package lsp

  1. Overview
  2. Docs



  • Fix missing super & subscripts in markdown documentation. (#1170)

  • Do not invoke dune at all if --fallback-read-dot-merlin flag is on. (#1173)

  • Fix semantic highlighting of infix operators that contain '.'. (#1186)

  • Disable highlighting unit as an enum member to fix comment highlighting bug. (#1185)

  • Improve type-on-hover and type-annotate efficiency by only formatting the type of the first enclosing. (#1191, #1196)

  • Fix the encoding of URI's to match how vscode does it (#1197)

  • Fix parsing of completion prefixes (#1181)


  • Compatibility with Odoc 2.3.0, with support for the introduced syntax: tables, and "codeblock output" (#1184)

  • Display text of references in doc strings (#1166)

  • Add mark/remove unused actions for open, types, for loop indexes, modules, match cases, rec, and constructors (#1141)

  • Offer auto-completion for the keyword in (#1217)



  • Fix file permissions used when specifying output files of pp and ppx. (#1153)



  • Support building with OCaml 5.0 and 5.1 (#1150)



  • Disable code lens by default. The support can be re-enabled by explicitly setting it in the configuration. (#1134)

  • Fix initilization of ocamlformat-rpc in some edge cases when ocamlformat is initialized concurrently (#1132)

  • Kill unnecessary $ dune ocaml-merlin with SIGTERM rather than SIGKILL (#1124)

  • Refactor comment parsing to use odoc-parser and cmarkit instead of octavius and omd (#1088)

    This allows users who migrated to omd 2.X to install ocaml-lsp-server in the same opam switch.

    We also slightly improved markdown generation support and fixed a couple in the generation of inline heading and module types.

  • Allow opening documents that were already open. This is a workaround for neovim's lsp client (#1067)

  • Disable type annotation for functions (#1054)

  • Respect codeActionLiteralSupport capability (#1046)

  • Fix a document syncing issue when utf-16 is the position encoding (#1004)

  • Disable "Type-annotate" action for code that is already annotated. (#1037), fixes #1036

  • Fix semantic highlighting of long identifiers when using preprocessors (#1049, fixes #1034)

  • Fix the type of DocumentSelector in cram document registration (#1068)

  • Accept the --clientProcessId command line argument. (#1074)

  • Accept --port as a synonym for --socket. (#1075)

  • Fix connecting to dune rpc on Windows. (#1080)


  • Add "Remove type annotation" code action. (#1039)

  • Support settings through didChangeConfiguration notification (#1103)

  • Add "Extract local" and "Extract function" code actions. (#870)

  • Depend directly on merlin-lib 4.9 (#1070)



  • Fix race condition when a document was being edited and dune in watch mode was running (#1005, fixes #941, #1003)



  • Enable semantic highlighting support by default (#933)

  • Support connecting over pipes and socket. Pipes on Windows aren't yet supported (#946)

    More about communication channels in LSP specification.

  • Re-enable ocamlformat-rpc for formatting code snippets (but not files and not on Windows) (#920, #939)

    One needs to have installed either ocamlformat package version > 0.21.0 or, otherwise, ocamlformat-rpc package. Note that previously ocamlformat-rpc came in a standalone OPAM package, but since ocamlformat version > 0.21.0, it comes within ocamlformat package.

  • Add custom ocamllsp/hoverExtended request (#561)

  • Support utf-8 position encoding clients (#919)

    More about position encoding in LSP specification.

  • Show unwrapped module alias types on hovering over module names. This is due to upgrading to merlin 4.7 and using merlin's verbosity=smart by default (#942)


  • Respect the client's completion item resolve and preSelect capabilities (#925, #936)

  • Disable polling for dune's watch mode on Windows and OCaml 4.14.0 (#935)

  • Fix semantic highlighting of "long identifiers," e.g., Foo.Bar.x (#932)

  • Fix syncing of document contents:

    • For ranges that span an entire line (#927)

    • Previously, whole line edits would incorrectly eat the newline characters (#971)



  • Fix random requests failing after switching documents (#904, fixes #898)

  • Do not offer related diagnostic information unless the user enables in client capabilities (#905)

  • Do not offer diagnostic tags unless the client supports them (#909)

  • Do not attach extra data to diagnostics unless the client supports this (#910)

  • Use /bin/sh instead of /bin/bash. This fixes ocamllsp on NixOS



  • Fix various server crashes when opening non OCaml/Reason files. Files such as dune, cram, etc. would cause the server to crash. (#884, fixes #871)

