Make accessor required for table-level index defs in C#

crates/bindings-csharp/Codegen.Tests/fixtures/diag/Lib.cs

@@ -441,10 +441,17 @@ public MyStruct(int x)
 [SpacetimeDB.Index.BTree(Accessor = "TestIndexWithoutColumns")]
 [SpacetimeDB.Index.BTree(Accessor = "TestIndexWithEmptyColumns", Columns = [])]
 [SpacetimeDB.Index.BTree(Accessor = "TestUnknownColumns", Columns = ["UnknownColumn"])]
+[SpacetimeDB.Index.BTree(Columns = ["SelfIndexingColumn"])]
+[SpacetimeDB.Index.BTree(
+    Name = "TestCanonicalNameWithoutAccessor",
+    Columns = ["SecondaryIndexingColumn"]
+)]
 public partial struct TestIndexIssues
 {
     [SpacetimeDB.Index.BTree(Accessor = "TestUnexpectedColumns", Columns = ["UnexpectedColumn"])]
     public int SelfIndexingColumn;
+
+    public int SecondaryIndexingColumn;
 }
 
 [SpacetimeDB.Table(

crates/bindings-csharp/Codegen.Tests/fixtures/diag/snapshots/Module.verified.txt

@@ -140,7 +140,7 @@ public partial record TestTableTaggedEnum : SpacetimeDB.TaggedEnum<(int X, int Y
 [SpacetimeDB.Index.BTree(Accessor = "TestIndexWithEmptyColumns", Columns = [])]
 [SpacetimeDB.Index.BTree(Accessor = "TestUnknownColumns", Columns = ["UnknownColumn"])]
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-public partial struct TestIndexIssues
+[SpacetimeDB.Index.BTree(Columns = ["SelfIndexingColumn"])]
 */
       Message: Could not find the specified column UnknownColumn in TestIndexIssues.,
       Severity: Error,
@@ -154,6 +154,46 @@ public partial struct TestIndexIssues
       }
     },
     {/*
+[SpacetimeDB.Index.BTree(Accessor = "TestUnknownColumns", Columns = ["UnknownColumn"])]
+[SpacetimeDB.Index.BTree(Columns = ["SelfIndexingColumn"])]
+ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+[SpacetimeDB.Index.BTree(
+*/
+      Message: Index attribute on a table declaration must specify Accessor. Field-level index attributes may omit Accessor and default to the field name.,
+      Severity: Error,
+      Descriptor: {
+        Id: STDB0029,
+        Title: Table-level index attributes must specify Accessor,
+        MessageFormat: Index attribute on a table declaration must specify Accessor. Field-level index attributes may omit Accessor and default to the field name.,
+        Category: SpacetimeDB,
+        DefaultSeverity: Error,
+        IsEnabledByDefault: true
+      }
+    },
+    {/*
+[SpacetimeDB.Index.BTree(Columns = ["SelfIndexingColumn"])]
+[SpacetimeDB.Index.BTree(
+ ^^^^^^^^^^^^^^^^^^^^^^^^
+    Name = "TestCanonicalNameWithoutAccessor",
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+    Columns = ["SecondaryIndexingColumn"]
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+)]
+^
+public partial struct TestIndexIssues
+*/
+      Message: Index attribute on a table declaration must specify Accessor. Field-level index attributes may omit Accessor and default to the field name.,
+      Severity: Error,
+      Descriptor: {
+        Id: STDB0029,
+        Title: Table-level index attributes must specify Accessor,
+        MessageFormat: Index attribute on a table declaration must specify Accessor. Field-level index attributes may omit Accessor and default to the field name.,
+        Category: SpacetimeDB,
+        DefaultSeverity: Error,
+        IsEnabledByDefault: true
+      }
+    },
+    {/*
 
 [SpacetimeDB.Table(
  ^^^^^^^^^^^^^^^^^^

crates/bindings-csharp/Codegen/Diag.cs

@@ -257,4 +257,13 @@ string typeName
                 $"[SpacetimeDB.Settings] is declared multiple times: {string.Join(", ", fullNames)}",
             _ => Location.None
         );
+
+    public static readonly ErrorDescriptor<AttributeData> TableLevelIndexMissingAccessor =
+        new(
+            group,
+            "Table-level index attributes must specify Accessor",
+            _ =>
+                $"Index attribute on a table declaration must specify Accessor. Field-level index attributes may omit Accessor and default to the field name.",
+            attr => attr
+        );
 }

crates/bindings-csharp/Codegen/Module.cs

@@ -407,6 +407,11 @@ DiagReporter diag
                 .ToImmutableArray()
         )
     {
+        if (string.IsNullOrWhiteSpace(attr.Accessor))
+        {
+            diag.Report(ErrorDescriptor.TableLevelIndexMissingAccessor, data);
+        }
+
         if (attr.Columns.Length == 0)
         {
             diag.Report(ErrorDescriptor.EmptyIndexColumns, data);