[clang-format] add MaxSingleLinesInBracedList style option

The use of Cpp11BracedListStyle with BinPackParameters=False
avoids bin packing until reaching a hard-coded limit of 20 items.
This is an arbitrary choice. Introduce a new style option to
allow setting a configurable limit of items.

Author: gedare

clang/include/clang/Format/Format.h

@@ -2515,6 +2515,9 @@ struct FormatStyle {
   /// (e.g. a type or variable name), clang-format formats as if the ``{}`` were
   /// the parentheses of a function call with that name. If there is no name,
   /// a zero-length name is assumed.
+  ///
+  /// ``BinPackArguments`` may be ignored for initializer lists with more than
+  /// ``MaxSingleLinesInBracedList`` items.
   /// \code
   ///    true:                                  false:
   ///    vector<int> x{1, 2, 3, 4};     vs.     vector<int> x{ 1, 2, 3, 4 };
@@ -3391,6 +3394,21 @@ struct FormatStyle {
   /// \version 3.7
   unsigned MaxEmptyLinesToKeep;
 
+  /// The maximum number of single item lines to keep in a braced list when
+  /// ``BinPackArguments`` is ``false`` before formatting items in columns.
+  /// Defaults to 20.
+  /// \code
+  ///    MaxSingleLinesInBracedList: 5  vs.     MaxSingleLinesInBracedList: 4
+  ///    vector<int> x{                         vector<int> x{1, 2, 3, 4, 5};
+  ///                1,
+  ///                2,
+  ///                3,
+  ///                4,
+  ///                5};
+  /// \endcode
+  /// \version 20
+  unsigned MaxSingleLinesInBracedList;
+
   /// Different ways to indent namespace contents.
   enum NamespaceIndentationKind : int8_t {
     /// Don't indent in namespaces.
@@ -5204,6 +5222,7 @@ struct FormatStyle {
            LineEnding == R.LineEnding && MacroBlockBegin == R.MacroBlockBegin &&
            MacroBlockEnd == R.MacroBlockEnd && Macros == R.Macros &&
            MaxEmptyLinesToKeep == R.MaxEmptyLinesToKeep &&
+           MaxSingleLinesInBracedList == R.MaxSingleLinesInBracedList &&
            NamespaceIndentation == R.NamespaceIndentation &&
            NamespaceMacros == R.NamespaceMacros &&
            ObjCBinPackProtocolList == R.ObjCBinPackProtocolList &&

clang/lib/Format/Format.cpp

@@ -1059,6 +1059,8 @@ template <> struct MappingTraits<FormatStyle> {
     IO.mapOptional("Macros", Style.Macros);
     IO.mapOptional("MainIncludeChar", Style.IncludeStyle.MainIncludeChar);
     IO.mapOptional("MaxEmptyLinesToKeep", Style.MaxEmptyLinesToKeep);
+    IO.mapOptional("MaxSingleLinesInBracedList",
+                   Style.MaxSingleLinesInBracedList);
     IO.mapOptional("NamespaceIndentation", Style.NamespaceIndentation);
     IO.mapOptional("NamespaceMacros", Style.NamespaceMacros);
     IO.mapOptional("ObjCBinPackProtocolList", Style.ObjCBinPackProtocolList);
@@ -1569,6 +1571,7 @@ FormatStyle getLLVMStyle(FormatStyle::LanguageKind Language) {
   LLVMStyle.Language = Language;
   LLVMStyle.LineEnding = FormatStyle::LE_DeriveLF;
   LLVMStyle.MaxEmptyLinesToKeep = 1;
+  LLVMStyle.MaxSingleLinesInBracedList = 20;
   LLVMStyle.NamespaceIndentation = FormatStyle::NI_None;
   LLVMStyle.ObjCBinPackProtocolList = FormatStyle::BPS_Auto;
   LLVMStyle.ObjCBlockIndentWidth = 2;

clang/lib/Format/FormatToken.cpp

@@ -174,7 +174,7 @@ void CommaSeparatedList::precomputeFormattingInfos(const FormatToken *Token) {
   // have many items (20 or more) or we allow bin-packing of function call
   // arguments.
   if (Style.Cpp11BracedListStyle && !Style.BinPackArguments &&
-      Commas.size() < 19) {
+      Commas.size() <= Style.MaxSingleLinesInBracedList) {
     return;
   }
 

clang/unittests/Format/FormatTest.cpp

@@ -14038,6 +14038,32 @@ TEST_F(FormatTest, LayoutCxx11BraceInitializers) {
       "    ffffff, ggggg,  hhhhhh, iiiiii, jjjjjj, kkkkkk,\n"
       "};",
       NoBinPacking);
+  NoBinPacking.MaxSingleLinesInBracedList = 22;
+  verifyFormat("const Aaaaaa aaaaa = {\n"
+               "    aaaaa,\n"
+               "    bbbbb,\n"
+               "    ccccc,\n"
+               "    ddddd,\n"
+               "    eeeee,\n"
+               "    ffffff,\n"
+               "    ggggg,\n"
+               "    hhhhhh,\n"
+               "    iiiiii,\n"
+               "    jjjjjj,\n"
+               "    kkkkkk,\n"
+               "    aaaaa,\n"
+               "    bbbbb,\n"
+               "    ccccc,\n"
+               "    ddddd,\n"
+               "    eeeee,\n"
+               "    ffffff,\n"
+               "    ggggg,\n"
+               "    hhhhhh,\n"
+               "    iiiiii,\n"
+               "    jjjjjj,\n"
+               "    kkkkkk,\n"
+               "};",
+               NoBinPacking);
 
   NoBinPacking.AlignAfterOpenBracket = FormatStyle::BAS_AlwaysBreak;
   verifyFormat("static uint8 CddDp83848Reg[] = {\n"