change conversion interface to allow failure

Author: ceastlund

ast/cinaps/gen_versions.ml

@@ -272,7 +272,7 @@ module Structure = struct
       Print.indented (fun () ->
         Print.println
           "match Node.unwrap (Unversioned.Private.transparent t) ~version with";
-        Print.println "| { name = %S; data } -> %s data"
+        Print.println "| Some { name = %S; data } -> %s data"
           node_name
           (ast_to_ty ~grammar ty);
         Print.println "| _ -> None")
@@ -281,7 +281,7 @@ module Structure = struct
       Print.indented (fun () ->
         Print.println
           "match Node.unwrap (Unversioned.Private.transparent t) ~version with";
-        Print.println "| { name = %S" node_name;
+        Print.println "| Some { name = %S" node_name;
         Print.indented (fun () ->
           Print.println "; data = Record [| %s |]"
             (String.concat ~sep:"; "
@@ -298,7 +298,7 @@ module Structure = struct
       Print.indented (fun () ->
         Print.println
           "match Node.unwrap (Unversioned.Private.transparent t) ~version with";
-        Print.println "| { name = %S; data } ->" node_name;
+        Print.println "| Some { name = %S; data } ->" node_name;
         Print.indented (fun () ->
           Print.println "begin";
           Print.indented (fun () ->

ast/node.ml

@@ -4,5 +4,14 @@ let version t = t.version
 
 let wrap ~version ast = { version; ast }
 
-let rec unwrap ~version:dst_version { ast; version = src_version } =
-  Astlib.History.convert Astlib.history ast ~src_version ~dst_version ~unwrap ~wrap
+let rec convert ~version:dst_version { ast; version = src_version } =
+  let version, ast =
+    Astlib.History.convert Astlib.history ast ~src_version ~dst_version ~unwrap ~wrap
+  in
+  { version; ast }
+
+and unwrap ~version t =
+  let t = convert t ~version in
+  if Astlib.Version.equal t.version version
+  then Some t.ast
+  else None

ast/node.mli

@@ -2,4 +2,4 @@ type t
 
 val version : t -> Astlib.Version.t
 val wrap : version:Astlib.Version.t -> t Astlib.Ast.t -> t
-val unwrap : version:Astlib.Version.t -> t -> t Astlib.Ast.t
+val unwrap : version:Astlib.Version.t -> t -> t Astlib.Ast.t option