[Clang-Format] Add ReferenceAlignment directive

This introduces ReferenceAlignment style option modeled around
PointerAlignment.
Style implementors can specify Left, Right, Middle or Pointer to
follow whatever the PointerAlignment option specifies.

Differential Revision: https://reviews.llvm.org/D104096

clang/docs/ClangFormatStyleOptions.rst

@@ -3236,6 +3236,38 @@ the configuration (without a prefix: ``Auto``).
           BasedOnStyle: llvm
           CanonicalDelimiter: 'cc'
 
+**ReferenceAlignment** (``ReferenceAlignmentStyle``)
+  Reference alignment style (overrides ``PointerAlignment`` for
+  references).
+
+  Possible values:
+
+  * ``RAS_Pointer`` (in configuration: ``Pointer``)
+    Align reference like ``PointerAlignment``.
+
+  * ``RAS_Left`` (in configuration: ``Left``)
+    Align reference to the left.
+
+    .. code-block:: c++
+
+      int& a;
+
+  * ``RAS_Right`` (in configuration: ``Right``)
+    Align reference to the right.
+
+    .. code-block:: c++
+
+      int &a;
+
+  * ``RAS_Middle`` (in configuration: ``Middle``)
+    Align reference in the middle.
+
+    .. code-block:: c++
+
+      int & a;
+
+
+
 **ReflowComments** (``bool``)
   If ``true``, clang-format will attempt to re-flow comments.
 

clang/include/clang/Format/Format.h

@@ -2725,7 +2725,7 @@ struct FormatStyle {
   /// (counted relative to leading non-whitespace column).
   unsigned PenaltyIndentedWhitespace;
 
-  /// The ``&`` and ``*`` alignment style.
+  /// The ``&``, ``&&`` and ``*`` alignment style.
   enum PointerAlignmentStyle : unsigned char {
     /// Align pointer to the left.
     /// \code
@@ -2820,6 +2820,31 @@ struct FormatStyle {
   /// \endcode
   std::vector<RawStringFormat> RawStringFormats;
 
+  /// \brief The ``&`` and ``&&`` alignment style.
+  enum ReferenceAlignmentStyle {
+    /// Align reference like ``PointerAlignment``.
+    RAS_Pointer,
+    /// Align reference to the left.
+    /// \code
+    ///   int& a;
+    /// \endcode
+    RAS_Left,
+    /// Align reference to the right.
+    /// \code
+    ///   int &a;
+    /// \endcode
+    RAS_Right,
+    /// Align reference in the middle.
+    /// \code
+    ///   int & a;
+    /// \endcode
+    RAS_Middle
+  };
+
+  /// \brief Reference alignment style (overrides ``PointerAlignment`` for
+  /// references).
+  ReferenceAlignmentStyle ReferenceAlignment;
+
   // clang-format off
   /// If ``true``, clang-format will attempt to re-flow comments.
   /// \code
@@ -3455,6 +3480,7 @@ struct FormatStyle {
                R.PenaltyBreakTemplateDeclaration &&
            PointerAlignment == R.PointerAlignment &&
            RawStringFormats == R.RawStringFormats &&
+           ReferenceAlignment == R.ReferenceAlignment &&
            ShortNamespaceLines == R.ShortNamespaceLines &&
            SortIncludes == R.SortIncludes &&
            SortJavaStaticImport == R.SortJavaStaticImport &&

clang/lib/Format/Format.cpp

@@ -417,6 +417,16 @@ struct ScalarEnumerationTraits<FormatStyle::SpaceAroundPointerQualifiersStyle> {
   }
 };
 
