Dart/Flutter "version solving failed" in CI

Pub could not find a set of package versions that satisfies every constraint in pubspec.yaml at once. Two packages - or a package and your Dart/Flutter SDK constraint - demand incompatible versions.

What this error means

flutter pub get (or dart pub get) fails with "version solving failed", explaining which constraints conflict. It is deterministic and reproduces locally with the same pubspec.yaml.

pub output

Because app depends on both http ^1.2.0 and legacy_pkg 0.5.0 which depends on
http ^0.13.0, version solving failed.

Running "flutter pub get" in app... failed.

Common causes

Incompatible package constraints

Two dependencies require non-overlapping versions of a shared package. Pub will not silently pick one - it reports the conflict.

An SDK constraint that excludes a release

Your environment: sdk: (or flutter:) bound may not overlap a package’s required SDK, leaving no solvable version.

How to fix it

Read the conflict and relax a constraint

Identify the two requirements that conflict in the message.
Loosen your own caret pin so the ranges overlap, if possible.
If two third-party packages conflict, upgrade the lagging one to a release that accepts the newer shared dependency.

Let pub suggest an upgrade path

Terminal

dart pub get --verbosity=all
dart pub upgrade --major-versions

Align the SDK constraint

Make sure your environment bound overlaps every dependency’s requirement.

pubspec.yaml

environment:
  sdk: ">=3.4.0 <4.0.0"
  flutter: ">=3.24.0"

How to prevent it

Commit pubspec.lock for apps so CI installs the resolved set.
Keep your SDK constraint aligned with your dependencies’ support.
Upgrade related packages together to keep shared deps compatible.