clang-format: Allow optimizer to break template declaration.

[Typz]

Summary

Introduce PenaltyBreakTemplateDeclaration to control the penalty,
and change AlwaysBreakTemplateDeclarations to an enum with 3 modes:

• None for automatic (e.g. penalty based) wrapping of template declaration
• BeforeFunction for always wrapping before functions, and applying penalty before classes (e.g. same as legacy behavior when AlwaysBreakTemplateDeclarations=false)
• Always for always wrapping (e.g. same as legacy behavior when AlwaysBreakTemplateDeclarations=true)

[Typz]

fix commit message

[Typz]

Force wrap after multi-line template declaration

[Typz]

If the template declaration spans multiple lines, force wrap before the function/class declaration

[Typz]

ping?

[djasper]

Please given an explanation of what you are trying to achieve with this change. Do you intend to set the penalty high so that clang-format does other things first before falling back to wrapping template declarations?

Why treat separate declarations differently wrt. wrapping the template declarations? Will this stop at classes vs. functions? I generally have doubts that this option carries it's weight. Do you have a style guide that explicitly tells you to do this?

[Typz]

In D42684#1013005, @djasper wrote:

Please given an explanation of what you are trying to achieve with this change. Do you intend to set the penalty high so that clang-format does other things first before falling back to wrapping template declarations?

Why treat separate declarations differently wrt. wrapping the template declarations? Will this stop at classes vs. functions? I generally have doubts that this option carries it's weight. Do you have a style guide that explicitly tells you to do this?

I set the penalty relatively high (200), i.e. the same penalty that I have set for PenaltyBreakAssignment, PenaltyBreakBeforeFirstCallParameter, and PenaltyReturnTypeOnItsOwnLine.
Basically we don't have a preference as to where the break should be, and we found that setting the same penalty for all these parameters (including the new PenaltyBreakTemplateDeclaration) gives really "natural" result: e.g. very close to how a user would optimize the code wrapping for readability.

At the moment AlwaysBreakTemplateDeclarations actually applies only to classes, thus templates are always wrapped before functions (unless it all fits on one line). A simpler change would have been to make AlwaysBreakTemplateDeclarations stick to its name, and let it apply to functions as well: but I figured with would break existing clang-format styles.

[djasper]

I think it's possible that this is just a bug/oversight. But I don't fully understand the case where it is not behaving as you expect. Can you give me an example (config setting + code that's not formatted as you expect)?

[Typz]

The problem I have is really related to the current AlwaysBreakTemplateDeclarations behavior, which does not apply to functions.
I set it to false, and I get this:

template<>
void aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(
    const bbbbbbbbbbbbbbbbbbb & cccccccccc);

instead of:

template<> void aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(
    const bbbbbbbbbbbbbbbbbbb & cccccccccc);

Then when this is fixed the penalty for breaking after the templates part is hardcoded to 10 (prec::Level::Relational), which was not always wrapping as expected (that is definitely subjective, but that is the beauty of penalties...)

[djasper]

In D42684#1022093, @Typz wrote:

The problem I have is really related to the current AlwaysBreakTemplateDeclarations behavior, which does not apply to functions.
I set it to false, and I get this:

template<>
void aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(
    const bbbbbbbbbbbbbbbbbbb & cccccccccc);

instead of:

template<> void aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(
    const bbbbbbbbbbbbbbbbbbb & cccccccccc);

Then when this is fixed the penalty for breaking after the templates part is hardcoded to 10 (prec::Level::Relational), which was not always wrapping as expected (that is definitely subjective, but that is the beauty of penalties...)

Ah, I see. However, you are misunderstanding what the parameter is meant to do (and I think what the name says). It is controlling whether we "always" break before the template declaration (even if everything would fit on just one line). Setting it to false, i.e. "not always" breaking, does not imply that there is any particular situation in which we need to keep it on the same line.

