[clang-format] New format param ObjCBinPackProtocolList

Summary:
This is an alternative approach to D42014 after some
investigation by stephanemoore@ and myself.

Previously, the format parameter `BinPackParameters` controlled both
C function parameter list bin-packing and Objective-C protocol conformance
list bin-packing.

We found in the Google style, some teams were changing
`BinPackParameters` from its default (`true`) to `false` so they could
lay out Objective-C protocol conformance list items one-per-line
instead of bin-packing them into as few lines as possible.

To allow teams to use one-per-line Objective-C protocol lists without
changing bin-packing for other areas like C function parameter lists,
this diff introduces a new LibFormat parameter
`ObjCBinPackProtocolList` to control the behavior just for ObjC
protocol conformance lists.

The new parameter is an enum which defaults to `Auto` to keep the
previous behavior (delegating to `BinPackParameters`).

Depends On D42649

Test Plan: New tests added. make -j12 FormatTests && ./tools/clang/unittests/Format/FormatTests

Reviewers: jolesiak, stephanemoore, djasper

Reviewed By: stephanemoore

Subscribers: Wizard, hokein, cfe-commits, klimek

Differential Revision: https://reviews.llvm.org/D42650

llvm-svn: 324131

2 files changed, 22 insertions, 1 deletions

diff --git a/clang/lib/Format/ContinuationIndenter.cpp b/clang/lib/Format/ContinuationIndenter.cpp
index 3711ee01c48..db4fe8f0a3f 100644
--- a/clang/lib/Format/ContinuationIndenter.cpp
+++ b/clang/lib/Format/ContinuationIndenter.cpp
@@ -1222,9 +1222,20 @@ void ContinuationIndenter::moveStatePastScopeOpener(LineState &State,
         Current.MatchingParen->getPreviousNonComment() &&
         Current.MatchingParen->getPreviousNonComment()->is(tok::comma);
 
+    // If ObjCBinPackProtocolList is unspecified, fall back to BinPackParameters
+    // for backwards compatibility.
+    bool ObjCBinPackProtocolList =
+        (Style.ObjCBinPackProtocolList == FormatStyle::BPS_Auto &&
+         Style.BinPackParameters) ||
+        Style.ObjCBinPackProtocolList == FormatStyle::BPS_Always;
+
+    bool BinPackDeclaration =
+        (State.Line->Type != LT_ObjCDecl && Style.BinPackParameters) ||
+        (State.Line->Type == LT_ObjCDecl && ObjCBinPackProtocolList);
+
     AvoidBinPacking =
         (Style.Language == FormatStyle::LK_JavaScript && EndsInComma) ||
-        (State.Line->MustBeDeclaration && !Style.BinPackParameters) ||
+        (State.Line->MustBeDeclaration && !BinPackDeclaration) ||
         (!State.Line->MustBeDeclaration && !Style.BinPackArguments) ||
         (Style.ExperimentalAutoDetectBinPacking &&
          (Current.PackingKind == PPK_OnePerLine ||
diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index 631d186e629..90b14e74f97 100644
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -105,6 +105,14 @@ template <> struct ScalarEnumerationTraits<FormatStyle::ShortFunctionStyle> {
   }
 };
 
+template <> struct ScalarEnumerationTraits<FormatStyle::BinPackStyle> {
+  static void enumeration(IO &IO, FormatStyle::BinPackStyle &Value) {
+    IO.enumCase(Value, "Auto", FormatStyle::BPS_Auto);
+    IO.enumCase(Value, "Always", FormatStyle::BPS_Always);
+    IO.enumCase(Value, "Never", FormatStyle::BPS_Never);
+  }
+};
+
 template <> struct ScalarEnumerationTraits<FormatStyle::BinaryOperatorStyle> {
   static void enumeration(IO &IO, FormatStyle::BinaryOperatorStyle &Value) {
     IO.enumCase(Value, "All", FormatStyle::BOS_All);
@@ -378,6 +386,7 @@ template <> struct MappingTraits<FormatStyle> {
     IO.mapOptional("MacroBlockEnd", Style.MacroBlockEnd);
     IO.mapOptional("MaxEmptyLinesToKeep", Style.MaxEmptyLinesToKeep);
     IO.mapOptional("NamespaceIndentation", Style.NamespaceIndentation);
+    IO.mapOptional("ObjCBinPackProtocolList", Style.ObjCBinPackProtocolList);
     IO.mapOptional("ObjCBlockIndentWidth", Style.ObjCBlockIndentWidth);
     IO.mapOptional("ObjCSpaceAfterProperty", Style.ObjCSpaceAfterProperty);
     IO.mapOptional("ObjCSpaceBeforeProtocolList",
@@ -637,6 +646,7 @@ FormatStyle getLLVMStyle() {
   LLVMStyle.MaxEmptyLinesToKeep = 1;
   LLVMStyle.KeepEmptyLinesAtTheStartOfBlocks = true;
   LLVMStyle.NamespaceIndentation = FormatStyle::NI_None;
+  LLVMStyle.ObjCBinPackProtocolList = FormatStyle::BPS_Auto;
   LLVMStyle.ObjCBlockIndentWidth = 2;
   LLVMStyle.ObjCSpaceAfterProperty = false;
   LLVMStyle.ObjCSpaceBeforeProtocolList = true;