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

7 files changed, 53 insertions, 13 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()) {
diff --git a/lib/Parse/ParseDeclCXX.cpp b/lib/Parse/ParseDeclCXX.cpp
index 6403caa27b..d558909603 100644
--- a/lib/Parse/ParseDeclCXX.cpp
+++ b/lib/Parse/ParseDeclCXX.cpp
@@ -576,6 +576,7 @@ bool Parser::ParseUsingDeclarator(unsigned Context, UsingDeclarator &D) {
             /*AllowDestructorName=*/true,
             /*AllowConstructorName=*/!(Tok.is(tok::identifier) &&
                                        NextToken().is(tok::equal)),
+            /*AllowDeductionGuide=*/false,
             nullptr, D.TemplateKWLoc, D.Name))
       return true;
   }
@@ -2426,8 +2427,8 @@ Parser::ParseCXXClassMemberDeclaration(AccessSpecifier AS,
       // Try to parse an unqualified-id.
       SourceLocation TemplateKWLoc;
       UnqualifiedId Name;
-      if (ParseUnqualifiedId(SS, false, true, true, nullptr, TemplateKWLoc,
-                             Name)) {
+      if (ParseUnqualifiedId(SS, false, true, true, false, nullptr,
+                             TemplateKWLoc, Name)) {
         SkipUntil(tok::semi);
         return nullptr;
       }
diff --git a/lib/Parse/ParseExpr.cpp b/lib/Parse/ParseExpr.cpp
index ee06c76f60..0c09614547 100644
--- a/lib/Parse/ParseExpr.cpp
+++ b/lib/Parse/ParseExpr.cpp
@@ -1693,6 +1693,7 @@ Parser::ParsePostfixExpressionSuffix(ExprResult LHS) {
                                     /*AllowDestructorName=*/true,
                                     /*AllowConstructorName=*/
                                       getLangOpts().MicrosoftExt, 
+                                    /*AllowDeductionGuide=*/false,
                                     ObjectType, TemplateKWLoc, Name)) {
         (void)Actions.CorrectDelayedTyposInExpr(LHS);
         LHS = ExprError();
diff --git a/lib/Parse/ParseExprCXX.cpp b/lib/Parse/ParseExprCXX.cpp
index cfda2cddec..1ba1695800 100644
--- a/lib/Parse/ParseExprCXX.cpp
+++ b/lib/Parse/ParseExprCXX.cpp
@@ -546,6 +546,7 @@ ExprResult Parser::tryParseCXXIdExpression(CXXScopeSpec &SS, bool isAddressOfOpe
                          /*EnteringContext=*/false,
                          /*AllowDestructorName=*/false,
                          /*AllowConstructorName=*/false,
+                         /*AllowDeductionGuide=*/false,
                          /*ObjectType=*/nullptr, TemplateKWLoc, Name))
     return ExprError();
 
@@ -2429,6 +2430,8 @@ bool Parser::ParseUnqualifiedIdOperator(CXXScopeSpec &SS, bool EnteringContext,
 ///
 /// \param AllowConstructorName whether we allow parsing a constructor name.
 ///
+/// \param AllowDeductionGuide whether we allow parsing a deduction guide name.
+///
 /// \param ObjectType if this unqualified-id occurs within a member access
 /// expression, the type of the base object whose member is being accessed.
 ///
@@ -2438,6 +2441,7 @@ bool Parser::ParseUnqualifiedIdOperator(CXXScopeSpec &SS, bool EnteringContext,
 bool Parser::ParseUnqualifiedId(CXXScopeSpec &SS, bool EnteringContext,
                                 bool AllowDestructorName,
                                 bool AllowConstructorName,
+                                bool AllowDeductionGuide,
                                 ParsedType ObjectType,
                                 SourceLocation& TemplateKWLoc,
                                 UnqualifiedId &Result) {
@@ -2466,6 +2470,7 @@ bool Parser::ParseUnqualifiedId(CXXScopeSpec &SS, bool EnteringContext,
       return false;
     }
 
