Major simplification of the ocamlbuild code governing parser choice.

src/Makefile

@@ -53,8 +53,7 @@ bootstrap: .versioncheck stage1 stage2 stage3
 # Build Menhir using ocamlyacc.
 
 stage1:
-	@$(OCAMLBUILD) -build-dir _stage1 -tag yacc_parser \
-	  menhir.$(TARGET)
+	@$(OCAMLBUILD) -build-dir _stage1 menhir.$(TARGET)
 
 # ----------------------------------------------------------------------------
 # Stage 2.

src/_tags

@@ -2,9 +2,6 @@
 # This is disabled when shipping.    (my_warnings)
 <*>: my_warnings
 
-# Tag both parser source files with origin_parser.
-<{yacc-parser,fancy-parser}.mly>:origin_parser
-
 # Menhir needs the Unix library.
 <menhir.{byte,native}>: use_unix
 

src/myocamlbuild.ml

@@ -13,29 +13,22 @@ let flags () =
 
 (* ---------------------------------------------------------------------------- *)
 
-(* A command for copying a file. *)
-
-let copy_file_from_tag src dst env build =
-  Cmd (S [A "cp"; T (tags_of_pathname src); P dst])
-
-(* ---------------------------------------------------------------------------- *)
-
 (* Dealing with the two parsers. *)
 
 (* Just for fun, Menhir comes with two parsers for its own input files. One is
    called [yacc-parser.mly] and is built using [ocamlyacc]. The other is called
    [fancy-parser.mly] and is built using Menhir. It depends on [standard.mly].
    The choice between the two parsers is determined by the presence of the tag
-   [yacc_parser] or [fancy_parser]. *)
+   [fancy_parser]. *)
 
 let parser_rule () =
-  (* The three dependencies. *)  
-  flag_and_dep ["origin_parser"; "yacc_parser"]  (P "yacc-parser.mly");
-  flag_and_dep ["origin_parser"; "fancy_parser"] (P "fancy-parser.mly");
-  dep ["origin_parser"; "fancy_parser"] ["standard.mly"];
-  (* The two rules. *)
-  rule  "yacc-parser -> parser" ~prod:"parser.mly" (copy_file_from_tag  "yacc-parser.mly" "parser.mly");
-  rule "fancy-parser -> parser" ~prod:"parser.mly" (copy_file_from_tag "fancy-parser.mly" "parser.mly")
+  let source =
+    mark_tag_used "fancy_parser";
+    if Tags.mem "fancy_parser" (tags_of_pathname "")
+    then "fancy-parser.mly"
+    else "yacc-parser.mly"
+  in
+  copy_rule "create parser.mly" source "parser.mly"
 
 (* ---------------------------------------------------------------------------- *)