run-codegen

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Translated

Runs the deterministic build_runner codegen pass (drift_dev, freezed, json_serializable, riverpod_generator) as one pinned command with --delete-conflicting-outputs, always before flutter analyze, never hand-editing or force-committing generated *.g.dart / *.freezed.dart / *.drift.dart output, watch only in local dev. Use when regenerating codegen, fixing "missing part file" / "conflicting outputs" / undefined generated-class analyzer errors, after editing a drift table or DAO, a freezed value object, a riverpod Notifier or provider, or a json_serializable model, or after a fresh git clone, branch switch, or pull.

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Sourcezakariaf/flutter-skills

Added on2026-09-27

NPX Install

npx skill4agent add zakariaf/flutter-skills run-codegen

SKILL.md Content

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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

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.
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.
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.
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.
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
```
.
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):

bash

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

```
flutter pub get
```
(resolve dependencies).

dart run build_runner build --delete-conflicting-outputs

(regenerate).

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:

bash

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.

Symptom	Do this
Analyzer flags an undefined class/getter that codegen should produce	Rerun the pinned build, then restart the analysis server. Do not "fix" the call site.
Errors reported inside a `.g.dart` / `.freezed.dart` / `*.drift.dart` file	The file is stale or the analyzer excludes are wrong. Regenerate first; never hand-edit generated output.
build_runner fails with analyzer errors in hand-written source	Fix the hand-written source — the generator cannot resolve an unanalyzable AST.
"Conflicting outputs" wall of text	Re-run with `--delete-conflicting-outputs` ; it clears stale outputs from renamed/deleted sources.

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