[cpp.line] Address string-literal vs s-char-sequence#8369
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AlisdairM
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| A preprocessing directive of the form | ||
| \begin{ncsimplebnf} | ||
| \terminal{\# line} digit-sequence \terminal{"} \opt{s-char-sequence} \terminal{"} new-line | ||
| \terminal{\# line} digit-sequence \terminal{"} \opt{string-literal} \terminal{"} new-line |
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No.
First, a string-literal includes the delimiting quotation marks, so this is a bad change.
Second, a string-literal allows for an encoding-prefix or rawness, but the status quo "form" match does not. So, this is a bad change, because it would appear to allow such prefixes (and we don't know what they mean in this context). A reference to "the character string literal" does not establish a suitable constraint.
Yes, p1 talks about a string-literal with zero context, and that's a bug that needs to be fixed, but this intro sentence is at issue, not the rest of the specification without further elaboration. What does C23 say in that area?
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The term "character string literal" is a well defined term establishing exactly that restriction, but if you prefer I will tackle this problem from the specification of what to do with the s-char-sequence instead.
My preferred resolution for C++29 would be to introduce character-string-literal as the quoted s-char-sequence in [lex.string], so that a string-literal is an encoding prefix followed by either a character-string-literal or a R raw-string-literal. That would allow us to use character-string-literal both here in [cpp.line] and [cpp.stringize], and potentially clean up other parts of the standard jumping around string literal syntax --- but that is more than I want to push into ballot review time, as that would clearly need Core review, better spent elsewhere.
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CWG2693 is related. |
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And see CWG3076 for the introduction of plain-string-literal (with no prefix), which might be useful here. But that's not editorial territory; there is too much subtlety to go wrong. |
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I have pushed a revision with the basis of my broader update, and will turn this into a draft PR. I suspect that my update will be in the direction of plain-string-literal but I think you cited the wrong core issue? Noted that the direction specifically for I will leave this now as potential C++29 material. |
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The text of this specification places a restriction on a string-literal that is not present in the grammar, although the grammar is an exact match for a string-literal with that restriction. The restricted term is also used when specifying the effects of the line directive with a string, so prefer to move string-literal into the grammar rather than strike that paragraph and adjust the effects. Added a cross-reference to where character string literal is defined as it may not be obvious to all readers that this is a term of power, even though it is defined as a term and has an index entry.
…terals There are several places in the grammar where we want to refer to a plain character string literal without a prefix and that is not raw. Introduce _character-string_ into the grammar to replace a quoted _s-char-sequence_ in a number of places, and move the `R` of a raw string literal into the _raw-string_ grammar so that _raw-string_ and _character-string_ are used consistently where they appear.
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The text of this specification places a restriction on a string-literal that is not present in the grammar, although the grammar is an exact match for a string-literal with that restriction.
The restricted term is also used when specifying the effects of the line directive with a string, so prefer to move string-literal into the grammar rather than strike that paragraph and adjust the specification for its effects.
Added a cross-reference to where character string literal is defined as it may not be obvious to all readers that this is a term of power, even though it is defined as a term and has an index entry.