[clang-format] Excess characters in a line when formatting of BlockIndent.

[red1bluelost]

Using the following config on the below code does not properly break the code into BlockIndent as it should. The static_assert line is formatted to exceed 80 character column limit.

From toying around, I noticed that if I changed the angle brackets (<, >) into parenthesis ((, )), the line is formatted correctly.

---
Language:                                  Cpp
AlignAfterOpenBracket:                     BlockIndent
ColumnLimit:                               80
...

#include <iterator>
#include <type_traits>

template <typename Category> struct S {
  static_assert(std::is_base_of_v<std::output_iterator_tag, Category> || std::is_base_of_v<std::input_iterator_tag, Category>);
};

The correct formatting would be:

  static_assert(
    std::is_base_of_v<std::output_iterator_tag, Category> ||
    std::is_base_of_v<std::input_iterator_tag, Category>
  );

[llvmbot]

@llvm/issue-subscribers-clang-format

[rymiel]

It appears the BlockIndent logic does in fact only concern itself with parens:

llvm-project/clang/lib/Format/ContinuationIndenter.cpp

Lines 1042 to 1045 in 1d43966

	if (PreviousNonComment && PreviousNonComment->is(tok::l_paren)) {
	CurrentState.BreakBeforeClosingParen =
	Style.AlignAfterOpenBracket == FormatStyle::BAS_BlockIndent;
	}

llvm-project/clang/lib/Format/ContinuationIndenter.cpp

Lines 1151 to 1154 in 1d43966

	if (Style.AlignAfterOpenBracket == FormatStyle::BAS_BlockIndent &&
	Current.is(tok::r_paren) && State.Stack.size() > 1) {
	return State.Stack[State.Stack.size() - 2].LastSpace;
	}

Also worth noting is that canBreak is always false after a template closer, which also inhibits some things

llvm-project/clang/lib/Format/TokenAnnotator.cpp

Lines 4965 to 4968 in 1d43966

	if (Left.isOneOf(TT_TemplateCloser, TT_UnaryOperator) ||
	Left.is(tok::kw_operator)) {
	return false;
	}

[rymiel]

Oops. Turns out this is actually documented:

llvm-project/clang/docs/ClangFormatStyleOptions.rst

Lines 229 to 231 in 1d43966

	.. warning::
	Note: This currently only applies to parentheses.

Making this more of a feature request, I suppose?

[red1bluelost]

I think it might still be a bug. I'm a little more concerned with the fact that it formats the code to exceed 80 characters. I toyed with the penalties of raising PenaltyExcessCharacter to be massive but it would still exceed 80 characters.

Oddly, if I add || false at the end it will properly break the static assert line.

  static_assert(
    std::is_base_of_v<std::output_iterator_tag, Category> ||
    std::is_base_of_v<std::input_iterator_tag, Category> || false
  );

[rymiel]

Tentative patch: https://reviews.llvm.org/D140267

The issue was that no space was allowed between >). This patch allows for that, but I'm not sure if it'll break anything else

[gedare]

Cannot reproduce on main:

clang-format --style="{BasedOnStyle: llvm, AlignAfterOpenBracket: BlockIndent, ColumnLimit: 80}" a.c
#include <iterator>
#include <type_traits>

template <typename Category> struct S {
  static_assert(
      std::is_base_of_v<std::output_iterator_tag, Category> ||
      std::is_base_of_v<std::input_iterator_tag, Category>
  );
};

[rymiel]

Fixed by 46bf67d