OCaml Changelog


Read the latest releases and updates from the OCaml ecosystem.

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  • Ppx processes are now executed correctly (#513)

Breaking Change

  • ocamllsp drops support for .merlin files, and as a consequence no longer depends on dot-merlin-reader. (#523)


  • New code action to automatically remove values, types, opens (#502)
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  • Fix debouncing of document updates. It was essentially completely broken in all but the most trivial cases. (#509 fixes #504)

  • Fix completion when passing named and functional arguments (#512)

On behalf of the ocaml-lsp team, I’m pleased to announce version 1.8.0. This release contains some quality of life bug fixes, better diagnostics locations, and a few new code actions. Happy hacking.

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  • Add a new code action Add missing rec keyword, which is available when adding a rec keyword can fix Unbound value ... error, e.g.,

    let fact n = if n = 0 then 1 else n * fact (n - 1)
                                      (* ^^^^ Unbound value fact *)

    Adding rec to the definition of fact will fix the problem. The new code action offers adding rec.

  • Use ocamlformat to properly format type snippets. This feature requires the ocamlformat-rpc opam package to be installed. (#386)

  • Add completion support for polymorphic variants, when it is possible to pin down the precise type. Examples (<|> stands for the cursor) when completion will work (#473)

    Function application:

    let foo (a: [`Alpha | `Beta]) = ()
    foo `A<|>

    Type explicitly shown:

    let a : [`Alpha | `Beta] = `B<|>

    Note: this is actually a bug fix, since we were ignoring the backtick when constructing the prefix for completion.

  • Parse merlin errors (best effort) into a more structured form. This allows reporting all locations as "related information" (#475)

  • Add support for Merlin Construct command as completion suggestions, i.e., show complex expressions that could complete the typed hole. (#472)

  • Add a code action Construct an expression that is shown when the cursor is at the end of the typed hole, i.e., _|, where | is the cursor. The code action simply triggers the client (currently only VS Code is supported) to show completion suggestions. (#472)

  • Change the formatting-on-save error notification to a warning notification (#472)

  • Code action to qualify ("put module name in identifiers") and unqualify ("remove module name from identifiers") module names in identifiers (#399)

    Starting from:

    open Unix
    let times = Unix.times ()
    let f x = x.Unix.tms_stime, x.Unix.tms_utime

    Calling "remove module name from identifiers" with the cursor on the open statement will produce:

    open Unix
    let times = times ()
    let f x = x.tms_stime, x.tms_utime

    Calling "put module name in identifiers" will restore:

    open Unix
    let times = Unix.times ()
    let f x = x.Unix.tms_stime, x.Unix.tms_utime


  • Handle workspace change notifications. Previously, the server would only use the set of workspaces given at startup to search for workspace symbols. After this change, workspace folders that are added later will also be considered. (#498)

  • Do not show "random" documentation on hover

  • Correctly rename a variable used as a named/optional argument (#478)

  • When reporting an error at the beginning of the file, use the first line not the second (#489)

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  • Add sub-errors as "related" information in diagnostics (#457)

  • Add support for navigating to a symbol inside a workspace (#398)

  • Show typed holes as errors

    Merlin has a concept of "typed holes" that are syntactically represented as _. Files that incorporate typed holes are not considered valid OCaml, but Merlin and OCaml-LSP support them. One example when such typed holes can occur is when on "destructs" a value, e.g., destructing (Some 1) will generate code match Some 1 with Some _ -> _ | None -> _. While the first underscore is a valid "match-all"/wildcard pattern, the rest of underscores are typed holes.

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  • Switch verbosity from 1 to 0. This is the same default that merlin uses. The old value for verbosity (#433)

  • Get fresh diagnostics (warning and error messages) on a file save (#438)

    Note: If you want the fresh diagnostics to take into account changes in other files, you likely need to rebuild your project. An easy way to get automatic rebuilds is to run dune in a watching mode, e.g.,[dune build --watch].

On behalf of the ocaml-lsp team, I'd like to announce version 1.6.0 of ocaml-lsp-server. The highlight of this release is the updated version of merlin which brings lots of new bug fixes.

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  • Code action to annotate a value with its type (#397)


  • Fix interface/implementation switching on Windows (#427)

  • Correctly parse project paths with spaces and other special characters that must be escaped.

  • Print types with -short-paths even if the project wasn't built yet

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  • Support 4.12 and drop support for all earlier versions

  • Update to the latest version of merlin

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  • Backport fixes from merlin (#382, #383)

  • Encode request & notification params in a list. This is required by the spec. (#351)

On behalf of the ocaml-lsp team, it is my pleasure to announce version 1.4.0. This release introduces support for automatic signature help. Signature help is not yet present in all possible contexts. We intend to improve to support as many relevant language constructs as possible in the future. Many thanks to @mnxn for implementing this feature.

The full change log is replicated at the end of this post for your convenience.

Happy Holidays!

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  • Support cancellation notifications when possible. (#323)

  • Implement signature help request for functions (#324)

  • Server LSP requests & notifications concurrently. Requests that require merlin are still serialized. (#330)

On behalf of the ocaml-lsp team, I’d like to announce version 1.3.0.

This release an improvement in keyword completion and a new code action. Keywords are now filtered by the context the user requested the completion, and there’s a new code action to quickly populate .mli files with the the inferred types from the .ml file.

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  • Code action to insert inferred module interface (#308)

  • Filter keywords by context (#307)

On behalf of the ocaml-lsp team, I’d like to announce version 1.2.0.

This version contains many bug fixes and some performance improvements A couple of interesting features made it in as well:

  • Auto-completion of OCaml keywords (not available for reason)
  • The ability to jump to the declaration of a value in the .mli.
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  • Add keyword completion

  • Add go to declaration functionality to jump to a value's specification in a .mli file (#294)


  • #245: correctly use mutexes on OpenBSD (#264)

  • #268: Do not use vendored libraries when building the lsp package (#260)

  • #271: Clear diagnostics when files are closed

  • Disable non-prefix completion. There's no reliably way to trigger it and it can be slow.

If you want to contribute to a new release announcement, check out the Contributing Guide on GitHub.