Add FULL OUTER JOIN support

[roji]

Fixes #37633.

Adds translation support for the new Queryable.FullJoin LINQ operator (dotnet/runtime#124787), mirroring the existing LeftJoin/RightJoin support added in #35451.

Summary

• Register QueryableMethods.FullJoin and dispatch it through the query pipeline (NavigationExpandingExpressionVisitor, QueryableMethodTranslatingExpressionVisitor).
• New FullJoinExpression SQL expression, with SelectExpression handling (both sides nullable), QuerySqlGenerator.VisitFullJoin, and AddFullJoin APIs.
• Providers: relational translation via TranslateFullJoin; InMemory and Cosmos report the operator as untranslatable.

Notes

• API shape: Unlike LeftJoin/RightJoin (which expose separate no-comparer and comparer overloads), FullJoin has a single overload with an optional trailing IEqualityComparer<TKey>. Every call therefore emits a 6-arg expression with a comparer argument (compiler-supplied null when omitted). We only translate the null-comparer case; a custom comparer produces a translation failure.
• Funcletizer: Because the comparer is a top-level operator argument, the default null would normally be parameterized — hiding from the translator whether a (non-translatable) custom comparer was supplied. IsParameterParameterizable now excludes IEqualityComparer<> arguments from parameterization, treating them like [NotParameterized]. This is the first single-overload-optional-comparer operator EF translates.

Latent RIGHT JOIN correctness fix (discovered while adding FULL JOIN)

SelectExpression.AddJoin previously left an outer Predicate as a post-join WHERE for nullable-outer joins. Once the outer side becomes nullable (RIGHT/FULL JOIN), a post-join WHERE on an outer column wrongly drops the unmatched rows (where the outer is NULL), collapsing the join toward an inner join. The outer is now pushed into a subquery (so its predicate is applied before the join) for RightJoin/FullJoin when it has a predicate.

This is the same invariant already handled for the inner side of LEFT JOIN; it was simply never applied to the nullable outer side. The fix corrects a pre-existing, latent RIGHT JOIN bug as well as FULL JOIN.

Consequences:

• Two pre-existing NorthwindBulkUpdates RIGHT JOIN tests had their behavior corrected. Update_with_RightJoin's verification now correctly sees the unmatched right-side rows as null outer entities; its assertion was tightened to assert that shape explicitly (all 8 F-customers returned, 6 unmatched/null, 2 matched and updated). Delete_with_RightJoin is unchanged at runtime (the deleted target is the nullable side, so affected-row counts are identical) — only its SQL baseline changed.
• SQL baselines updated for SqlServer and Sqlite.

Tests

New NorthwindJoinQuery tests (basic full join, unmatched rows on both sides, custom-comparer translation failure, plus a direct RightJoin_with_filtered_outer regression test) with provider overrides. Full SqlServer + Sqlite Query and BulkUpdates suites pass.

Depends on an SDK bump (global.json) to a preview that contains the FullJoin operator.

[Copilot]

Pull request overview

Adds translation support for the new Queryable.FullJoin LINQ operator, mirroring the existing LeftJoin/RightJoin infrastructure. Introduces a new FullJoinExpression, wires it through the query pipeline, and provides provider-specific handling for Relational (translated), InMemory and Cosmos (reported as untranslatable). Also fixes a latent RIGHT JOIN correctness bug where an outer-side predicate was incorrectly applied as a post-join WHERE, which would drop unmatched rows once the outer became nullable.

Changes:

• New FullJoinExpression and AddFullJoin/TranslateFullJoin/VisitFullJoin plumbing across SelectExpression, QuerySqlGenerator, and the relational/in-memory/cosmos translators, plus QueryableMethods.FullJoin registration and dispatch in NavigationExpandingExpressionVisitor/QueryableMethodTranslatingExpressionVisitor.
• ExpressionTreeFuncletizer now refuses to parameterize IEqualityComparer<> arguments, so the compiler-supplied default null on FullJoin is preserved as a constant and translation can distinguish a translatable from a non-translatable comparer.
• SelectExpression.AddJoin now pushes the outer into a subquery when it has a Predicate for RightJoin/FullJoin, fixing a latent RIGHT JOIN bug; SqlServer/Sqlite baselines and one tightened Update_with_RightJoin assertion are updated accordingly, plus new NorthwindJoinQueryTestBase tests cover full join and the right-join regression.

