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JuliaSyntax: fix anonymous function parsing #60221

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JuliaSyntax: fix anonymous function parsing #60221

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21 changes: 17 additions & 4 deletions JuliaSyntax/src/julia/parser.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -2218,10 +2218,23 @@ function parse_function_signature(ps::ParseState, is_function::Bool)
opts = parse_brackets(ps, K")") do had_commas, had_splat, num_semis, num_subexprs
_parsed_call = was_eventually_call(ps)
_maybe_grouping_parens = !had_commas && !had_splat && num_semis == 0 && num_subexprs == 1
# Skip intervening newlines only when the parentheses hold a single
# expression, which is the ambiguous case between a name like (::T)
# and an anonymous function parameter list.
next_kind = peek(ps, 2, skip_newlines=_maybe_grouping_parens)
# Check if there's a newline between `)` and the next `(` or `.`.
# We need to find where `)` is and check what immediately follows it.
# If peek(1, skip_newlines=false) is `)`, we're directly before it.
# Otherwise there's whitespace/newline before `)`.
next_token_pos = if peek(ps, 1, skip_newlines=false) == K")"
# Directly before ), token after ) is at 2
2
else
# There's whitespace before ), so ) is at 2
# and what follows ) is at 3
3
end
token_after_paren = peek(ps, next_token_pos, skip_newlines=false)
# If token_after_paren is a newline, this is an anonymous function
has_newline_after_paren = _maybe_grouping_parens && token_after_paren == K"NewlineWs"
# Get the next significant token to determine if we need to parse a call
next_kind = peek(ps, 2, skip_newlines=_maybe_grouping_parens && !has_newline_after_paren)
Comment on lines +2221 to +2237
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@fogti fogti Dec 7, 2025 •
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I think it would make a lot of sense to split the logic with a case distinction on _maybe_grouping_parens:

Suggested change
# Check if there's a newline between `)` and the next `(` or `.`.
# We need to find where `)` is and check what immediately follows it.
# If peek(1, skip_newlines=false) is `)`, we're directly before it.
# Otherwise there's whitespace/newline before `)`.
next_token_pos = if peek(ps, 1, skip_newlines=false) == K")"
# Directly before ), token after ) is at 2
2
else
# There's whitespace before ), so ) is at 2
# and what follows ) is at 3
3
end
token_after_paren = peek(ps, next_token_pos, skip_newlines=false)
# If token_after_paren is a newline, this is an anonymous function
has_newline_after_paren = _maybe_grouping_parens && token_after_paren == K"NewlineWs"
# Get the next significant token to determine if we need to parse a call
next_kind = peek(ps, 2, skip_newlines=_maybe_grouping_parens && !has_newline_after_paren)
next_kind = if _maybe_grouping_parens
# Check if there's a newline between `)` and the next `(` or `.`.
# We need to find where `)` is and check what immediately follows it.
# If peek(1, skip_newlines=false) is `)`, we're directly before it.
# Otherwise there's whitespace/newline before `)`.
next_token_pos = if peek(ps, 1, skip_newlines=false) == K")"
# Directly before ), token after ) is at 2
2
else
# There's whitespace before ), so ) is at 2
# and what follows ) is at 3
3
end
token_after_paren = peek(ps, next_token_pos, skip_newlines=false)
# If token_after_paren is a newline, this is an anonymous function
# Get the next significant token to determine if we need to parse a call
peek(ps, 2, skip_newlines= token_after_paren != K"NewlineWs")
else
# Get the next significant token to determine if we need to parse a call
peek(ps, 2, skip_newlines=false)
end

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@fogti fogti Dec 7, 2025

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Subsequently, it makes sense to inspect more closely what happens if _maybe_grouping_parens is true: If the next tokens are:

  • K")", K"NewlineWs", then we call peek(ps, 2, skip_newlines=false) = token_after_paren
  • K")", !K"NewlineWs", then we call peek(ps, 2, skip_newlines=true) = token_after_paren
  • !K")", x/*we expect K")" here, but don't check that*/, K"NewlineWs", then we call peek(ps, 2, skip_newlines=false)=token_after_paren (I think (hope I interpret it correctly) that __lookahead_index treats the case with skip_newlines=true such that it also skips newlines entirely, including in the count up to n=2)
  • !K")", x, !K"NewlineWs", then we call peek(ps, 2, skip_newlines=false)=token_after_paren`

So, I think we can omit the peek(ps, 2, skip_newlines= token_after_paren != K"NewlineWs") entirely.

Suggested change
# Check if there's a newline between `)` and the next `(` or `.`.
# We need to find where `)` is and check what immediately follows it.
# If peek(1, skip_newlines=false) is `)`, we're directly before it.
# Otherwise there's whitespace/newline before `)`.
next_token_pos = if peek(ps, 1, skip_newlines=false) == K")"
# Directly before ), token after ) is at 2
2
else
# There's whitespace before ), so ) is at 2
# and what follows ) is at 3
3
end
token_after_paren = peek(ps, next_token_pos, skip_newlines=false)
# If token_after_paren is a newline, this is an anonymous function
has_newline_after_paren = _maybe_grouping_parens && token_after_paren == K"NewlineWs"
# Get the next significant token to determine if we need to parse a call
next_kind = peek(ps, 2, skip_newlines=_maybe_grouping_parens && !has_newline_after_paren)
next_token_pos = if _maybe_grouping_paren
# Check if there's a newline between `)` and the next `(` or `.`.
# We need to find where `)` is and check what immediately follows it.
# If peek(1, skip_newlines=false) is `)`, we're directly before it.
# Otherwise there's whitespace/newline before `)`.
if peek(ps, 1, skip_newlines=false) == K")"
# Directly before ), token after ) is at 2
2
else
# There's whitespace before ), so ) is at 2
# and what follows ) is at 3
3
end
else
2
end
# Get the next significant token to determine if we need to parse a call
next_kind = peek(ps, next_token_pos, skip_newlines=false)

_needs_parse_call = next_kind ∈ KSet"( ."
_is_anon_func = (!_needs_parse_call && !_parsed_call) || had_commas
return (needs_parameters = _is_anon_func,
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2 changes: 2 additions & 0 deletions JuliaSyntax/test/parser.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -611,6 +611,8 @@ tests = [
"macro \$f() end" => "(macro (call (\$ f)) (block))"
"macro (\$f)() end" => "(macro (call (parens (\$ f))) (block))"
"function (x) body end"=> "(function (tuple-p x) (block body))"
"function (x)\n body\nend"=> "(function (tuple-p x) (block body))"
"function (x)\n() end" => "(function (tuple-p x) (block (tuple-p)))"
"function (x,y) end" => "(function (tuple-p x y) (block))"
"function (x,y,) end" => "(function (tuple-p-, x y) (block))"
"function (x=1) end" => "(function (tuple-p (= x 1)) (block))"
Expand Down