Merge 2023-02 CWG Motion 3

P2796R0 Core Language Working Group "ready" issues for the February, 2023 meeting; issue 2518

Author: tkoeppe

source/declarations.tex

@@ -257,14 +257,32 @@
 is contextually converted to \keyword{bool} and
 the converted expression shall be a constant expression\iref{expr.const}.
 If the value of the expression when
-so converted is \tcode{true}, the declaration has no
-effect. Otherwise, the program is ill-formed, and the resulting
+so converted is \tcode{true}
+or the expression is evaluated in the context of a template definition,
+the declaration has no
+effect. Otherwise,
+the \grammarterm{static_assert-declaration} fails,
+the program is ill-formed, and the resulting
 diagnostic message\iref{intro.compliance} should include the text of
 the \grammarterm{string-literal}, if one is supplied.
 \begin{example}
 \begin{codeblock}
 static_assert(sizeof(int) == sizeof(void*), "wrong pointer size");
 static_assert(sizeof(int[2]));          // OK, narrowing allowed
+
+template <class T>
+void f(T t) {
+  if constexpr (sizeof(T) == sizeof(int)) {
+    use(t);
+  } else {
+    static_assert(false, "must be int-sized");
+  }
+}
+
+void g(char c) {
+  f(0);                                 // OK
+  f(c);                                 // error on implementations where \tcode{sizeof(int) > 1}: must be \tcode{int}-sized
+}
 \end{codeblock}
 \end{example}
 

source/intro.tex

@@ -800,23 +800,37 @@
 \end{footnote}
 that program.
 \item
+\indextext{behavior!undefined}%
+If a program contains a violation of a rule for which no diagnostic is required,
+this document places no requirement on implementations
+with respect to that program.
+\item
 \indextext{message!diagnostic}%
-If a program contains a violation of any diagnosable rule or an occurrence
+Otherwise, if a program contains a violation of any diagnosable rule or an occurrence
 of a construct described in this document as ``conditionally-supported'' when
 the implementation does not support that construct, a conforming implementation
 shall issue at least one diagnostic message.
-\item
-\indextext{behavior!undefined}%
-If a program contains a violation of a rule for which no diagnostic
-is required, this document places no requirement on
-implementations with respect to that program.
 \end{itemize}
 \begin{note}
 During template argument deduction and substitution,
 certain constructs that in other contexts require a diagnostic
 are treated differently;
 see~\ref{temp.deduct}.
 \end{note}
+Furthermore, a conforming implementation
+\begin{itemize}
+\item
+shall not accept a preprocessing translation unit containing
+a \tcode{\#error} preprocessing directive\iref{cpp.error},
+\item
+shall issue at least one diagnostic message for
+each \tcode{\#warning} or \tcode{\#error} preprocessing directive
+not following a \tcode{\#error} preprocessing directive in
+a preprocessing translation unit, and
+\item
+shall not accept a translation unit with
+a \grammarterm{static_assert-declaration} that fails\iref{dcl.pre}.
+\end{itemize}
 
 \pnum
 \indextext{conformance requirements!library|(}%

source/lex.tex

@@ -33,7 +33,7 @@
 and source files included\iref{cpp.include} via the preprocessing
 directive \tcode{\#include}, less any source lines skipped by any of the
 conditional inclusion\iref{cpp.cond} preprocessing directives, is
-called a \defn{translation unit}.
+called a \defnadj{preprocessing}{translation unit}.
 \begin{note}
 A \Cpp{} program need not all be translated at the same time.
 \end{note}
@@ -168,8 +168,10 @@
 
 \item Whitespace characters separating tokens are no longer
 significant. Each preprocessing token is converted into a
-token\iref{lex.token}. The resulting tokens are syntactically and
-semantically analyzed and translated as a translation unit.
+token\iref{lex.token}. The resulting tokens
+constitute a \defn{translation unit} and
+are syntactically and
+semantically analyzed and translated.
 \begin{note}
 The process of analyzing and translating the tokens can occasionally
 result in one token being replaced by a sequence of other

source/templates.tex

@@ -4444,7 +4444,9 @@
 The program is ill-formed, no diagnostic required, if:
 \begin{itemize}
 \item
-no valid specialization can be generated for a template
+no valid specialization,
+ignoring \grammarterm{static_assert-declaration}{s} that fail,
+can be generated for a template
 or a substatement of a constexpr if statement\iref{stmt.if} within a template
 and the template is not instantiated, or
 \item