Show a summary per file

File	Description
src/EFCore/Query/QueryableMethods.cs	Registers the Queryable.FullJoin MethodInfo (6-arg overload).
src/EFCore/Query/QueryableMethodTranslatingExpressionVisitor.cs	Dispatches FullJoin (null-comparer only) and adds abstract TranslateFullJoin.
src/EFCore/Query/Internal/NavigationExpandingExpressionVisitor.cs	Handles FullJoin in navigation expansion; rebuilds the call with trailing null comparer and marks both shapers nullable.
src/EFCore/Query/Internal/ExpressionTreeFuncletizer.cs	Excludes IEqualityComparer<> parameters from parameterization.
src/EFCore/EFCore.baseline.json	API baseline additions for FullJoin/TranslateFullJoin.
src/EFCore.Relational/Query/SqlExpressions/FullJoinExpression.cs	New FullJoinExpression mirroring RightJoinExpression.
src/EFCore.Relational/Query/SqlExpressions/SelectExpression.cs	Adds JoinType.FullJoin, both-sides nullable handling, identifier nullability, and the outer-predicate pushdown fix for RIGHT/FULL JOIN.
src/EFCore.Relational/Query/QuerySqlGenerator.cs	Emits FULL JOIN SQL via VisitFullJoin.
src/EFCore.Relational/Query/RelationalQueryableMethodTranslatingExpressionVisitor.cs	Implements relational TranslateFullJoin.
src/EFCore.Relational/EFCore.Relational.baseline.json	API baseline additions for the new expression and AddFullJoin/VisitFullJoin/TranslateFullJoin members.
src/EFCore.InMemory/Query/Internal/InMemoryQueryableMethodTranslatingExpressionVisitor.cs	Returns null (untranslatable) for FullJoin.
src/EFCore.Cosmos/Query/Internal/CosmosQueryableMethodTranslatingExpressionVisitor.cs	Reports FullJoin as untranslatable with the cross-document error.
test/EFCore.Specification.Tests/Query/NorthwindJoinQueryTestBase.cs	New FullJoin, unmatched-both-sides, custom-comparer, and RightJoin_with_filtered_outer tests.
test/EFCore.Specification.Tests/BulkUpdates/NorthwindBulkUpdatesTestBase.cs	Tightens Update_with_RightJoin assertion to verify null outer entries for unmatched rows.
test/EFCore.InMemory.FunctionalTests/Query/NorthwindJoinQueryInMemoryTest.cs	Overrides new tests with AssertTranslationFailed.
test/EFCore.SqlServer.FunctionalTests/Query/NorthwindJoinQuerySqlServerTest.cs	SqlServer SQL baselines for the new join tests.
test/EFCore.SqlServer.FunctionalTests/BulkUpdates/NorthwindBulkUpdatesSqlServerTest.cs	Updated SqlServer SQL baselines reflecting the outer-predicate pushdown.
test/EFCore.Sqlite.FunctionalTests/BulkUpdates/NorthwindBulkUpdatesSqliteTest.cs	Updated Sqlite SQL baselines reflecting the outer-predicate pushdown.
global.json	Bumps SDK to a preview that contains the FullJoin operator.

Copilot's findings

• Files reviewed: 19/19 changed files
• Comments generated: 0

[github-actions]

API review baseline changes for src/EFCore.Relational/EFCore.Relational.baseline.json

Show diff

The diff below was generated by ApiChief between the base and the PR.

  class Microsoft.EntityFrameworkCore.Query.QuerySqlGenerator : System.Linq.Expressions.ExpressionVisitor
+ virtual Expression VisitFullJoin(FullJoinExpression fullJoinExpression);

  class Microsoft.EntityFrameworkCore.Query.RelationalQueryableMethodTranslatingExpressionVisitor :
      Microsoft.EntityFrameworkCore.Query.QueryableMethodTranslatingExpressionVisitor
+ override ShapedQueryExpression? TranslateFullJoin(ShapedQueryExpression outer, ShapedQueryExpression inner, LambdaExpression outerKeySelector,
+     LambdaExpression innerKeySelector, LambdaExpression resultSelector);

+ class Microsoft.EntityFrameworkCore.Query.SqlExpressions.FullJoinExpression : Microsoft.EntityFrameworkCore.Query.SqlExpressions.PredicateJoinExpressionBase
+ override bool Equals(object? obj);
+ FullJoinExpression(TableExpressionBase table, SqlExpression joinPredicate, bool prunable = false);
+ override int GetHashCode();
+ override void Print(ExpressionPrinter expressionPrinter);
+ override Expression Quote();
+ virtual FullJoinExpression Update(TableExpressionBase table);
+ virtual FullJoinExpression Update(TableExpressionBase table, SqlExpression joinPredicate);
+ virtual FullJoinExpression WithAnnotations(IReadOnlyDictionary<string, IAnnotation> annotations);

  sealed class Microsoft.EntityFrameworkCore.Query.SqlExpressions.SelectExpression : Microsoft.EntityFrameworkCore.Query.SqlExpressions.TableExpressionBase
+ Expression AddFullJoin(ShapedQueryExpression innerSource, SqlExpression joinPredicate, Expression outerShaper);
+ void AddFullJoin(SelectExpression innerSelectExpression, SqlExpression joinPredicate);

API review baseline changes for src/EFCore/EFCore.baseline.json

Show diff

The diff below was generated by ApiChief between the base and the PR.

  abstract class Microsoft.EntityFrameworkCore.Query.QueryableMethodTranslatingExpressionVisitor : System.Linq.Expressions.ExpressionVisitor
+ abstract ShapedQueryExpression? TranslateFullJoin(ShapedQueryExpression outer, ShapedQueryExpression inner, LambdaExpression outerKeySelector,
+     LambdaExpression innerKeySelector, LambdaExpression resultSelector);

  static class Microsoft.EntityFrameworkCore.Query.QueryableMethods
+ static MethodInfo FullJoin { get; }