[c++20] Implement tweaked __VA_OPT__ rules from P1042R1:

 * __VA_OPT__ is expanded if the *expanded* __VA_ARGS__ is non-empty,
   not if the original argument contained no tokens.
 * Placemarkers at the start and end of __VA_OPT__ are retained just
   long enough to paste them with adjacent ## operators. We never paste
   "across" a discarded placemarker.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@359964 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 31 insertions, 8 deletions

diff --git a/include/clang/Lex/MacroArgs.h b/include/clang/Lex/MacroArgs.h
index c2ba4eb2c3..8806f2d8c6 100644
--- a/include/clang/Lex/MacroArgs.h
+++ b/include/clang/Lex/MacroArgs.h
@@ -112,18 +112,19 @@ public:
   bool isVarargsElidedUse() const { return VarargsElided; }
 
   /// Returns true if the macro was defined with a variadic (ellipsis) parameter
-  /// AND was invoked with at least one token supplied as a variadic argument.
+  /// AND was invoked with at least one token supplied as a variadic argument
+  /// (after pre-expansion).
   ///
   /// \code
   ///   #define F(a)  a
   ///   #define V(a, ...) __VA_OPT__(a)
-  ///   F()    <-- returns false on this invocation.
-  ///   V(,a)  <-- returns true on this invocation.
-  ///   V(,)   <-- returns false on this invocation.
+  ///   F()     <-- returns false on this invocation.
+  ///   V(,a)   <-- returns true on this invocation.
+  ///   V(,)    <-- returns false on this invocation.
+  ///   V(,F()) <-- returns false on this invocation.
   /// \endcode
   ///
-
-  bool invokedWithVariadicArgument(const MacroInfo *const MI) const;
+  bool invokedWithVariadicArgument(const MacroInfo *const MI, Preprocessor &PP);
 
   /// StringifyArgument - Implement C99 6.10.3.2p2, converting a sequence of
   /// tokens into the literal string token that should be produced by the C #
diff --git a/include/clang/Lex/VariadicMacroSupport.h b/include/clang/Lex/VariadicMacroSupport.h
index 4274a4ddbd..989e0ac703 100644
--- a/include/clang/Lex/VariadicMacroSupport.h
+++ b/include/clang/Lex/VariadicMacroSupport.h
@@ -113,6 +113,8 @@ namespace clang {
       UnmatchedOpeningParens.push_back(LParenLoc);
     }
 
+    /// Are we at the top level within the __VA_OPT__?
+    bool isAtTopLevel() const { return UnmatchedOpeningParens.size() == 1; }
   };
 
   /// A class for tracking whether we're inside a VA_OPT during a
@@ -135,7 +137,8 @@ namespace clang {
 
     unsigned StringifyBefore : 1;
     unsigned CharifyBefore : 1;
-
+    unsigned BeginsWithPlaceholder : 1;
+    unsigned EndsWithPlaceholder : 1;
 
     bool hasStringifyBefore() const {
       assert(!isReset() &&
@@ -151,7 +154,8 @@ namespace clang {
   public:
     VAOptExpansionContext(Preprocessor &PP)
         : VAOptDefinitionContext(PP), LeadingSpaceForStringifiedToken(false),
-          StringifyBefore(false), CharifyBefore(false) {
+          StringifyBefore(false), CharifyBefore(false),
+          BeginsWithPlaceholder(false), EndsWithPlaceholder(false) {
       SyntheticEOFToken.startToken();
       SyntheticEOFToken.setKind(tok::eof);
     }
@@ -162,6 +166,8 @@ namespace clang {
       LeadingSpaceForStringifiedToken = false;
       StringifyBefore = false;
       CharifyBefore = false;
+      BeginsWithPlaceholder = false;
+      EndsWithPlaceholder = false;
     }
 
     const Token &getEOFTok() const { return SyntheticEOFToken; }
@@ -174,7 +180,23 @@ namespace clang {
       LeadingSpaceForStringifiedToken = HasLeadingSpace;
     }
 
+    void hasPlaceholderAfterHashhashAtStart() { BeginsWithPlaceholder = true; }
+    void hasPlaceholderBeforeRParen() {
+      if (isAtTopLevel())
+        EndsWithPlaceholder = true;
+    }
+
 
+    bool beginsWithPlaceholder() const {
+      assert(!isReset() &&
+             "Must only be called if the state has not been reset");
+      return BeginsWithPlaceholder;
+    }
+    bool endsWithPlaceholder() const {
+      assert(!isReset() &&
+             "Must only be called if the state has not been reset");
+      return EndsWithPlaceholder;
+    }
 
     bool hasCharifyBefore() const {
       assert(!isReset() &&