[clang] adding explicit(bool) from c++2a

this patch adds support for the explicit bool specifier.

Changes:
- The parsing for the explicit(bool) specifier was added in ParseDecl.cpp.
- The storage of the explicit specifier was changed. the explicit specifier was stored as a boolean value in the FunctionDeclBitfields and in the DeclSpec class. now it is stored as a PointerIntPair<Expr*, 2> with a flag and a potential expression in CXXConstructorDecl, CXXDeductionGuideDecl, CXXConversionDecl and in the DeclSpec class.
- Following the AST change, Serialization, ASTMatchers, ASTComparator and ASTPrinter were adapted.
- Template instantiation was adapted to instantiate the potential expressions of the explicit(bool) specifier When instantiating their associated declaration.
- The Add*Candidate functions were adapted, they now take a Boolean indicating if the context allowing explicit constructor or conversion function and this boolean is used to remove invalid overloads that required template instantiation to be detected.
- Test for Semantic and Serialization were added.

This patch is not yet complete. I still need to check that interaction with CTAD and deduction guides is correct. and add more tests for AST operations. But I wanted first feedback.
Perhaps this patch should be spited in smaller patches, but making each patch testable as a standalone may be tricky.

Patch by Tyker

Differential Revision: https://reviews.llvm.org/D60934

llvm-svn: 359949

1 files changed, 18 insertions, 4 deletions

diff --git a/clang/lib/AST/DeclPrinter.cpp b/clang/lib/AST/DeclPrinter.cpp
index c98ec3b85d4..36c5d10f718 100644
--- a/clang/lib/AST/DeclPrinter.cpp
+++ b/clang/lib/AST/DeclPrinter.cpp
@@ -552,6 +552,21 @@ void DeclPrinter::VisitEnumConstantDecl(EnumConstantDecl *D) {
   }
 }
 
+static void printExplicitSpecifier(ExplicitSpecifier ES, llvm::raw_ostream &Out,
+                                   PrintingPolicy &Policy,
+                                   unsigned Indentation) {
+  std::string Proto = "explicit";
+  llvm::raw_string_ostream EOut(Proto);
+  if (ES.getExpr()) {
+    EOut << "(";
+    ES.getExpr()->printPretty(EOut, nullptr, Policy, Indentation);
+    EOut << ")";
+  }
+  EOut << " ";
+  EOut.flush();
+  Out << EOut.str();
+}
+
 void DeclPrinter::VisitFunctionDecl(FunctionDecl *D) {
   if (!D->getDescribedFunctionTemplate() &&
       !D->isFunctionTemplateSpecialization())
@@ -582,10 +597,9 @@ void DeclPrinter::VisitFunctionDecl(FunctionDecl *D) {
     if (D->isVirtualAsWritten()) Out << "virtual ";
     if (D->isModulePrivate())    Out << "__module_private__ ";
     if (D->isConstexpr() && !D->isExplicitlyDefaulted()) Out << "constexpr ";
-    if ((CDecl && CDecl->isExplicitSpecified()) ||
-        (ConversionDecl && ConversionDecl->isExplicitSpecified()) ||
-        (GuideDecl && GuideDecl->isExplicitSpecified()))
-      Out << "explicit ";
+    ExplicitSpecifier ExplicitSpec = ExplicitSpecifier::getFromDecl(D);
+    if (ExplicitSpec.isSpecified())
+      printExplicitSpecifier(ExplicitSpec, Out, Policy, Indentation);
   }
 
   PrintingPolicy SubPolicy(Policy);