I understand what you want to achieve, but I don't think it is related to whether this is a function or a class declaration, i.e. clang-format also does:

template <typename T>
class AAAAAAAAAAAAAAAAAAAAAAAAAAAA
    : BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB {};

although the template declaration would easily fit on the same line.

So this change does not seem like the right one to make in order to get the options to be more intuitive and for you to get the behavior you want. I'll try to think about how to achieve that. Do you have any ideas?

[Typz]

Indeed, seems to apply to classes as well. Maybe I was mislead by my testing, where I did not get the case (possibly because we use ConstructorInitializerAllOnOneLineOrOnePerLine=true, so the continuation indenter only sees "short" class declarations unless breaking the template is required because the name is too long).

So just to be clear, are you saying the whole approach is not the right one, or simply that the "names" of each modes are not?
For the name, maybe something like may be better:

• Never
• MultiLineDeclaration, or maybe even MultiLine
• Always

[djasper]

In D42684#1022219, @Typz wrote:

Indeed, seems to apply to classes as well. Maybe I was mislead by my testing, where I did not get the case (possibly because we use ConstructorInitializerAllOnOneLineOrOnePerLine=true, so the continuation indenter only sees "short" class declarations unless breaking the template is required because the name is too long).

Not sure how that style flag is related to class declarations, but ok ;).

So just to be clear, are you saying the whole approach is not the right one, or simply that the "names" of each modes are not?
For the name, maybe something like may be better:

• Never
• MultiLineDeclaration, or maybe even MultiLine
• Always

Ah, yeah, maybe it's just the name. "AlwaysBreak: Never" and "AlwaysBreak: Always" seem not very intuitive to interpret, though. How about just: No, Yes, MultiLine?

[Typz]

Change options values to No/MultiLine/Yes.

[Typz]

ping?

[Typz]

ping?

[Typz]

@djasper : ping?

[djasper]

Some last comments, but basically looks good.

include/clang/Format/Format.h

352

Don't forget to run docs/tools/dump_format_style.py to update the docs.

355

I think it'd be worth having a case here that would actually be formatted differently with BTDS_MultiLine.

lib/Format/TokenAnnotator.cpp

2248

Indentation is off

[Typz]

Rebase on latest master & address review comments

include/clang/Format/Format.h

struct FormatStyle {
   /// \code
   ///    true:                                  false:
   ///    aaaa =                         vs.     aaaa = "bbbb"
   ///        "bbbb"                                    "cccc";
   ///        "cccc";
   /// \endcode
   bool AlwaysBreakBeforeMultilineStrings;
 
-  /// \brief If ``true``, always break after the ``template<...>`` of a template
-  /// declaration.
+  /// \brief Different ways to break after the template declaration.
+  enum BreakTemplateDeclarationsStyle {
+      /// Do not force break before declaration.
+      /// ``PenaltyBreakTemplateDeclaration`` is taken into account.
       /// \code
-  ///    true:                                  false:
-  ///    template <typename T>          vs.     template <typename T> class C {};
-  ///    class C {};
+      ///    template <typename T> T foo() {
+      ///    }
+      /// \endcode
+      BTDS_No,
+      /// Force break after template declaration only when the following
+      /// declaration spans multiple lines.
+      /// \code
+      ///    template <typename T> T foo(int a) {
+      ///    }
+      ///
+      ///    template <typename T>
+      ///    T foo(int aaaaaaaaaaaaaaaaaaaaa
+      ///          int bbbbbbbbbbbbbbbbbbbbb) {
+      ///    }
       /// \endcode
-  bool AlwaysBreakTemplateDeclarations;
+      BTDS_MultiLine,
+      /// Always break after template declaration.
+      /// \code
+      ///    template <typename T>
+      ///    T foo() {
+      ///    }
+      /// \endcode
+      BTDS_Yes
+  };
+
+  /// \brief The template declaration breaking style to use.
+  BreakTemplateDeclarationsStyle AlwaysBreakTemplateDeclarations;
 
