Propagate block return types to method return types#112
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Methods like `map` return generic types parameterized by block return values
(e.g., `[1,2].map { |x| x.to_s }` → `Array[String]`). Without this, the
type checker could not infer the element type of collections produced by
block-yielding methods, causing false positives on subsequent method calls.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Pull request overview
This PR improves generic return inference for block-yielding methods so method results can reflect block body return types.
Changes:
- Adds generic RBS type parsing and uses it when loading cached RBS method signatures.
- Introduces
BlockReturnTypeBoxto substitute block return types into method return types. - Adds Ruby and Rust tests for generic parsing and block return propagation.
Reviewed changes
Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.
Show a summary per file
| File | Description |
|---|---|
test/range_test.rb |
Updates expected Range#to_a inference to resolved Array[Integer]. |
test/block_test.rb |
Adds coverage for map block return propagation and related cases. |
core/src/rbs/converter.rs |
Adds parsing for generic RBS types and tests. |
core/src/graph/mod.rs |
Re-exports BlockReturnTypeBox. |
core/src/graph/box.rs |
Adds return type variable resolution and block return propagation box. |
core/src/checker.rs |
Uses RbsTypeConverter::parse for cached return types. |
core/src/cache/rbs_cache.rs |
Removes the old simple return type parser usage. |
core/src/analyzer/dispatch.rs |
Wires block processing results into BlockReturnTypeBox. |
core/src/analyzer/blocks.rs |
Returns block parameter vertices plus the block body’s last expression vertex. |
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| for recv_ty in &recv_types { | ||
| let Some(info) = genv.resolve_method(recv_ty, &self.method_name) else { | ||
| continue; | ||
| }; | ||
|
|
||
| // Reuse resolve_return_type with block_return_union to substitute | ||
| // both receiver type variables and block output type variables in one pass. | ||
| if let Some(resolved) = | ||
| resolve_return_type(&info.return_type, recv_ty, Some(&block_return_union)) |
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| if let Some(body_vtx) = block_result.body_last_vtx { | ||
| let box_id = genv.alloc_box_id(); | ||
| let ret_box = BlockReturnTypeBox::new( | ||
| box_id, | ||
| recv_vtx, | ||
| method_name, | ||
| body_vtx, | ||
| ret_vtx, | ||
| ); | ||
| genv.register_box(box_id, Box::new(ret_box)); | ||
| } |
| type_args: resolved_args, | ||
| }) | ||
| } | ||
| _ => Some(return_type.clone()), |
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| let type_args: Vec<Type> = split_type_args(args_str) | ||
| .into_iter() | ||
| .map(Self::parse) | ||
| .collect(); |
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Motivation
Methods like
mapreturn generic types parameterized by block return values (e.g.,[1,2].map { |x| x.to_s }→Array[String]). Without this propagation, the type checker could not infer the element type of collections produced by block-yielding methods, causing false positives on subsequent method calls like.upcase.Changes
BlockResultstruct to return block body's last expression vertex fromblocks.rsBlockReturnTypeBoxthat observes block return type and substitutes type variables in method return typesRbsTypeConverter::parseto handle generic types (e.g.,Array[Elem],Hash[K, V])is_type_variable_name/is_block_type_variable_nameas module-level functions and addresolve_return_typefor shared type variable resolutionSerializableMethodInfo::return_type()method (replaced byRbsTypeConverter::parse)Checked
cargo test --libpassesbundle exec rake testpasses🤖 Generated with Claude Code