analyze: convert a user &object block argument through to_proc

[ryanseys]

recv.iter(&obj) where obj is a user object defining #to_proc was rejected. Ruby calls obj.to_proc exactly once to obtain the block, then runs that proc per element.

This adds an analysis pre-pass that hoists __tproc = obj.to_proc to the statement enclosing the call and rewrites the block argument to the hoisted local, so the existing value-callable desugar forwards the once-computed proc. Hoisting (rather than cloning obj into the block body) makes to_proc run a single time — observable when it has a side effect or returns a stateful proc — matching Ruby's &obj semantics. The pass declines, leaving the existing loud reject, when it cannot locate the enclosing statement.

Covered by test/user_to_proc_block_arg.rb (map / select / count iterators, an inline &Obj.new and a variable-held converter, and a side-effecting to_proc that proves single evaluation), with ruby as the oracle.

A to_proc that returns a lambda capturing self/ivars and then escapes its object is a separate, pre-existing limitation (it fails the same way for a direct pr = obj.to_proc; arr.map(&pr)), so it is out of scope here.

[gemini-code-assist]

Code Review

This pull request introduces a new desugaring pass, desugar_to_proc_block_arg, which hoists the evaluation of to_proc on user objects passed as block arguments to ensure it is evaluated exactly once, matching Ruby's behavior. Feedback is provided regarding the helper function tp_enclosing_stmt, which currently has a worst-case complexity of O(N^2); an O(N) optimization using a single top-down recursive traversal is suggested to prevent potential compilation slowdowns on large ASTs.

Important

The consumer version of Gemini Code Assist on GitHub is being sunset. Starting June 18, 2026, new organization installations will be blocked, and all code review activity will officially cease on July 17, 2026.
For more details on the timeline and next steps, please review the Help Documentation.