[clang-format] Add BreakBeforeTemplateClose option

Author: leijurv

clang/docs/ClangFormatStyleOptions.rst

@@ -3416,6 +3416,27 @@ the configuration (without a prefix: ``Auto``).
 
 
 
+.. _BreakBeforeTemplateClose:
+
+**BreakBeforeTemplateClose** (``Boolean``) :versionbadge:`clang-format 20` :ref:`¶ <BreakBeforeTemplateClose>`
+  If ``true``, a line break will be placed before the ``>`` in a multiline
+  template declaration.
+
+  .. code-block:: c++
+
+     true:
+     template <
+         typename Foo,
+         typename Bar,
+         typename Baz
+     >
+
+     false:
+     template <
+         typename Foo,
+         typename Bar,
+         typename Baz>
+
 .. _BreakBeforeTernaryOperators:
 
 **BreakBeforeTernaryOperators** (``Boolean``) :versionbadge:`clang-format 3.7` :ref:`¶ <BreakBeforeTernaryOperators>`

clang/docs/ReleaseNotes.rst

@@ -976,6 +976,7 @@ clang-format
   ``Never``, and ``true`` to ``Always``.
 - Adds ``RemoveEmptyLinesInUnwrappedLines`` option.
 - Adds ``KeepFormFeed`` option and set it to ``true`` for ``GNU`` style.
+- Adds ``BreakBeforeTemplateClose`` option.
 
 libclang
 --------

clang/include/clang/Format/Format.h

@@ -2248,6 +2248,25 @@ struct FormatStyle {
   /// \version 16
   BreakBeforeInlineASMColonStyle BreakBeforeInlineASMColon;
 
+  /// If ``true``, a line break will be placed before the ``>`` in a multiline
+  /// template declaration.
+  /// \code
+  ///    true:
+  ///    template <
+  ///        typename Foo,
+  ///        typename Bar,
+  ///        typename Baz
+  ///    >
+  ///
+  ///    false:
+  ///    template <
+  ///        typename Foo,
+  ///        typename Bar,
+  ///        typename Baz>
+  /// \endcode
+  /// \version 20
+  bool BreakBeforeTemplateClose;
+
   /// If ``true``, ternary operators will be placed after line breaks.
   /// \code
   ///    true:
@@ -5184,6 +5203,7 @@ struct FormatStyle {
            BreakBeforeBraces == R.BreakBeforeBraces &&
            BreakBeforeConceptDeclarations == R.BreakBeforeConceptDeclarations &&
            BreakBeforeInlineASMColon == R.BreakBeforeInlineASMColon &&
+           BreakBeforeTemplateClose == R.BreakBeforeTemplateClose &&
            BreakBeforeTernaryOperators == R.BreakBeforeTernaryOperators &&
            BreakBinaryOperations == R.BreakBinaryOperations &&
            BreakConstructorInitializers == R.BreakConstructorInitializers &&

clang/lib/Format/ContinuationIndenter.cpp

@@ -382,10 +382,25 @@ bool ContinuationIndenter::canBreak(const LineState &State) {
   return !State.NoLineBreak && !CurrentState.NoLineBreak;
 }
 
+bool isMatchingBraceOnSameLine(const FormatToken *Token) {
+  if (!Token->MatchingParen)
+    return false;
+  const FormatToken *Matching = Token->MatchingParen;
+  const FormatToken *Current = Token;
+  while (Current && Current != Matching) {
+    if (Current->NewlinesBefore > 0)
+      return false;
+    Current = Current->Previous;
+  }
+  return true;
+}
+
 bool ContinuationIndenter::mustBreak(const LineState &State) {
   const FormatToken &Current = *State.NextToken;
   const FormatToken &Previous = *Current.Previous;
   const auto &CurrentState = State.Stack.back();
+  if (Current.ClosesTemplateDeclaration && Style.BreakBeforeTemplateClose)
+    return !isMatchingBraceOnSameLine(State.NextToken);
   if (Style.BraceWrapping.BeforeLambdaBody && Current.CanBreakBefore &&
       Current.is(TT_LambdaLBrace) && Previous.isNot(TT_LineComment)) {
     auto LambdaBodyLength = getLengthToMatchingParen(Current, State.Stack);
@@ -1370,6 +1385,10 @@ unsigned ContinuationIndenter::getNewLineColumn(const LineState &State) {
       State.Stack.size() > 1) {
     return State.Stack[State.Stack.size() - 2].LastSpace;
   }
+  if (Current.ClosesTemplateDeclaration && Style.BreakBeforeTemplateClose &&
+      State.Stack.size() > 1) {
+    return State.Stack[State.Stack.size() - 2].LastSpace;
+  }
   if (NextNonComment->is(TT_TemplateString) && NextNonComment->closesScope())
     return State.Stack[State.Stack.size() - 2].LastSpace;
   // Field labels in a nested type should be aligned to the brace. For example

