[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, 3 insertions, 1 deletions

diff --git a/clang/lib/AST/DeclPrinter.cpp b/clang/lib/AST/DeclPrinter.cpp
index 78a7afdbf09..65532ec4967 100644
--- a/clang/lib/AST/DeclPrinter.cpp
+++ b/clang/lib/AST/DeclPrinter.cpp
@@ -610,7 +610,9 @@ void DeclPrinter::VisitFunctionDecl(FunctionDecl *D) {
     if (D->isInlineSpecified())  Out << "inline ";
     if (D->isVirtualAsWritten()) Out << "virtual ";
     if (D->isModulePrivate())    Out << "__module_private__ ";
-    if (D->isConstexpr() && !D->isExplicitlyDefaulted()) Out << "constexpr ";
+    if (D->isConstexprSpecified() && !D->isExplicitlyDefaulted())
+      Out << "constexpr ";
+    if (D->isConsteval())        Out << "consteval ";
     ExplicitSpecifier ExplicitSpec = ExplicitSpecifier::getFromDecl(D);
     if (ExplicitSpec.isSpecified())
       printExplicitSpecifier(ExplicitSpec, Out, Policy, Indentation);