Fix using anonymous unions in the function variables

Cesium.CodeGen.Tests/CodeGenDeclarationsTests.cs

@@ -43,4 +43,13 @@ public Task ConstTypeDef() => DoTest(
         @"
 typedef int myint;
 static const myint i = 0;");
+
+    [Fact]
+    public Task AnonymousUnionVariableInsideFunction() => DoTest(
+        @"int main()
+{
+    union {int i;} t;
+    t.i = 0;
+}
+");
 }

Cesium.CodeGen.Tests/verified/CodeGenDeclarationsTests.AnonymousUnionVariableInsideFunction.verified.txt

@@ -0,0 +1,18 @@
+System.Int32 <Module>::main()
+  Locals:
+    <typedef>_Union_Int_i V_0
+  IL_0000: ldloca.s V_0
+  IL_0002: ldc.i4.0
+  IL_0003: stfld System.Int32 <typedef>_Union_Int_i::i
+  IL_0008: ldc.i4.0
+  IL_0009: ret
+
+System.Int32 <Module>::<SyntheticEntrypoint>()
+  Locals:
+    System.Int32 V_0
+  IL_0000: call System.Int32 <Module>::main()
+  IL_0005: stloc.s V_0
+  IL_0007: ldloc.s V_0
+  IL_0009: call System.Void Cesium.Runtime.RuntimeHelpers::Exit(System.Int32)
+  IL_000e: ldloc.s V_0
+  IL_0010: ret

Cesium.CodeGen/Contexts/TranslationUnitContext.cs

@@ -315,6 +315,11 @@ internal void EnsureAnonymousTypeGenerated(IType? type)
                 structTypePtr.EmitType(this);
             }
         }
+
+        if (type is StructType structTypeAnon && structTypeAnon.IsAnon)
+        {
+            structTypeAnon.EmitType(this);
+        }
     }
 
     private TypeDefinition GetOrCreateTranslationUnitType()

Cesium.CodeGen/Ir/Expressions/Values/LValueInstanceField.cs

@@ -102,7 +102,7 @@ protected override FieldReference GetField(IEmitScope scope)
         }
 
         List<FieldDefinition>? path = null;
-
+        scope.Context.EnsureAnonymousTypeGenerated(_structType);
         var valueTypeReference = _structType.Resolve(scope.Context);
         var valueTypeDef = valueTypeReference.Resolve();
 

Cesium.IntegrationTests/structs/structs_unions.nonportable.c

@@ -22,7 +22,20 @@ typedef struct {
     } s;
 } foo;
 
+int test() {
+    union {
+        long l;
+        int i;
+    } x;
+    x.l = 10;
+    return x.i;
+}
+
 int main() {
+    if (test() != 10) {
+        return -1;
+    }
+
     foo f;
     f._1 = 2;
     f._2a = 10;