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P1854R4 Making non-encodable string literals ill-formed #6317

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Jul 16, 2023
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P1854R4 Making non-encodable string literals ill-formed #6317

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56 changes: 12 additions & 44 deletions source/lex.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -1436,42 +1436,21 @@
\indextext{type!\idxcode{char32_t}}%
\indextext{wide-character}%
\indextext{type!\idxcode{wchar_t}}%
A \defnx{non-encodable character literal}{literal!character!non-encodable}
is a \grammarterm{character-literal}
whose \grammarterm{c-char-sequence} consists of a single \grammarterm{c-char}
that is not a \grammarterm{numeric-escape-sequence} and
that specifies a character
that either lacks representation in the literal's associated character encoding
or that cannot be encoded as a single code unit.
A \defnadj{multicharacter}{literal} is a \grammarterm{character-literal}
whose \grammarterm{c-char-sequence} consists of
more than one \grammarterm{c-char}.
The \grammarterm{encoding-prefix} of
a non-encodable character literal or a multicharacter literal
shall be absent.
Such \grammarterm{character-literal}s are conditionally-supported.
A multicharacter literal shall not have an \grammarterm{encoding-prefix}.
If a multicharacter literal contains a \grammarterm{c-char}
that is not encodable as a single code unit in the ordinary literal encoding,
the program is ill-formed.
Multicharacter literals are conditionally-supported.

\pnum
The kind of a \grammarterm{character-literal},
its type, and its associated character encoding\iref{lex.charset}
are determined by
its \grammarterm{encoding-prefix} and its \grammarterm{c-char-sequence}
as defined by \tref{lex.ccon.literal}.
The special cases for
non-encodable character literals and multicharacter literals
take precedence over the base kind.
\begin{note}
The associated character encoding for ordinary character literals
determines encodability,
but does not determine the value of
non-encodable ordinary character literals or
ordinary multicharacter literals.
The examples in \tref{lex.ccon.literal}
for non-encodable ordinary character literals assume that
the specified character lacks representation in
the ordinary literal encoding or
that encoding the character would require more than one code unit.
\end{note}

\begin{floattable}{Character literals}{lex.ccon.literal}
{l|l|l|l|l}
Expand All @@ -1482,15 +1461,10 @@
none &
\defnx{ordinary character literal}{literal!character!ordinary} &
\keyword{char} &
ordinary &
ordinary literal &
\tcode{'v'} \\ \cline{2-3}\cline{5-5}
&
non-encodable ordinary character literal &
\keyword{int} &
literal &
\tcode{'\textbackslash U0001F525'} \\ \cline{2-3}\cline{5-5}
&
ordinary multicharacter literal &
multicharacter literal &
\keyword{int} &
encoding &
\tcode{'abcd'} \\ \hline
Expand Down Expand Up @@ -1522,8 +1496,7 @@
the value of a \grammarterm{character-literal} is determined
using the range of representable values
of the \grammarterm{character-literal}'s type in translation phase 7.
A non-encodable character literal or a multicharacter literal
has an
A multicharacter literal has an
\impldef{value of non-encodable character literal or multicharacter literal}
value.
The value of any other kind of \grammarterm{character-literal}
Expand All @@ -1537,12 +1510,10 @@
\grammarterm{universal-character-name}
is the code unit value of the specified character
as encoded in the literal's associated character encoding.
\begin{note}
If the specified character lacks
representation in the literal's associated character encoding or
if it cannot be encoded as a single code unit,
then the literal is a non-encodable character literal.
\end{note}
then the program is ill-formed.
\item
A \grammarterm{character-literal} with
a \grammarterm{c-char-sequence} consisting of
Expand All @@ -1568,7 +1539,7 @@
$v$ does not exceed the range of representable values of the corresponding unsigned type for the underlying type of the \grammarterm{character-literal}'s type,
then the value is the unique value of the \grammarterm{character-literal}'s type \tcode{T} that is congruent to $v$ modulo $2^N$, where $N$ is the width of \tcode{T}.
\item
Otherwise, the \grammarterm{character-literal} is ill-formed.
Otherwise, the program is ill-formed.
\end{itemize}
\item
A \grammarterm{character-literal} with
Expand Down Expand Up @@ -2006,10 +1977,7 @@
is encoded to a code unit sequence
using the \grammarterm{string-literal}'s associated character encoding.
If a character lacks representation in the associated character encoding,
then the \grammarterm{string-literal} is conditionally-supported and
an
\impldef{code unit sequence for non-representable \grammarterm{string-literal}}
code unit sequence is encoded.
then the program is ill-formed.
\begin{note}
No character lacks representation in any Unicode encoding form.
\end{note}
Expand Down Expand Up @@ -2050,7 +2018,7 @@
the \grammarterm{string-literal}'s array element type \tcode{T}
that is congruent to $v$ modulo $2^N$, where $N$ is the width of \tcode{T}.
\item
Otherwise, the \grammarterm{string-literal} is ill-formed.
Otherwise, the program is ill-formed.
\end{itemize}
When encoding a stateful character encoding,
these sequences should have no effect on encoding state.
Expand Down