Give the RBS instance type its type arguments - #480
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Type.default_param_map built the `*instance` entry with an empty argument
list, so a singleton method declared to return `instance` lost its type
arguments, and crashed when that result reached a type variable check
(SigTyVarNode#typecheck got nil instead of an actual argument). After
base_type the receiver is always an Instance or a Singleton, so
get_instance_type is always defined.
table = Hash[[["a", "b"]]] # Hash.[] is declared as `-> instance`
"foo".gsub(/o/, table) # gsub takes `hash[String, _ToS]`
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Motivation / Background
This Pull Request has been created because passing the result of
Hash[...]toString#gsubcrashes TypeProf:Hash.[]returnsinstance, butType.default_param_mapbuilt the*instanceentry with an empty argument list, so matching the result againstgsub's generichash[String, _ToS]left a type variable with no actual argument. ruby/ruby aborts onlib/cgi/escape.rbfor this reason.Detail
The fix delegates to
Type::Singleton#get_instance_type, which already fills the arguments in; afterbase_typethe receiver is always anInstanceor aSingleton, so it is always defined.instancenow prints with its type arguments, so a singleton method returning it reportsGen[untyped]where it used to reportGen, which is what an explicitGen[T]return type has always printed. The added scenario covers that output as well as the crash above.🤖 Generated with Claude Code