filter unavailable optional libs for utop

CHANGES.md

@@ -19,6 +19,9 @@ next
 - Fix compatibility with OCaml 4.12.0 when compiling empty archives; no .a file
   is generated. (#3576, @dra27)
 
+- `$ dune utop` no longer tries to load optional libraries that are unavailable
+  (#3612, fixes #3188, @anuragsoni)
+
 2.6.1 (02/07/2020)
 ------------------
 

src/dune/utop.ml

@@ -51,7 +51,15 @@ let libs_and_ppx_under_dir sctx ~db ~dir =
                  Implementations are selected using the default implementation
                  feature. *)
               let not_impl = Option.is_none (Lib_info.implements info) in
-              if not_impl && Path.is_descendant ~of_:(Path.build dir) src_dir
+              let not_hidden =
+                match Lib_info.enabled info with
+                | Normal -> true
+                | Optional -> Result.is_ok (Lib.requires lib)
+                | Disabled_because_of_enabled_if -> false
+              in
+              if
+                not_impl && not_hidden
+                && Path.is_descendant ~of_:(Path.build dir) src_dir
               then
                 match Lib_info.kind info with
                 | Lib_kind.Ppx_rewriter _

test/blackbox-tests/dune.inc

@@ -1338,6 +1338,14 @@
    test-cases/github3180
    (progn (run dune-cram run run.t) (diff? run.t run.t.corrected)))))
 
+(rule
+ (alias github3188)
+ (deps (package dune) (source_tree test-cases/github3188) (alias test-deps))
+ (action
+  (chdir
+   test-cases/github3188
+   (progn (run dune-cram run run.t) (diff? run.t run.t.corrected)))))
+
 (rule
  (alias github3440)
  (deps (package dune) (source_tree test-cases/github3440) (alias test-deps))
@@ -3121,6 +3129,7 @@
   (alias github3043)
   (alias github3046)
   (alias github3180)
+  (alias github3188)
   (alias github3440)
   (alias github3490)
   (alias github3530)

test/blackbox-tests/gen_tests.ml

@@ -253,6 +253,7 @@ let exclusions =
   ; make "mdx-stanza" ~external_deps:true
   ; make "toplevel-integration" ~external_deps:true
   ; make "bisect-ppx/main" ~external_deps:true
+  ; make "github3188" ~external_deps:true
   ]
   |> String_map.of_list_map_exn ~f:(fun (test : Test.t) -> (test.path, test))
 

test/blackbox-tests/test-cases/github3188/run.t

@@ -0,0 +1,15 @@
+This test makes sure that the utop subcommand does not load optional libraries.
+
+  $ mkdir testutop
+  $ cat <<EOF > testutop/dune
+  > (library
+  >  (name testutop)
+  >  (optional)
+  >  (libraries does_not_exist))
+  > EOF
+  $ echo 'let run () = print_endline "this will never run"' > testutop/testutop.ml
+  $ echo "(lang dune 2.0)" > dune-project
+  $ echo 'let () = print_endline "No Error"' > init_test.ml
+
+  $ dune utop testutop -- init_test.ml
+  No Error