Add helpful exception when a property’s backing field cannot be found.

Fixes #35219

Author: kawasaniac

src/EFCore.Design/Properties/DesignStrings.Designer.cs

@@ -126,9 +126,6 @@
   <data name="BadMigrationName" xml:space="preserve">
     <value>The migration name '{name}' is not valid. Migration names cannot contain any of the following characters: '{characters}'.</value>
   </data>
-  <data name="MigrationNameRequired" xml:space="preserve">
-    <value>A migration name must be specified.</value>
-  </data>
   <data name="BadSequenceType" xml:space="preserve">
     <value>Sequence '{sequenceName}' cannot be scaffolded because it uses type '{typeName}' which is unsupported.</value>
   </data>
@@ -162,6 +159,9 @@
   <data name="CompilationMustBeLoaded" xml:space="preserve">
     <value>A compilation must be loaded.</value>
   </data>
+  <data name="CompiledModelBackingFieldNotFound" xml:space="preserve">
+    <value>Backing field for property '{entityType}.{propertyName}' could not be inferred. Use a matching field name or configure with 'HasField()'.</value>
+  </data>
   <data name="CompiledModelConstructorBinding" xml:space="preserve">
     <value>The entity type '{entityType}' has a custom constructor binding. Compiled model can't be generated, because custom constructor bindings are not supported. Configure the custom constructor binding in '{customize}' in a partial '{className}' class instead.</value>
   </data>
@@ -193,6 +193,9 @@ Consider changing your target project to the DbContext project by using the Pack
   <data name="CouldNotGetInterceptableLocation" xml:space="preserve">
     <value>Couldn't get interceptable location for: '{node}'.</value>
   </data>
+  <data name="CreatingAndApplyingMigration" xml:space="preserve">
+    <value>Creating and applying migration '{migrationName}'.</value>
+  </data>
   <data name="DatabaseDropped" xml:space="preserve">
     <value>Successfully dropped database '{name}'.</value>
   </data>
@@ -208,6 +211,9 @@ Consider changing your target project to the DbContext project by using the Pack
   <data name="DuplicateMigrationName" xml:space="preserve">
     <value>The name '{migrationName}' is used by an existing migration.</value>
   </data>
+  <data name="DynamicMigrationNotFound" xml:space="preserve">
+    <value>The dynamic migration '{migrationId}' was not found. Only migrations applied in the current session using CreateAndApplyMigration can be reverted.</value>
+  </data>
   <data name="DynamicQueryNotSupported" xml:space="preserve">
     <value>Dynamic LINQ queries are not supported when precompiling queries.</value>
   </data>
@@ -289,14 +295,27 @@ Consider changing your target project to the DbContext project by using the Pack
   <data name="ManuallyDeleted" xml:space="preserve">
     <value>The model snapshot and the backing model of the last migration are different. Continuing under the assumption that the last migration was deleted manually.</value>
   </data>
+  <data name="MigrationCompilationFailed" xml:space="preserve">
+    <value>Failed to compile migration '{migrationId}'. Errors:
+{errors}</value>
+  </data>
+  <data name="MigrationCreatedAndApplied" xml:space="preserve">
+    <value>Migration '{migrationId}' was successfully created and applied.</value>
+  </data>
   <data name="MigrationDescription" xml:space="preserve">
     <value>The target migration. If '0', all migrations will be reverted. Defaults to the last migration.</value>
   </data>
+  <data name="MigrationNameRequired" xml:space="preserve">
+    <value>A migration name must be specified.</value>
+  </data>
   <data name="MigrationsAssemblyMismatch" xml:space="preserve">
     <value>Your target project '{assembly}' doesn't match your migrations assembly '{migrationsAssembly}'. Either change your target project or change your migrations assembly.
 Change your migrations assembly by using DbContextOptionsBuilder. E.g. options.UseSqlServer(connection, b =&gt; b.MigrationsAssembly("{assembly}")). By default, the migrations assembly is the assembly containing the DbContext.
 Change your target project to the migrations project by using the Package Manager Console's Default project drop-down list, or by executing "dotnet ef" from the directory containing the migrations project.</value>
   </data>
+  <data name="MigrationTypeNotFound" xml:space="preserve">
+    <value>Could not find migration type with ID '{migrationId}' in the compiled assembly.</value>
+  </data>
   <data name="MSBuildWorkspaceDiagnostics" xml:space="preserve">
     <value>MSBuild Workspace diagnostics:{diagnostics}</value>
   </data>
@@ -342,6 +361,9 @@ Change your target project to the migrations project by using the Package Manage
   <data name="NoDesignTimeServices" xml:space="preserve">
     <value>No design-time services were found.</value>
   </data>
+  <data name="NoDynamicMigrationsToRevert" xml:space="preserve">
+    <value>No dynamic migrations have been applied in the current session. Only migrations applied using CreateAndApplyMigration can be reverted with RevertMigration.</value>
+  </data>
   <data name="NoLanguageService" xml:space="preserve">
     <value>The project language '{language}' isn't supported by the built-in {service} service. You can try looking for an additional NuGet package which supports this language; moving your DbContext type to a C# class library referenced by this project; or manually implementing and registering the design-time service for the programming language.</value>
   </data>
@@ -360,12 +382,6 @@ Change your target project to the migrations project by using the Package Manage
   <data name="NoPendingModelChanges" xml:space="preserve">
     <value>No changes have been made to the model since the last migration.</value>
   </data>
-  <data name="NoDynamicMigrationsToRevert" xml:space="preserve">
-    <value>No dynamic migrations have been applied in the current session. Only migrations applied using CreateAndApplyMigration can be reverted with RevertMigration.</value>
-  </data>
-  <data name="DynamicMigrationNotFound" xml:space="preserve">
-    <value>The dynamic migration '{migrationId}' was not found. Only migrations applied in the current session using CreateAndApplyMigration can be reverted.</value>
-  </data>
   <data name="NoReferencedServices" xml:space="preserve">
     <value>No referenced design-time services were found.</value>
   </data>
@@ -499,17 +515,4 @@ Change your target project to the migrations project by using the Package Manage
   <data name="WritingSnapshot" xml:space="preserve">
     <value>Writing model snapshot to '{file}'.</value>
   </data>
-  <data name="MigrationCompilationFailed" xml:space="preserve">
-    <value>Failed to compile migration '{migrationId}'. Errors:
-{errors}</value>
-  </data>
-  <data name="MigrationTypeNotFound" xml:space="preserve">
-    <value>Could not find migration type with ID '{migrationId}' in the compiled assembly.</value>
-  </data>
-  <data name="CreatingAndApplyingMigration" xml:space="preserve">
-    <value>Creating and applying migration '{migrationName}'.</value>
-  </data>
-  <data name="MigrationCreatedAndApplied" xml:space="preserve">
-    <value>Migration '{migrationId}' was successfully created and applied.</value>
-  </data>
 </root>

