fix(codegen): route const rest exports through the closure spread call (#10197)

changelog.d/10197-namespace-spread-call-var.md

@@ -0,0 +1,3 @@
+### Fixed
+
+- `ns.member(...spread)` on a `const`-bound rest-parameter export (`export const mergeAll = (...ctxs) => …`, e.g. effect's `Context.mergeAll(...contexts)` inside `Layer.mergeAll`) now calls the closure; the spread fast path treated the export's value getter as the function body and evaluated to the function instead (#10197).

crates/perry-codegen/src/expr/call_spread.rs

@@ -431,7 +431,24 @@ pub(crate) fn lower(ctx: &mut FnCtx<'_>, expr: &Expr) -> Result<String> {
                     } else {
                         ctx.imported_func_has_rest.contains(property)
                     };
-                    if ctx.namespace_imports.contains(ns_name) && has_rest && declared_count == 1 {
+                    // #10197: a `let`/`const`-bound export (`export const
+                    // mergeAll = (...ctxs) => …`) has no callable
+                    // `perry_fn_<src>__<name>` — that symbol is its zero-arg
+                    // VALUE getter — so bundling the spread into it returns
+                    // the closure instead of calling it (effect's
+                    // `Context.mergeAll(...contexts)` in `Layer.mergeAll`).
+                    // Mirror `try_lower_namespace_member_call`: vars take the
+                    // closure-callee path below, which reads the value and
+                    // applies the spread through
+                    // `js_closure_call_apply_with_spread`.
+                    let is_var = ctx
+                        .imported_vars
+                        .contains(&crate::namespace_member_var_key(ns_name, property));
+                    if ctx.namespace_imports.contains(ns_name)
+                        && has_rest
+                        && declared_count == 1
+                        && !is_var
+                    {
                         let source_prefix_opt = ctx
                             .namespace_member_prefixes
                             .get(&(ns_name.clone(), property.clone()))

crates/perry/tests/source_graph_export_regressions.rs

@@ -956,3 +956,5 @@ fn mixed_type_and_value_specifier_import_keeps_runtime_edge() {
 }
 #[path = "source_graph_export_regressions/issue_10160.rs"]
 mod issue_10160;
+#[path = "source_graph_export_regressions/issue_10197.rs"]
+mod issue_10197;

crates/perry/tests/source_graph_export_regressions/issue_10197.rs

@@ -0,0 +1,41 @@
+//! `ns.member(...spread)` on a `const`-bound rest-parameter export must call
+//! the closure, not evaluate to it (#10197).
+
+use super::{compile_and_run, write};
+
+fn lib(dir: &std::path::Path) {
+    write(
+        dir,
+        "lib.ts",
+        "export const count = (...xs: any[]) => xs.length\n\
+         export const mergeAll = (...ctxs: any[]) => {\n\
+         \x20 const m = new Map()\n\
+         \x20 for (let i = 0; i < ctxs.length; i++) ctxs[i].mapUnsafe.forEach((v: any, k: any) => m.set(k, v))\n\
+         \x20 return { mapUnsafe: m }\n\
+         }\n\
+         export function countFn(...xs: any[]) { return xs.length }\n\
+         export const mk = (k: string) => ({ mapUnsafe: new Map([[k, k.length]]) })\n\
+         export const fill = (n: number, f: (i: number) => any) => { const out = new Array(n); for (let i = 0; i < n; i++) out[i] = f(i); return out }\n",
+    );
+}
+
+#[test]
+fn namespace_member_spread_call_invokes_const_rest_exports() {
+    let dir = tempfile::tempdir().unwrap();
+    lib(dir.path());
+    write(
+        dir.path(),
+        "main.ts",
+        "import * as Lib from \"./lib\"\n\
+         import { fill, mk } from \"./lib\"\n\
+         const other = fill(3, (i) => mk(\"k\".repeat(i + 1)))\n\
+         console.log(Lib.count(...other), Lib.count(0, ...other), Lib.countFn(...other), Lib.countFn(0, ...other))\n\
+         console.log(Lib.mergeAll(...other).mapUnsafe.size, (Lib as any)[\"mergeAll\"](...other).mapUnsafe.size)\n\
+         const inner = (context: any) => Lib.mergeAll(...(context as any))\n\
+         console.log(inner(other).mapUnsafe.size, Lib.mk(...([\"zz\"] as [string])).mapUnsafe.size)\n",
+    );
+    assert_eq!(
+        compile_and_run(dir.path(), "main.ts"),
+        "3 4 3 4\n3 3\n3 1\n"
+    );
+}