  • Ignore unknown tags in merlin configuration to improve forward compatibility with Dune. (#883)



  • Code action for inlining let bindings within a module or expression. (#847)

  • Tag "unused code" and "deprecated" warnings, allowing clients to better display them. (#848)

  • Refresh merlin configuration after every dune build in watch mode (#853)


  • Respect showDocument capabilities. Do not offer commands or code actions that rely on this request without client support. (#836)

  • Fix signatureHelp on .mll files: avoid "Document.dune" exceptions



  • Fix cwd when executing ppx (#805)



  • Code actions for jumping to related files (.ml, .mli, etc.) (#795)


  • Allow cancellation of workspace symbols requests (#777)

  • Fix unintentionally interleaved jsonrpc IO that would corrupt the session (#786)

  • Ignore SIGPIPE . (#788)



  • Fix a bad interaction between inferred interfaces and promotion code actions in watch mode (#753)

  • Fix URI parsing (#739 fixes #471 and #459)



  • Fix shutting down an already closed socket (#740)



  • Fix preprocessing, ppx, and reason support (#735 fixes #696, #706)

  • Support include in folding ranges (#730)



  • Fix cancellation mechanism for all requests (#707)

  • Allow cancellation of formatting requests (#707)

  • Add --fallback-read-dot-merlin to the LSP Server (#705). If ocamllsp is started with this new flag, it will fall back to looking for Merlin configuration in .merlin files rather than calling dune ocaml-merlin. (#705)

  • Support folding more ranges (#692)



  • Stop leaking file descriptors like a sieve (#701)


  • Fix process termination. Once the lsp server is stepped, the process will gracefully terminate (#697, fixes #694)

  • Forward stderr from dune's merlin configuration to the lsp server's stderr (#697)



  • Fix bug with large buffers being resized incorrectly in Lev

  • Add folding ranges for more AST types (#680)



  • Enable dune rpc integration by default (#691, fixes #690)



  • Fix running external processes on Windows



  • Fix Uri handling on Windows

  • Fix build on MSVC 2015



  • Add support for dune in watch mode. The lsp server will now display build errors in the diagnostics and offer promotion code actions.

  • Re-introduce ocamlformat-rpc (#599, fixes #495)


  • Fix workspace symbols that could have a wrong path in some cases (#675)



  • Compatiblity with OCaml 4.14.0



  • Patch merlin to remove the result module



  • Use newer versions of ocamlformat-rpc-lib (fixes #697)



  • Fix more debouncing bugs (#629)



  • Catch merlin desturct exceptions (#626)

  • Fix broken debouncing (#627)



  • Fix executing ppx executables



  • Add better support for code folding: more folds and more precise folds


  • Fix infer interface code action crash when implementation source does not exist (#597)

  • Improve error message when the reason plugin for merlin is absent (#608)

  • Fix chdir races when running ppx (#550)

  • More accurate completion kinds. New completion kinds for variants and fields. Removed inaccurate completion kinds for constructors and types. (#510)

  • Fix handling request cancellation (#616)



  • Disable functionality reliant on ocamlformat-rpc for now (#555)

  • 4.13 compatiblity

1.9.0 (11/21/2021)


  • 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)

1.8.3 (09/26/2021)

  • 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)

1.8.2 (09/14/2021)

  • Disable experimental dune support. It was accidentally left enabled.

1.8.1 (09/12/2021)

  • Update to latest merlin.

1.8.0 (08/19/2021)


  • 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)


  • 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


  • 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)

1.7.0 (07/28/2021)


  • 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.

1.6.1 (05/17/2020)


  • 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].

1.6.0 (04/30/2020)


  • 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

1.5.0 (03/18/2020)

  • Support 4.12 and drop support for all earlier versions

  • Update to the latest version of merlin

1.4.1 (03/16/2020)


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

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

1.4.0 (12/17/2020)


  • 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)

1.3.0 (11/23/2020)


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

  • Filter keywords by context (#307)

1.2.0 (11/16/2020)


  • 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.

1.1.0 (10/14/2020)


  • Implement a command to switch between module interfaces and implementations (#254)


  • Do not crash on invalid positions (#248)

  • add missing record fields to list of completions (#253)

  • do not offer destruct as a code action in interface files (#255)

1.0.0 (08/28/2020)

  • Initial Release


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