+template <>
+struct ScalarEnumerationTraits<FormatStyle::ReferenceAlignmentStyle> {
+  static void enumeration(IO &IO, FormatStyle::ReferenceAlignmentStyle &Value) {
+    IO.enumCase(Value, "Pointer", FormatStyle::RAS_Pointer);
+    IO.enumCase(Value, "Middle", FormatStyle::RAS_Middle);
+    IO.enumCase(Value, "Left", FormatStyle::RAS_Left);
+    IO.enumCase(Value, "Right", FormatStyle::RAS_Right);
+  }
+};
+
 template <>
 struct ScalarEnumerationTraits<FormatStyle::SpaceBeforeParensOptions> {
   static void enumeration(IO &IO,
@@ -692,6 +702,7 @@ template <> struct MappingTraits<FormatStyle> {
     IO.mapOptional("PointerAlignment", Style.PointerAlignment);
     IO.mapOptional("PPIndentWidth", Style.PPIndentWidth);
     IO.mapOptional("RawStringFormats", Style.RawStringFormats);
+    IO.mapOptional("ReferenceAlignment", Style.ReferenceAlignment);
     IO.mapOptional("ReflowComments", Style.ReflowComments);
     IO.mapOptional("ShortNamespaceLines", Style.ShortNamespaceLines);
     IO.mapOptional("SortIncludes", Style.SortIncludes);
@@ -1065,6 +1076,7 @@ FormatStyle getLLVMStyle(FormatStyle::LanguageKind Language) {
   LLVMStyle.ObjCSpaceAfterProperty = false;
   LLVMStyle.ObjCSpaceBeforeProtocolList = true;
   LLVMStyle.PointerAlignment = FormatStyle::PAS_Right;
+  LLVMStyle.ReferenceAlignment = FormatStyle::RAS_Pointer;
   LLVMStyle.ShortNamespaceLines = 1;
   LLVMStyle.SpacesBeforeTrailingComments = 1;
   LLVMStyle.Standard = FormatStyle::LS_Latest;
@@ -1755,10 +1767,12 @@ private:
         Tok = Tok->Next;
       }
     }
-    if (Style.DerivePointerAlignment)
+    if (Style.DerivePointerAlignment) {
       Style.PointerAlignment = countVariableAlignments(AnnotatedLines) <= 0
                                    ? FormatStyle::PAS_Left
                                    : FormatStyle::PAS_Right;
+      Style.ReferenceAlignment = FormatStyle::RAS_Pointer;
+    }
     if (Style.Standard == FormatStyle::LS_Auto)
       Style.Standard = hasCpp03IncompatibleFormat(AnnotatedLines)
                            ? FormatStyle::LS_Latest

clang/lib/Format/TokenAnnotator.cpp

@@ -2988,16 +2988,17 @@ bool TokenAnnotator::spaceRequiredBetween(const AnnotatedLine &Line,
          Style.SpaceAroundPointerQualifiers == FormatStyle::SAPQ_Both) &&
         (Left.is(TT_AttributeParen) || Left.canBePointerOrReferenceQualifier()))
       return true;
-    return (Left.Tok.isLiteral() ||
+    return (
+        Left.Tok.isLiteral() ||
         (!Left.isOneOf(TT_PointerOrReference, tok::l_paren) &&
-             (Style.PointerAlignment != FormatStyle::PAS_Left ||
+         (getTokenPointerOrReferenceAlignment(Right) != FormatStyle::PAS_Left ||
           (Line.IsMultiVariableDeclStmt &&
            (Left.NestingLevel == 0 ||
             (Left.NestingLevel == 1 && Line.First->is(tok::kw_for)))))));
   }
   if (Right.is(TT_FunctionTypeLParen) && Left.isNot(tok::l_paren) &&
       (!Left.is(TT_PointerOrReference) ||
-       (Style.PointerAlignment != FormatStyle::PAS_Right &&
+       (getTokenPointerOrReferenceAlignment(Left) != FormatStyle::PAS_Right &&
         !Line.IsMultiVariableDeclStmt)))
     return true;
   if (Left.is(TT_PointerOrReference)) {
@@ -3013,7 +3014,8 @@ bool TokenAnnotator::spaceRequiredBetween(const AnnotatedLine &Line,
            (Right.is(tok::l_brace) && Right.is(BK_Block)) ||
            (!Right.isOneOf(TT_PointerOrReference, TT_ArraySubscriptLSquare,
                            tok::l_paren) &&
-            (Style.PointerAlignment != FormatStyle::PAS_Right &&
+            (getTokenPointerOrReferenceAlignment(Left) !=
+                 FormatStyle::PAS_Right &&
              !Line.IsMultiVariableDeclStmt) &&
             Left.Previous &&
             !Left.Previous->isOneOf(tok::l_paren, tok::coloncolon,
@@ -3182,7 +3184,7 @@ bool TokenAnnotator::spaceRequiredBetween(const AnnotatedLine &Line,
     // Match const and volatile ref-qualifiers without any additional
     // qualifiers such as
     // void Fn() const &;
-    return Style.PointerAlignment != FormatStyle::PAS_Left;
+    return getTokenReferenceAlignment(Right) != FormatStyle::PAS_Left;
   return true;
 }
 
