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Go-to-definition does not work on custom operators #1915

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WardBrian opened this issue Mar 27, 2025 · 4 comments · May be fixed by #1917
Open

Go-to-definition does not work on custom operators #1915

WardBrian opened this issue Mar 27, 2025 · 4 comments · May be fixed by #1917
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@WardBrian
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WardBrian commented Mar 27, 2025 •
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Go-to-definition doesn't work on (all) custom operators, which would be very useful for navigating DSLs.

For example,

let ( := ) v a = Printf.printf "%s = %d" v a
let () = "foo" := 3
(*              ^ *)

If I place my cursor at the point indicated by the ^, go-to-definition does nothing.

Similarly, for custom indexing operators:

let (.%{;..}) a k = Printf.printf "%s.coeffRef(%d);\n" a k.(0)
let (.%{ }) a k = Printf.printf "%s.coeffRef(%d);\n" a k
let name = "baz"
let () = name.%{2;4}
let () = name.%{5}

Placing the cursor at the % on either like 4 or 5 does not succeed.

Originally opened as ocamllabs/vscode-ocaml-platform#1766
@WardBrian
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I should also say, if someone is willing to give me a few pointers on how to get started and what the scope of this is, I'd be more than willing to have a go at contributing the fix myself!

@voodoos
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voodoos commented Mar 28, 2025

Here is how I would proceed:

  • Write a test illustrating the wrong behavior (similar as https://github.com/ocaml/merlin/blob/main/tests/test-dirs/locate/issue949.t)
  • Such a test would already be welcome as a contribution
  • Then you can use that test to print some logs by adding -log-file - to the $MERLIN command line.
  • I expect these to guide you toward Query_commands (the entry point for Merlin analyses)
  • My bet would be an issue with reconstruct_identifier (here) that Merlin uses to reparse the identifier under the cursor.
  • You can also have a look at the asts in the test by using the commands $MERLIN single dump -what parsetree ... and dump -what typedtree

@WardBrian
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Huh. I started writing the test and was surprised when the output actually was what I expected. I then tried M-x merlin-locate in Emacs and it also worked. Going back into VSCode, it now works too -- so maybe I just hadn't run a dune clean && dune build recently enough. My binary operators also seem to be working now.

Things that aren't:

A custom definition of ( := ) is returning Not a valid identifier, and the custom indexing operators are failing. I'll see if I can at least contribute a test for those.

@WardBrian WardBrian linked a pull request Mar 31, 2025 that will close this issue
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@WardBrian
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Thanks @voodoos -- your hints were very helpful (and your hunch about reconstruct_identifier right on the money). I've taken a crack at it over in #1917

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Improve location of some custom operators WardBrian/merlin
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@voodoos @WardBrian