What differences exist in error metadata between `pug.render` and `pug.renderFile` when `filename` is omitted?

Metadata Divergence in Pug Rendering

When the filename option is omitted, pug.render and pug.renderFile handle error metadata differently because they derive their source identity from different inputs. In pug.render, the source is a string; without a filename, there is no file system reference to attach to the error. In pug.renderFile, the first argument is the path to the file, which Pug implicitly uses as the filename for error reporting.

Impact on Async Filters and Location Data

For pug.render, omitting the filename typically results in error objects that lack line, column, and filename properties. When an async filter throws an error, Pug attempts to augment the error with template location data. If no filename was provided during the render call, this augmentation fails, and the resulting error object contains only the standard JavaScript stack trace without template-specific coordinates.

Behavioral Comparison

Feature	pug.render (no filename)	pug.renderFile (no filename)
Filename Property	Undefined/Absent	Resolved source path
Line/Column Data	Absent in async filter errors	Present (if error is in source)
Source Identity	Synthetic/Anonymous	Implicitly derived from path

Verification Steps

To verify this behavior in your specific environment (assumed Pug 3.x), you can use the following scoped test:

1. Create a template with an async filter that throws an error.
2. Execute pug.render(templateString, {}) and inspect the caught error object for .line and .column.
3. Execute pug.renderFile('path/to/template.pug', {}) and verify that the error object includes the file path and location metadata.

Assumptions and Uncertainties

This analysis assumes a standard Node.js environment. While this behavior is consistent across Pug 2.x and 3.x, there is no official stability guarantee across minor version releases regarding the exact shape of the error object. Furthermore, pug.renderFile may produce inconsistent results in serverless environments where the file path is synthetic or inaccessible at runtime.

Missing Diagnostic: Are you using a custom cache implementation for compiled functions? Cached functions may retain the metadata of the initial render call, potentially masking the omission of filename in subsequent calls.