[C++20] add Basic consteval specifier

Summary:
this revision adds Lexing, Parsing and Basic Semantic for the consteval specifier as specified by http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1073r3.html

with this patch, the consteval specifier is treated as constexpr but can only be applied to function declaration.

Changes:
 - add the consteval keyword.
 - add parsing of consteval specifier for normal declarations and lambdas expressions.
 - add the whether a declaration is constexpr is now represented by and enum everywhere except for variable because they can't be consteval.
 - adapt diagnostic about constexpr to print constexpr or consteval depending on the case.
 - add tests for basic semantic.

Reviewers: rsmith, martong, shafik

Reviewed By: rsmith

Subscribers: eraman, efriedma, rnkovacs, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D61790

llvm-svn: 363362

1 files changed, 13 insertions, 4 deletions

diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 5589297..2c9045d 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -2487,8 +2487,9 @@ void Parser::ParseSpecifierQualifierList(DeclSpec &DS, AccessSpecifier AS,
   }
 
   // Issue diagnostic and remove constexpr specifier if present.
-  if (DS.isConstexprSpecified() && DSC != DeclSpecContext::DSC_condition) {
-    Diag(DS.getConstexprSpecLoc(), diag::err_typename_invalid_constexpr);
+  if (DS.hasConstexprSpecifier() && DSC != DeclSpecContext::DSC_condition) {
+    Diag(DS.getConstexprSpecLoc(), diag::err_typename_invalid_constexpr)
+        << (DS.getConstexprSpecifier() == CSK_consteval);
     DS.ClearConstexprSpec();
   }
 }
@@ -3626,7 +3627,12 @@ void Parser::ParseDeclarationSpecifiers(DeclSpec &DS,
 
     // constexpr
     case tok::kw_constexpr:
-      isInvalid = DS.SetConstexprSpec(Loc, PrevSpec, DiagID);
+      isInvalid = DS.SetConstexprSpec(CSK_constexpr, Loc, PrevSpec, DiagID);
+      break;
+
+    // consteval
+    case tok::kw_consteval:
+      isInvalid = DS.SetConstexprSpec(CSK_consteval, Loc, PrevSpec, DiagID);
       break;
 
     // type-specifier
@@ -5031,6 +5037,9 @@ bool Parser::isDeclarationSpecifier(bool DisambiguatingWithExpression) {
   case tok::annot_decltype:
   case tok::kw_constexpr:
 
+    // C++20 consteval.
+  case tok::kw_consteval:
+
     // C11 _Atomic
   case tok::kw__Atomic:
     return true;
@@ -6267,7 +6276,7 @@ void Parser::ParseFunctionDeclarator(Declarator &D,
            Actions.CurContext->isRecord());
 
       Qualifiers Q = Qualifiers::fromCVRUMask(DS.getTypeQualifiers());
-      if (D.getDeclSpec().isConstexprSpecified() && !getLangOpts().CPlusPlus14)
+      if (D.getDeclSpec().hasConstexprSpecifier() && !getLangOpts().CPlusPlus14)
         Q.addConst();
       // FIXME: Collect C++ address spaces.
       // If there are multiple different address spaces, the source is invalid.