dolmen_type.0.5 lower bounds failure with seq

[mseri]

Fails with

#=== ERROR while compiling dolmen_type.0.5 ====================================#
# context              2.1.2 | linux/x86_64 | ocaml-base-compiler.4.14.0 | file:///home/opam/opam-repository
# path                 ~/.opam/4.14/.opam-switch/build/dolmen_type.0.5
# command              ~/.opam/opam-init/hooks/sandbox.sh build dune build -p dolmen_type -j 31
# exit-code            1
# env-file             ~/.opam/log/dolmen_type-24-0fa409.env
# output-file          ~/.opam/log/dolmen_type-24-0fa409.out
### output ###
# (cd _build/default && /home/opam/.opam/4.14/bin/ocamlc.opt -w -40 -g -bin-annot -I src/typecheck/.dolmen_type.objs/byte -I /home/opam/.opam/4.14/lib/dolmen -I /home/opam/.opam/4.14/lib/dolmen/intf -I /home/opam/.opam/4.14/lib/dolmen/smtlib2 -I /home/opam/.opam/4.14/lib/dolmen/std -I /home/opam/.opam/4.14/lib/dolmen/tptp -I /home/opam/.opam/4.14/lib/spelll -I /home/opam/.opam/4.14/lib/uutf -intf-suffix .ml -no-alias-deps -open Dolmen_type -o src/typecheck/.dolmen_type.objs/byte/dolmen_type__Misc.cmo -c -impl src/typecheck/misc.ml)
# File "src/typecheck/misc.ml", line 241, characters 23-48:
# 241 |     match seq_to_list_ (I.retrieve ~limit:0 t s) with
#                              ^^^^^^^^^^^^^^^^^^^^^^^^^
# Error: This expression has type 'a Seq/1.t
#        but an expression was expected of type
#          'b Stdlib.Seq.t = unit -> 'b Stdlib.Seq.node
#        Seq/1.t is abstract because no corresponding cmi file was found in path.
# (cd _build/default && /home/opam/.opam/4.14/bin/ocamlopt.opt -w -40 -g -I src/typecheck/.dolmen_type.objs/byte -I src/typecheck/.dolmen_type.objs/native -I /home/opam/.opam/4.14/lib/dolmen -I /home/opam/.opam/4.14/lib/dolmen/intf -I /home/opam/.opam/4.14/lib/dolmen/smtlib2 -I /home/opam/.opam/4.14/lib/dolmen/std -I /home/opam/.opam/4.14/lib/dolmen/tptp -I /home/opam/.opam/4.14/lib/spelll -I /home/opam/.opam/4.14/lib/uutf -intf-suffix .ml -no-alias-deps -open Dolmen_type -o src/typecheck/.dolmen_type.objs/native/dolmen_type__Misc.cmx -c -impl src/typecheck/misc.ml)
# File "src/typecheck/misc.ml", line 241, characters 23-48:
# 241 |     match seq_to_list_ (I.retrieve ~limit:0 t s) with
#                              ^^^^^^^^^^^^^^^^^^^^^^^^^
# Error: This expression has type 'a Seq/1.t
#        but an expression was expected of type
#          'b Stdlib.Seq.t = unit -> 'b Stdlib.Seq.node
#        Seq/1.t is abstract because no corresponding cmi file was found in path.

See discussion in https://github.com/ocaml/opam-repository/pull/21570#discussion_r901589037 (this is also where the issue was noticed)

[Gbury]

Is there a way to know what versions of the dependencies trigger this build failure ?

[mseri]

It appeared downgrading seq from base to 0.2.2 on ocaml >= 4.12. I cannot find the old ci run due to the force push unfortunately, but you should be able to replicate by installing dolmen 0.5 on ocaml >= 4.12 and use https://github.com/ocaml/opam-repository/wiki/Lower-bound-check---DYI

[Gbury]

thanks, i'll look into that

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[Gbury]

Sorry for being late on this one.

So after a bit of searching it appears that the main root of the problem is an unfortunate interaction between dune's implicit_transitive_deps and the seq compatibility package (plus a small mistake on my part of course, ^^).

Basically, the spelll package (used directly by dolmen_type) uses the seq compatibility package, and exposes some function returning a _ Seq.t which resolves the the definition of the seq package, which aliases it to _ Stdlib.Seq.t.

Now, the problem is that dolmen does not declare a dependance on seq because when reading the doc of spelll I naively assumed Seq.t referrred to the stdlib one, whereas it refers to the one from seq.

Since dolmen_type does not have seq in its dependencies, and it uses (implicit_transitive_deps false), then the cmis of seq are not visible when compiling dolmen_type and thus without the type equality between seq's Seq.t and the stdlib's, we have the type error.

The following patch fixes the build error locally:

diff --git a/dolmen_type.opam b/dolmen_type.opam
index 6ab32a1e..00e04a8f 100644
--- a/dolmen_type.opam
+++ b/dolmen_type.opam
@@ -13,6 +13,7 @@ depends: [
   "dolmen" {= version }
   "dune" { >= "2.7" }
   "spelll"
+  "seq"
   "uutf"
   "odoc" { with-doc }
 ]
diff --git a/src/typecheck/dune b/src/typecheck/dune
index 2c47267c..1dbbafe1 100644
--- a/src/typecheck/dune
+++ b/src/typecheck/dune
@@ -4,7 +4,7 @@
   (instrumentation (backend bisect_ppx))
   (libraries
     ; external deps
-    spelll uutf
+    spelll uutf seq
     ; dolmen standard deps
     dolmen dolmen.std dolmen.intf
     ; some additional explicit deps for version types

I don't know if you prefer that I create a version 0.5.1 with the patch, or if it's better to change the 0.5 release with this patch.

[kit-ty-kate]

The best course of action would be to simply add:

conflicts: [
  "seq" {!= "base"}
]

to dolmen_type.0.5. This is already the only way people are successfully compiling dolmen_type.0.5 so this would only enforce it.

[Gbury]

Ok, do you want me to make a PR for that ?

[kit-ty-kate]

Yes please, that would be highly welcome