[clang-format] Add option AllowShortRecordOnASingleLine

clang/docs/ClangFormatStyleOptions.rst

@@ -2103,6 +2103,42 @@ the configuration (without a prefix: ``Auto``).
 **AllowShortNamespacesOnASingleLine** (``Boolean``) :versionbadge:`clang-format 20` :ref:`¶ <AllowShortNamespacesOnASingleLine>`
   If ``true``, ``namespace a { class b; }`` can be put on a single line.
 
+.. _AllowShortRecordOnASingleLine:
+
+**AllowShortRecordOnASingleLine** (``ShortRecordStyle``) :versionbadge:`clang-format 22` :ref:`¶ <AllowShortRecordOnASingleLine>`
+  Dependent on the value, ``struct bar { int i; };`` can be put on a single
+  line.
+
+  Possible values:
+
+  * ``SRS_Never`` (in configuration: ``Never``)
+    Never merge records into a single line.
+
+  * ``SRS_EmptyIfAttached`` (in configuration: ``EmptyIfAttached``)
+    Only merge empty records if the opening brace was not wrapped,
+    i.e. the corresponding ``BraceWrapping.After...`` option was not set.
+
+  * ``SRS_Empty`` (in configuration: ``Empty``)
+    Only merge empty records.
+
+    .. code-block:: c++
+
+      struct foo {};
+      struct bar
+      {
+        int i;
+      };
+
+  * ``SRS_Always`` (in configuration: ``Always``)
+    Merge all records that fit on a single line.
+
+    .. code-block:: c++
+
+      struct foo {};
+      struct bar { int i; };
+
+
+
 .. _AlwaysBreakAfterDefinitionReturnType:
 
 **AlwaysBreakAfterDefinitionReturnType** (``DefinitionReturnTypeBreakingStyle``) :versionbadge:`clang-format 3.7` :ref:`¶ <AlwaysBreakAfterDefinitionReturnType>`

clang/docs/ReleaseNotes.rst

@@ -592,6 +592,7 @@ clang-format
   literals.
 - Add ``Leave`` suboption to ``IndentPPDirectives``.
 - Add ``AllowBreakBeforeQtProperty`` option.
+- Add ``AllowShortRecordOnASingleLine`` option and set it to ``EmptyIfAttached`` for LLVM style.
 
 libclang
 --------

clang/include/clang/Format/Format.h

@@ -998,6 +998,36 @@ struct FormatStyle {
   /// \version 20
   bool AllowShortNamespacesOnASingleLine;
 
+  /// Different styles for merging short records (``class``,``struct``, and
+  /// ``union``).
+  enum ShortRecordStyle : int8_t {
+    /// Never merge records into a single line.
+    SRS_Never,
+    /// Only merge empty records if the opening brace was not wrapped,
+    /// i.e. the corresponding ``BraceWrapping.After...`` option was not set.
+    SRS_EmptyIfAttached,
+    /// Only merge empty records.
+    /// \code
+    ///   struct foo {};
+    ///   struct bar
+    ///   {
+    ///     int i;
+    ///   };
+    /// \endcode
+    SRS_Empty,
+    /// Merge all records that fit on a single line.
+    /// \code
+    ///   struct foo {};
+    ///   struct bar { int i; };
+    /// \endcode
+    SRS_Always
+  };
+
+  /// Dependent on the value, ``struct bar { int i; };`` can be put on a single
+  /// line.
+  /// \version 22
+  ShortRecordStyle AllowShortRecordOnASingleLine;
+
   /// Different ways to break after the function definition return type.
   /// This option is **deprecated** and is retained for backwards compatibility.
   enum DefinitionReturnTypeBreakingStyle : int8_t {
@@ -5481,6 +5511,7 @@ struct FormatStyle {
            AllowShortLoopsOnASingleLine == R.AllowShortLoopsOnASingleLine &&
            AllowShortNamespacesOnASingleLine ==
                R.AllowShortNamespacesOnASingleLine &&
+           AllowShortRecordOnASingleLine == R.AllowShortRecordOnASingleLine &&
            AlwaysBreakBeforeMultilineStrings ==
                R.AlwaysBreakBeforeMultilineStrings &&
            AttributeMacros == R.AttributeMacros &&

clang/lib/Format/Format.cpp

@@ -681,6 +681,15 @@ template <> struct ScalarEnumerationTraits<FormatStyle::ShortLambdaStyle> {
   }
 };
 