clang/lib/Format/Format.cpp

@@ -1000,6 +1000,7 @@ template <> struct MappingTraits<FormatStyle> {
     IO.mapOptional("BreakBeforeBraces", Style.BreakBeforeBraces);
     IO.mapOptional("BreakBeforeInlineASMColon",
                    Style.BreakBeforeInlineASMColon);
+    IO.mapOptional("BreakBeforeTemplateClose", Style.BreakBeforeTemplateClose);
     IO.mapOptional("BreakBeforeTernaryOperators",
                    Style.BreakBeforeTernaryOperators);
     IO.mapOptional("BreakBinaryOperations", Style.BreakBinaryOperations);
@@ -1514,6 +1515,7 @@ FormatStyle getLLVMStyle(FormatStyle::LanguageKind Language) {
   LLVMStyle.BreakBeforeBraces = FormatStyle::BS_Attach;
   LLVMStyle.BreakBeforeConceptDeclarations = FormatStyle::BBCDS_Always;
   LLVMStyle.BreakBeforeInlineASMColon = FormatStyle::BBIAS_OnlyMultiline;
+  LLVMStyle.BreakBeforeTemplateClose = false;
   LLVMStyle.BreakBeforeTernaryOperators = true;
   LLVMStyle.BreakBinaryOperations = FormatStyle::BBO_Never;
   LLVMStyle.BreakConstructorInitializers = FormatStyle::BCIS_BeforeColon;

clang/unittests/Format/ConfigParseTest.cpp

@@ -162,6 +162,7 @@ TEST(ConfigParseTest, ParsesConfigurationBools) {
   CHECK_PARSE_BOOL(BinPackArguments);
   CHECK_PARSE_BOOL(BreakAdjacentStringLiterals);
   CHECK_PARSE_BOOL(BreakAfterJavaFieldAnnotations);
+  CHECK_PARSE_BOOL(BreakBeforeTemplateClose);
   CHECK_PARSE_BOOL(BreakBeforeTernaryOperators);
   CHECK_PARSE_BOOL(BreakStringLiterals);
   CHECK_PARSE_BOOL(CompactNamespaces);

clang/unittests/Format/FormatTest.cpp

@@ -11077,6 +11077,84 @@ TEST_F(FormatTest, WrapsTemplateDeclarationsWithComments) {
       Style);
 }
 
+TEST_F(FormatTest, BreakBeforeTemplateClose) {
+  FormatStyle Style = getGoogleStyle(FormatStyle::LK_Cpp);
+  Style.ColumnLimit = 0;
+  verifyNoChange("template <typename Foo>\n"
+                 "void foo() {}",
+                 Style);
+  verifyNoChange("template <\n"
+                 "    typename Foo,\n"
+                 "    typename Bar>\n"
+                 "void foo() {}",
+                 Style);
+  // when BreakBeforeTemplateClose is off, this line break is removed:
+  verifyFormat("template <\n"
+               "    typename Foo,\n"
+               "    typename Bar>\n"
+               "void foo() {}",
+               "template <\n"
+               "    typename Foo,\n"
+               "    typename Bar\n"
+               ">\n"
+               "void foo() {}",
+               Style);
+  Style.BreakBeforeTemplateClose = true;
+  // BreakBeforeTemplateClose should NOT force multiline templates
+  verifyNoChange("template <typename Foo>\n"
+                 "void foo() {}",
+                 Style);
+  verifyNoChange("template <typename Foo, typename Bar>\n"
+                 "void foo() {}",
+                 Style);
+  // it should allow a line break:
+  verifyNoChange("template <\n"
+                 "    typename Foo\n"
+                 ">\n"
+                 "void foo() {}",
+                 Style);
+  verifyNoChange("template <\n"
+                 "    typename Foo,\n"
+                 "    typename Bar\n"
+                 ">\n"
+                 "void foo() {}",
+                 Style);
+  // it should add a line break if not already present:
+  verifyFormat("template <\n"
+               "    typename Foo\n"
+               ">\n"
+               "void foo() {}",
+               "template <\n"
+               "    typename Foo>\n"
+               "void foo() {}",
+               Style);
+  verifyFormat("template <\n"
+               "    typename Foo,\n"
+               "    typename Bar\n"
+               ">\n"
+               "void foo() {}",
+               "template <\n"
+               "    typename Foo,\n"
+               "    typename Bar>\n"
+               "void foo() {}",
+               Style);
+  // when within an indent scope, the > should be placed appropriately:
+  verifyFormat("struct Baz {\n"
+               "  template <\n"
+               "      typename Foo,\n"
+               "      typename Bar\n"
+               "  >\n"
+               "  void foo() {}\n"
+               "};",
+               "struct Baz {\n"
+               "  template <\n"
+               "      typename Foo,\n"
+               "      typename Bar>\n"
+               "  void foo() {}\n"
+               "};",
+               Style);
+}
+
 TEST_F(FormatTest, WrapsTemplateParameters) {
   FormatStyle Style = getLLVMStyle();
   Style.AlignAfterOpenBracket = FormatStyle::BAS_DontAlign;