clang-format: Allow optimizer to break template declaration.

Summary:
Introduce `PenaltyBreakTemplateDeclaration` to control the penalty,
and change `AlwaysBreakTemplateDeclarations` to an enum with 3 modes:
* `No` for regular, penalty based, wrapping of template declaration
* `MultiLine` for always wrapping before multi-line declarations (e.g.
  same as legacy behavior when `AlwaysBreakTemplateDeclarations=false`)
* `Yes` for always wrapping (e.g. same as legacy behavior when
  `AlwaysBreakTemplateDeclarations=true`)

Reviewers: krasimir, djasper, klimek

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D42684

llvm-svn: 332436

3 files changed, 29 insertions, 5 deletions

diff --git a/clang/lib/Format/ContinuationIndenter.cpp b/clang/lib/Format/ContinuationIndenter.cpp
index 20eb5c03b8b..9a07c5ed591 100644
--- a/clang/lib/Format/ContinuationIndenter.cpp
+++ b/clang/lib/Format/ContinuationIndenter.cpp
@@ -402,6 +402,12 @@ bool ContinuationIndenter::mustBreak(const LineState &State) {
         Style.Language == FormatStyle::LK_JavaScript))
     return true;
 
+  // If the template declaration spans multiple lines, force wrap before the
+  // function/class declaration
+  if (Previous.ClosesTemplateDeclaration &&
+      State.Stack.back().BreakBeforeParameter)
+    return true;
+
   if (State.Column <= NewLineColumn)
     return false;
 
@@ -453,7 +459,7 @@ bool ContinuationIndenter::mustBreak(const LineState &State) {
     // for cases where the entire line does not fit on a single line as a
     // different LineFormatter would be used otherwise.
     if (Previous.ClosesTemplateDeclaration)
-      return true;
+      return Style.AlwaysBreakTemplateDeclarations != FormatStyle::BTDS_No;
     if (Previous.is(TT_FunctionAnnotationRParen))
       return true;
     if (Previous.is(TT_LeadingJavaAnnotation) && Current.isNot(tok::l_paren) &&
diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index f3681a715e4..c6de92b3caf 100644
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -169,6 +169,19 @@ struct ScalarEnumerationTraits<FormatStyle::ReturnTypeBreakingStyle> {
 };
 
 template <>
+struct ScalarEnumerationTraits<FormatStyle::BreakTemplateDeclarationsStyle> {
+  static void enumeration(IO &IO, FormatStyle::BreakTemplateDeclarationsStyle &Value) {
+    IO.enumCase(Value, "No", FormatStyle::BTDS_No);
+    IO.enumCase(Value, "MultiLine", FormatStyle::BTDS_MultiLine);
+    IO.enumCase(Value, "Yes", FormatStyle::BTDS_Yes);
+
+    // For backward compatibility.
+    IO.enumCase(Value, "false", FormatStyle::BTDS_MultiLine);
+    IO.enumCase(Value, "true", FormatStyle::BTDS_Yes);
+  }
+};
+
+template <>
 struct ScalarEnumerationTraits<FormatStyle::DefinitionReturnTypeBreakingStyle> {
   static void
   enumeration(IO &IO, FormatStyle::DefinitionReturnTypeBreakingStyle &Value) {
@@ -400,6 +413,8 @@ template <> struct MappingTraits<FormatStyle> {
     IO.mapOptional("PenaltyBreakFirstLessLess",
                    Style.PenaltyBreakFirstLessLess);
     IO.mapOptional("PenaltyBreakString", Style.PenaltyBreakString);
+    IO.mapOptional("PenaltyBreakTemplateDeclaration",
+                   Style.PenaltyBreakTemplateDeclaration);
     IO.mapOptional("PenaltyExcessCharacter", Style.PenaltyExcessCharacter);
     IO.mapOptional("PenaltyReturnTypeOnItsOwnLine",
                    Style.PenaltyReturnTypeOnItsOwnLine);
@@ -598,7 +613,7 @@ FormatStyle getLLVMStyle() {
   LLVMStyle.AlwaysBreakAfterReturnType = FormatStyle::RTBS_None;
   LLVMStyle.AlwaysBreakAfterDefinitionReturnType = FormatStyle::DRTBS_None;
   LLVMStyle.AlwaysBreakBeforeMultilineStrings = false;
-  LLVMStyle.AlwaysBreakTemplateDeclarations = false;
+  LLVMStyle.AlwaysBreakTemplateDeclarations = FormatStyle::BTDS_MultiLine;
   LLVMStyle.BinPackArguments = true;
   LLVMStyle.BinPackParameters = true;
   LLVMStyle.BreakBeforeBinaryOperators = FormatStyle::BOS_None;
@@ -670,6 +685,7 @@ FormatStyle getLLVMStyle() {
   LLVMStyle.PenaltyExcessCharacter = 1000000;
   LLVMStyle.PenaltyReturnTypeOnItsOwnLine = 60;
   LLVMStyle.PenaltyBreakBeforeFirstCallParameter = 19;
+  LLVMStyle.PenaltyBreakTemplateDeclaration = prec::Relational;
 
