[clang-format] Add BreakBeforeTemplateCloser option (#118046)

In clang-format, multiline templates have the `>` on the same line as
the last parameter:

```c++
template <
    typename Foo,
    typename Bar>
void foo() {
```

I would like to add an option to put the `>` on the next line, like
this:

```c++
template <
    typename Foo,
    typename Bar
>
void foo() {
```

An example of a large project that uses this style is NVIDIA's CUTLASS,
here is an example:


https://github.com/NVIDIA/cutlass/blob/main/include/cutlass/epilogue/dispatch_policy.hpp#L149-L156

My reasoning is that it reminds me of this style of braces:

```c++
if (foo()) {
    bar();
    baz();}
```

Most people agree this is better:

```c++
if (foo()) {
    bar();
    baz();
}
```

---------

Co-authored-by: Owen Pan <owenpiano@gmail.com>

4 files changed, 38 insertions, 16 deletions

diff --git a/clang/lib/Format/ContinuationIndenter.cpp b/clang/lib/Format/ContinuationIndenter.cpp
index 6f7d213..3e51b4aa 100644
--- a/clang/lib/Format/ContinuationIndenter.cpp
+++ b/clang/lib/Format/ContinuationIndenter.cpp
@@ -349,6 +349,13 @@ bool ContinuationIndenter::canBreak(const LineState &State) {
     }
   }
 
+  // Don't allow breaking before a closing brace of a block-indented braced list
+  // initializer if there isn't already a break.
+  if (Current.is(tok::r_brace) && Current.MatchingParen &&
+      Current.isBlockIndentedInitRBrace(Style)) {
+    return CurrentState.BreakBeforeClosingBrace;
+  }
+
   // Allow breaking before the right parens with block indentation if there was
   // a break after the left parens, which is tracked by BreakBeforeClosingParen.
   if (Style.AlignAfterOpenBracket == FormatStyle::BAS_BlockIndent &&
@@ -356,12 +363,8 @@ bool ContinuationIndenter::canBreak(const LineState &State) {
     return CurrentState.BreakBeforeClosingParen;
   }
 
-  // Don't allow breaking before a closing brace of a block-indented braced list
-  // initializer if there isn't already a break.
-  if (Current.is(tok::r_brace) && Current.MatchingParen &&
-      Current.isBlockIndentedInitRBrace(Style)) {
-    return CurrentState.BreakBeforeClosingBrace;
-  }
+  if (Style.BreakBeforeTemplateCloser && Current.is(TT_TemplateCloser))
+    return CurrentState.BreakBeforeClosingAngle;
 
   // If binary operators are moved to the next line (including commas for some
   // styles of constructor initializers), that's always ok.
@@ -414,6 +417,8 @@ bool ContinuationIndenter::mustBreak(const LineState &State) {
   }
   if (CurrentState.BreakBeforeClosingParen && Current.is(tok::r_paren))
     return true;
+  if (CurrentState.BreakBeforeClosingAngle && Current.is(TT_TemplateCloser))
+    return true;
   if (Style.Language == FormatStyle::LK_ObjC &&
       Style.ObjCBreakBeforeNestedBlockParam &&
       Current.ObjCSelectorNameParts > 1 &&
@@ -1243,6 +1248,9 @@ unsigned ContinuationIndenter::addTokenOnNewLine(LineState &State,
         Style.AlignAfterOpenBracket == FormatStyle::BAS_BlockIndent;
   }
 
+  if (PreviousNonComment && PreviousNonComment->is(TT_TemplateOpener))
+    CurrentState.BreakBeforeClosingAngle = Style.BreakBeforeTemplateCloser;
+
   if (CurrentState.AvoidBinPacking) {
     // If we are breaking after '(', '{', '<', or this is the break after a ':'
     // to start a member initializer list in a constructor, this should not
@@ -1379,6 +1387,10 @@ unsigned ContinuationIndenter::getNewLineColumn(const LineState &State) {
       State.Stack.size() > 1) {
     return State.Stack[State.Stack.size() - 2].LastSpace;
   }
+  if (Style.BreakBeforeTemplateCloser && Current.is(TT_TemplateCloser) &&
+      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
diff --git a/clang/lib/Format/ContinuationIndenter.h b/clang/lib/Format/ContinuationIndenter.h
index 18441e1..ac354aa 100644
--- a/clang/lib/Format/ContinuationIndenter.h
+++ b/clang/lib/Format/ContinuationIndenter.h
@@ -200,14 +200,15 @@ struct ParenState {
       : Tok(Tok), Indent(Indent), LastSpace(LastSpace),
         NestedBlockIndent(Indent), IsAligned(false),
         BreakBeforeClosingBrace(false), BreakBeforeClosingParen(false),
-        AvoidBinPacking(AvoidBinPacking), BreakBeforeParameter(false),
-        NoLineBreak(NoLineBreak), NoLineBreakInOperand(false),
-        LastOperatorWrapped(true), ContainsLineBreak(false),
-        ContainsUnwrappedBuilder(false), AlignColons(true),
-        ObjCSelectorNameFound(false), HasMultipleNestedBlocks(false),
-        NestedBlockInlined(false), IsInsideObjCArrayLiteral(false),
-        IsCSharpGenericTypeConstraint(false), IsChainedConditional(false),
-        IsWrappedConditional(false), UnindentOperator(false) {}
+        BreakBeforeClosingAngle(false), AvoidBinPacking(AvoidBinPacking),
+        BreakBeforeParameter(false), NoLineBreak(NoLineBreak),
+        NoLineBreakInOperand(false), LastOperatorWrapped(true),
+        ContainsLineBreak(false), ContainsUnwrappedBuilder(false),
+        AlignColons(true), ObjCSelectorNameFound(false),
+        HasMultipleNestedBlocks(false), NestedBlockInlined(false),
+        IsInsideObjCArrayLiteral(false), IsCSharpGenericTypeConstraint(false),
+        IsChainedConditional(false), IsWrappedConditional(false),
+        UnindentOperator(false) {}
 
