Add a static flag in EF that will be set when code is being executed …

…for design-time discovery (#28508)

src/EFCore.Design/Design/DbContextActivator.cs

@@ -43,6 +43,8 @@ public static DbContext CreateInstance(
     {
         Check.NotNull(contextType, nameof(contextType));
 
+        EF.IsDesignTime = true;
+
         return new DbContextOperations(
                 new OperationReporter(reportHandler),
                 contextType.Assembly,

src/EFCore.Design/Design/OperationExecutor.cs

@@ -706,6 +706,7 @@ protected OperationBase(IOperationResultHandler resultHandler)
         /// <param name="action">The action to execute.</param>
         protected virtual void Execute(Action action)
         {
+            EF.IsDesignTime = true;
             try
             {
                 action();
@@ -714,6 +715,10 @@ protected virtual void Execute(Action action)
             {
                 _resultHandler.OnError(ex.GetType().FullName!, ex.Message, ex.ToString());
             }
+            finally
+            {
+                EF.IsDesignTime = false;
+            }
         }
 
         /// <summary>

src/EFCore/EF.cs

@@ -17,6 +17,22 @@ public static partial class EF
     internal static readonly MethodInfo PropertyMethod
         = typeof(EF).GetTypeInfo().GetDeclaredMethod(nameof(Property))!;
 
+    /// <summary>
+    ///     This flag is set to <see langword="true" /> when code is being run from a design-time tool, such
+    ///     as "dotnet ef" or one of the Package Manager Console PowerShell commands "Add-Migration", "Update-Database", etc.
+    /// </summary>
+    /// <remarks>
+    ///     <para>
+    ///         This flag can be inspected to change application behavior. For example, if the application is being executed by an EF
+    ///         design-time tool, then it may choose to skip executing migrations commands as part of startup.
+    ///     </para>
+    ///     <para>
+    ///         See <see href="https://aka.ms/efcore-docs-commandline">EF Core command-line reference </see> for more information
+    ///         and examples.
+    ///     </para>
+    /// </remarks>
+    public static bool IsDesignTime { get; set; }
+
     /// <summary>
     ///     References a given property or navigation on an entity instance. This is useful for shadow state properties, for
     ///     which no CLR property exists. Currently this method can only be used in LINQ queries and can not be used to

test/EFCore.Design.Tests/Design/DbContextActivatorTest.cs

@@ -8,28 +8,40 @@ public class DbContextActivatorTest
     [ConditionalFact]
     public void CreateInstance_works()
     {
+        EF.IsDesignTime = false;
+
         var result = DbContextActivator.CreateInstance(typeof(TestContext));
 
         Assert.IsType<TestContext>(result);
+
+        Assert.True(EF.IsDesignTime);
     }
 
     [ConditionalFact]
     public void CreateInstance_with_arguments_works()
     {
+        EF.IsDesignTime = false;
+
         var result = DbContextActivator.CreateInstance(
             typeof(TestContext),
             null,
             null,
             new[] { "A", "B" });
 
         Assert.IsType<TestContext>(result);
+
+        Assert.True(EF.IsDesignTime);
     }
 
     private class TestContext : DbContext
     {
         protected override void OnConfiguring(DbContextOptionsBuilder options)
-            => options
+        {
+            Assert.True(EF.IsDesignTime);
+
+            options
                 .EnableServiceProviderCaching(false)
                 .UseInMemoryDatabase(nameof(DbContextActivatorTest));
+        }
     }
 }

test/EFCore.Design.Tests/Design/OperationExecutorTest.cs

@@ -17,6 +17,24 @@ public void Ctor_validates_arguments()
 
     public class OperationBaseTests
     {
+        [ConditionalFact]
+        public void Operations_have_design_time_flag_set()
+        {
+            EF.IsDesignTime = false;
+
+            var handler = new OperationResultHandler();
+            var result = "Twilight Sparkle";
+
+            new MockOperation<string>(handler, () =>
+            {
+                Assert.True(EF.IsDesignTime);
+                return result;
+            });
+
+            Assert.False(EF.IsDesignTime);
+            Assert.Equal(result, handler.Result);
+        }
+
         [ConditionalFact]
         public void Execute_catches_exceptions()
         {