Support recursive environment variable fallback in .yarnrc.yml #7005
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…allbacks correctly
…nvironment variable replacements
pvcresin
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pvcresin
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Dec 8, 2025
| "title": "JSON Schema for Yarnrc files", | ||
| "$schema": "https://json-schema.org/draft/2019-09/schema#", | ||
| "description": "Yarnrc files (named this way because they must be called `.yarnrc.yml`) are the one place where you'll be able to configure Yarn's internal settings. While Yarn will automatically find them in the parent directories, they should usually be kept at the root of your project (often your repository). **Starting from the v2, they must be written in valid Yaml and have the right extension** (simply calling your file `.yarnrc` won't do).\n\nEnvironment variables can be accessed from setting definitions by using the `${NAME}` syntax when defining the values. By default Yarn will require the variables to be present, but this can be turned off by using either `${NAME-fallback}` (which will return `fallback` if `NAME` isn't set) or `${NAME:-fallback}` (which will return `fallback` if `NAME` isn't set, or is an empty string).\n\nFinally, note that most settings can also be defined through environment variables (at least for the simpler ones; arrays and objects aren't supported yet). To do this, just prefix the names and write them in snake case: `YARN_CACHE_FOLDER` will set the cache folder (such values will overwrite any that might have been defined in the RC files - use them sparingly).", | ||
| "description": "Yarnrc files (named this way because they must be called `.yarnrc.yml`) are the one place where you'll be able to configure Yarn's internal settings. While Yarn will automatically find them in the parent directories, they should usually be kept at the root of your project (often your repository). **Starting from the v2, they must be written in valid Yaml and have the right extension** (simply calling your file `.yarnrc` won't do).\n\nEnvironment variables can be accessed from setting definitions by using the `${NAME}` syntax when defining the values. By default Yarn will require the variables to be present, but this can be turned off by using either `${NAME-fallback}` (which will return `fallback` if `NAME` isn't set) or `${NAME:-fallback}` (which will return `fallback` if `NAME` isn't set, or is an empty string). You can also nest this syntax, for example `${PRIMARY:-${SECONDARY:-fallback}}`, which first checks PRIMARY, then SECONDARY, and finally falls back to fallback.\n\nFinally, note that most settings can also be defined through environment variables (at least for the simpler ones; arrays and objects aren't supported yet). To do this, just prefix the names and write them in snake case: `YARN_CACHE_FOLDER` will set the cache folder (such values will overwrite any that might have been defined in the RC files - use them sparingly).", |
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You can also nest this syntax, for example
${PRIMARY:-${SECONDARY:-fallback}}, which first checks PRIMARY, then SECONDARY, and finally falls back to fallback.
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@arcanis I would like to hear your opinion. |
clemyan
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Dec 11, 2025
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| export function replaceEnvVariables(value: string, {env}: {env: {[key: string]: string | undefined}}) { | ||
| const regex = /\\?\${(?<variableName>[\d\w_]+)(?<colon>:)?(?:-(?<fallback>[^}]*))?}/g; | ||
| const regex = /\\?\${(?<variableName>[\d\w_]+)(?<colon>:)?(?:-(?<fallback>(?:[^}]|}(?=}))*))?}/g; |
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This only works if the variable is the last thing in the fallback, so ${A:-${B}x} would fail
As there is no balancing groups in regex in JS, there are just 2 ways to properly support nested variables as far as I can see:
- Do multiple passes to replace variables from the deepest-nested one, like how
dotenv-expanddoes it - Actually write a PDA-like parser
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What's the problem this PR addresses?
Support
${PRIMARY_VAR:-${SECONDARY_VAR:-fallback-value}}.This would bring Yarn's configuration behavior closer to standard shell (Bash/Zsh) parity.
I really need this feature right now.
Resolves #6998
How did you fix it?
Added an implementation to recursively look for environment variables.
Checklist