fix(turbopack): merged alias lost module factory for missing type import

[fireairforce]

fix scope hoisting with missing export type binding cause module factory lost:

[gemini-code-assist]

Summary of Changes

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This pull request addresses a critical issue in Turbopack where merged aliases were losing their module factories, particularly affecting import namespaces due to incorrect scope hoisting and missing export type bindings. The changes introduce a more robust module merging process that correctly identifies and exposes module factories for these cases, ensuring that bundled modules behave as expected and preventing runtime errors related to missing module definitions.

Highlights

• Module Merging Logic: Enhanced the merge_modules function to correctly handle and return fallback_import_idents, which are crucial for preserving module factories for aliased imports.
• Module Factory Exposure: Updated the mechanism for determining additional_ids to ensure that module factories are properly exposed for modules identified by fallback_import_idents or those explicitly marked as external.
• Configuration Cleanup: Removed a redundant ..Default::default() spread from the decorators configuration, simplifying the code.

Changelog

• turbopack/crates/turbopack-ecmascript/src/lib.rs
  • Modified the merge_modules function signature and return type to include fallback_import_idents.
  • Refactored the logic for collecting additional_ids to incorporate fallback_import_idents when determining which module factories to expose.
• turbopack/crates/turbopack-ecmascript/src/transform/mod.rs
  • Removed redundant ..Default::default() from the decorators configuration.

Activity

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[gemini-code-assist]

Code Review

This pull request appears to fix an issue in Turbopack's scope hoisting where a module factory was being lost. This is achieved by passing around fallback_import_idents from the module merging step and using this information to correctly identify all modules that require a module factory. The logic seems sound. I've included one suggestion to optimize a loop by avoiding unnecessary object creation, which should provide a minor performance benefit. The other change in transform/mod.rs appears to be a necessary code cleanup, possibly due to a dependency update, and looks correct.

[gemini-code-assist]

For a minor performance improvement, you can avoid the cost of creating fallback_ident (which involves string formatting, mangling, and atom interning) when exposure == MergeableModuleExposure::External is true. By checking for this condition first and returning early, you can skip the unnecessary work inside this filter_map closure.

                    if module == first_entry {
                        return None;
                    }
                    if exposure == MergeableModuleExposure::External {
                        return Some(module_id);
                    }
                    let fallback_ident: Atom =
                        crate::magic_identifier::mangle(&format!("imported module {module_id}"))
                            .into();
                    if fallback_import_idents.contains(&fallback_ident) {
                        Some(module_id)
                    } else {
                        None
                    }