Track prunability of inner joins on the expression itself

Instead of on a private list on SelectExpression.
Part of dotnet#31049

EFCore.sln.DotSettings

@@ -315,6 +315,7 @@ The .NET Foundation licenses this file to you under the MIT license.
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=pluralizer/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=Poolable/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=Postgre/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/UserDictionary/Words/=prunable/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=pushdown/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=queryables/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=remapper/@EntryIndexedValue">True</s:Boolean>

src/EFCore.Relational/Query/SqlExpressions/CrossApplyExpression.cs

@@ -24,7 +24,7 @@ public CrossApplyExpression(TableExpressionBase table)
     }
 
     private CrossApplyExpression(TableExpressionBase table, IEnumerable<IAnnotation>? annotations)
-        : base(table, annotations)
+        : base(table, prunable: false, annotations)
     {
     }
 

src/EFCore.Relational/Query/SqlExpressions/CrossJoinExpression.cs

@@ -24,7 +24,7 @@ public CrossJoinExpression(TableExpressionBase table)
     }
 
     private CrossJoinExpression(TableExpressionBase table, IEnumerable<IAnnotation>? annotations)
-        : base(table, annotations)
+        : base(table, prunable: false, annotations)
     {
     }
 

src/EFCore.Relational/Query/SqlExpressions/InnerJoinExpression.cs

@@ -19,16 +19,18 @@ public class InnerJoinExpression : PredicateJoinExpressionBase
     /// </summary>
     /// <param name="table">A table source to INNER JOIN with.</param>
     /// <param name="joinPredicate">A predicate to use for the join.</param>
-    public InnerJoinExpression(TableExpressionBase table, SqlExpression joinPredicate)
-        : this(table, joinPredicate, annotations: null)
+    /// <param name="prunable">Whether this join expression may be pruned if nothing references a column on it.</param>
+    public InnerJoinExpression(TableExpressionBase table, SqlExpression joinPredicate, bool prunable = false)
+        : this(table, joinPredicate, prunable, annotations: null)
     {
     }
 
     private InnerJoinExpression(
         TableExpressionBase table,
         SqlExpression joinPredicate,
+        bool prunable,
         IEnumerable<IAnnotation>? annotations)
-        : base(table, joinPredicate, annotations)
+        : base(table, joinPredicate, prunable, annotations)
     {
     }
 
@@ -41,7 +43,7 @@ private InnerJoinExpression(
     /// <returns>This expression if no children changed, or an expression with the updated children.</returns>
     public override InnerJoinExpression Update(TableExpressionBase table, SqlExpression joinPredicate)
         => table != Table || joinPredicate != JoinPredicate
-            ? new InnerJoinExpression(table, joinPredicate, GetAnnotations())
+            ? new InnerJoinExpression(table, joinPredicate, IsPrunable, GetAnnotations())
             : this;
 
     /// <summary>
@@ -52,12 +54,12 @@ public override InnerJoinExpression Update(TableExpressionBase table, SqlExpress
     /// <returns>This expression if no children changed, or an expression with the updated children.</returns>
     public override InnerJoinExpression Update(TableExpressionBase table)
         => table != Table
-            ? new InnerJoinExpression(table, JoinPredicate, GetAnnotations())
+            ? new InnerJoinExpression(table, JoinPredicate, IsPrunable, GetAnnotations())
             : this;
 
     /// <inheritdoc />
     protected override TableExpressionBase CreateWithAnnotations(IEnumerable<IAnnotation> annotations)
-        => new InnerJoinExpression(Table, JoinPredicate, annotations);
+        => new InnerJoinExpression(Table, JoinPredicate, IsPrunable, annotations);
 
