diff --git a/crates/oxc_span/src/generated/assert_layouts.rs b/crates/oxc_span/src/generated/assert_layouts.rs
index 0b7e12f99e74d..f0a278de5c6db 100644
--- a/crates/oxc_span/src/generated/assert_layouts.rs
+++ b/crates/oxc_span/src/generated/assert_layouts.rs
@@ -16,6 +16,9 @@ const _: () = {
 
     assert!(size_of::<SourceType>() == 3);
     assert!(align_of::<SourceType>() == 1);
+    assert!(offset_of!(SourceType, language) == 0);
+    assert!(offset_of!(SourceType, module_kind) == 1);
+    assert!(offset_of!(SourceType, variant) == 2);
 
     assert!(size_of::<Language>() == 1);
     assert!(align_of::<Language>() == 1);
@@ -36,6 +39,9 @@ const _: () = {
 
     assert!(size_of::<SourceType>() == 3);
     assert!(align_of::<SourceType>() == 1);
+    assert!(offset_of!(SourceType, language) == 0);
+    assert!(offset_of!(SourceType, module_kind) == 1);
+    assert!(offset_of!(SourceType, variant) == 2);
 
     assert!(size_of::<Language>() == 1);
     assert!(align_of::<Language>() == 1);
diff --git a/tasks/ast_tools/src/generators/assert_layouts.rs b/tasks/ast_tools/src/generators/assert_layouts.rs
index 321ea69a05605..8b93273237425 100644
--- a/tasks/ast_tools/src/generators/assert_layouts.rs
+++ b/tasks/ast_tools/src/generators/assert_layouts.rs
@@ -444,9 +444,9 @@ fn generate_layout_assertions_for_struct<'s>(
         let size_align_assertions = generate_size_align_assertions(layout, struct_ident);
 
         let offset_asserts = struct_def.fields.iter().filter_map(|field| {
-            if field.visibility != Visibility::Public {
-                // Cannot create assertions for fields which are not public, as assertions
-                // are generated in `oxc_ast` crate, and those types are in other crates
+            if struct_def.is_foreign || field.visibility == Visibility::Private {
+                // Cannot create assertions for private fields (cant access them)
+                // or foreign types (we don't know what fields they have)
                 return None;
             }
 
diff --git a/tasks/ast_tools/src/parse/load.rs b/tasks/ast_tools/src/parse/load.rs
index 0a95da709e4eb..c9fdd4823a0a0 100644
--- a/tasks/ast_tools/src/parse/load.rs
+++ b/tasks/ast_tools/src/parse/load.rs
@@ -64,13 +64,13 @@ pub fn load_file(
 }
 
 fn parse_struct(item: ItemStruct, file_id: FileId) -> Option<(StructSkeleton, /* is_meta */ bool)> {
-    let (name, is_meta) = get_type_name(&item.attrs, &item.ident)?;
-    Some((StructSkeleton { name, file_id, item }, is_meta))
+    let (name, is_foreign, is_meta) = get_type_name(&item.attrs, &item.ident)?;
+    Some((StructSkeleton { name, is_foreign, file_id, item }, is_meta))
 }
 
 fn parse_enum(item: ItemEnum, file_id: FileId) -> Option<(EnumSkeleton, /* is_meta */ bool)> {
-    let (name, is_meta) = get_type_name(&item.attrs, &item.ident)?;
-    Some((EnumSkeleton { name, file_id, item, inherits: vec![] }, is_meta))
+    let (name, is_foreign, is_meta) = get_type_name(&item.attrs, &item.ident)?;
+    Some((EnumSkeleton { name, is_foreign, file_id, item, inherits: vec![] }, is_meta))
 }
 
 fn parse_macro(item: &ItemMacro, file_id: FileId) -> Option<EnumSkeleton> {
@@ -96,7 +96,7 @@ fn parse_macro(item: &ItemMacro, file_id: FileId) -> Option<EnumSkeleton> {
             let where_clause = input.parse::<Option<WhereClause>>()?;
             assert!(where_clause.is_none(), "Types with `where` clauses are not supported");
 
-            let Some((name, false)) = get_type_name(&attrs, &ident) else {
+            let Some((name, false, false)) = get_type_name(&attrs, &ident) else {
                 panic!("Enum in `inherit_variants!` macro must have `#[ast]` attr: {ident}");
             };
 
@@ -126,7 +126,7 @@ fn parse_macro(item: &ItemMacro, file_id: FileId) -> Option<EnumSkeleton> {
             }
 
             let item = ItemEnum { attrs, vis, enum_token, ident, generics, brace_token, variants };
-            Ok(EnumSkeleton { name, file_id, item, inherits })
+            Ok(EnumSkeleton { name, is_foreign: false, file_id, item, inherits })
         })
         .expect("Failed to parse contents of `inherit_variants!` macro");
 