   /// \brief If ``false``, a function call's arguments will either be all on the
   /// same line or will have one line each.
   /// \code
   ///   true:
   ///   void f() {
   ///     f(aaaaaaaaaaaaaaaaaaaa, aaaaaaaaaaaaaaaaaaaa,
   ///       aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa);

   unsigned PenaltyBreakComment;
 
   /// \brief The penalty for breaking before the first ``<<``.
   unsigned PenaltyBreakFirstLessLess;
 
   /// \brief The penalty for each line break introduced inside a string literal.
   unsigned PenaltyBreakString;
 
+  /// \brief The penalty for breaking after template declaration.
+  unsigned PenaltyBreakTemplateDeclaration;
+
   /// \brief The penalty for each character outside of the column limit.
   unsigned PenaltyExcessCharacter;
 
   /// \brief Penalty for putting the return type of a function onto its own
   /// line.
   unsigned PenaltyReturnTypeOnItsOwnLine;
 
   /// \brief The ``&`` and ``*`` alignment style.
return AccessModifierOffset == R.AccessModifierOffset &&
                R.PenaltyBreakAssignment &&
            PenaltyBreakBeforeFirstCallParameter ==
                R.PenaltyBreakBeforeFirstCallParameter &&
            PenaltyBreakComment == R.PenaltyBreakComment &&
            PenaltyBreakFirstLessLess == R.PenaltyBreakFirstLessLess &&
            PenaltyBreakString == R.PenaltyBreakString &&
            PenaltyExcessCharacter == R.PenaltyExcessCharacter &&
            PenaltyReturnTypeOnItsOwnLine == R.PenaltyReturnTypeOnItsOwnLine &&
+           PenaltyBreakTemplateDeclaration ==
+               R.PenaltyBreakTemplateDeclaration &&
            PointerAlignment == R.PointerAlignment &&
            RawStringFormats == R.RawStringFormats &&
            SpaceAfterCStyleCast == R.SpaceAfterCStyleCast &&
            SpaceAfterTemplateKeyword == R.SpaceAfterTemplateKeyword &&
            SpaceBeforeAssignmentOperators == R.SpaceBeforeAssignmentOperators &&
            SpaceBeforeCtorInitializerColon ==
                R.SpaceBeforeCtorInitializerColon &&
            SpaceBeforeInheritanceColon == R.SpaceBeforeInheritanceColon &&

lib/Format/ContinuationIndenter.cpp

if (startsSegmentOfBuilderTypeCall(Current) &&
       //   SomeFunction(function() {
       //     ...
       //   }.bind(...));
       // FIXME: We should find a more generic solution to this problem.
       !(State.Column <= NewLineColumn &&
         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;
 
   if (Style.AlwaysBreakBeforeMultilineStrings &&
       (NewLineColumn == State.FirstIndent + Style.ContinuationIndentWidth ||
        Previous.is(tok::comma) || Current.NestingLevel < 2) &&
       !Previous.isOneOf(tok::kw_return, tok::lessless, tok::at) &&
       !Previous.isOneOf(TT_InlineASMColon, TT_ConditionalExpr) &&
if (Current.is(tok::lessless) && Current.isNot(TT_OverloadedOperator) &&
       State.Stack.back().FirstLessLess == 0)
     return true;
 
   if (Current.NestingLevel == 0 && !Current.isTrailingComment()) {
     // Always break after "template <...>" and leading annotations. This is only
     // 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) &&
         Current.isNot(TT_LeadingJavaAnnotation))
       return true;
   }
 
   // If the return type spans multiple lines, wrap before the function name.

lib/Format/Format.cpp

static void enumeration(IO &IO, FormatStyle::ReturnTypeBreakingStyle &Value) {
     IO.enumCase(Value, "TopLevel", FormatStyle::RTBS_TopLevel);
     IO.enumCase(Value, "TopLevelDefinitions",
                 FormatStyle::RTBS_TopLevelDefinitions);
     IO.enumCase(Value, "AllDefinitions", FormatStyle::RTBS_AllDefinitions);
   }
 };
 
