Support DROP INDEX CONCURRENTLY

src/EFCore.PG/Migrations/Internal/NpgsqlMigrationsAnnotationProvider.cs

@@ -31,4 +31,19 @@ public NpgsqlMigrationsAnnotationProvider(MigrationsAnnotationProviderDependenci
     /// </summary>
     public override IEnumerable<IAnnotation> ForRemove(IRelationalModel model)
         => model.Model.GetAnnotations().Where(NpgsqlAnnotationHelper.IsRelationalModelAnnotation);
+
+    /// <summary>
+    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
+    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
+    ///     any release. You should only use it directly in your code with extreme caution and knowing that
+    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
+    /// </summary>
+    public override IEnumerable<IAnnotation> ForRemove(ITableIndex index)
+    {
+        // Model validation ensures that these facets are the same on all mapped indexes
+        if (index.MappedIndexes.First().IsCreatedConcurrently() is { } isCreatedConcurrently)
+        {
+            yield return new Annotation(NpgsqlAnnotationNames.CreatedConcurrently, isCreatedConcurrently);
+        }
+    }
 }

src/EFCore.PG/Migrations/NpgsqlMigrationsSqlGenerator.cs

@@ -1491,14 +1491,21 @@ protected override void Generate(
         Check.NotNull(operation, nameof(operation));
         Check.NotNull(builder, nameof(builder));
 
-        builder
-            .Append("DROP INDEX ")
-            .Append(DelimitIdentifier(operation.Name, operation.Schema));
+        builder.Append("DROP INDEX ");
+
+        var concurrently = operation[NpgsqlAnnotationNames.CreatedConcurrently] as bool? == true;
+        if (concurrently)
+        {
+            builder.Append("CONCURRENTLY ");
+        }
+
+        builder.Append(DelimitIdentifier(operation.Name, operation.Schema));
 
         if (terminate)
         {
             builder.AppendLine(";");
-            EndStatement(builder);
+            // Concurrent indexes cannot be dropped within a transaction
+            EndStatement(builder, suppressTransaction: concurrently);
         }
     }
 

test/EFCore.PG.FunctionalTests/Migrations/MigrationsNpgsqlTest.cs

@@ -2019,6 +2019,24 @@ await Test(
         AssertSql("""CREATE INDEX CONCURRENTLY "IX_People_Age" ON "People" ("Age");""");
     }
 
+    [Fact]
+    public virtual async Task Drop_index_concurrently()
+    {
+        await Test(
+            builder => builder.Entity(
+                "People", e =>
+                {
+                    e.Property<int>("Id");
+                    e.Property<int>("Age");
+                }),
+            builder => builder.Entity("People").HasIndex("Age")
+                .IsCreatedConcurrently(),
+            _ => { },
+            asserter: null); // No scaffolding for IsCreatedConcurrently
+
+        AssertSql("""DROP INDEX CONCURRENTLY "IX_People_Age";""");
+    }
+
     [Fact]
     public virtual async Task Create_index_with_method()
     {

test/EFCore.PG.FunctionalTests/Migrations/NpgsqlMigrationsSqlGeneratorTest.cs

@@ -619,6 +619,43 @@ public override void InsertDataOperation_throws_for_unsupported_column_types()
 
 #pragma warning restore 618
 
+    [Fact]
+    public virtual void DropIndexOperation_concurrently()
+    {
+        Generate(
+            new DropIndexOperation
+            {
+                Name = "IX_People_Name",
+                Table = "People",
+                Schema = "dbo",
+                [NpgsqlAnnotationNames.CreatedConcurrently] = true
+            });
+
+        AssertSql(
+            """
+DROP INDEX CONCURRENTLY dbo."IX_People_Name";
+
+""");
+    }
+
+    [Fact]
+    public virtual void DropIndexOperation_not_concurrently()
+    {
+        Generate(
+            new DropIndexOperation
+            {
+                Name = "IX_People_Name",
+                Table = "People",
+                Schema = "dbo"
+            });
+
+        AssertSql(
+            """
+DROP INDEX dbo."IX_People_Name";
+
+""");
+    }
+
     protected override string GetGeometryCollectionStoreType()
         => "GEOMETRY(GEOMETRYCOLLECTION)";
 }