+template <> struct ScalarEnumerationTraits<FormatStyle::ShortRecordStyle> {
+  static void enumeration(IO &IO, FormatStyle::ShortRecordStyle &Value) {
+    IO.enumCase(Value, "Never", FormatStyle::SRS_Never);
+    IO.enumCase(Value, "EmptyIfAttached", FormatStyle::SRS_EmptyIfAttached);
+    IO.enumCase(Value, "Empty", FormatStyle::SRS_Empty);
+    IO.enumCase(Value, "Always", FormatStyle::SRS_Always);
+  }
+};
+
 template <> struct MappingTraits<FormatStyle::SortIncludesOptions> {
   static void enumInput(IO &IO, FormatStyle::SortIncludesOptions &Value) {
     IO.enumCase(Value, "Never", FormatStyle::SortIncludesOptions({}));
@@ -1050,6 +1059,8 @@ template <> struct MappingTraits<FormatStyle> {
                    Style.AllowShortLoopsOnASingleLine);
     IO.mapOptional("AllowShortNamespacesOnASingleLine",
                    Style.AllowShortNamespacesOnASingleLine);
+    IO.mapOptional("AllowShortRecordOnASingleLine",
+                   Style.AllowShortRecordOnASingleLine);
     IO.mapOptional("AlwaysBreakAfterDefinitionReturnType",
                    Style.AlwaysBreakAfterDefinitionReturnType);
     IO.mapOptional("AlwaysBreakBeforeMultilineStrings",
@@ -1580,6 +1591,7 @@ FormatStyle getLLVMStyle(FormatStyle::LanguageKind Language) {
   LLVMStyle.AllowShortLambdasOnASingleLine = FormatStyle::SLS_All;
   LLVMStyle.AllowShortLoopsOnASingleLine = false;
   LLVMStyle.AllowShortNamespacesOnASingleLine = false;
+  LLVMStyle.AllowShortRecordOnASingleLine = FormatStyle::SRS_EmptyIfAttached;
   LLVMStyle.AlwaysBreakAfterDefinitionReturnType = FormatStyle::DRTBS_None;
   LLVMStyle.AlwaysBreakBeforeMultilineStrings = false;
   LLVMStyle.AttributeMacros.push_back("__capability");

clang/lib/Format/TokenAnnotator.cpp

@@ -5956,12 +5956,16 @@ bool TokenAnnotator::mustBreakBefore(const AnnotatedLine &Line,
       return true;
     }
 
-    // Don't attempt to interpret struct return types as structs.
+    // Don't attempt to interpret record return types as records.
+    // FIXME: Not covered by tests.
     if (Right.isNot(TT_FunctionLBrace)) {
-      return (Line.startsWith(tok::kw_class) &&
-              Style.BraceWrapping.AfterClass) ||
-             (Line.startsWith(tok::kw_struct) &&
-              Style.BraceWrapping.AfterStruct);
+      return Style.AllowShortRecordOnASingleLine == FormatStyle::SRS_Never &&
+             ((Line.startsWith(tok::kw_class) &&
+               Style.BraceWrapping.AfterClass) ||
+              (Line.startsWith(tok::kw_struct) &&
+               Style.BraceWrapping.AfterStruct) ||
+              (Line.startsWith(tok::kw_union) &&
+               Style.BraceWrapping.AfterUnion));
     }
   }
 

clang/lib/Format/UnwrappedLineFormatter.cpp

@@ -10,6 +10,7 @@
 #include "FormatToken.h"
 #include "NamespaceEndCommentsFixer.h"
 #include "WhitespaceManager.h"
+#include "clang/Basic/TokenKinds.h"
 #include "llvm/Support/Debug.h"
 #include <queue>
 