 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) {
     IO.enumCase(Value, "None", FormatStyle::DRTBS_None);
     IO.enumCase(Value, "All", FormatStyle::DRTBS_All);
     IO.enumCase(Value, "TopLevel", FormatStyle::DRTBS_TopLevel);
 
     // For backward compatibility.
IO.mapOptional("ObjCSpaceBeforeProtocolList",
                    Style.ObjCSpaceBeforeProtocolList);
     IO.mapOptional("PenaltyBreakAssignment", Style.PenaltyBreakAssignment);
     IO.mapOptional("PenaltyBreakBeforeFirstCallParameter",
                    Style.PenaltyBreakBeforeFirstCallParameter);
     IO.mapOptional("PenaltyBreakComment", Style.PenaltyBreakComment);
     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);
     IO.mapOptional("PointerAlignment", Style.PointerAlignment);
     IO.mapOptional("RawStringFormats", Style.RawStringFormats);
     IO.mapOptional("ReflowComments", Style.ReflowComments);
     IO.mapOptional("SortIncludes", Style.SortIncludes);
     IO.mapOptional("SortUsingDeclarations", Style.SortUsingDeclarations);
FormatStyle getLLVMStyle() {
   LLVMStyle.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_All;
   LLVMStyle.AllowShortBlocksOnASingleLine = false;
   LLVMStyle.AllowShortCaseLabelsOnASingleLine = false;
   LLVMStyle.AllowShortIfStatementsOnASingleLine = false;
   LLVMStyle.AllowShortLoopsOnASingleLine = false;
   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;
   LLVMStyle.BreakBeforeTernaryOperators = true;
   LLVMStyle.BreakBeforeBraces = FormatStyle::BS_Attach;
   LLVMStyle.BraceWrapping = {false, false, false, false, false,
                              false, false, false, false, false,
                              false, false, true,  true,  true};
FormatStyle getLLVMStyle() {
 
   LLVMStyle.PenaltyBreakAssignment = prec::Assignment;
   LLVMStyle.PenaltyBreakComment = 300;
   LLVMStyle.PenaltyBreakFirstLessLess = 120;
   LLVMStyle.PenaltyBreakString = 1000;
   LLVMStyle.PenaltyExcessCharacter = 1000000;
   LLVMStyle.PenaltyReturnTypeOnItsOwnLine = 60;
   LLVMStyle.PenaltyBreakBeforeFirstCallParameter = 19;
+  LLVMStyle.PenaltyBreakTemplateDeclaration = prec::Relational;
 
   LLVMStyle.DisableFormat = false;
   LLVMStyle.SortIncludes = true;
   LLVMStyle.SortUsingDeclarations = true;
 
   return LLVMStyle;
 }
 
 FormatStyle getGoogleStyle(FormatStyle::LanguageKind Language) {
   if (Language == FormatStyle::LK_TextProto) {
     FormatStyle GoogleStyle = getGoogleStyle(FormatStyle::LK_Proto);
     GoogleStyle.Language = FormatStyle::LK_TextProto;
 
     return GoogleStyle;
   }
 
   FormatStyle GoogleStyle = getLLVMStyle();
   GoogleStyle.Language = Language;
 
