fix: preserve $ characters in interpolated error message values

[anxkhn]

• Closes

Additional details

stripIndent() (packages/errors/src/stripIndent.ts) is the substitution engine behind the errTemplate tagged-template system that formats Cypress error messages. errTemplate calls stripIndent(templateStrings, ...templateArgs) and stripIndent splices each interpolated value into a <<i>> placeholder with:

result = result.replace(`<<${i}>>`, `${arg}`)

String.prototype.replace with a string replacement interprets $ sequences in that replacement. Since the search argument here is a literal placeholder (no capture groups), the sequences that apply are $& (the matched placeholder), $` (text before the match), $' (text after the match), and $$ (an escaped $). So any interpolated value containing one of those was corrupted in the rendered error. For example, an error that embeds JSON-stringified data:

• value: {"expr":"a$&b"}
• rendered (before): ... {"expr":"a<<0>>b"} (the raw <<0>> placeholder leaks back in via $&)
• rendered (after): ... {"expr":"a$&b"}

The fix passes a replacer function instead of a string. A function's return value is inserted literally and is not subject to $-pattern interpretation, so values are rendered verbatim. This is a one-line change with no behavior change for any value that does not contain those $ sequences; the package's 160 error-render snapshot tests are unaffected.

This is a self-identified correctness fix with no linked issue. Per CONTRIBUTING.md, purely mechanical/correctness fixes may be submitted without a prior issue as long as the reasoning is explained here. Happy to open a tracking issue first if the maintainers prefer.

---

Note

Low Risk
One-line behavioral fix in internal error templating with a targeted unit test; no public API or runtime test-path changes beyond clearer error messages.

Overview
Fixes garbled Cypress error text when errTemplate / stripIndent splice interpolated values that contain JavaScript replacement patterns ($&, $`, $', $$).

stripIndent now passes a replacer function to String.prototype.replace instead of a string replacement, so interpolated args (for example JSON in config validation errors) render verbatim. A unit test covers the regression, and 15.18.1 changelog documents the user-facing fix.

^{Reviewed by Cursor Bugbot for commit 25e3109. Bugbot is set up for automated code reviews on this repo. Configure here.}

Steps to test

A new unit test in packages/errors/test/stripIndent.spec.ts covers this. To reproduce manually:

1. yarn workspace @packages/errors test -- test/stripIndent.spec.ts
2. The added case interpolates a value containing $&, $`, $' and $$ and asserts it renders verbatim. On the previous code it renders the corrupted string (e.g. leaking <<0>> and re-inserting surrounding text); with this change it renders the value unchanged.

The full package suite (yarn workspace @packages/errors test, 184 tests including the 160 visualSnapshotErrors renders) and yarn workspace @packages/errors check-ts both pass.

How has the user experience changed?

Cypress error messages that interpolate a value containing $&, $`, $' or $$ (for example JSON-stringified data shown in a config-validation error) are now rendered exactly as-is instead of being garbled by JavaScript's replacement-pattern handling. There is no visual change for messages whose interpolated values do not contain those sequences.

PR Tasks

• [na] Is there an associated issue with maintainer approval for PR submission?
• Have tests been added/updated?
• [na] Has a PR for user-facing changes been opened in cypress-documentation?
• [na] Have API changes been updated in the type definitions?

[cypress-app-bot]

• Create a Draft Pull Request if your PR is not ready for review. Mark the PR as Ready for Review when you're ready for a Cypress team member to review the PR.

[jennifer-shehane]

@anxkhn Please add a changelog entry