[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

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@359949 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 19 insertions, 9 deletions

diff --git a/lib/Sema/DeclSpec.cpp b/lib/Sema/DeclSpec.cpp
index 4f3e2faa8e..df2792289e 100644
--- a/lib/Sema/DeclSpec.cpp
+++ b/lib/Sema/DeclSpec.cpp
@@ -445,7 +445,7 @@ unsigned DeclSpec::getParsedSpecifiers() const {
   if (hasTypeSpecifier())
     Res |= PQ_TypeSpecifier;
 
-  if (FS_inline_specified || FS_virtual_specified || FS_explicit_specified ||
+  if (FS_inline_specified || FS_virtual_specified || hasExplicitSpecifier() ||
       FS_noreturn_specified || FS_forceinline_specified)
     Res |= PQ_FunctionSpecifier;
   return Res;
@@ -944,17 +944,24 @@ bool DeclSpec::setFunctionSpecVirtual(SourceLocation Loc,
 }
 
 bool DeclSpec::setFunctionSpecExplicit(SourceLocation Loc,
-                                       const char *&PrevSpec,
-                                       unsigned &DiagID) {
+                                       const char *&PrevSpec, unsigned &DiagID,
+                                       ExplicitSpecifier ExplicitSpec,
+                                       SourceLocation CloseParenLoc) {
+  assert((ExplicitSpec.getKind() == ExplicitSpecKind::ResolvedTrue ||
+          ExplicitSpec.getExpr()) &&
+         "invalid ExplicitSpecifier");
   // 'explicit explicit' is ok, but warn as this is likely not what the user
   // intended.
-  if (FS_explicit_specified) {
-    DiagID = diag::warn_duplicate_declspec;
+  if (hasExplicitSpecifier()) {
+    DiagID = (ExplicitSpec.getExpr() || FS_explicit_specifier.getExpr())
+                 ? diag::err_duplicate_declspec
+                 : diag::ext_warn_duplicate_declspec;
     PrevSpec = "explicit";
     return true;
   }
-  FS_explicit_specified = true;
+  FS_explicit_specifier = ExplicitSpec;
   FS_explicitLoc = Loc;
+  FS_explicitCloseParenLoc = CloseParenLoc;
   return false;
 }
 
@@ -1293,23 +1300,26 @@ void DeclSpec::Finish(Sema &S, const PrintingPolicy &Policy) {
   //   The explicit specifier shall be used only in the declaration of
   //   a constructor or conversion function within its class
   //   definition;
-  if (isFriendSpecified() && (isVirtualSpecified() || isExplicitSpecified())) {
+  if (isFriendSpecified() && (isVirtualSpecified() || hasExplicitSpecifier())) {
     StringRef Keyword;
+    FixItHint Hint;
     SourceLocation SCLoc;
 
     if (isVirtualSpecified()) {
       Keyword = "virtual";
       SCLoc = getVirtualSpecLoc();
+      Hint = FixItHint::CreateRemoval(SCLoc);
     } else {
       Keyword = "explicit";
       SCLoc = getExplicitSpecLoc();
+      Hint = FixItHint::CreateRemoval(getExplicitSpecRange());
     }
 
-    FixItHint Hint = FixItHint::CreateRemoval(SCLoc);
     S.Diag(SCLoc, diag::err_friend_decl_spec)
       << Keyword << Hint;
 
-    FS_virtual_specified = FS_explicit_specified = false;
+    FS_virtual_specified = false;
+    FS_explicit_specifier = ExplicitSpecifier();
     FS_virtualLoc = FS_explicitLoc = SourceLocation();
   }