fix: preserve nested CJS constructor function names

changelog.d/11009-cjs-function-names.md

@@ -0,0 +1,3 @@
+### Fixed
+
+- Preserve the declared `.name` of nested function constructors exported from CommonJS modules, including values built by a factory and inspected through `constructor.name`.

crates/perry-hir/src/lower_decl/body_stmt/nested_fn_decl.rs

@@ -284,6 +284,11 @@ pub(super) fn lower_nested_fn_decl(
     // tag has to be applied here too.
     ctx.function_valued_locals.insert(local_id);
 
+    // Nested declarations become inline closures rather than entries in
+    // `module.functions`. Preserve the declared name for function.name;
+    // codegen cannot infer it from a Let inside another closure's body.
+    ctx.closure_display_names.insert(func_id, func_name.clone());
+
     let closure = Expr::Closure {
         func_id,
         params,

crates/perry/tests/issue_10702_cjs_function_name.rs

@@ -0,0 +1,66 @@
+//! A CJS default export preserves the name of its function constructor.
+
+use std::path::PathBuf;
+use std::process::Command;
+
+#[test]
+fn imported_cjs_function_constructor_keeps_its_name() {
+    let dir = tempfile::tempdir().expect("tempdir");
+    let entry = dir.path().join("main.ts");
+    let library = dir.path().join("lib.cjs");
+    let binary = dir.path().join("main_bin");
+    std::fs::write(
+        &library,
+        r#"
+function clone() {
+  function Ledger(value) { this.value = value; }
+  Ledger.prototype = { constructor: Ledger, getValue() { return this.value; } };
+  return Ledger;
+}
+module.exports = clone();
+"#,
+    )
+    .expect("write CJS library");
+    std::fs::write(
+        &entry,
+        r#"
+import Ledger from "./lib.cjs";
+const value = new Ledger(5);
+console.log("NAMES", Ledger.name, value.constructor.name);
+console.log("VALUE", value instanceof Ledger, value.getValue());
+"#,
+    )
+    .expect("write entry");
+
+    let compiler = PathBuf::from(env!("CARGO_BIN_EXE_perry"));
+    let compile = Command::new(compiler)
+        .current_dir(dir.path())
+        .arg("compile")
+        .arg(&entry)
+        .arg("-o")
+        .arg(&binary)
+        .arg("--no-cache")
+        .output()
+        .expect("compile fixture");
+    assert!(
+        compile.status.success(),
+        "compile failed\nstdout:\n{}\nstderr:\n{}",
+        String::from_utf8_lossy(&compile.stdout),
+        String::from_utf8_lossy(&compile.stderr)
+    );
+
+    let run = Command::new(binary)
+        .current_dir(dir.path())
+        .output()
+        .expect("run fixture");
+    assert!(
+        run.status.success(),
+        "fixture failed\nstdout:\n{}\nstderr:\n{}",
+        String::from_utf8_lossy(&run.stdout),
+        String::from_utf8_lossy(&run.stderr)
+    );
+    assert_eq!(
+        String::from_utf8_lossy(&run.stdout),
+        "NAMES Ledger Ledger\nVALUE true 5\n"
+    );
+}