Inconsistent glob pattern resolution in nested monorepo configurations

Question

When utilizing a monorepo structure with nested biome.json files, the ignore property occasionally fails to resolve paths consistently across different environments. While local development respects the root-level ignores, production CI/CD pipelines often process files that should be excluded based on nested glob patterns.The discrepancy arises when complex glob patterns are defined relative to the project root but executed from a subdirectory that contains its own configuration. It is unclear if the Biome engine merges these patterns hierarchically or if the nearest configuration file takes absolute precedence, potentially leaving un-linted or improperly formatted files in production builds.
How does Biome resolve conflicting ignore patterns when multiple configuration files exist in a directory tree? Is there a documented mechanism to ensure global ignore patterns are strictly enforced across all sub-package boundaries?

Siddharth · Answer

Direct AnswerBiome uses a nearest-configuration-wins strategy. When multiple biome.json files exist in a directory tree, the configuration file closest to the file being processed takes absolute precedence—ignore patterns are not merged hierarchically. A nested biome.json completely replaces the root configuration for files under its directory.There is no built-in mechanism to enforce root-level ignore patterns across sub-package boundaries. To achieve consistent ignores, you must either duplicate the patterns in every nested configuration or run Biome exclusively from the repository root with a single configuration file.Confirmed BehaviorPrecedence rule: For any target file, Biome walks upward from the file's directory and uses the first biome.json it encounters.Glob resolution: Patterns in ignore are resolved relative to the directory containing that specific biome.json, not the repository root.No inheritance: A nested config does not inherit or extend the root config; it replaces it entirely for its subtree.Why Local vs CI DiffersThe discrepancy you observe typically stems from the current working directory (CWD) at invocation time:Local: You likely run biome check from the repo root, so the root config governs everything.CI: The pipeline may invoke Biome from a subdirectory (e.g., packages/api), causing the nested config to take effect and the root ignores to be ignored.Verification StepsFrom the repository root, run:biome lint --files-ignore-unknown=true . 2>&1 | head -20From a nested package directory (e.g., packages/ui), run the same command.Compare the file lists. Files appearing in the second run but not the first are being processed due to the nested config's precedence.WorkaroundsOption A: Single Root Configuration (Recommended)Remove all nested biome.json files. Keep one at the repo root with all ignore patterns defined relative to the root. Run Biome exclusively from the root in CI.Option B: Explicit DuplicationCopy the root ignore array into every nested biome.json, adjusting paths to be relative to each nested config's directory.Option C: CI EnforcementAdd a CI step that validates no nested biome.json files exist, or that all nested configs contain the required ignore patterns.One Diagnostic NeededWhat is the exact biome invocation command and working directory in your CI pipeline? (e.g., cd packages/api && biome check . vs biome check packages/api from root). This determines whether the fix is a config change or a CI script change.

Inconsistent glob pattern resolution in nested monorepo configurations

1 answer

Direct Answer

Confirmed Behavior

Why Local vs CI Differs

Verification Steps

Workarounds

Option A: Single Root Configuration (Recommended)

Option B: Explicit Duplication

Option C: CI Enforcement

One Diagnostic Needed

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