[Parse] refactor Lexer by made NulCharacterKind type

Author: omochi

include/swift/Parse/Lexer.h

@@ -461,6 +461,16 @@ class Lexer {
   };
 
 private:
+  /// Nul character meaning kind.
+  enum class NulCharacterKind {
+    /// String buffer terminator.
+    BufferEnd,
+    /// Embedded nul character.
+    Embedded,
+    /// Code completion marker.
+    CodeCompletion
+  };
+
   /// For a source location in the current buffer, returns the corresponding
   /// pointer.
   const char *getBufferPtrForSourceLoc(SourceLoc Loc) const {
@@ -520,6 +530,8 @@ class Lexer {
   /// Try to lex conflict markers by checking for the presence of the start and
   /// end of the marker in diff3 or Perforce style respectively.
   bool tryLexConflictMarker(bool EatNewline);
+
+  NulCharacterKind getNulCharacterKind(const char *Ptr) const;
 };
 
 /// Given an ordered token \param Array , get the iterator pointing to the first

lib/Parse/Lexer.cpp

@@ -351,16 +351,19 @@ void Lexer::skipToEndOfLine(bool EatNewline) {
       }
       break;   // Otherwise, eat other characters.
     case 0:
-      // If this is a random nul character in the middle of a buffer, skip it as
-      // whitespace.
-      if (CurPtr-1 != BufferEnd) {
+      switch (getNulCharacterKind(CurPtr - 1)) {
+      case NulCharacterKind::Embedded:
+        // If this is a random nul character in the middle of a buffer, skip it
+        // as whitespace.
         diagnoseEmbeddedNul(Diags, CurPtr-1);
-        break;
+        LLVM_FALLTHROUGH;
+      case NulCharacterKind::CodeCompletion:
+        continue;
+      case NulCharacterKind::BufferEnd:
+        // Otherwise, the last line of the file does not have a newline.
+        --CurPtr;
+        return;
       }
-
-      // Otherwise, the last line of the file does not have a newline.
-      --CurPtr;
-      return;
     }
   }
 }
@@ -422,26 +425,30 @@ void Lexer::skipSlashStarComment() {
 
       break;   // Otherwise, eat other characters.
     case 0:
-      // If this is a random nul character in the middle of a buffer, skip it as
-      // whitespace.
-      if (CurPtr-1 != BufferEnd) {
-        diagnoseEmbeddedNul(Diags, CurPtr-1);
-        break;
-      }
-      
-      // Otherwise, we have an unterminated /* comment.
-      --CurPtr;
+      switch (getNulCharacterKind(CurPtr - 1)) {
+      case NulCharacterKind::Embedded:
+        // If this is a random nul character in the middle of a buffer, skip it
+        // as whitespace.
+        diagnoseEmbeddedNul(Diags, CurPtr - 1);
+        LLVM_FALLTHROUGH;
+      case NulCharacterKind::CodeCompletion:
+        continue;
+      case NulCharacterKind::BufferEnd: {
+        // Otherwise, we have an unterminated /* comment.
+        --CurPtr;
 
-      // Count how many levels deep we are.
-      llvm::SmallString<8> Terminator("*/");
-      while (--Depth != 0)
-        Terminator += "*/";
+        // Count how many levels deep we are.
+        llvm::SmallString<8> Terminator("*/");
+        while (--Depth != 0)
+          Terminator += "*/";
 
-      const char *EOL = (CurPtr[-1] == '\n') ? (CurPtr - 1) : CurPtr;
-      diagnose(EOL, diag::lex_unterminated_block_comment)
-        .fixItInsert(getSourceLoc(EOL), Terminator);
-      diagnose(StartPtr, diag::lex_comment_start);
-      return;
+        const char *EOL = (CurPtr[-1] == '\n') ? (CurPtr - 1) : CurPtr;
+        diagnose(EOL, diag::lex_unterminated_block_comment)
+            .fixItInsert(getSourceLoc(EOL), Terminator);
+        diagnose(StartPtr, diag::lex_comment_start);
+        return;
+      }
+      }
     }
   }
 }
@@ -1857,6 +1864,16 @@ bool Lexer::tryLexConflictMarker(bool EatNewline) {
   return false;
 }
 
+Lexer::NulCharacterKind Lexer::getNulCharacterKind(const char *Ptr) const {
+  assert(Ptr != nullptr && *Ptr == 0);
+  if (Ptr == CodeCompletionPtr) {
+    return NulCharacterKind::CodeCompletion;
+  }
+  if (Ptr == BufferEnd) {
+    return NulCharacterKind::BufferEnd;
+  }
+  return NulCharacterKind::Embedded;
+}
 
 void Lexer::tryLexEditorPlaceholder() {
   assert(CurPtr[-1] == '<' && CurPtr[0] == '#');
@@ -2164,22 +2181,23 @@ void Lexer::lexImpl() {
     return formToken(tok::unknown, TokStart);
 
   case 0:
-    if (CurPtr-1 == CodeCompletionPtr)
+    switch (getNulCharacterKind(CurPtr - 1)) {
+    case NulCharacterKind::CodeCompletion:
       return formToken(tok::code_complete, TokStart);
 
-    // If this is a random nul character in the middle of a buffer, skip it as
-    // whitespace.
-    if (CurPtr-1 != BufferEnd) {
+    case NulCharacterKind::Embedded:
+      // If this is a random nul character in the middle of a buffer, skip it as
+      // whitespace.
       diagnoseEmbeddedNul(Diags, CurPtr-1);
       goto Restart;
+    case NulCharacterKind::BufferEnd:
+      // Otherwise, this is the real end of the buffer.  Put CurPtr back into
+      // buffer bounds.
+      --CurPtr;
+      // Return EOF.
+      return formToken(tok::eof, TokStart);
     }
 
-    // Otherwise, this is the real end of the buffer.  Put CurPtr back into
-    // buffer bounds.
-    --CurPtr;
-    // Return EOF.
-    return formToken(tok::eof, TokStart);
-
   case '@': return formToken(tok::at_sign, TokStart);
   case '{': return formToken(tok::l_brace, TokStart);
   case '[': {