Accept block-pass arguments for optional blocks - #2261
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soutaro
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Aug 13, 2026
`&:sym` and `&method(:name)` failed to type check when the method
declares an optional block:
```
test.rb:1:13: [error] Cannot pass a value of type `::Proc` as a block-pass-argument of type `(^(::Integer) -> void | nil)`
│ ::Proc <: (^(::Integer) -> void | nil)
│ ::Proc <: ^(::Integer) -> void
│
│ Diagnostic ID: Ruby::BlockTypeMismatch
│
└ Foo.new.each(&:to_s)
~~~~~~
```
Both are special cased in `:block_pass` so that `Symbol#to_proc` and
`Method#to_proc` are given a proc type built from the expected block
type. The special cases match on `AST::Types::Proc`, but the hint of a
block-pass argument is `^(...) -> ... | nil` when the block is optional,
so neither applied and the argument kept the plain `::Proc` type it
converts to.
Hint the argument with the block type itself instead of the union.
`BlockPassArg` builds both, so it exposes `proc_type` next to
`node_type`, and the union stays where it belongs -- the subtyping check
that lets `nil` through for an optional block.
Fixes #1207
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Nx2PCA7ngK5EZkgNtHM5b6
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Fixes #1207.
&:symand&method(:name)fail against an optional block:The
Symbol#to_proc/Method#to_procspecial cases in:block_passmatch onAST::Types::Proc, but the hint of a block-pass argument is^(...) -> ... | nilwhen the block is optional, so neither runs and the argument keeps the plain::Procit converts to.Fixed by hinting the argument with the block type itself.
BlockPassArgbuilds both, so it exposesproc_typenext tonode_type, and the union stays where it belongs — the subtyping check that letsnilthrough for an optional block.This removes the need for ruby/rbs#3060.