     /// <inheritdoc />
     protected override void Print(ExpressionPrinter expressionPrinter)

src/EFCore.Relational/Query/SqlExpressions/JoinExpressionBase.cs

@@ -18,27 +18,26 @@ public abstract class JoinExpressionBase : TableExpressionBase
     ///     Creates a new instance of the <see cref="JoinExpressionBase" /> class.
     /// </summary>
     /// <param name="table">A table source to join with.</param>
-    protected JoinExpressionBase(TableExpressionBase table)
-        : this(table, annotations: null)
-    {
-    }
-
-    /// <summary>
-    ///     Creates a new instance of the <see cref="JoinExpressionBase" /> class.
-    /// </summary>
-    /// <param name="table">A table source to join with.</param>
+    /// <param name="prunable">Whether this join expression may be pruned if nothing references a column on it.</param>
     /// <param name="annotations">A collection of annotations associated with this expression.</param>
-    protected JoinExpressionBase(TableExpressionBase table, IEnumerable<IAnnotation>? annotations)
+    protected JoinExpressionBase(TableExpressionBase table, bool prunable, IEnumerable<IAnnotation>? annotations = null)
         : base(alias: null, annotations)
     {
         Table = table;
+        IsPrunable = prunable;
     }
 
     /// <summary>
     ///     Gets the underlying table source to join with.
     /// </summary>
     public virtual TableExpressionBase Table { get; }
 
+    /// <summary>
+    ///     Whether this join expression may be pruned if nothing references a column on it. This isn't the case, for example, when an
+    ///     INNER JOIN is used to filter out rows.
+    /// </summary>
+    public virtual bool IsPrunable { get; }
+
     /// <summary>
     ///     Creates a new expression that is like this one, but using the supplied children. If all of the children are the same, it will
     ///     return this expression.

src/EFCore.Relational/Query/SqlExpressions/LeftJoinExpression.cs

@@ -19,16 +19,18 @@ public class LeftJoinExpression : PredicateJoinExpressionBase
     /// </summary>
     /// <param name="table">A table source to LEFT JOIN with.</param>
     /// <param name="joinPredicate">A predicate to use for the join.</param>
-    public LeftJoinExpression(TableExpressionBase table, SqlExpression joinPredicate)
-        : this(table, joinPredicate, annotations: null)
+    /// <param name="prunable">Whether this join expression may be pruned if nothing references a column on it.</param>
+    public LeftJoinExpression(TableExpressionBase table, SqlExpression joinPredicate, bool prunable = false)
+        : this(table, joinPredicate, prunable, annotations: null)
     {
     }
 
     private LeftJoinExpression(
         TableExpressionBase table,
         SqlExpression joinPredicate,
-        IEnumerable<IAnnotation>? annotations)
-        : base(table, joinPredicate, annotations)
+        bool prunable,
+        IEnumerable<IAnnotation>? annotations = null)
+        : base(table, joinPredicate, prunable, annotations)
     {
     }
 
@@ -41,7 +43,7 @@ private LeftJoinExpression(
     /// <returns>This expression if no children changed, or an expression with the updated children.</returns>
     public override LeftJoinExpression Update(TableExpressionBase table, SqlExpression joinPredicate)
         => table != Table || joinPredicate != JoinPredicate
-            ? new LeftJoinExpression(table, joinPredicate, GetAnnotations())
+            ? new LeftJoinExpression(table, joinPredicate, IsPrunable, GetAnnotations())
             : this;
 
     /// <summary>
@@ -52,12 +54,12 @@ public override LeftJoinExpression Update(TableExpressionBase table, SqlExpressi
     /// <returns>This expression if no children changed, or an expression with the updated children.</returns>
     public override LeftJoinExpression Update(TableExpressionBase table)
         => table != Table
-            ? new LeftJoinExpression(table, JoinPredicate, GetAnnotations())
+            ? new LeftJoinExpression(table, JoinPredicate, IsPrunable, GetAnnotations())
             : this;
 
     /// <inheritdoc />
     protected override TableExpressionBase CreateWithAnnotations(IEnumerable<IAnnotation> annotations)
-        => new LeftJoinExpression(Table, JoinPredicate, annotations);
+        => new LeftJoinExpression(Table, JoinPredicate, IsPrunable, annotations);
 