@@ -3534,11 +3536,11 @@ bool TokenAnnotator::spaceRequiredBefore(const AnnotatedLine &Line,
   // Space before TT_StructuredBindingLSquare.
   if (Right.is(TT_StructuredBindingLSquare))
     return !Left.isOneOf(tok::amp, tok::ampamp) ||
-           Style.PointerAlignment != FormatStyle::PAS_Right;
+           getTokenReferenceAlignment(Left) != FormatStyle::PAS_Right;
   // Space before & or && following a TT_StructuredBindingLSquare.
   if (Right.Next && Right.Next->is(TT_StructuredBindingLSquare) &&
       Right.isOneOf(tok::amp, tok::ampamp))
-    return Style.PointerAlignment != FormatStyle::PAS_Left;
+    return getTokenReferenceAlignment(Right) != FormatStyle::PAS_Left;
   if ((Right.is(TT_BinaryOperator) && !Left.is(tok::l_paren)) ||
       (Left.isOneOf(TT_BinaryOperator, TT_ConditionalExpr) &&
        !Right.is(tok::r_paren)))
@@ -4034,7 +4036,8 @@ bool TokenAnnotator::canBreakBefore(const AnnotatedLine &Line,
     return !Right.is(tok::l_paren);
   if (Right.is(TT_PointerOrReference))
     return Line.IsMultiVariableDeclStmt ||
-           (Style.PointerAlignment == FormatStyle::PAS_Right &&
+           (getTokenPointerOrReferenceAlignment(Right) ==
+                FormatStyle::PAS_Right &&
             (!Right.Next || Right.Next->isNot(TT_FunctionDeclarationName)));
   if (Right.isOneOf(TT_StartOfName, TT_FunctionDeclarationName) ||
       Right.is(tok::kw_operator))
@@ -4249,5 +4252,41 @@ void TokenAnnotator::printDebugInfo(const AnnotatedLine &Line) {
   llvm::errs() << "----\n";
 }
 
+FormatStyle::PointerAlignmentStyle
+TokenAnnotator::getTokenReferenceAlignment(const FormatToken &Reference) {
+  assert(Reference.isOneOf(tok::amp, tok::ampamp));
+  switch (Style.ReferenceAlignment) {
+  case FormatStyle::RAS_Pointer:
+    return Style.PointerAlignment;
+  case FormatStyle::RAS_Left:
+    return FormatStyle::PAS_Left;
+  case FormatStyle::RAS_Right:
+    return FormatStyle::PAS_Right;
+  case FormatStyle::RAS_Middle:
+    return FormatStyle::PAS_Middle;
+  }
+  assert(0); //"Unhandled value of ReferenceAlignment"
+  return Style.PointerAlignment;
+}
+
+FormatStyle::PointerAlignmentStyle
+TokenAnnotator::getTokenPointerOrReferenceAlignment(
+    const FormatToken &PointerOrReference) {
+  if (PointerOrReference.isOneOf(tok::amp, tok::ampamp)) {
+    switch (Style.ReferenceAlignment) {
+    case FormatStyle::RAS_Pointer:
+      return Style.PointerAlignment;
+    case FormatStyle::RAS_Left:
+      return FormatStyle::PAS_Left;
+    case FormatStyle::RAS_Right:
+      return FormatStyle::PAS_Right;
+    case FormatStyle::RAS_Middle:
+      return FormatStyle::PAS_Middle;
+    }
+  }
+  assert(PointerOrReference.is(tok::star));
+  return Style.PointerAlignment;
+}
+
 } // namespace format
 } // namespace clang

clang/lib/Format/TokenAnnotator.h

@@ -195,6 +195,11 @@ private:
   FormatToken *calculateInitializerColumnList(AnnotatedLine &Line,
                                               FormatToken *CurrentToken,
                                               unsigned Depth);
+  FormatStyle::PointerAlignmentStyle
+  getTokenReferenceAlignment(const FormatToken &PointerOrReference);
+
+  FormatStyle::PointerAlignmentStyle
+  getTokenPointerOrReferenceAlignment(const FormatToken &PointerOrReference);
 
   const FormatStyle &Style;
 

clang/unittests/Format/FormatTest.cpp

@@ -1789,6 +1789,98 @@ TEST_F(FormatTest, ElseIf) {
                getLLVMStyleWithColumns(62));
 }
 