@@ -266,15 +267,22 @@ class LineJoiner {
       }
     }
 
+    // Try merging record blocks that have had their left brace wrapped into
+    // a single line.
+    if (NextLine.First->isOneOf(TT_ClassLBrace, TT_StructLBrace,
+                                TT_UnionLBrace)) {
+      if (unsigned MergedLines = tryMergeRecord(I, E, Limit))
+        return MergedLines;
+    }
+
     const auto *PreviousLine = I != AnnotatedLines.begin() ? I[-1] : nullptr;
-    // Handle empty record blocks where the brace has already been wrapped.
+
+    // Handle blocks where the brace has already been wrapped.
     if (PreviousLine && TheLine->Last->is(tok::l_brace) &&
         TheLine->First == TheLine->Last) {
-      bool EmptyBlock = NextLine.First->is(tok::r_brace);
+      const bool EmptyBlock = NextLine.First->is(tok::r_brace);
 
-      const FormatToken *Tok = PreviousLine->First;
-      if (Tok && Tok->is(tok::comment))
-        Tok = Tok->getNextNonComment();
+      const FormatToken *Tok = PreviousLine->getFirstNonComment();
 
       if (Tok && Tok->getNamespaceToken()) {
         return !Style.BraceWrapping.SplitEmptyNamespace && EmptyBlock
@@ -284,8 +292,11 @@ class LineJoiner {
 
       if (Tok && Tok->is(tok::kw_typedef))
         Tok = Tok->getNextNonComment();
-      if (Tok && Tok->isOneOf(tok::kw_class, tok::kw_struct, tok::kw_union,
-                              tok::kw_extern, Keywords.kw_interface)) {
+
+      if (Tok && Tok->isOneOf(tok::kw_class, tok::kw_struct, tok::kw_union))
+        return tryMergeRecord(I, E, Limit);
+
+      if (Tok && Tok->isOneOf(tok::kw_extern, Keywords.kw_interface)) {
         return !Style.BraceWrapping.SplitEmptyRecord && EmptyBlock
                    ? tryMergeSimpleBlock(I, E, Limit)
                    : 0;
@@ -498,13 +509,9 @@ class LineJoiner {
         ShouldMerge = Style.AllowShortEnumsOnASingleLine;
       } else if (TheLine->Last->is(TT_CompoundRequirementLBrace)) {
         ShouldMerge = Style.AllowShortCompoundRequirementOnASingleLine;
-      } else if (TheLine->Last->isOneOf(TT_ClassLBrace, TT_StructLBrace)) {
-        // NOTE: We use AfterClass (whereas AfterStruct exists) for both classes
-        // and structs, but it seems that wrapping is still handled correctly
-        // elsewhere.
-        ShouldMerge = !Style.BraceWrapping.AfterClass ||
-                      (NextLine.First->is(tok::r_brace) &&
-                       !Style.BraceWrapping.SplitEmptyRecord);
+      } else if (TheLine->Last->isOneOf(TT_ClassLBrace, TT_StructLBrace,
+                                        TT_UnionLBrace)) {
+        return tryMergeRecord(I, E, Limit);
       } else if (TheLine->InPPDirective ||
                  TheLine->First->isNoneOf(tok::kw_class, tok::kw_enum,
                                           tok::kw_struct)) {
@@ -574,6 +581,73 @@ class LineJoiner {
     return 0;
   }
 
