Run codegen (build_runner)

A deterministic, low-freedom runbook: regenerate all annotation-driven code in one pass, then analyze. Run the pinned command exactly as written — do not modify it, add flags, or hand-edit generated files. Applies whenever a source file carries a codegen annotation (@freezed, @JsonSerializable, @riverpod, @DriftDatabase, a drift table) and its *.g.dart / *.freezed.dart / *.drift.dart part is missing or stale.

Non-negotiable rules

1. Run codegen BEFORE flutter analyze. A fresh clone, branch switch, or freshly edited annotated file has no generated part on disk. Analyzing that tree produces misleading "missing part file" and undefined-class errors that describe the missing output, not a real code defect — regenerate, then analyze.
2. Use the pinned command verbatim, always with --delete-conflicting-outputs. Without it, build_runner refuses to overwrite an output it did not write this run and fails with a wall of "conflicting outputs" text. That is a stale-file collision, not a bug — do not go hunting for one.
3. Never hand-edit a generated file. The next build silently reverts it and takes your edit with it. Change the annotated source — the drift table, the freezed class, the Notifier, the ARB — and rerun.
4. Never git add -f a generated file. Whether generated code is committed or gitignored is one decision owned by codegen-and-toolchain; whichever the repo chose, never force-add an artifact past the ignore rules or commit one the current source would not reproduce.
5. watch is a local-dev convenience, never CI or a pre-commit hook. CI and the pre-analyze step always use the one-shot build.
6. Fix hand-written source first. The generator reads a resolved AST; it cannot generate from source that does not analyze. An unrelated error anywhere in lib/ can block generation of a table or provider — clear those before blaming codegen.

The canonical command

Run from the package root (single-package app) or the workspace root (multi-package repo):

dart run build_runner build --delete-conflicting-outputs

This is the first step in every CI lane and on every fresh clone, before format and analyze.

Standard sequence on a fresh clone, pull, or branch switch

1. flutter pub get (resolve dependencies).
2. dart run build_runner build --delete-conflicting-outputs (regenerate).
3. Only then flutter analyze.

Skipping step 2 is the single most common cause of a red analyzer on a clone whose code is actually fine.

Dev iteration (optional watch)

For an active edit loop on annotated sources, run the watcher instead of a one-shot build; it rebuilds affected outputs on save:

dart run build_runner watch --delete-conflicting-outputs

Stop the watcher before running the one-shot build — two concurrent build_runner processes over the same tree race on outputs.

When multi-package (workspace)

build_runner runs per-package: one invocation regenerates the current package plus its path-dependency packages, not automatically every sibling in the workspace. So running the single command at the workspace root covers the root package and its path dependencies in one pass, but a coordinator-style root that does not itself depend on every member will not regenerate those siblings. For full multi-package regeneration, use the repo-level fan-out wrapper (e.g. melos run gen) that runs the command over every workspace member; prefer it when the workspace is bootstrapped. To deliberately scope one package during development, run the same command from that package's directory. Builder scoping (which files each builder reads) lives in each package's build.yaml, owned by codegen-and-toolchain.

When codegen and the analyzer disagree

The analyzer reads files on disk; build_runner writes them. A disagreement almost always means the disk is behind, not that the code is wrong.

Anti-patterns

• Running flutter analyze before codegen on a fresh tree — you chase phantom missing-part errors that regeneration erases.
• Dropping --delete-conflicting-outputs — the first rename or deletion fails the whole run on a stale-output collision.
• Editing a .g.dart / .freezed.dart / .drift.dart by hand — the next build reverts it; the fix belongs in the annotated source.
• git add -f on a gitignored generated file — bypasses the repo's committed-vs-gitignored decision and ships a possibly-stale artifact.
• build_runner watch in CI or a pre-commit hook — non-deterministic; CI must use the one-shot build.

Definition of done

• The pinned dart run build_runner build --delete-conflicting-outputs ran at the package/workspace root without "conflicting outputs" errors.
• It ran before flutter analyze, which is now green.
• No generated file was hand-edited or force-added.
• No build_runner watch process is wired into CI or hooks.

Related skills

• See codegen-and-toolchain for the knowledge behind this runbook: build.yaml builder scoping, the commit-vs-gitignore-generated-code decision, SDK pinning, and analyzer/coverage excludes for generated files.
• See run-migration for the drift schema-snapshot and migration ritual that wraps drift_dev make-migrations around this codegen pass.
• See ci-pipeline-and-gates for the CI freshness gate that reruns this command and diffs the tree.
• See lint-and-style-config for the analyzer excludes that keep generated files out of lint scope.

References

• build_runner: https://pub.dev/packages/build_runner
• Dart tools — build_runner usage: https://dart.dev/tools/build_runner
• drift codegen: https://drift.simonbinder.eu/docs/getting-started/
• freezed: https://pub.dev/packages/freezed
• riverpod_generator: https://pub.dev/packages/riverpod_generator