   GoogleStyle.AccessModifierOffset = -1;
   GoogleStyle.AlignEscapedNewlines = FormatStyle::ENAS_Left;
   GoogleStyle.AllowShortIfStatementsOnASingleLine = true;
   GoogleStyle.AllowShortLoopsOnASingleLine = true;
   GoogleStyle.AlwaysBreakBeforeMultilineStrings = true;
-  GoogleStyle.AlwaysBreakTemplateDeclarations = true;
+  GoogleStyle.AlwaysBreakTemplateDeclarations = FormatStyle::BTDS_Yes;
   GoogleStyle.ConstructorInitializerAllOnOneLineOrOnePerLine = true;
   GoogleStyle.DerivePointerAlignment = true;
   GoogleStyle.IncludeCategories = {
       {"^<ext/.*\\.h>", 2}, {"^<.*\\.h>", 1}, {"^<.*", 2}, {".*", 3}};
   GoogleStyle.IncludeIsMainRegex = "([-_](test|unittest))?$";
   GoogleStyle.IndentCaseLabels = true;
   GoogleStyle.KeepEmptyLinesAtTheStartOfBlocks = false;
   GoogleStyle.ObjCBinPackProtocolList = FormatStyle::BPS_Never;

 
 FormatStyle getMozillaStyle() {
   FormatStyle MozillaStyle = getLLVMStyle();
   MozillaStyle.AllowAllParametersOfDeclarationOnNextLine = false;
   MozillaStyle.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_Inline;
   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;
   MozillaStyle.BreakConstructorInitializers = FormatStyle::BCIS_BeforeComma;
   MozillaStyle.BreakBeforeInheritanceComma = true;
   MozillaStyle.ConstructorInitializerIndentWidth = 2;
   MozillaStyle.ContinuationIndentWidth = 2;
   MozillaStyle.Cpp11BracedListStyle = false;

lib/Format/TokenAnnotator.cpp

if (Right.is(tok::lessless) && Left.isLabelString() &&
     return 25;
   if (Right.is(tok::lessless)) {
     // Breaking at a << is really cheap.
     if (!Left.is(tok::r_paren) || Right.OperatorIndex > 0)
       // Slightly prefer to break before the first one in log-like statements.
       return 2;
     return 1;
   }
+  if (Left.ClosesTemplateDeclaration)
+      return Style.PenaltyBreakTemplateDeclaration;
   if (Left.is(TT_ConditionalExpr))
     return prec::Conditional;
   prec::Level Level = Left.getPrecedence();
   if (Level == prec::Unknown)
     Level = Right.getPrecedence();
   if (Level == prec::Assignment)
     return Style.PenaltyBreakAssignment;
   if (Level != prec::Unknown)
if (Right.Previous->IsUnterminatedLiteral)
     return true;
   if (Right.is(tok::lessless) && Right.Next &&
       Right.Previous->is(tok::string_literal) &&
       Right.Next->is(tok::string_literal))
     return true;
   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 &&
       !Style.ConstructorInitializerAllOnOneLineOrOnePerLine)
     return true;
   if (Right.is(TT_CtorInitializerColon) &&
       Style.BreakConstructorInitializers == FormatStyle::BCIS_BeforeComma &&
       !Style.ConstructorInitializerAllOnOneLineOrOnePerLine)

unittests/Format/FormatTest.cpp

EXPECT_EQ("static_cast<A< //\n"
             format("static_cast<A<//\n"
                    "    B>*>(\n"
                    "\n"
                    "    );"));
   verifyFormat("int aaaaaaaaaaaaaaaaaaaaaaaaaaaaa(\n"
                "    const typename aaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaa);");
 
