Dart Resolve Package Conflicts

Managing Dart Dependencies

Contents

• Core Concepts
• Version Constraints
• Workflow: Auditing Dependencies
• Workflow: Upgrading Dependencies
• Workflow: Resolving Version Conflicts
• Examples

Core Concepts

Dart enforces a strict single-version rule for dependencies: a project and all its transitive dependencies must resolve to a single, shared version of any given package. This prevents runtime type mismatches but introduces the risk of "version lock."

To mitigate version lock, Dart relies on version constraints rather than pinned versions in the pubspec.yaml. The pubspec.lock file maintains the exact resolved versions for reproducible builds.

Understand the output columns of dart pub outdated:

• Current: The version currently recorded in pubspec.lock.
• Upgradable: The latest version allowed by the constraints in pubspec.yaml. dart pub upgrade resolves to this.
• Resolvable: The absolute latest version that can be resolved when factoring in all other dependencies in the project.
• Latest: The latest published version of the package (excluding prereleases).

Version Constraints

• Use Caret Syntax: Always use caret syntax (e.g., ^1.2.3) for dependencies in pubspec.yaml. This allows pub to select newer, non-breaking versions (up to, but not including, the next major version) during resolution.
• Tighten Dev Dependencies: Set the lower bound of dev_dependencies to the exact version currently used. This reduces resolution complexity and prevents older, incompatible dev tools from being selected.
• Enforce Lockfiles in CI: Use dart pub get --enforce-lockfile in CI/CD pipelines to ensure the exact versions tested locally are used in production.

Workflow: Auditing Dependencies

Run this workflow periodically to identify stale packages that may impact stability or performance.

Task Progress:

• Run dart pub outdated.
• Review the Upgradable column to identify packages that can be updated without modifying pubspec.yaml.
• Review the Resolvable column to identify packages that require constraint modifications in pubspec.yaml to update.
• Identify any packages marked as retracted or discontinued.

Workflow: Upgrading Dependencies

Use conditional logic based on the audit results to upgrade dependencies.

Task Progress:

• If updating to "Upgradable" versions:
  • Run dart pub upgrade.
  • Run dart pub upgrade --tighten to automatically update the lower bounds in pubspec.yaml to match the newly resolved versions.
• If updating to "Resolvable" versions (Major updates):
  • Manually edit pubspec.yaml to bump the version constraint to match the "Resolvable" column (e.g., change ^0.11.0 to ^0.12.1).
  • Run dart pub upgrade to resolve the new constraints and update pubspec.lock.
• Feedback Loop:
  • Run dart analyze -> review errors -> fix breaking API changes.
  • Run dart test -> review failures -> fix regressions.

Workflow: Resolving Version Conflicts

When pub cannot find a set of concrete versions that satisfy all constraints, or when dealing with a retracted package version, manipulate the lockfile surgically.

NEVER delete the entire pubspec.lock file and run dart pub get. This causes uncontrolled upgrades across the entire dependency graph.

Task Progress:

• Open pubspec.lock.
• Locate the specific YAML block for the conflicting or retracted package.
• Delete ONLY that package's entry from the lockfile.
• Run dart pub get to fetch the newest compatible, non-retracted version for that specific package.
• Feedback Loop:
  • Run dart pub deps -> verify the dependency graph resolves correctly.
  • If resolution fails, identify the transitive dependency causing the lock, update its constraint in pubspec.yaml, and retry.

Examples

Tightening Constraints

When dart pub outdated shows a package is resolvable to a higher minor/patch version, use the --tighten flag to update the pubspec.yaml automatically.

Input (pubspec.yaml):

yamlCopy code
dependencies:
  http: ^0.13.0

Command:

bashCopy code
dart pub upgrade --tighten http

Output (pubspec.yaml):

yamlCopy code
dependencies:
  http: ^0.13.5

Surgical Lockfile Removal

If package_a is retracted or locked in a conflict, remove only its block from pubspec.lock.

Before (pubspec.lock):

yamlCopy code
packages:
  package_a:
    dependency: "direct main"
    description:
      name: package_a
      url: "https://pub.dev"
    source: hosted
    version: "1.0.0" # Retracted version
  package_b:
    dependency: "direct main"
    # ...

Action: Delete the package_a block entirely. Leave package_b untouched. Run dart pub get.