Replace `StateError` with `ProviderMissingLastValueError` when disposing a provider with no value emitted

[AlexV525]

Related Issues

Working towards https://github.com/rrousselGit/riverpod/discussions/3223

Throwing an error would be acceptable, but users have to write hard-coded strings to match and escape:

void handleExceptions(Object error) {
  if (error case final StateError error when error.message.contains('was disposed during loading state, yet no value could be emitted.') {
    // ignore
    return;
  }
}

The PR adds ProviderMissingLastValueError so the error could be gracefully caught and handled specifically.

Checklist

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• [x] I have updated the CHANGELOG.md of the relevant packages. Changelog files must be edited under the form:

  ## Unreleased fix/major/minor
  
  - Description of your change. (thanks to @yourGithubId)
  

• [ ] If this contains new features or behavior changes, I have updated the documentation to match those changes.

Summary by CodeRabbit

Summary by CodeRabbit

• Bug Fixes

  • Improved error reporting when disposing a provider that has not emitted any value. The error type is now more specific, making it easier to identify and understand this scenario.

• Documentation

  • Updated changelog to reflect the new error type for provider disposal without emitted values.

• Tests

  • Updated tests to expect the new, more specific error type when a provider is disposed before emitting a value.

[coderabbitai[bot]]

Walkthrough

This change introduces a new error class, ProviderMissingLastValueError, to replace the generic StateError when disposing a provider that never emitted a value. The changelog is updated, the error handling in the provider core is refactored, and related tests are updated to expect the new error type.

Changes

File(s)	Change Summary
packages/riverpod/CHANGELOG.md	Added entry describing the new ProviderMissingLastValueError for providers disposed without a value.
packages/riverpod/lib/src/core/element.dart	Removed private _missingLastValueError, added ProviderMissingLastValueError class, updated usage.
packages/riverpod/test/old/legacy_providers/stream_provider/stream_provider_test.dart	Updated test to expect ProviderMissingLastValueError instead of generic StateError.

Possibly related PRs

• rrousselGit/riverpod#4150: Introduced the ElementWithFuture mixin with async state management; this PR refactors error handling within that mixin by replacing a private error method with a dedicated error class.

Suggested reviewers

• rrousselGit

Poem

In the garden of code, a new error does bloom,
No more generic shadows, specificity resumes!
Providers now whisper, with clarity they cry,
"Missing last value!"—a truth you can't deny.
The river flows onward, with type-safety in view,
🐇✨ Here’s to precise errors—cheers to something new!

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Reviewing files that changed from the base of the PR and between c812128d5984ea7f6024175be0117009d4665bc8 and 5480cc7a5bb6451b9486713847c3b59b809e536f.

📒 Files selected for processing (2)

• packages/riverpod/lib/src/core/element.dart (2 hunks)
• packages/riverpod/test/old/legacy_providers/stream_provider/stream_provider_test.dart (2 hunks)

🚧 Files skipped from review as they are similar to previous changes (2)

• packages/riverpod/lib/src/core/element.dart
• packages/riverpod/test/old/legacy_providers/stream_provider/stream_provider_test.dart

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[AlexV525]

Checks are failing for unrelated reasons.

[rrousselGit]

Please make an issue first. I need to understand the use case

[AlexV525]

Created https://github.com/rrousselGit/riverpod/issues/4168

[rrousselGit]

Closing while we first agree on how to solve https://github.com/rrousselGit/riverpod/issues/4168