     /// <inheritdoc />
     protected override void Print(ExpressionPrinter expressionPrinter)

src/EFCore.Relational/Query/SqlExpressions/OuterApplyExpression.cs

@@ -24,7 +24,7 @@ public OuterApplyExpression(TableExpressionBase table)
     }
 
     private OuterApplyExpression(TableExpressionBase table, IEnumerable<IAnnotation>? annotations)
-        : base(table, annotations)
+        : base(table, prunable: false, annotations)
     {
     }
 

src/EFCore.Relational/Query/SqlExpressions/PredicateJoinExpressionBase.cs

@@ -19,22 +19,14 @@ public abstract class PredicateJoinExpressionBase : JoinExpressionBase
     /// </summary>
     /// <param name="table">A table source to join with.</param>
     /// <param name="joinPredicate">A predicate to use for the join.</param>
-    protected PredicateJoinExpressionBase(TableExpressionBase table, SqlExpression joinPredicate)
-        : this(table, joinPredicate, annotations: null)
-    {
-    }
-
-    /// <summary>
-    ///     Creates a new instance of the <see cref="PredicateJoinExpressionBase" /> class.
-    /// </summary>
-    /// <param name="table">A table source to join with.</param>
-    /// <param name="joinPredicate">A predicate to use for the join.</param>
+    /// <param name="prunable">Whether this join expression may be pruned if nothing references a column on it.</param>
     /// <param name="annotations">A collection of annotations associated with this expression.</param>
     protected PredicateJoinExpressionBase(
         TableExpressionBase table,
         SqlExpression joinPredicate,
-        IEnumerable<IAnnotation>? annotations)
-        : base(table, annotations)
+        bool prunable,
+        IEnumerable<IAnnotation>? annotations = null)
+        : base(table, prunable, annotations)
     {
         JoinPredicate = joinPredicate;
     }

src/EFCore.Relational/Query/SqlExpressions/SelectExpression.Helper.cs

@@ -804,8 +804,6 @@ private sealed class CloningExpressionVisitor : ExpressionVisitor
                         _mutable = selectExpression._mutable
                     };
 
-                    newSelectExpression._removableJoinTables.AddRange(selectExpression._removableJoinTables);
-
                     foreach (var kvp in selectExpression._tpcDiscriminatorValues)
                     {
                         newSelectExpression._tpcDiscriminatorValues[tpcTablesMap[kvp.Key]] = kvp.Value;

src/EFCore.Relational/Query/SqlExpressions/SelectExpression.cs

@@ -35,7 +35,6 @@ public sealed partial class SelectExpression : TableExpressionBase
 
     private readonly List<(ColumnExpression Column, ValueComparer Comparer)> _identifier = new();
     private readonly List<(ColumnExpression Column, ValueComparer Comparer)> _childIdentifiers = new();
-    private readonly List<int> _removableJoinTables = new();
 
     private readonly Dictionary<TpcTablesExpression, (ColumnExpression, List<string>)> _tpcDiscriminatorValues
         = new(ReferenceEqualityComparer.Instance);
@@ -225,8 +224,7 @@ internal SelectExpression(IEntityType entityType, ISqlExpressionFactory sqlExpre
                         .Zip(keyColumns, sqlExpressionFactory.Equal)
                         .Aggregate(sqlExpressionFactory.AndAlso);
 
-                    var joinExpression = new LeftJoinExpression(tableExpression, joinPredicate);
-                    _removableJoinTables.Add(_tables.Count);
+                    var joinExpression = new LeftJoinExpression(tableExpression, joinPredicate, prunable: true);
                     AddTable(joinExpression, tableReferenceExpression);
                 }
 
@@ -435,8 +433,7 @@ _projectionMapping[new ProjectionMember()] =
                                     .Zip(innerColumns, sqlExpressionFactory.Equal)
                                     .Aggregate(sqlExpressionFactory.AndAlso);
 
-                                var joinExpression = new InnerJoinExpression(tableExpression, joinPredicate);
-                                _removableJoinTables.Add(_tables.Count);
+                                var joinExpression = new InnerJoinExpression(tableExpression, joinPredicate, prunable: true);
                                 AddTable(joinExpression, tableReferenceExpression);
                             }
                         }
@@ -2496,8 +2493,6 @@ private void ApplySetOperation(SetOperationType setOperationType, SelectExpressi
         _projectionMapping.Clear();
         select1._identifier.AddRange(_identifier);
         _identifier.Clear();
-        select1._removableJoinTables.AddRange(_removableJoinTables);
-        _removableJoinTables.Clear();
         foreach (var kvp in _tpcDiscriminatorValues)
         {
             select1._tpcDiscriminatorValues[kvp.Key] = kvp.Value;
@@ -3045,8 +3040,7 @@ static IReadOnlyDictionary<IProperty, ColumnExpression> GetPropertyExpressions(
                                     .Zip(innerColumns, sqlExpressionFactory.Equal)
                                     .Aggregate(sqlExpressionFactory.AndAlso);
 