+TEST_F(FormatTest, SeparatePointerReferenceAlignment) {
+  FormatStyle Style = getLLVMStyle();
+  // Check first the default LLVM style
+  // Style.PointerAlignment = FormatStyle::PAS_Right;
+  // Style.ReferenceAlignment = FormatStyle::RAS_Pointer;
+  verifyFormat("int *f1(int *a, int &b, int &&c);", Style);
+  verifyFormat("int &f2(int &&c, int *a, int &b);", Style);
+  verifyFormat("int &&f3(int &b, int &&c, int *a);", Style);
+  verifyFormat("int *f1(int &a) const &;", Style);
+  verifyFormat("int *f1(int &a) const & = 0;", Style);
+  verifyFormat("int *a = f1();", Style);
+  verifyFormat("int &b = f2();", Style);
+  verifyFormat("int &&c = f3();", Style);
+
+  Style.AlignConsecutiveDeclarations = FormatStyle::ACS_Consecutive;
+  verifyFormat("Const unsigned int *c;\n"
+               "const unsigned int *d;\n"
+               "Const unsigned int &e;\n"
+               "const unsigned int &f;\n"
+               "const unsigned    &&g;\n"
+               "Const unsigned      h;",
+               Style);
+
+  Style.PointerAlignment = FormatStyle::PAS_Left;
+  Style.ReferenceAlignment = FormatStyle::RAS_Pointer;
+  verifyFormat("int* f1(int* a, int& b, int&& c);", Style);
+  verifyFormat("int& f2(int&& c, int* a, int& b);", Style);
+  verifyFormat("int&& f3(int& b, int&& c, int* a);", Style);
+  verifyFormat("int* f1(int& a) const& = 0;", Style);
+  verifyFormat("int* a = f1();", Style);
+  verifyFormat("int& b = f2();", Style);
+  verifyFormat("int&& c = f3();", Style);
+
+  Style.AlignConsecutiveDeclarations = FormatStyle::ACS_Consecutive;
+  verifyFormat("Const unsigned int* c;\n"
+               "const unsigned int* d;\n"
+               "Const unsigned int& e;\n"
+               "const unsigned int& f;\n"
+               "const unsigned&&    g;\n"
+               "Const unsigned      h;",
+               Style);
+
+  Style.PointerAlignment = FormatStyle::PAS_Right;
+  Style.ReferenceAlignment = FormatStyle::RAS_Left;
+  verifyFormat("int *f1(int *a, int& b, int&& c);", Style);
+  verifyFormat("int& f2(int&& c, int *a, int& b);", Style);
+  verifyFormat("int&& f3(int& b, int&& c, int *a);", Style);
+  verifyFormat("int *a = f1();", Style);
+  verifyFormat("int& b = f2();", Style);
+  verifyFormat("int&& c = f3();", Style);
+
+  Style.AlignConsecutiveDeclarations = FormatStyle::ACS_Consecutive;
+  verifyFormat("Const unsigned int *c;\n"
+               "const unsigned int *d;\n"
+               "Const unsigned int& e;\n"
+               "const unsigned int& f;\n"
+               "const unsigned      g;\n"
+               "Const unsigned      h;",
+               Style);
+
+  Style.PointerAlignment = FormatStyle::PAS_Left;
+  Style.ReferenceAlignment = FormatStyle::RAS_Middle;
+  verifyFormat("int* f1(int* a, int & b, int && c);", Style);
+  verifyFormat("int & f2(int && c, int* a, int & b);", Style);
+  verifyFormat("int && f3(int & b, int && c, int* a);", Style);
+  verifyFormat("int* a = f1();", Style);
+  verifyFormat("int & b = f2();", Style);
+  verifyFormat("int && c = f3();", Style);
+
+  Style.AlignConsecutiveDeclarations = FormatStyle::ACS_Consecutive;
+  verifyFormat("Const unsigned int*  c;\n"
+               "const unsigned int*  d;\n"
+               "Const unsigned int & e;\n"
+               "const unsigned int & f;\n"
+               "const unsigned &&    g;\n"
+               "Const unsigned       h;",
+               Style);
+
+  Style.PointerAlignment = FormatStyle::PAS_Middle;
+  Style.ReferenceAlignment = FormatStyle::RAS_Right;
+  verifyFormat("int * f1(int * a, int &b, int &&c);", Style);
+  verifyFormat("int &f2(int &&c, int * a, int &b);", Style);
+  verifyFormat("int &&f3(int &b, int &&c, int * a);", Style);
+  verifyFormat("int * a = f1();", Style);
+  verifyFormat("int &b = f2();", Style);
+  verifyFormat("int &&c = f3();", Style);
+
+  // FIXME: we don't handle this yet, so output may be arbitrary until it's
+  // specifically handled
+  // verifyFormat("int Add2(BTree * &Root, char * szToAdd)", Style);
+}
+
 TEST_F(FormatTest, FormatsForLoop) {
   verifyFormat(
       "for (int VeryVeryLongLoopVariable = 0; VeryVeryLongLoopVariable < 10;\n"
@@ -18013,6 +18105,15 @@ TEST_F(FormatTest, ParsesConfiguration) {
               FormatStyle::PAS_Right);
   CHECK_PARSE("PointerAlignment: Middle", PointerAlignment,
               FormatStyle::PAS_Middle);
+  Style.ReferenceAlignment = FormatStyle::RAS_Middle;
+  CHECK_PARSE("ReferenceAlignment: Pointer", ReferenceAlignment,
+              FormatStyle::RAS_Pointer);
+  CHECK_PARSE("ReferenceAlignment: Left", ReferenceAlignment,
+              FormatStyle::RAS_Left);
+  CHECK_PARSE("ReferenceAlignment: Right", ReferenceAlignment,
+              FormatStyle::RAS_Right);
+  CHECK_PARSE("ReferenceAlignment: Middle", ReferenceAlignment,
+              FormatStyle::RAS_Middle);
   // For backward compatibility:
   CHECK_PARSE("PointerBindsToType: Left", PointerAlignment,
               FormatStyle::PAS_Left);