+    ParsedTemplateTy TemplateName;
     if (AllowConstructorName && 
         Actions.isCurrentClassName(*Id, getCurScope(), &SS)) {
       // We have parsed a constructor name.
@@ -2474,6 +2479,12 @@ bool Parser::ParseUnqualifiedId(CXXScopeSpec &SS, bool EnteringContext,
                                           /*IsCtorOrDtorName=*/true,
                                           /*NonTrivialTypeSourceInfo=*/true);
       Result.setConstructorName(Ty, IdLoc, IdLoc);
+    } else if (getLangOpts().CPlusPlus1z &&
+               AllowDeductionGuide && SS.isEmpty() &&
+               Actions.isDeductionGuideName(getCurScope(), *Id, IdLoc,
+                                            &TemplateName)) {
+      // We have parsed a template-name naming a deduction guide.
+      Result.setDeductionGuideName(TemplateName, IdLoc);
     } else {
       // We have parsed an identifier.
       Result.setIdentifier(Id, IdLoc);      
diff --git a/lib/Parse/ParseOpenMP.cpp b/lib/Parse/ParseOpenMP.cpp
index cab7d3432d..574ed6ee59 100644
--- a/lib/Parse/ParseOpenMP.cpp
+++ b/lib/Parse/ParseOpenMP.cpp
@@ -1053,7 +1053,7 @@ bool Parser::ParseOpenMPSimpleVarList(
       IsCorrect = false;
       SkipUntil(tok::comma, tok::r_paren, tok::annot_pragma_openmp_end,
                 StopBeforeMatch);
-    } else if (ParseUnqualifiedId(SS, false, false, false, nullptr,
+    } else if (ParseUnqualifiedId(SS, false, false, false, false, nullptr,
                                   TemplateKWLoc, Name)) {
       IsCorrect = false;
       SkipUntil(tok::comma, tok::r_paren, tok::annot_pragma_openmp_end,
@@ -1557,8 +1557,9 @@ static bool ParseReductionId(Parser &P, CXXScopeSpec &ReductionIdScopeSpec,
   }
   return P.ParseUnqualifiedId(ReductionIdScopeSpec, /*EnteringContext*/ false,
                               /*AllowDestructorName*/ false,
-                              /*AllowConstructorName*/ false, nullptr,
-                              TemplateKWLoc, ReductionId);
+                              /*AllowConstructorName*/ false,
+                              /*AllowDeductionGuide*/ false,
+                              nullptr, TemplateKWLoc, ReductionId);
 }
 
 /// Parses clauses with list.
diff --git a/lib/Parse/ParseStmtAsm.cpp b/lib/Parse/ParseStmtAsm.cpp
index 7fd9fa2146..59e96d982a 100644
--- a/lib/Parse/ParseStmtAsm.cpp
+++ b/lib/Parse/ParseStmtAsm.cpp
@@ -224,6 +224,7 @@ ExprResult Parser::ParseMSAsmIdentifier(llvm::SmallVectorImpl<Token> &LineToks,
                                  /*EnteringContext=*/false,
                                  /*AllowDestructorName=*/false,
                                  /*AllowConstructorName=*/false,
+                                 /*AllowDeductionGuide=*/false,
                                  /*ObjectType=*/nullptr, TemplateKWLoc, Id);
     // Perform the lookup.
     Result = Actions.LookupInlineAsmIdentifier(SS, TemplateKWLoc, Id, Info,
diff --git a/lib/Parse/Parser.cpp b/lib/Parse/Parser.cpp
index 8713bb2c23..9030ebff0f 100644
--- a/lib/Parse/Parser.cpp
+++ b/lib/Parse/Parser.cpp
@@ -1966,8 +1966,10 @@ bool Parser::ParseMicrosoftIfExistsCondition(IfExistsCondition& Result) {
 
   // Parse the unqualified-id.
   SourceLocation TemplateKWLoc; // FIXME: parsed, but unused.
-  if (ParseUnqualifiedId(Result.SS, false, true, true, nullptr, TemplateKWLoc,
-                         Result.Name)) {
+  if (ParseUnqualifiedId(
+          Result.SS, /*EnteringContext*/false, /*AllowDestructorName*/true,
+          /*AllowConstructorName*/true, /*AllowDeductionGuide*/false, nullptr,
+          TemplateKWLoc, Result.Name)) {
     T.skipToEnd();
     return true;
   }