merlin-lib 4.9-501preview

Error log

The package failed to build. The error log from opam follows.

Opam plugin "depext" may require upgrading/reinstalling. Reinstall the plugin on the current switch? [Y/n] y
The following actions will be performed:
  - recompile opam-depext 1.2.1-1

<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
-> retrieved opam-depext.1.2.1-1  (cached)
-> removed   opam-depext.1.2.1-1
-> installed opam-depext.1.2.1-1
Done.

<><> opam-depext.1.2.1-1 installed successfully <><><><><><><><><><><><><><><><>
=> opam-depext is unnecessary when used with opam >= 2.1. Please use opam install directly instead
# Run eval $(opam env) to update the current shell environment

<><> Carrying on to "opam depext -viy merlin.4.9-501preview yojson.2.1.2 seq.base ocamlfind.1.9.6 merlin-lib.4.9-501preview dune.3.13.0 dot-merlin-reader.4.9 csexp.1.5.2 cppo.1.6.9" 

You are using opam 2.1+, where external dependency handling has been integrated: consider calling opam directly, the 'depext' plugin interface is provided for backwards compatibility only
# Detecting depexts using vars: arch=x86_64, os=linux, os-distribution=debian, os-family=debian
[ERROR] No solution for merlin.4.9-501preview & yojson.2.1.2 & seq.base & ocamlfind.1.9.6 & merlin-lib.4.9-501preview & dune.3.13.0 & dot-merlin-reader.4.9 & csexp.1.5.2 & cppo.1.6.9:   * No agreement on the version of ocaml:
            - (invariant) -> ocaml-base-compiler >= 5.1.1 -> ocaml = 5.1.1
            - merlin = 4.9-501preview -> ocaml < 5.1.1
            You can temporarily relax the switch invariant with `--update-invariant'
          * Incompatible packages:
            - (invariant) -> ocaml-base-compiler >= 5.1.1
            - merlin = 4.9-501preview -> ocaml < 5.1.1 -> dkml-base-compiler
          * Missing dependency:
            - merlin = 4.9-501preview -> ocaml < 5.1.1 -> ocaml-base-compiler < 3.07+1 | ocaml-system < 3.07+1 | ocaml-variants < 3.8~
            not available because the package is pinned to version 5.1.1
            unmet availability conditions: 'sys-ocaml-version = "3.07"'
            no matching version
          * Missing dependency:
            - merlin = 4.9-501preview -> ocaml < 5.1.1 -> ocaml-base-compiler = 3.07+1 | ocaml-system = 3.07+1 | ocaml-variants < 3.8~
            not available because the package is pinned to version 5.1.1
            unmet availability conditions: 'sys-ocaml-version = "3.07+1"'
            no matching version
          * Missing dependency:
            - merlin = 4.9-501preview -> ocaml < 5.1.1 -> ocaml-base-compiler = 3.07+2 | ocaml-system = 3.07+2 | ocaml-variants < 3.8~
            not available because the package is pinned to version 5.1.1
            unmet availability conditions: 'sys-ocaml-version = "3.07+2"'
            no matching version
          * Missing dependency:
            - merlin = 4.9-501preview -> ocaml < 5.1.1 -> ocaml-base-compiler = 3.08.0 | ocaml-system < 3.08.1~ | ocaml-variants < 3.08.1~
            not available because the package is pinned to version 5.1.1
            unmet availability conditions, e.g. 'sys-ocaml-version = "3.08.0"'
            no matching version
          * Missing dependency:
            - merlin = 4.9-501preview -> ocaml < 5.1.1 -> ocaml-base-compiler = 3.08.1 | ocaml-system < 3.08.2~ | ocaml-variants < 3.08.2~
            not available because the package is pinned to version 5.1.1
            unmet availability conditions, e.g. 'sys-ocaml-version = "3.08.1"'
            no matching version
          * Missing dependency:
            - merlin = 4.9-501preview -> ocaml < 5.1.1 -> ocaml-base-compiler = 3.08.2 | ocaml-system < 3.08.3~ | ocaml-variants < 3.08.3~
            not available because the package is pinned to version 5.1.1
            unmet availability conditions, e.g. 'sys-ocaml-version = "3.08.2"'
            no matching version
          * Missing dependency:
            - merlin = 4.9-501preview -> ocaml < 5.1.1 -> ocaml-base-compiler = 3.08.3 | ocaml-system < 3.08.4~ | ocaml-variants < 3.08.4~
            not available because the package is pinned to version 5.1.1
            unmet availability conditions, e.g. 'sys-ocaml-version = "3.08.3"'
            no matching version
          * Missing dependency:
            - merlin = 4.9-501preview -> ocaml < 5.1.1 -> ocaml-base-compiler = 3.08.4 | ocaml-system < 3.08.5~ | ocaml-variants < 3.08.5~
            not available because the package is pinned to version 5.1.1
            unmet availability conditions, e.g. 'sys-ocaml-version = "3.08.4"'
            no matching version
          * Missing dependency:
            - merlin = 4.9-501preview -> ocaml < 5.1.1 -> ocaml-base-compiler = 3.09.0 | ocaml-system < 3.09.1~ | ocaml-variants < 3.09.1~
            not available because the package is pinned to version 5.1.1
            unmet availability conditions, e.g. 'sys-ocaml-version = "3.09.0"'
            no matching version
          * Missing dependency:
            - merlin = 4.9-501preview -> ocaml < 5.1.1 -> ocaml-variants >= 4.05.1 -> ocaml-beta
            unmet availability conditions: 'enable-ocaml-beta-repository'


Command failed: opam --cli=2.1 list --readonly --external '--resolve=merlin.4.9-501preview,yojson.2.1.2,seq.base,ocamlfind.1.9.6,merlin-lib.4.9-501preview,dune.3.13.0,dot-merlin-reader.4.9,csexp.1.5.2,cppo.1.6.9' returned 20