   FormatStyle AlwaysBreak = getLLVMStyle();
-  AlwaysBreak.AlwaysBreakTemplateDeclarations = true;
+  AlwaysBreak.AlwaysBreakTemplateDeclarations = FormatStyle::BTDS_Yes;
   verifyFormat("template <typename T>\nclass C {};", AlwaysBreak);
   verifyFormat("template <typename T>\nvoid f();", AlwaysBreak);
   verifyFormat("template <typename T>\nvoid f() {}", AlwaysBreak);
   verifyFormat("void aaaaaaaaaaaaaaaaaaa<aaaaaaaaaaaaaaaaaaaaaaaaaaaaa,\n"
                "                         bbbbbbbbbbbbbbbbbbbbbbbbbbbb>(\n"
                "    ccccccccccccccccccccccccccccccccccccccccccccccc);");
   verifyFormat("template <template <typename> class Fooooooo,\n"
                "          template <typename> class Baaaaaaar>\n"
                "struct C {};",
                AlwaysBreak);
   verifyFormat("template <typename T> // T can be A, B or C.\n"
                "struct C {};",
                AlwaysBreak);
   verifyFormat("template <enum E> class A {\n"
                "public:\n"
                "  E *f();\n"
                "};");
+
+  FormatStyle NeverBreak = getLLVMStyle();
+  NeverBreak.AlwaysBreakTemplateDeclarations = FormatStyle::BTDS_No;
+  verifyFormat("template <typename T> class C {};", NeverBreak);
+  verifyFormat("template <typename T> void f();", NeverBreak);
+  verifyFormat("template <typename T> void f() {}", NeverBreak);
+  verifyFormat("template <typename T>\nvoid foo(aaaaaaaaaaaaaaaaaaaaaaaaaa bbbbbbbbbbbbbbbbbbbb) {}",
+               NeverBreak);
+  verifyFormat("void aaaaaaaaaaaaaaaaaaa<aaaaaaaaaaaaaaaaaaaaaaaaaaaaa,\n"
+               "                         bbbbbbbbbbbbbbbbbbbbbbbbbbbb>(\n"
+               "    ccccccccccccccccccccccccccccccccccccccccccccccc);",
+               NeverBreak);
+  verifyFormat("template <template <typename> class Fooooooo,\n"
+               "          template <typename> class Baaaaaaar>\n"
+               "struct C {};",
+               NeverBreak);
+  verifyFormat("template <typename T> // T can be A, B or C.\n"
+               "struct C {};",
+               NeverBreak);
+  verifyFormat("template <enum E> class A {\n"
+               "public:\n"
+               "  E *f();\n"
+               "};", NeverBreak);
+  NeverBreak.PenaltyBreakTemplateDeclaration = 100;
+  verifyFormat("template <typename T> void\nfoo(aaaaaaaaaaaaaaaaaaaaaaaaaa bbbbbbbbbbbbbbbbbbbb) {}",
+               NeverBreak);
 }
 
