Warn instead of failing on opam files

CHANGES.md

@@ -28,6 +28,9 @@ unreleased
 - Do not list private modules in the generated index. (#2009, fix #2008,
   @rgrinberg)
 
+- Warn instead of failing if an opam file fails to parse. This opam file can
+  still be used to define scope. (#2023, @rgrinberg)
+
 1.8.2 (10/03/2019)
 ------------------
 

src/dune_project.ml

@@ -612,9 +612,21 @@ let load ~dir ~files =
       match Filename.split_extension fn with
       | (pkg, ".opam") when pkg <> "" ->
         let version_from_opam_file =
-          let opam = Opam_file.load (Path.relative dir fn) in
-          match Opam_file.get_field opam "version" with
-          | Some (String (_, s)) -> Some s
+          let open Option.O in
+          let* opam =
+            let opam_file = Path.relative dir fn in
+            match Opam_file.load opam_file with
+            | s -> Some s
+            | exception exn ->
+              Errors.warn (Loc.in_file opam_file)
+                "Unable to read opam file. This package's version field will\
+                 be [email protected]: %a@."
+                Exn.pp exn;
+              None
+          in
+          let* version = Opam_file.get_field opam "version" in
+          match version with
+          | String (_, s) -> Some s
           | _ -> None
         in
         let name = Package.Name.of_string pkg in

src/stdune/exn.ml

@@ -52,7 +52,10 @@ let pp_uncaught ~backtrace fmt exn =
      | @{<error>Internal error@}: Uncaught exception.\n\
      %s\n\
      \\%s@."
-    line s line;
+    line s line
+
+let pp fmt exn =
+  Format.pp_print_string fmt (Printexc.to_string exn)
 
 include
   ((struct

src/stdune/exn.mli

@@ -34,6 +34,8 @@ val protectx : 'a -> f:('a -> 'b) -> finally:('a -> unit) -> 'b
 
 val pp_uncaught : backtrace:string -> Format.formatter -> t -> unit
 
+val pp : Format.formatter -> t -> unit
+
 val raise_with_backtrace: exn -> Printexc.raw_backtrace -> _
 
 val equal : t -> t -> bool