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[#2185] Do not check for pattern anomalies on type mismatch with error recovery

Motivation and Context

This MR resolves a crash arising from a type mismatch when a matchee's type and a pattern's type are different.

Related issues

Resolves #2185 (closed).

Checklist for the LIGO Language Server

  • I checked whether I need to update the file for the plugin and did so if necessary:
    • If I implemented a new LSP request, I added it to the list of supported features that may be disabled
    • If I implemented a new LSP method, I added it to the list of supported functionality
  • I checked that my changes work in Emacs, Vim, and Visual Studio Code
  • (Before merging) The commit history is squashed and prettified, and follows the Serokell commit policy, or the MR is set to squash the commits


Check commit messages for details.


  • compiler
  • website
  • webide
  • vscode-plugin
  • debugger

Types of changes

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Breaking change (fix or feature that would cause existing functionality to not work as expected)
  • Performance improvement (non-breaking change that improves performance)
  • None (change with no changelog)


If typer error recovery is enabled (on for the language server), and the user writes code where there is a mismatch between a scrutinee's type and a pattern's type, it will probably lead to a crash. For example, in the following code:

type t = Unit

let Unit = ()

let () =
  match () with
  | Unit -> ()

The scrutinee (Unit : t) and the pattern (() : unit) have mismatched types (t is not the same as unit), leading to a crash.

With the changes from this changelog, this crash should no longer occur.


  • Changes follow the existing coding style (use dune @fmt to check).
  • Tests for the changes have been added (for bug fixes / feature).
  • Documentation has been updated.
  • Changelog description has been added (if appropriate).
  • Start titles under ## Changelog section with #### (if appropriate).
  • There is no image or uploaded file in changelog
  • Examples in changed behaviour have been added to the changelog (for breaking change / feature).
Edited by Heitor Toledo Lassarote de Paula

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