Implement and document --infer-protocol-supported.

doc/macros.tex

@@ -135,6 +135,7 @@
 \newcommand{\oinfer}{\oo{infer}}
 \newcommand{\oinferwrite}{\oo{infer-write-query}}
 \newcommand{\oinferread}{\oo{infer-read-reply}}
+\newcommand{\oinferprotocolsupported}{\oo{infer-protocol-supported}}
 \newcommand{\oinspection}{\oo{inspection}}
 \newcommand{\ointerpret}{\oo{interpret}}
 \newcommand{\ointerpretshowcst}{\oo{interpret-show-cst}}

doc/main.tex

@@ -3839,6 +3839,16 @@ assumes that the file \nt{sigfilename} contains the result of running
 so as to obtain the \ocaml type of every semantic action, then proceeds
 normally to generate a parser.
 
+\docskip
+
+This protocol was introduced on 2018/05/23; earlier versions of \menhir do not
+support it. Its existence can be tested as follows:
+
+\docswitch{\oinferprotocolsupported} When invoked with this switch,
+\menhir immediately terminates with exit code 0. An earlier version
+of \menhir, which does not support this protocol, would display a
+help message and terminate with a nonzero exit code.
+
 \subsection{Compilation flags}
 \label{sec:build:flags}
 

src/settings.ml

@@ -307,6 +307,7 @@ let options = Arg.align [
   "--follow-construction", Arg.Set follow, " (undocumented)";
   "--graph", Arg.Set graph, " Write a dependency graph to a .dot file";
   "--infer", Arg.Unit enable_infer, " Invoke ocamlc to do type inference";
+  "--infer-protocol-supported", Arg.Unit (fun () -> exit 0), " Stop with exit code 0";
   "--infer-write-query", Arg.String enable_write_query, "<filename> Write mock .ml file";
   "--infer-read-reply", Arg.String enable_read_reply, "<filename> Read inferred .mli file";
   "--inspection", Arg.Set inspection, " Generate the inspection API";