Fails to infer the type of `my_instance = SomeClass.new`

[eliwang2025-ws]

Description

Ruby LSP Information

VS Code Version

1.99.3

Ruby LSP Extension Version

0.9.16

Ruby LSP Server Version

0.23.14

Ruby LSP Add-ons

Ruby Version

3.4.2

Ruby Version Manager

rbenv

Installed Extensions

Click to expand

• ruby-lsp (0.9.16)

Ruby LSP Settings

Click to expand

Workspace

{}

User

{
 "enabledFeatures": {
 "codeActions": true,
 "diagnostics": true,
 "documentHighlights": true,
 "documentLink": true,
 "documentSymbols": true,
 "foldingRanges": true,
 "formatting": true,
 "hover": true,
 "inlayHint": true,
 "onTypeFormatting": true,
 "selectionRanges": true,
 "semanticHighlighting": true,
 "completion": true,
 "codeLens": true,
 "definition": true,
 "workspaceSymbol": true,
 "signatureHelp": true,
 "typeHierarchy": true
 },
 "featuresConfiguration": {},
 "addonSettings": {},
 "rubyVersionManager": {
 "identifier": "auto"
 },
 "customRubyCommand": "",
 "formatter": "auto",
 "linters": null,
 "bundleGemfile": "",
 "testTimeout": 30,
 "branch": "",
 "pullDiagnosticsOn": "both",
 "useBundlerCompose": false,
 "bypassTypechecker": false,
 "rubyExecutablePath": "",
 "indexing": {},
 "erbSupport": true,
 "featureFlags": {},
 "sigOpacityLevel": "1"
}

Reproduction steps

Create an empty ruby file, put

class SomeClass
 def print_debug_info
 end
end

sc = SomeClass.new

Hover the mouse over the variable sc I don't see its type. And type sc. in the following lines, print_debug_info is not among the auto suggestions, while method_missing is, along with a bunch of others.

Is this something wrong with my configuration? I did a bit of searching, noticed that when I type SomeClass.new, the suggestion comes from class.rbs, where the .new method is marked untyped. And I talked to Google Gemini a bit, it replied that the .rbs system lacks generics for the moment, something like Class<T> in Java, therefore the return value can only be untyped for the moment.

Not sure if this is true, but should ruby-lsp make some workaround about this? It's just everyday life.

[vinistock]

Thank you for the report. We do currently offer inference when you're immediately using the result of new, like SomeClass.new.print_debug_info.

Carrying the type analysis beyond that requires a more elaborate implementation of a type system. We started having to remember which variables are currently inside scope, what their types are and we need at least the basics of type unions to express things.

There's a bit of discussion regarding this here and in our roadmap and design docs.

For the time being, the Ruby LSP will not have a full type system implementation to be able to perform more complex type flow analysis. We did an exploration to understand how far we could take type checking without requiring any annotations from users, to see if it was worth trying to handle cases like this.

Unfortunately, our findings pointed out that we are not able to achieve significant correctness without type annotations and the effort to implement full type flow analysis does not justify the minimal improvements in correctness for handling scenarios like these. If you require more complete analysis and accuracy, you may want to consider adopting Sorbet or Steep.

[eliwang2025-ws]

Thank you for the informative response!