 TEST_F(FormatTest, WrapsTemplateParameters) {
   FormatStyle Style = getLLVMStyle();
   Style.AlignAfterOpenBracket = FormatStyle::BAS_DontAlign;
   Style.BreakBeforeBinaryOperators = FormatStyle::BOS_None;
   verifyFormat(
       "template <typename... a> struct q {};\n"
TEST_F(FormatTest, ParsesConfigurationBools) {
   CHECK_PARSE_BOOL(AlignTrailingComments);
   CHECK_PARSE_BOOL(AlignConsecutiveAssignments);
   CHECK_PARSE_BOOL(AlignConsecutiveDeclarations);
   CHECK_PARSE_BOOL(AllowAllParametersOfDeclarationOnNextLine);
   CHECK_PARSE_BOOL(AllowShortBlocksOnASingleLine);
   CHECK_PARSE_BOOL(AllowShortCaseLabelsOnASingleLine);
   CHECK_PARSE_BOOL(AllowShortIfStatementsOnASingleLine);
   CHECK_PARSE_BOOL(AllowShortLoopsOnASingleLine);
-  CHECK_PARSE_BOOL(AlwaysBreakTemplateDeclarations);
   CHECK_PARSE_BOOL(BinPackArguments);
   CHECK_PARSE_BOOL(BinPackParameters);
   CHECK_PARSE_BOOL(BreakAfterJavaFieldAnnotations);
   CHECK_PARSE_BOOL(BreakBeforeTernaryOperators);
   CHECK_PARSE_BOOL(BreakStringLiterals);
   CHECK_PARSE_BOOL(BreakBeforeInheritanceComma)
   CHECK_PARSE_BOOL(CompactNamespaces);
   CHECK_PARSE_BOOL(ConstructorInitializerAllOnOneLineOrOnePerLine);
CHECK_PARSE("ConstructorInitializerIndentWidth: 1234",
               ConstructorInitializerIndentWidth, 1234u);
   CHECK_PARSE("ObjCBlockIndentWidth: 1234", ObjCBlockIndentWidth, 1234u);
   CHECK_PARSE("ColumnLimit: 1234", ColumnLimit, 1234u);
   CHECK_PARSE("MaxEmptyLinesToKeep: 1234", MaxEmptyLinesToKeep, 1234u);
   CHECK_PARSE("PenaltyBreakAssignment: 1234",
               PenaltyBreakAssignment, 1234u);
   CHECK_PARSE("PenaltyBreakBeforeFirstCallParameter: 1234",
               PenaltyBreakBeforeFirstCallParameter, 1234u);
+  CHECK_PARSE("PenaltyBreakTemplateDeclaration: 1234",
+              PenaltyBreakTemplateDeclaration, 1234u);
   CHECK_PARSE("PenaltyExcessCharacter: 1234", PenaltyExcessCharacter, 1234u);
   CHECK_PARSE("PenaltyReturnTypeOnItsOwnLine: 1234",
               PenaltyReturnTypeOnItsOwnLine, 1234u);
   CHECK_PARSE("SpacesBeforeTrailingComments: 1234",
               SpacesBeforeTrailingComments, 1234u);
   CHECK_PARSE("IndentWidth: 32", IndentWidth, 32u);
   CHECK_PARSE("ContinuationIndentWidth: 11", ContinuationIndentWidth, 11u);
   CHECK_PARSE("CommentPragmas: '// abc$'", CommentPragmas, "// abc$");
TEST_F(FormatTest, ParsesConfiguration) {
   CHECK_PARSE("AlwaysBreakAfterReturnType: TopLevel",
               AlwaysBreakAfterReturnType, FormatStyle::RTBS_TopLevel);
   CHECK_PARSE("AlwaysBreakAfterReturnType: AllDefinitions",
               AlwaysBreakAfterReturnType, FormatStyle::RTBS_AllDefinitions);
   CHECK_PARSE("AlwaysBreakAfterReturnType: TopLevelDefinitions",
               AlwaysBreakAfterReturnType,
               FormatStyle::RTBS_TopLevelDefinitions);
 
+  Style.AlwaysBreakTemplateDeclarations = FormatStyle::BTDS_Yes;
+  CHECK_PARSE("AlwaysBreakTemplateDeclarations: No", AlwaysBreakTemplateDeclarations,
+              FormatStyle::BTDS_No);
+  CHECK_PARSE("AlwaysBreakTemplateDeclarations: MultiLine", AlwaysBreakTemplateDeclarations,
+              FormatStyle::BTDS_MultiLine);
+  CHECK_PARSE("AlwaysBreakTemplateDeclarations: Yes", AlwaysBreakTemplateDeclarations,
+              FormatStyle::BTDS_Yes);
+  CHECK_PARSE("AlwaysBreakTemplateDeclarations: false", AlwaysBreakTemplateDeclarations,
+              FormatStyle::BTDS_MultiLine);
+  CHECK_PARSE("AlwaysBreakTemplateDeclarations: true", AlwaysBreakTemplateDeclarations,
+              FormatStyle::BTDS_Yes);
+
   Style.AlwaysBreakAfterDefinitionReturnType = FormatStyle::DRTBS_All;
   CHECK_PARSE("AlwaysBreakAfterDefinitionReturnType: None",
               AlwaysBreakAfterDefinitionReturnType, FormatStyle::DRTBS_None);
   CHECK_PARSE("AlwaysBreakAfterDefinitionReturnType: All",
               AlwaysBreakAfterDefinitionReturnType, FormatStyle::DRTBS_All);
   CHECK_PARSE("AlwaysBreakAfterDefinitionReturnType: TopLevel",
               AlwaysBreakAfterDefinitionReturnType,
               FormatStyle::DRTBS_TopLevel);