+  unsigned tryMergeRecord(ArrayRef<AnnotatedLine *>::const_iterator I,
+                          ArrayRef<AnnotatedLine *>::const_iterator E,
+                          unsigned Limit) {
+    const auto *Line = I[0];
+    const auto *NextLine = I[1];
+
+    // Current line begins both record and block, brace was not wrapped.
+    if (Line->Last->isOneOf(TT_StructLBrace, TT_ClassLBrace, TT_UnionLBrace)) {
+      auto ShouldWrapLBrace = [&](TokenType LBraceType) {
+        switch (LBraceType) {
+        case TT_StructLBrace:
+          return Style.BraceWrapping.AfterStruct;
+        case TT_ClassLBrace:
+          return Style.BraceWrapping.AfterClass;
+        case TT_UnionLBrace:
+          return Style.BraceWrapping.AfterUnion;
+        default:
+          return false;
+        };
+      };
+
+      auto TryMergeShortRecord = [&] {
+        switch (Style.AllowShortRecordOnASingleLine) {
+        case FormatStyle::SRS_Never:
+          return false;
+        case FormatStyle::SRS_Always:
+          return true;
+        default:
+          return NextLine->First->is(tok::r_brace);
+        }
+      };
+
+      if (Style.AllowShortRecordOnASingleLine != FormatStyle::SRS_Never &&
+          (!ShouldWrapLBrace(Line->Last->getType()) ||
+           (!Style.BraceWrapping.SplitEmptyRecord && TryMergeShortRecord()))) {
+        return tryMergeSimpleBlock(I, E, Limit);
+      }
+    }
+
+    // Cases where the l_brace was wrapped.
+    // Current line begins record, next line block.
+    if (NextLine->First->isOneOf(TT_ClassLBrace, TT_StructLBrace,
+                                 TT_UnionLBrace)) {
+      if (I + 2 == E || I[2]->First->is(tok::r_brace) ||
+          Style.AllowShortRecordOnASingleLine != FormatStyle::SRS_Always) {
+        return 0;
+      }
+
+      return tryMergeSimpleBlock(I, E, Limit);
+    }
+
+    // Previous line begins record, current line block.
+    if (I != AnnotatedLines.begin() &&
+        I[-1]->First->isOneOf(tok::kw_struct, tok::kw_class, tok::kw_union)) {
+      const bool IsEmptyBlock =
+          Line->Last->is(tok::l_brace) && NextLine->First->is(tok::r_brace);
+
+      if ((IsEmptyBlock && !Style.BraceWrapping.SplitEmptyRecord) ||
+          (!IsEmptyBlock &&
+           Style.AllowShortBlocksOnASingleLine == FormatStyle::SBS_Always)) {
+        return tryMergeSimpleBlock(I, E, Limit);
+      }
+    }
+
+    return 0;
+  }
+
   unsigned
   tryMergeSimplePPDirective(ArrayRef<AnnotatedLine *>::const_iterator I,
                             ArrayRef<AnnotatedLine *>::const_iterator E,
@@ -879,10 +953,17 @@ class LineJoiner {
         return 1;
       } else if (Limit != 0 && !Line.startsWithNamespace() &&
                  !startsExternCBlock(Line)) {
-        // We don't merge short records.
-        if (isRecordLBrace(*Line.Last))
+        // Merge short records only when requested.
+        if (Line.Last->isOneOf(TT_EnumLBrace, TT_RecordLBrace))
           return 0;
 
+        if (Line.Last->isOneOf(TT_ClassLBrace, TT_StructLBrace,
+                               TT_UnionLBrace) &&
+            Line.Last != Line.First &&
+            Style.AllowShortRecordOnASingleLine != FormatStyle::SRS_Always) {
+          return 0;
+        }
+
         // Check that we still have three lines and they fit into the limit.
         if (I + 2 == E || I[2]->Type == LT_Invalid)
           return 0;
@@ -934,9 +1015,17 @@ class LineJoiner {
         return 0;
       Limit -= 2;
       unsigned MergedLines = 0;
-      if (Style.AllowShortBlocksOnASingleLine != FormatStyle::SBS_Never ||
-          (I[1]->First == I[1]->Last && I + 2 != E &&
-           I[2]->First->is(tok::r_brace))) {
+
+      auto TryMergeBlock = [&] {
+        if (Style.AllowShortBlocksOnASingleLine != FormatStyle::SBS_Never ||
+            Style.AllowShortRecordOnASingleLine == FormatStyle::SRS_Always) {
+          return true;
+        }
+        return I[1]->First == I[1]->Last && I + 2 != E &&
+               I[2]->First->is(tok::r_brace);
+      };
+
+      if (TryMergeBlock()) {
         MergedLines = tryMergeSimpleBlock(I + 1, E, Limit);
         // If we managed to merge the block, count the statement header, which
         // is on a separate line.