   /// \brief The token opening this parenthesis level, or nullptr if this level
   /// is opened by fake parenthesis.
@@ -280,6 +281,9 @@ struct ParenState {
   /// was a newline after the beginning left paren.
   bool BreakBeforeClosingParen : 1;
 
+  /// Whether a newline needs to be inserted before a closing angle `>`.
+  bool BreakBeforeClosingAngle : 1;
+
   /// Avoid bin packing, i.e. multiple parameters/elements on multiple
   /// lines, in this context.
   bool AvoidBinPacking : 1;
@@ -367,6 +371,8 @@ struct ParenState {
       return BreakBeforeClosingBrace;
     if (BreakBeforeClosingParen != Other.BreakBeforeClosingParen)
       return BreakBeforeClosingParen;
+    if (BreakBeforeClosingAngle != Other.BreakBeforeClosingAngle)
+      return BreakBeforeClosingAngle;
     if (QuestionColumn != Other.QuestionColumn)
       return QuestionColumn < Other.QuestionColumn;
     if (AvoidBinPacking != Other.AvoidBinPacking)
diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index f02bf95..387daad 100644
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -1014,6 +1014,8 @@ template <> struct MappingTraits<FormatStyle> {
     IO.mapOptional("BreakBeforeBraces", Style.BreakBeforeBraces);
     IO.mapOptional("BreakBeforeInlineASMColon",
                    Style.BreakBeforeInlineASMColon);
+    IO.mapOptional("BreakBeforeTemplateCloser",
+                   Style.BreakBeforeTemplateCloser);
     IO.mapOptional("BreakBeforeTernaryOperators",
                    Style.BreakBeforeTernaryOperators);
     IO.mapOptional("BreakBinaryOperations", Style.BreakBinaryOperations);
@@ -1535,6 +1537,7 @@ FormatStyle getLLVMStyle(FormatStyle::LanguageKind Language) {
   LLVMStyle.BreakBeforeBraces = FormatStyle::BS_Attach;
   LLVMStyle.BreakBeforeConceptDeclarations = FormatStyle::BBCDS_Always;
   LLVMStyle.BreakBeforeInlineASMColon = FormatStyle::BBIAS_OnlyMultiline;
+  LLVMStyle.BreakBeforeTemplateCloser = false;
   LLVMStyle.BreakBeforeTernaryOperators = true;
   LLVMStyle.BreakBinaryOperations = FormatStyle::BBO_Never;
   LLVMStyle.BreakConstructorInitializers = FormatStyle::BCIS_BeforeColon;
diff --git a/clang/lib/Format/TokenAnnotator.cpp b/clang/lib/Format/TokenAnnotator.cpp
index f25332e..94fd7ba 100644
--- a/clang/lib/Format/TokenAnnotator.cpp
+++ b/clang/lib/Format/TokenAnnotator.cpp
@@ -6180,6 +6180,9 @@ bool TokenAnnotator::canBreakBefore(const AnnotatedLine &Line,
     return false;
   }
 
+  if (Right.is(TT_TemplateCloser))
+    return Style.BreakBeforeTemplateCloser;
+
   if (Left.is(tok::at))
     return false;
   if (Left.Tok.getObjCKeywordID() == tok::objc_interface)
@@ -6328,8 +6331,6 @@ bool TokenAnnotator::canBreakBefore(const AnnotatedLine &Line,
   if (Right.is(TT_ImplicitStringLiteral))
     return false;
 
-  if (Right.is(TT_TemplateCloser))
-    return false;
   if (Right.is(tok::r_square) && Right.MatchingParen &&
       Right.MatchingParen->is(TT_LambdaLSquare)) {
     return false;