Closure body `() => new <ImportedClass>(...)` inside a compilePackages module fails to link or silently collapses to the class id

[proggeramlug]

Repro

Minimal package under node_modules/repro-pkg2/:

// node_modules/repro-pkg2/dialect.js
export class PgDialect {
  constructor(opts) { this.casing = opts ? opts.casing : undefined; }
}

// node_modules/repro-pkg2/db.js
export class PgDatabase {
  constructor(dialect, session, schema) {
    this.dialect = dialect;
    this.session = session;
    this.schema = schema;
  }
}

// node_modules/repro-pkg2/session.js
export class PgRemoteSession {
  constructor(callback, dialect, schema, opts) {
    this.callback = callback;
    this.dialect = dialect;
  }
}

// node_modules/repro-pkg2/index.js
import { PgDatabase } from './db.js';
import { PgDialect } from './dialect.js';
import { PgRemoteSession } from './session.js';

class PgRemoteDatabase extends PgDatabase {
  static x = "PgRemoteDatabase";
}

export function drizzle(
  callback,
  config = {},
  _dialect = () => new PgDialect({ casing: config.casing })
) {
  const dialect = _dialect();
  const session = new PgRemoteSession(callback, dialect, undefined, {});
  return new PgRemoteDatabase(dialect, session, undefined);
}

// package.json
{ "perry": { "compilePackages": ["repro-pkg2"] } }

// probe_repro2.ts
import { drizzle } from 'repro-pkg2';
const db = drizzle(async (q, params, _m) => ({ rows: [] }));
console.log('db.dialect=', db.dialect);

Perry compile:

Undefined symbols for architecture arm64:
  "_node_modules_repro_pkg2_dialect_js__PgDialect_constructor", referenced from:
      _perry_closure_node_modules_repro_pkg2_index_js__1 in node_modules_repro_pkg2_index_js.o
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1

Bun output (correct):

[drizzle] _dialect typeof= function
[drizzle] dialect= PgDialect { casing: undefined } truthy= true
db.dialect= PgDialect { casing: undefined }

What I think is going on

The default-param arrow () => new PgDialect(...) becomes a closure (_perry_closure_..._index_js__1). Its emitted body calls _node_modules_repro_pkg2_dialect_js__PgDialect_constructor, but that symbol isn't being declared / emitted on the source-module side under compilePackages. Compare to a top-level new PgDialect(...) in the same module which links fine — the constructor emit only fails when the call site is inside a closure body.

Different but related symptom in drizzle-orm

In a real drizzle-orm 0.45.2 compile (drizzle-orm/pg-proxy/driver.js has the exact same shape — function drizzle(callback, config = {}, _dialect = () => new PgDialect({ casing: config.casing }))), the link succeeds, but at runtime typeof _dialect === 'number' and its value is 1.26e-321, which is f64::from_bits(269) where 269 is PgDialect's class id. Calling _dialect() returns undefined. As if the closure was replaced by the raw class-id-as-f64 of the class whose constructor it was supposed to call.

Diagnostic edits I tried in drizzle's compiled file didn't change the value:

• Move the assignment out of the default param: if (_dialect === undefined) _dialect = () => new PgDialect(...) → still typeof _dialect === 'number'.
• Replace with a regular function expression: function() { return new PgDialect(...) } — same.
• Replace with a closure that doesn't reference PgDialect at all: function() { return 42 } → STILL typeof _dialect === 'number', same 1.26e-321 value.

Last point is the smoking gun: regardless of what we assign to _dialect, it always reads back as f64::from_bits(269) (PgDialect's class id). So storage for _dialect is being aliased to PgDialect — assignments to _dialect are no-op'd because perry's HIR / codegen statically pre-bound it to PgDialect.

I suspect a default-param desugar pass that:

1. Sees _dialect = () => new PgDialect(...)
2. "Constant-folds" the arrow to a reference to PgDialect itself (treating arrow-returning-new C(...) as alias-to-C)
3. Stores PgDialect's class id (NaN-unboxed f64 raw bits) into _dialect's slot at function entry
4. Marks _dialect as static-bound, so subsequent assignments (_dialect = anything else) get DCE'd

But I haven't located the offending pass.

Where I'd start digging

crates/perry-hir/src/lower_decl.rs — build_default_param_stmts and the function-decl param-default desugar paths. Especially anything that pattern-matches () => new <Class>(...) as a special shape. Compare to lambda-body lowering for closures inside compilePackages packages.

crates/perry-codegen/src/... — closure emit when the body is new <ImportedClass>(...) and the source class lives in a sibling .js file under the same compilePackages package.

The link-failure form (_node_modules_repro_pkg2_dialect_js__PgDialect_constructor) is the easier entry point — it's a missing extern declaration that should be straightforward to trace from the closure's emitted IR back to the symbol it references.

Why it matters for #488

Blocks the drizzle + @perryts/postgres acceptance test (#488). After #585 (cross-module instanceof) and #586 (thenable assimilation) landed in v0.5.692, drizzle's db.insert(...) / db.select(...) paths now reach the dialect-call layer, where this bug surfaces because db.dialect is undefined.

Workaround

Patch drizzle to construct the dialect directly (no closure):

// in drizzle-orm/pg-proxy/driver.js
function drizzle(callback, config = {}) {
  const dialect = new PgDialect({ casing: config.casing });
  // ...
}

Confirmed working with this patch — db.dialect is set, insert proceeds past the dialect lookup. (Then runs into a separate hang in the actual query-execute path that I haven't dug into yet — likely the next blocker but distinct.)