src/EFCore.Design/Properties/DesignStrings.resx

@@ -1769,7 +1769,9 @@ private void RegisterPrivateAccessors(
         Dictionary<Type, HashSet<MemberInfo>> unsafeAccessorTypes,
         ref Dictionary<MemberInfo, QualifiedName>? memberAccessReplacements)
     {
-        var member = property.GetMemberInfo(forMaterialization, forSet);
+        var member = property.GetMemberInfo(forMaterialization, forSet) ?? throw new InvalidOperationException(
+                DesignStrings.CompiledModelBackingFieldNotFound(property.DeclaringType.ShortName(), property.Name));
+
         switch (member)
         {
             case FieldInfo field:
@@ -1799,6 +1801,7 @@ private void RegisterPrivateAccessors(
         }
 
         memberAccessReplacements ??= [];
+
         var methodName = LinqToCSharpSyntaxTranslator.GetUnsafeAccessorName(member);
 
         var declaringType = member.DeclaringType!;

src/EFCore.Design/Scaffolding/Internal/CSharpRuntimeModelCodeGenerator.cs

@@ -9,6 +9,7 @@
 using System.Net.NetworkInformation;
 using System.Runtime.CompilerServices;
 using System.Text.Json;
+using Microsoft.EntityFrameworkCore.Internal;
 using Microsoft.EntityFrameworkCore.Metadata.Internal;
 using Microsoft.EntityFrameworkCore.Storage.Json;
 using Microsoft.EntityFrameworkCore.ValueGeneration.Internal;
@@ -1167,6 +1168,20 @@ public virtual Task ComplexTypes()
             },
             options: new CompiledModelCodeGenerationOptions { UseNullableReferenceTypes = true, ForNativeAot = true });
 
+    [ConditionalFact]
+    public virtual Task CompiledModelBackingFieldNotFound()
+        => Test(
+            modelBuilder =>
+            {
+                modelBuilder.Entity<EntityWithNoBackingFieldCollection>(eb =>
+                {
+                    eb.Property(e => e.Collection)
+                        .UsePropertyAccessMode(PropertyAccessMode.FieldDuringConstruction);
+                });
+            },
+            options: new CompiledModelCodeGenerationOptions { ForNativeAot = true },
+            expectedExceptionMessage: DesignStrings.CompiledModelBackingFieldNotFound("EntityWithNoBackingFieldCollection", "Collection"));
+
     protected virtual void BuildComplexTypesModel(ModelBuilder modelBuilder)
     {
         modelBuilder.Entity<PrincipalBase>(eb =>
@@ -1790,6 +1805,12 @@ public class Data
         public byte[]? Blob { get; set; }
     }
 
+    public class EntityWithNoBackingFieldCollection
+    {
+        public int Id { get; set; }
+        public IList<int> Collection => new List<int>();
+    }
+
     public class PrincipalBase : AbstractBase
     {
         public new long? Id { get; set; }