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doc/architecture/decisions/0004-use-biome.md

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+# 4. Use Biome
+
+Date: 2024-02-14
+
+## Status
+
+Accepted
+
+## Context
+
+As documented in the dxw tech team RFC [Use linting tools across all of our
+projects][linters], we use linters and formatters to ensure a standard approach
+to the way our code is structured within files.
+
+For JavaScript and TypeScript, we often use some combination of [ESLint][],
+[Standard][], and [Prettier][] for these purposes, and had been using ESLint and
+Prettier here. However, we've encountered issues getting this to play nice with
+[Bun][] in various local development environments, and experiments with Standard
+have also proved problematic.
+
+While setting the codebase up to work with a particular set of rules is often
+the bulk of the work with linters (rather than ongoing maintenance), the issues
+we've encountered on this project have taken time away from more interesting
+experiments with state machines, WebSockets, and so on.
+
+[Biome][] is a relatively new linter and formatter. Having been built in Rust,
+it's highly performant. It provides a substantial set of [linting rules][] by
+default, [many of which come from ESLint or ESLint plugins][linting rule
+sources], and has a similar philosophy to Prettier on [opinionated formatting][]
+(limited configuration).
+
+## Decision
+
+We will use Biome for linting and formatting our TypeScript and JSON files.
+
+## Consequences
+
+- We will have fewer decisions to make about what linting and formatting rules
+  to apply
+- We may be unable to use some of the more niche ESLint rules or third-party
+  plugins
+- We should be able to revert/switch to another linter/formatter if we encounter
+  issues
+
+[Biome]: https://biomejs.dev
+[Bun]: ./0002-use-bun.md
+[ESLint]: https://github.com/search?q=org:dxw+%22eslint%22:+path:package.json&type=code
+[linters]: https://github.com/dxw/tech-team-rfcs/blob/main/tools-and-technology/rfc-035-use-linting-tools-across-all-our-projects.md
+[linting rule sources]: https://biomejs.dev/linter/rules-sources/#rules-from-other-sources
+[linting rules]: https://biomejs.dev/linter/rules
+[opinionated formatting]: https://biomejs.dev/formatter
+[Prettier]: https://github.com/search?q=org:dxw+%22prettier%22:+path:package.json&type=code
+[Standard]: https://github.com/search?q=org%3Adxw+%22standard%22%3A+path%3Apackage.json&type=code