   LLVMStyle.DisableFormat = false;
   LLVMStyle.SortIncludes = true;
@@ -694,7 +710,7 @@ FormatStyle getGoogleStyle(FormatStyle::LanguageKind Language) {
   GoogleStyle.AllowShortIfStatementsOnASingleLine = true;
   GoogleStyle.AllowShortLoopsOnASingleLine = true;
   GoogleStyle.AlwaysBreakBeforeMultilineStrings = true;
-  GoogleStyle.AlwaysBreakTemplateDeclarations = true;
+  GoogleStyle.AlwaysBreakTemplateDeclarations = FormatStyle::BTDS_Yes;
   GoogleStyle.ConstructorInitializerAllOnOneLineOrOnePerLine = true;
   GoogleStyle.DerivePointerAlignment = true;
   GoogleStyle.IncludeStyle.IncludeCategories = {
@@ -819,7 +835,7 @@ FormatStyle getMozillaStyle() {
   MozillaStyle.AlwaysBreakAfterReturnType = FormatStyle::RTBS_TopLevel;
   MozillaStyle.AlwaysBreakAfterDefinitionReturnType =
       FormatStyle::DRTBS_TopLevel;
-  MozillaStyle.AlwaysBreakTemplateDeclarations = true;
+  MozillaStyle.AlwaysBreakTemplateDeclarations = FormatStyle::BTDS_Yes;
   MozillaStyle.BinPackParameters = false;
   MozillaStyle.BinPackArguments = false;
   MozillaStyle.BreakBeforeBraces = FormatStyle::BS_Mozilla;
diff --git a/clang/lib/Format/TokenAnnotator.cpp b/clang/lib/Format/TokenAnnotator.cpp
index 61773e5b4a8..5f13d103a6b 100644
--- a/clang/lib/Format/TokenAnnotator.cpp
+++ b/clang/lib/Format/TokenAnnotator.cpp
@@ -2338,6 +2338,8 @@ unsigned TokenAnnotator::splitPenalty(const AnnotatedLine &Line,
       return 2;
     return 1;
   }
+  if (Left.ClosesTemplateDeclaration)
+    return Style.PenaltyBreakTemplateDeclaration;
   if (Left.is(TT_ConditionalExpr))
     return prec::Conditional;
   prec::Level Level = Left.getPrecedence();
@@ -2869,7 +2871,7 @@ bool TokenAnnotator::mustBreakBefore(const AnnotatedLine &Line,
   if (Right.Previous->ClosesTemplateDeclaration &&
       Right.Previous->MatchingParen &&
       Right.Previous->MatchingParen->NestingLevel == 0 &&
-      Style.AlwaysBreakTemplateDeclarations)
+      Style.AlwaysBreakTemplateDeclarations == FormatStyle::BTDS_Yes)
     return true;
   if (Right.is(TT_CtorInitializerComma) &&
       Style.BreakConstructorInitializers == FormatStyle::BCIS_BeforeComma &&