clang-format: Add SpaceBeforeTemplateParameterList option

[MyDeveloperDay]

Summary

Adds an option to control whether a space is inserted between "template" and "<". Currently a space is always inserted (as the LLVM style requires), but to me this seems like the less popular option.

Looking at a few files from Mozilla and Chromium they seem to also skip the space. Should this option be disabled for their styles?

[djasper]

This has come up before (read up on the list) and the decision is not to support it. In short, this is so un-important, that it is not worth a configuration option.

[MyDeveloperDay]

This revision would require unit tests to proceed

[MyDeveloperDay]

Style guide suggesting enforcing a space after template keyword

https://mesos.readthedocs.io/en/1.1.0/c++-style-guide/

[MyDeveloperDay]

include/clang/Format/Format.h

500

I suggest we make this an enumeration

enum {
Unaltered,
Never,
Always,
}

Introducing this into a codebase means we need to select a suitable default, doing nothing would in my view be the best default and introducing anything new now will cause a tidal wave of changes on any existing formatted code base

LLVM alone it pretty much 50/50 on if they use a space or not

[MyDeveloperDay]

This I believe is covered by SpaceAfterTemplateKeyword which does the same thing

include/clang/Format/Format.h

enum SpaceBeforeParensOptions {
     /// when determined by other style rules (after unary operators, opening
     /// parentheses, etc.)
     SBPO_Always
   };
 
   /// \brief Defines in which cases to put a space before opening parentheses.
   SpaceBeforeParensOptions SpaceBeforeParens;
 
+  /// If \c true, a space is inserted between 'template' and the opening angle
+  /// bracket of a template parameter list.
+  bool SpaceBeforeTemplateParameterList;
+
   /// \brief If \c true, spaces may be inserted into '()'.
   bool SpaceInEmptyParentheses;
 
   /// \brief The number of spaces before trailing line comments
   /// (\c // - comments).
   ///
   /// This does not affect trailing block comments (\c /**/ - comments) as those
   /// commonly have different usage patterns and a number of special cases.
return AccessModifierOffset == R.AccessModifierOffset &&
            PenaltyBreakFirstLessLess == R.PenaltyBreakFirstLessLess &&
            PenaltyBreakString == R.PenaltyBreakString &&
            PenaltyExcessCharacter == R.PenaltyExcessCharacter &&
            PenaltyReturnTypeOnItsOwnLine == R.PenaltyReturnTypeOnItsOwnLine &&
            PointerAlignment == R.PointerAlignment &&
            SpaceAfterCStyleCast == R.SpaceAfterCStyleCast &&
            SpaceBeforeAssignmentOperators == R.SpaceBeforeAssignmentOperators &&
            SpaceBeforeParens == R.SpaceBeforeParens &&
+           SpaceBeforeTemplateParameterList ==
+               R.SpaceBeforeTemplateParameterList &&
            SpaceInEmptyParentheses == R.SpaceInEmptyParentheses &&
            SpacesBeforeTrailingComments == R.SpacesBeforeTrailingComments &&
            SpacesInAngles == R.SpacesInAngles &&
            SpacesInContainerLiterals == R.SpacesInContainerLiterals &&
            SpacesInCStyleCastParentheses == R.SpacesInCStyleCastParentheses &&
            SpacesInParentheses == R.SpacesInParentheses &&
            SpacesInSquareBrackets == R.SpacesInSquareBrackets &&
            Standard == R.Standard && TabWidth == R.TabWidth &&

lib/Format/Format.cpp

static void mapping(IO &IO, FormatStyle &Style) {
     IO.mapOptional("PenaltyReturnTypeOnItsOwnLine",
                    Style.PenaltyReturnTypeOnItsOwnLine);
     IO.mapOptional("SortIncludes", Style.SortIncludes);
     IO.mapOptional("PointerAlignment", Style.PointerAlignment);
     IO.mapOptional("SpaceAfterCStyleCast", Style.SpaceAfterCStyleCast);
     IO.mapOptional("SpaceBeforeAssignmentOperators",
                    Style.SpaceBeforeAssignmentOperators);
     IO.mapOptional("SpaceBeforeParens", Style.SpaceBeforeParens);
+    IO.mapOptional("SpaceBeforeTemplateParameterList",
+                   Style.SpaceBeforeTemplateParameterList);
     IO.mapOptional("SpaceInEmptyParentheses", Style.SpaceInEmptyParentheses);
     IO.mapOptional("SpacesBeforeTrailingComments",
                    Style.SpacesBeforeTrailingComments);
     IO.mapOptional("SpacesInAngles", Style.SpacesInAngles);
     IO.mapOptional("SpacesInContainerLiterals",
                    Style.SpacesInContainerLiterals);
     IO.mapOptional("SpacesInCStyleCastParentheses",
                    Style.SpacesInCStyleCastParentheses);
FormatStyle getLLVMStyle() {
   LLVMStyle.UseTab = FormatStyle::UT_Never;
   LLVMStyle.SpacesInParentheses = false;
   LLVMStyle.SpacesInSquareBrackets = false;
   LLVMStyle.SpaceInEmptyParentheses = false;
   LLVMStyle.SpacesInContainerLiterals = true;
   LLVMStyle.SpacesInCStyleCastParentheses = false;
   LLVMStyle.SpaceAfterCStyleCast = false;
   LLVMStyle.SpaceBeforeParens = FormatStyle::SBPO_ControlStatements;
+  LLVMStyle.SpaceBeforeTemplateParameterList = true;
   LLVMStyle.SpaceBeforeAssignmentOperators = true;
   LLVMStyle.SpacesInAngles = false;
 
   LLVMStyle.PenaltyBreakComment = 300;
   LLVMStyle.PenaltyBreakFirstLessLess = 120;
   LLVMStyle.PenaltyBreakString = 1000;
   LLVMStyle.PenaltyExcessCharacter = 1000000;
   LLVMStyle.PenaltyReturnTypeOnItsOwnLine = 60;

lib/Format/TokenAnnotator.cpp

if (Left.is(tok::l_paren) && Right.is(tok::r_paren))
     return Style.SpaceInEmptyParentheses;
   if (Left.is(tok::l_paren) || Right.is(tok::r_paren))
     return (Right.is(TT_CastRParen) ||
             (Left.MatchingParen && Left.MatchingParen->is(TT_CastRParen)))
                ? Style.SpacesInCStyleCastParentheses
                : Style.SpacesInParentheses;
   if (Right.isOneOf(tok::semi, tok::comma))
     return false;
+  if (Right.is(tok::less) && Left.is(tok::kw_template))
+    return Style.SpaceBeforeTemplateParameterList;
   if (Right.is(tok::less) &&
-      (Left.is(tok::kw_template) ||
-       (Line.Type == LT_ObjCDecl && Style.ObjCSpaceBeforeProtocolList)))
+      (Line.Type == LT_ObjCDecl && Style.ObjCSpaceBeforeProtocolList))
     return true;
   if (Left.isOneOf(tok::exclaim, tok::tilde))
     return false;
   if (Left.is(tok::at) &&
       Right.isOneOf(tok::identifier, tok::string_literal, tok::char_constant,
                     tok::numeric_constant, tok::l_paren, tok::l_brace,
                     tok::kw_true, tok::kw_false))
     return false;