fix(transform): #5925 — keep comma-sequence operands ahead of hoisted awaits

[proggeramlug]

Problem — #5925

The plain-async pre-pass hoists every nested Expr::Await into a let __await_N = await <operand>; above the containing statement. For a comma sequence, that moves the awaited operand's evaluation above the sequence's earlier operands:

this.authCodeListener = new Listener, this.port = await this.authCodeListener.start();

hoists to (pre-fix):

let __await_N = await this.authCodeListener.start();   // reads the field's PRE-assignment value: null
this.authCodeListener = new Listener, this.port = __await_N;

• node: GOT 42
• perry-compiled: ERR TypeError: Cannot read properties of null (reading 'start')

Minifiers comma-fold consecutive statements, so any const x = new X(); const y = await x.m(); pair in bundled async code hits this — observed in a real-world 13 MB bundle where it broke an auth flow's listener startup. Conditional branches (#342) and logical RHS (#5434) already have dedicated lifts for this class of unsound hoist; Expr::Sequence had none. Reproduces on current origin/main (v0.5.1219).

Fix

lift_sequence_with_await: when a sequence contains an await, lift the non-final operands to statements pushed onto hoisted (each recursively hoisted first, so awaits inside earlier operands suspend in evaluation order), leaving the final operand as the expression value. The __await_N let the caller hoists for the final operand then lands AFTER the lifted operands. Wired into:

• hoist_awaits_in_expr_full (nested sequences), and
• hoist_awaits_avoiding_top_level (statement-position sequences — re-processed after the lift so a final-operand await stays in the linearizer's directly-handled position).

The generator yield hoist (generator/hoist_yields.rs) has the same latent gap for yield-in-sequence; noted in #5925 as a follow-up rather than piggybacking untested changes here.

Validation

• Repro passes post-fix (GOT 42); fails on stock main.
• New e2e tests crates/perry/tests/issue_5925_seq_await_order.rs:
  • the async transform: await hoisted above earlier comma-sequence operands — awaited receiver reads its pre-assignment value #5925 field-assignment shape (GOT 42);
  • sequences in let-init and return position, plus an await in an earlier operand — asserts values AND cross-function side-effect ordering (ORDER after-sink,first,second). Both pass locally with cargo test --release -p perry --test issue_5925_seq_await_order (2 passed).

Fixes #5925.

https://claude.ai/code/session_01K1w6WLaFNKhf4aNxeSWHy6

Summary by CodeRabbit

• Bug Fixes

  • Fixed await handling in comma-separated expressions so evaluation order is preserved correctly in more cases.
  • Resolved an issue where earlier parts of a sequence could be skipped or read in the wrong order around await.

• Tests

  • Added regression coverage for sequence-and-await ordering in assignment, let initialization, and return scenarios.
  • Verified expected output order for async evaluation paths.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 27995425-4653-4ec9-8ee1-c09fa5faddd7

📥 Commits

Reviewing files that changed from the base of the PR and between 42e2401 and 796ffbb.

📒 Files selected for processing (2)

• crates/perry-transform/src/async_to_generator.rs
• crates/perry/tests/issue_5925_seq_await_order.rs

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📝 Walkthrough

Walkthrough

The async-to-generator pre-pass now special-cases Expr::Sequence expressions containing await, lifting non-final comma operands into separate statements before hoisting the awaited final operand, preserving JavaScript comma evaluation order. New regression tests validate this fix for issue #5925.

Changes

Sequence-aware await hoisting fix

Layer / File(s)	Summary
Sequence-aware hoisting logic crates/perry-transform/src/async_to_generator.rs	hoist_awaits_in_expr_full and hoist_awaits_avoiding_top_level detect await-containing comma sequences and lift non-final operands into statements first; a new lift_sequence_with_await helper performs the lift, hoisting awaits inside each lifted operand before leaving the final operand in place.
Regression tests for issue #5925 crates/perry/tests/issue_5925_seq_await_order.rs	New tests compile and run TypeScript snippets covering assignment-then-await via comma sequences, and awaits in earlier operands within let-init and return positions, asserting correct evaluation order and values.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Sequence Diagram(s)

sequenceDiagram
  participant Source as "Source Sequence Expr"
  participant Hoister as "hoist_awaits_avoiding_top_level"
  participant Lifter as "lift_sequence_with_await"
  participant Stmts as "Lifted Statements"

  Source->>Hoister: sequence expr containing await
  Hoister->>Lifter: detect await in sequence, delegate lifting
  Lifter->>Stmts: push non-final operands as statements (hoisted in order)
  Lifter->>Hoister: return final operand in place
  Hoister->>Hoister: hoist await from final operand as __await_N

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is concise and accurately summarizes the main fix to async transform sequence ordering.
Description check	✅ Passed	The description covers the problem, fix, linked issue, and validation, though it doesn't follow the template headings exactly.
Linked Issues check	✅ Passed	The code and tests address #5925 by hoisting non-final sequence operands before awaited final operands in both handled paths.
Out of Scope Changes check	✅ Passed	The changes stay focused on the async sequence-hoisting bug and its regression tests, with no unrelated scope added.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/async-seq-await-order

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