-                                var joinExpression = new LeftJoinExpression(tableExpression, joinPredicate);
-                                selectExpression._removableJoinTables.Add(selectExpression._tables.Count);
+                                var joinExpression = new LeftJoinExpression(tableExpression, joinPredicate, prunable: true);
                                 selectExpression.AddTable(joinExpression, tableReferenceExpression);
                             }
                         }
@@ -3129,8 +3123,7 @@ static IReadOnlyDictionary<IProperty, ColumnExpression> GetPropertyExpressions(
                         .Zip(innerColumns, sqlExpressionFactory.Equal)
                         .Aggregate(sqlExpressionFactory.AndAlso);
 
-                    var joinExpression = new LeftJoinExpression(tableExpression, joinPredicate);
-                    selectExpression._removableJoinTables.Add(selectExpression._tables.Count);
+                    var joinExpression = new LeftJoinExpression(tableExpression, joinPredicate, prunable: true);
                     selectExpression.AddTable(joinExpression, tableReferenceExpression);
                 }
             }
@@ -3974,8 +3967,6 @@ private SqlRemappingVisitor PushdownIntoSubqueryInternal(bool liftOrderings = tr
         Offset = null;
         Limit = null;
         _preGroupByIdentifier = null;
-        subquery._removableJoinTables.AddRange(_removableJoinTables);
-        _removableJoinTables.Clear();
         foreach (var kvp in _tpcDiscriminatorValues)
         {
             subquery._tpcDiscriminatorValues[kvp.Key] = kvp.Value;
@@ -4439,11 +4430,9 @@ public void Prune(SqlTreePruner pruningVisitor, bool pruneProjection)
 
             if (!referencedColumnMap.ContainsKey(wrappedTable)
                 // Note that we only prune joins; pruning the main is more complex because other tables need to unwrap joins to be main.
-                // TODO: why not CrossApplyExpression/CrossJoin (any join basically)?
-                && table is LeftJoinExpression or OuterApplyExpression or InnerJoinExpression
-                // Only prune InnerJoin if it's in the removable list; since inner joins filter out rows, it may be needed even if it's not
-                // referenced from anywhere in the query.
-                && _removableJoinTables.Contains(i))
+                // We also only prune joins explicitly marked as prunable; otherwise e.g. an inner join may be needed to filter out rows
+                // even if no column references it.
+                && table is JoinExpressionBase { IsPrunable: true })
             {
                 _tables.RemoveAt(i);
                 _tableReferences.RemoveAt(i);
@@ -4821,7 +4810,6 @@ private Expression VisitChildren(ExpressionVisitor visitor, bool updateColumns)
                     _usedAliases = _usedAliases,
                     _mutable = false
                 };
-                newSelectExpression._removableJoinTables.AddRange(_removableJoinTables);
                 foreach (var kvp in newTpcDiscriminatorValues)
                 {
                     newSelectExpression._tpcDiscriminatorValues[kvp.Key] = kvp.Value;

src/EFCore.Relational/Query/SqlExpressions/TableExpressionBase.cs

@@ -17,22 +17,12 @@ public abstract class TableExpressionBase : Expression, IPrintableExpression
 {
     private readonly IReadOnlyDictionary<string, IAnnotation>? _annotations;
 
-    /// <summary>
-    ///     Creates a new instance of the <see cref="TableExpressionBase" /> class.
-    /// </summary>
-    /// <param name="alias">A string alias for the table source.</param>
-    protected TableExpressionBase(string? alias)
-        : this(alias, annotations: null)
-    {
-        Alias = alias;
-    }
-
     /// <summary>
     ///     Creates a new instance of the <see cref="TableExpressionBase" /> class.
     /// </summary>
     /// <param name="alias">A string alias for the table source.</param>
     /// <param name="annotations">A collection of annotations associated with this expression.</param>
-    protected TableExpressionBase(string? alias, IEnumerable<IAnnotation>? annotations)
+    protected TableExpressionBase(string? alias, IEnumerable<IAnnotation>? annotations = null)
     {
         Alias = alias;