(X)   :    (the name of a bit-field cannot be parenthesized).
@@ -4749,7 +4764,7 @@ bool Parser::isConstructorDeclarator(bool IsUnqualified) {
         //
         // FIXME: We can actually do this whether or not the name is qualified,
         // because if it is qualified in this context it must be being used as
-        // a constructor name. However, we do not implement that rule correctly
+        // a constructor name.
         // currently, so we're somewhat conservative here.
         IsConstructor = IsUnqualified;
       }
@@ -5280,21 +5295,29 @@ void Parser::ParseDirectDeclarator(Declarator &D) {
       // We found something that indicates the start of an unqualified-id.
       // Parse that unqualified-id.
       bool AllowConstructorName;
-      if (D.getDeclSpec().hasTypeSpecifier())
+      bool AllowDeductionGuide;
+      if (D.getDeclSpec().hasTypeSpecifier()) {
         AllowConstructorName = false;
-      else if (D.getCXXScopeSpec().isSet())
+        AllowDeductionGuide = false;
+      } else if (D.getCXXScopeSpec().isSet()) {
         AllowConstructorName =
           (D.getContext() == Declarator::FileContext ||
            D.getContext() == Declarator::MemberContext);
-      else
+        AllowDeductionGuide = false;
+      } else {
         AllowConstructorName = (D.getContext() == Declarator::MemberContext);
+        AllowDeductionGuide = 
+          (D.getContext() == Declarator::FileContext ||
+           D.getContext() == Declarator::MemberContext);
+      }
 
       SourceLocation TemplateKWLoc;
       bool HadScope = D.getCXXScopeSpec().isValid();
       if (ParseUnqualifiedId(D.getCXXScopeSpec(),
                              /*EnteringContext=*/true,
                              /*AllowDestructorName=*/true, AllowConstructorName,
-                             nullptr, TemplateKWLoc, D.getName()) ||
+                             AllowDeductionGuide, nullptr, TemplateKWLoc,
+                             D.getName()) ||
           // Once we're past the identifier, if the scope was bad, mark the
           // whole declarator bad.
           D.getCXXScopeSpec().isInvalid()) {