Also detect --menhir flag

Signed-off-by: Nicolás Ojeda Bär <n.oje.bar@gmail.com>

src/dune_rules/menhir/menhir_rules.ml

@@ -193,7 +193,7 @@ module Run (P : PARAMS) = struct
      is the three-step process where Menhir is invoked twice and OCaml type
      inference is performed in between. *)
 
-  let process3 base ~cmly (stanza : stanza) : unit Memo.t =
+  let process3 base ~cmly ~explain (stanza : stanza) : unit Memo.t =
     let open Memo.O in
     let expanded_flags = expand_flags stanza.flags in
     (* 1. A first invocation of Menhir creates a mock [.ml] file. *)
@@ -234,7 +234,7 @@ module Run (P : PARAMS) = struct
     let* () =
       Module_compilation.ocamlc_i ~deps cctx mock_module ~output:(inferred_mli base)
     in
-    let explain_flags = explain_flags base stanza.explain in
+    let explain_flags = explain_flags base (stanza.explain || explain) in
     (* 3. A second invocation of Menhir reads the inferred [.mli] file. *)
     menhir
       [ Command.Args.dyn expanded_flags
@@ -254,9 +254,9 @@ module Run (P : PARAMS) = struct
   (* [process3 stanza] converts a Menhir stanza into a set of build rules. This
      is a simpler one-step process where Menhir is invoked directly. *)
 
-  let process1 base ~cmly (stanza : stanza) : unit Memo.t =
+  let process1 base ~cmly ~explain (stanza : stanza) : unit Memo.t =
     let expanded_flags = expand_flags stanza.flags in
-    let explain_flags = explain_flags base stanza.explain in
+    let explain_flags = explain_flags base (stanza.explain || explain) in
     menhir
       [ Command.Args.dyn expanded_flags
       ; S explain_flags
@@ -278,22 +278,23 @@ module Run (P : PARAMS) = struct
 
   let process (stanza : stanza) : unit Memo.t =
     let base = Option.value_exn stanza.merge_into in
-    let ocaml_type_inference_disabled, cmly =
+    let ocaml_type_inference_disabled, cmly, explain =
       Ordered_set_lang.Unexpanded.fold_strings
         stanza.flags
-        ~init:(false, false)
-        ~f:(fun pos sw ((only_tokens, cmly) as acc) ->
+        ~init:(false, false, false)
+        ~f:(fun pos sw ((only_tokens, cmly, explain) as acc) ->
           match pos with
           | Neg -> acc
           | Pos ->
             (match String_with_vars.text_only sw with
-             | Some "--only-tokens" -> true, cmly
-             | Some "--cmly" -> only_tokens, true
+             | Some "--only-tokens" -> true, cmly, explain
+             | Some "--cmly" -> only_tokens, true, explain
+             | Some "--explain" -> only_tokens, cmly, true
              | Some _ | None -> acc))
     in
     if ocaml_type_inference_disabled || not stanza.infer
-    then process1 base stanza ~cmly
-    else process3 base stanza ~cmly
+    then process1 base stanza ~cmly ~explain
+    else process3 base stanza ~cmly ~explain
   ;;
 
   (* ------------------------------------------------------------------------ *)

test/blackbox-tests/test-cases/menhir/explain.t

@@ -84,6 +84,9 @@ Let's check that the conflicts file has been generated successfully:
   START . 
 
 
+
+
+
 Let's check that it stops being generated if we remove the (explain) field:
 
   $ cat >dune <<EOF
@@ -99,3 +102,44 @@ Let's check that it stops being generated if we remove the (explain) field:
   Warning: in total, 1 production is never reduced.
 
   $ ! test -f _build/default/parser.conflicts
+
+Let's check that we can also generate the .conflicts file by passing the --explain flag directly:
+
+  $ cat >dune <<EOF
+  > (menhir (modules parser) (flags --explain))
+  > (library (name lib))
+  > EOF
+
+  $ dune build
+  Warning: one state has reduce/reduce conflicts.
+  Warning: one reduce/reduce conflict was arbitrarily resolved.
+  File "parser.mly", line 4, characters 15-20:
+  Warning: production start -> START is never reduced.
+  Warning: in total, 1 production is never reduced.
+
+  $ cat _build/default/parser.conflicts
+
+  ** Conflict (reduce/reduce) in state 1.
+  ** Token involved: #
+  ** This state is reached from start after reading:
+
+  START
+
+  ** The derivations that appear below have the following common factor:
+  ** (The question mark symbol (?) represents the spot where the derivations begin to differ.)
+
+  start // lookahead token is inherited
+  (?)
+
+  ** In state 1, looking ahead at #, reducing production
+  ** start -> START
+  ** is permitted because of the following sub-derivation:
+
+  START . 
+
+  ** In state 1, looking ahead at #, reducing production
+  ** start -> START
+  ** is permitted because of the following sub-derivation:
+
+  START . 
+