Warn when pending model changes may be caused by an outdated migration snapshot

[Copilot]

Adds a warning (RelationalEventId.OldMigrationVersionWarning) when Migrate()/MigrateAsync() detects pending model changes and the model snapshot's ProductVersion major version is older than the running EF Core major version. In this scenario the warning fires instead of PendingModelChangesWarning, because the detected changes may be artifacts of snapshot-generation differences in the older EF Core version rather than actual model changes.

Changes

• Migrator.ValidateMigrations() — refactored to use early-return guards for the no-migrations and no-snapshot cases; the version check is now placed inside the PendingModelChangesWarning else-branch so it only fires when pending model changes are detected and the model is deterministic
• Trigger condition — OldMigrationVersionWarning fires instead of PendingModelChangesWarning when:
  • targetMigration is null (default Migrate() path)
  • HasPendingModelChanges() returns true
  • The model changes are deterministic (not from HasData with random values)
  • The snapshot's major version is less than the current EF Core major version
• Major-version-only comparison — avoids noise from minor/patch/pre-release updates; implemented via a TryGetMajorVersion local function using AsSpan without substring allocation
• MigrationVersionEventData — new event data type extending DbContextTypeEventData, carrying the DbContext type and the snapshot version string
• RelationalEventId.OldMigrationVersionWarning — new event ID; configurable via ConfigureWarnings

// Treat as error
optionsBuilder.ConfigureWarnings(w =>
    w.Throw(RelationalEventId.OldMigrationVersionWarning));

// Suppress
optionsBuilder.ConfigureWarnings(w =>
    w.Ignore(RelationalEventId.OldMigrationVersionWarning));

[Copilot]

Pull request overview

Adds a new relational diagnostics warning emitted during Migrate()/MigrateAsync() when the model snapshot was produced by an older EF Core major version, to help surface scenarios where users may be missing snapshot-generation fixes after upgrading.

Changes:

• Emit RelationalEventId.OldMigrationVersionWarning from Migrator.ValidateMigrations() based on snapshot ProductVersion major vs current EF Core major.
• Introduce MigrationVersionEventData and corresponding logging plumbing (RelationalLoggerExtensions, resources, logging definitions, and event id).
• Add functional/spec test wiring to validate the warning (including a SqlServer test which throws on the warning).

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
test/EFCore.SqlServer.FunctionalTests/Migrations/MigrationsInfrastructureSqlServerTest.cs	Adds sync/async tests that configure the new warning to throw and assert the resulting exception message.
test/EFCore.Relational.Specification.Tests/Migrations/MigrationsInfrastructureTestBase.cs	Ensures the new warning is captured in migration test logging configuration.
src/EFCore.Relational/Properties/RelationalStrings.resx	Adds localized message template for the new warning.
src/EFCore.Relational/Properties/RelationalStrings.Designer.cs	Adds the strongly-typed logging resource accessor and event definition for the new warning.
src/EFCore.Relational/Migrations/Internal/Migrator.cs	Implements snapshot-version major parsing and emits the warning during migration validation.
src/EFCore.Relational/Diagnostics/RelationalLoggingDefinitions.cs	Adds a logging definition slot for the new event.
src/EFCore.Relational/Diagnostics/RelationalLoggerExtensions.cs	Adds logger extension method + DiagnosticSource event dispatch for the new warning.
src/EFCore.Relational/Diagnostics/RelationalEventId.cs	Registers OldMigrationVersionWarning as a new migrations event id.
src/EFCore.Relational/Diagnostics/MigrationVersionEventData.cs	Adds the DiagnosticSource payload type carrying migration TypeInfo and snapshot version string.

Files not reviewed (1)

• src/EFCore.Relational/Properties/RelationalStrings.Designer.cs: Language not supported

[Copilot]

Pull request overview

Copilot reviewed 9 out of 10 changed files in this pull request and generated 3 comments.

Files not reviewed (1)

• src/EFCore.Relational/Properties/RelationalStrings.Designer.cs: Language not supported

[Copilot]

The XML doc summary for LogOldMigrationVersion doesn't match the actual resource text in RelationalStrings.resx (it includes extra wording like "The current version is newer" / "any"). Since this file is typically generated from the .resx, please regenerate/update the designer so the docs stay in sync with the resource value.

Suggested change

	/// The last migration '{migrationName}' was created with EF Core version '{efVersion}'. The current version is newer. Consider adding a new empty migration to take advantage of any bug fixes and improvements in the current version of EF Core.
	/// The last migration '{migrationName}' was created with EF Core version '{efVersion}'. Consider adding a new empty migration to take advantage of bug fixes and improvements in the current version of EF Core.

[roji]

@AndriySvyryd does this mean all users will systematically start getting warnings the moment they upgrade to EF 11, if they have migrations generated with EF 10? If so, what are trying to achieve with that, given that 100% of EF users will get that warning (and I'm not sure what action they're expected to take)? Or have I misunderstood?

[AndriySvyryd]

@roji This is to avoid confusion from spurious pending model changes warning due to an old snapshot. I'll change the logic to make it clearer