Newlines in some constructs within interpolated regular string literals

[svick]

When looking at the spec for interpolated string literals because of dotnet/roslyn#26814, I found some discrepancies: as far as I can tell, the lexical grammar says that in some specific cases, newlines should be allowed within interpolated regular (i.e. non-verbatim) string literals.

Specifically, those cases are when the single_regular_balanced_text_character rule is not used and instead one of the rules delimited_comment, string_literal or interpolated_string_literal is used.

I think the intention is that newlines should not be allowed in those cases and the compiler does not allow them.

Consider this expression:

$"{@"
"}"

I believe the lexical grammar in the spec says this should be parsed as:

• interpolated_string_literal
• '$' interpolated_regular_string_literal
• '$' interpolated_regular_string_start interpolated_regular_string_literal_body interpolated_regular_string_end
• '$' '"' interpolated_regular_string_character* '{' interpolated_regular_string_literal_body interpolated_regular_string_end
• '$' '"' '{' interpolated_regular_string_literal_body interpolated_regular_string_end
• '$' '"' '{' regular_balanced_text interpolated_regular_string_end
• '$' '"' '{' regular_balanced_text_part+ interpolated_regular_string_end
• '$' '"' '{' regular_balanced_text_part interpolated_regular_string_end
• '$' '"' '{' string_literal interpolated_regular_string_end
• '$' '"' '{' verbatim_string_literal interpolated_regular_string_end
• '$' '"' '{' '@"' verbatim_string_literal_character* '"' interpolated_regular_string_end
• '$' '"' '{' '@"' verbatim_string_literal_character '"' interpolated_regular_string_end
• '$' '"' '{' '@"' '<Line feed character (U+000A)>' '"' interpolated_regular_string_end
• '$' '"' '{' '@"' '<Line feed character (U+000A)>' '"' interpolation_format? '}' interpolated_regular_string_characters_after_brace? '"'
• '$' '"' '{' '@"' '<Line feed character (U+000A)>' '"' '}' interpolated_regular_string_characters_after_brace? '"'
• '$' '"' '{' '@"' '<Line feed character (U+000A)>' '"' '}' '"'

Thus, according to my reading of the spec, this expression should be valid, even though it goes against the presumed intention of interpolated regular string literals and even though the compiler does not allow it.

Is this really a bug in the spec? If not, where am I wrong?

[Joe4evr]

Should maybe be noted: adding one more @ character solves it.

[svick]

@Joe4evr Right, that turns the expression into an interpolated verbatim string literal, where newlines are allowed.

[jcouv]

Tagging @gafter

[Unknown6656]

Also consider allowing:

IEnumerable <...> list = ...;
string s = $"This is my enumeration: {string.Join(", ", from x in list
                                                        where x.SomeCondition
                                                        select Process(x))}";

[CyrusNajmabadi]

@svick My reading of the spec agrees with yours.