clang/lib/Format/UnwrappedLineParser.cpp

@@ -948,20 +948,26 @@ static bool isIIFE(const UnwrappedLine &Line,
 }
 
 static bool ShouldBreakBeforeBrace(const FormatStyle &Style,
-                                   const FormatToken &InitialToken) {
+                                   const FormatToken &InitialToken,
+                                   bool IsEmptyBlock) {
   tok::TokenKind Kind = InitialToken.Tok.getKind();
   if (InitialToken.is(TT_NamespaceMacro))
     Kind = tok::kw_namespace;
 
+  const bool WrapRecordAllowed =
+      !IsEmptyBlock ||
+      Style.AllowShortRecordOnASingleLine < FormatStyle::SRS_Empty ||
+      Style.BraceWrapping.SplitEmptyRecord;
+
   switch (Kind) {
   case tok::kw_namespace:
     return Style.BraceWrapping.AfterNamespace;
   case tok::kw_class:
-    return Style.BraceWrapping.AfterClass;
+    return Style.BraceWrapping.AfterClass && WrapRecordAllowed;
   case tok::kw_union:
-    return Style.BraceWrapping.AfterUnion;
+    return Style.BraceWrapping.AfterUnion && WrapRecordAllowed;
   case tok::kw_struct:
-    return Style.BraceWrapping.AfterStruct;
+    return Style.BraceWrapping.AfterStruct && WrapRecordAllowed;
   case tok::kw_enum:
     return Style.BraceWrapping.AfterEnum;
   default:
@@ -3200,8 +3206,10 @@ void UnwrappedLineParser::parseNamespace() {
   if (FormatTok->is(tok::l_brace)) {
     FormatTok->setFinalizedType(TT_NamespaceLBrace);
 
-    if (ShouldBreakBeforeBrace(Style, InitialToken))
+    if (ShouldBreakBeforeBrace(Style, InitialToken,
+                               Tokens->peekNextToken()->is(tok::r_brace))) {
       addUnwrappedLine();
+    }
 
     unsigned AddLevels =
         Style.NamespaceIndentation == FormatStyle::NI_All ||
@@ -3865,7 +3873,8 @@ bool UnwrappedLineParser::parseEnum() {
   }
 
   if (!Style.AllowShortEnumsOnASingleLine &&
-      ShouldBreakBeforeBrace(Style, InitialToken)) {
+      ShouldBreakBeforeBrace(Style, InitialToken,
+                             Tokens->peekNextToken()->is(tok::r_brace))) {
     addUnwrappedLine();
   }
   // Parse enum body.
@@ -4160,8 +4169,10 @@ void UnwrappedLineParser::parseRecord(bool ParseAsExpr, bool IsJavaRecord) {
     if (ParseAsExpr) {
       parseChildBlock();
     } else {
-      if (ShouldBreakBeforeBrace(Style, InitialToken))
+      if (ShouldBreakBeforeBrace(Style, InitialToken,
+                                 Tokens->peekNextToken()->is(tok::r_brace))) {
         addUnwrappedLine();
+      }
 
       unsigned AddLevels = Style.IndentAccessModifiers ? 2u : 1u;
       parseBlock(/*MustBeDeclaration=*/true, AddLevels, /*MunchSemi=*/false);