Merge 2022-07 CWG Motion 5

P2437R1 Support for #warning

Author: tkoeppe

source/preprocessor.tex

@@ -56,6 +56,7 @@
     \terminal{\# undef  } identifier new-line\br
     \terminal{\# line   } pp-tokens new-line\br
     \terminal{\# error  } \opt{pp-tokens} new-line\br
+    \terminal{\# warning} \opt{pp-tokens} new-line\br
     \terminal{\# pragma } \opt{pp-tokens} new-line\br
     \terminal{\# }new-line
 \end{bnf}
@@ -1603,18 +1604,21 @@
 one of the two previous forms, the behavior is undefined;
 otherwise, the result is processed as appropriate.
 
-\rSec1[cpp.error]{Error directive}%
+\rSec1[cpp.error]{Diagnostic directives}%
 \indextext{preprocessing directive!error}%
+\indextext{preprocessing directive!diagnostic}%
+\indextext{preprocessing directive!warning}%
 \indextext{\idxcode{\#error}|see{preprocessing directive, error}}
 
 \pnum
-A preprocessing directive of the form
+A preprocessing directive of either of the following forms
 \begin{ncsimplebnf}
-\terminal{\# error} \opt{pp-tokens} new-line
+\terminal{\# error} \opt{pp-tokens} new-line\br
+\terminal{\# warning} \opt{pp-tokens} new-line
 \end{ncsimplebnf}
 causes the implementation to produce
-a diagnostic message that should include the specified sequence of preprocessing tokens,
-and renders the program ill-formed.
+a diagnostic message that should include the specified sequence of preprocessing tokens;
+the \tcode{\# error} directive renders the program ill-formed.
 
 \rSec1[cpp.pragma]{Pragma directive}%
 \indextext{preprocessing directive!pragma}%