From c7b9c2cd3e69ed0d30cd54d790a026508a5d8960 Mon Sep 17 00:00:00 2001
From: Jeremie Dimino <jdimino@janestreet.com>
Date: Thu, 29 Mar 2018 15:04:14 -0400
Subject: [PATCH] Fix #661: better error when a public library is defined twice

---
 CHANGES.md   |  5 ++++-
 src/scope.ml | 19 ++++++++++++++++++-
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/CHANGES.md b/CHANGES.md
index 8fae978d..4aaaf113 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -34,7 +34,10 @@ next
 
 - Fix a regression introduced by beta19 where the generated merlin
   files didn't include the right `-ppx` flags in some cases (#658
-  fixess #657 @diml)
+  fixes #657 @diml)
+
+- Fix error messaage when a public library is defined twice. Before
+  jbuilder would raise an uncaught exception (Fixes #661, @diml)
 
 1.0+beta19.1 (21/03/2018)
 -------------------------
diff --git a/src/scope.ml b/src/scope.ml
index e376c1f7..844e1769 100644
--- a/src/scope.ml
+++ b/src/scope.ml
@@ -77,7 +77,24 @@ module DB = struct
           match lib.public with
           | None -> None
           | Some p -> Some (p.name, lib.scope_name))
-        |> String_map.of_list_exn
+        |> String_map.of_list
+        |> function
+        | Ok x -> x
+        | Error (name, _, _) ->
+          match
+            List.filter_map internal_libs ~f:(fun (_dir, lib) ->
+              match lib.public with
+              | None   -> None
+              | Some p -> Option.some_if (name = p.name) lib.buildable.loc)
+          with
+          | [] | [_] -> assert false
+          | loc1 :: loc2 :: _ ->
+            die "Public library %S is defined twice:\n\
+                 - %s\n\
+                 - %s"
+              name
+              (Loc.to_file_colon_line loc1)
+              (Loc.to_file_colon_line loc2)
       in
       Lib.DB.create ()
         ~parent:installed_libs