warning 52: change wording (Jacques Garrigue and Mark Shinwell)

Changes

@@ -47,6 +47,12 @@ OCaml 4.04.0:
   "transitive" heap size of a value
   (Alain Frisch, review by Marc Shinwell and Damien Doligez)
 
+### Manual:
+
+- PR#7245, GPR#565: clarification to the wording and documentation
+  of Warning 52 (fragile constant pattern)
+  (Gabriel Scherer, William, Adrien Nader, Jacques Garrigue)
+
 ### Build system:
 
 - GPR#324: Compiler developpers only: Adding new primitives to the

manual/manual/cmds/comp.etex

@@ -801,9 +801,9 @@ This section describes and explains in detail some warnings:
 
 >    | Foo "specific value" -> 0
 >          ^^^^^^^^^^^^^^^^
-> Warning 52: the argument of this constructor should not be matched against a
-> constant pattern; the actual value of the argument could change
-> in the future.
+> Warning 52: Code should not depend on the actual values of
+> this constructor's arguments. They are only for information
+> and may change in future versions. (See manual section 8.5)
 \end{verbatim}
 
   In particular, all built-in exceptions with a string argument have

utils/warnings.ml

@@ -438,9 +438,9 @@ let message = function
       Printf.sprintf "expected tailcall"
   | Fragile_literal_pattern ->
       Printf.sprintf
-        "the argument of this constructor should not be matched against a\n\
-         constant pattern; the actual value of the argument could change\n\
-         in the future."
+        "Code should not depend on the actual values of\n\
+         this constructor's arguments. They are only for information\n\
+         and may change in future versions. (See manual section 8.5)"
   | Unreachable_case ->
       "this match case is unreachable.\n\
        Consider replacing it with a refutation case '<pat> -> .'"