@@ -147,7 +147,7 @@ fn parse_macro(item: &ItemMacro, file_id: FileId) -> Option<EnumSkeleton> {
 fn get_type_name(
     attrs: &[Attribute],
     ident: &Ident,
-) -> Option<(/* type name */ String, /* is_meta */ bool)> {
+) -> Option<(/* type name */ String, /* is_foreign */ bool, /* is_meta */ bool)> {
     let mut has_ast_attr = false;
     let mut has_meta_attr = false;
     let mut foreign_name = None;
@@ -178,9 +178,13 @@ fn get_type_name(
             !has_ast_attr,
             "Type cannot be tagged with both `#[ast]` and `#[ast_meta]`: `{ident}`"
         );
-        Some((ident_name(ident), true))
+        Some((ident_name(ident), false, true))
     } else if has_ast_attr {
-        Some((foreign_name.unwrap_or_else(|| ident_name(ident)), false))
+        if let Some(foreign_name) = foreign_name {
+            Some((foreign_name, true, false))
+        } else {
+            Some((ident_name(ident), false, false))
+        }
     } else {
         None
     }
diff --git a/tasks/ast_tools/src/parse/parse.rs b/tasks/ast_tools/src/parse/parse.rs
index f2890d0bf3db9..56ad7c0b0e8cf 100644
--- a/tasks/ast_tools/src/parse/parse.rs
+++ b/tasks/ast_tools/src/parse/parse.rs
@@ -204,7 +204,7 @@ impl<'c> Parser<'c> {
 
     /// Parse [`StructSkeleton`] to yield a [`TypeDef`].
     fn parse_struct(&mut self, type_id: TypeId, skeleton: StructSkeleton) -> TypeDef {
-        let StructSkeleton { name, item, file_id } = skeleton;
+        let StructSkeleton { name, item, is_foreign, file_id } = skeleton;
         let has_lifetime = check_generics(&item.generics, &name);
         let fields = self.parse_fields(&item.fields);
         let (generated_derives, plural_name) =
@@ -214,6 +214,7 @@ impl<'c> Parser<'c> {
             name,
             plural_name,
             has_lifetime,
+            is_foreign,
             file_id,
             generated_derives,
             fields,
@@ -277,7 +278,7 @@ impl<'c> Parser<'c> {
 
     /// Parse [`EnumSkeleton`] to yield a [`TypeDef`].
     fn parse_enum(&mut self, type_id: TypeId, skeleton: EnumSkeleton) -> TypeDef {
-        let EnumSkeleton { name, item, inherits, file_id } = skeleton;
+        let EnumSkeleton { name, item, inherits, is_foreign, file_id } = skeleton;
         let has_lifetime = check_generics(&item.generics, &name);
         let variants = item.variants.iter().map(|variant| self.parse_variant(variant)).collect();
         let inherits = inherits.into_iter().map(|name| self.type_id(&name)).collect();
@@ -288,6 +289,7 @@ impl<'c> Parser<'c> {
             name,
             plural_name,
             has_lifetime,
+            is_foreign,
             file_id,
             generated_derives,
             variants,
diff --git a/tasks/ast_tools/src/parse/skeleton.rs b/tasks/ast_tools/src/parse/skeleton.rs
index 5379f7ac64dee..9a3eb9aa89917 100644
--- a/tasks/ast_tools/src/parse/skeleton.rs
+++ b/tasks/ast_tools/src/parse/skeleton.rs
@@ -18,6 +18,7 @@ pub enum Skeleton {
 #[derive(Debug)]
 pub struct StructSkeleton {
     pub name: String,
+    pub is_foreign: bool,
     pub file_id: FileId,
     pub item: ItemStruct,
 }
@@ -25,6 +26,7 @@ pub struct StructSkeleton {
 #[derive(Debug)]
 pub struct EnumSkeleton {
     pub name: String,
+    pub is_foreign: bool,
     pub file_id: FileId,
     pub item: ItemEnum,
     pub inherits: Vec<String>,
diff --git a/tasks/ast_tools/src/schema/defs/enum.rs b/tasks/ast_tools/src/schema/defs/enum.rs
index c1beb864c3611..48d72264e89aa 100644
--- a/tasks/ast_tools/src/schema/defs/enum.rs
+++ b/tasks/ast_tools/src/schema/defs/enum.rs
@@ -29,6 +29,8 @@ pub struct EnumDef {
     pub name: String,
     pub plural_name: Option<String>,
     pub has_lifetime: bool,
+    #[expect(unused)]
+    pub is_foreign: bool,
     pub file_id: FileId,
     pub generated_derives: Derives,
     pub variants: Vec<VariantDef>,
@@ -51,6 +53,7 @@ impl EnumDef {
         name: String,
         plural_name: Option<String>,
         has_lifetime: bool,
+        is_foreign: bool,
         file_id: FileId,
         generated_derives: Derives,
         variants: Vec<VariantDef>,
@@ -61,6 +64,7 @@ impl EnumDef {
             name,
             plural_name,
             has_lifetime,
+            is_foreign,
             file_id,
             generated_derives,
             variants,
diff --git a/tasks/ast_tools/src/schema/defs/struct.rs b/tasks/ast_tools/src/schema/defs/struct.rs
index 31dc5ee63eb99..74bf91cd8a58f 100644
--- a/tasks/ast_tools/src/schema/defs/struct.rs
+++ b/tasks/ast_tools/src/schema/defs/struct.rs
@@ -27,6 +27,7 @@ pub struct StructDef {
     pub name: String,
     pub plural_name: Option<String>,
     pub has_lifetime: bool,
+    pub is_foreign: bool,
     pub file_id: FileId,
     pub generated_derives: Derives,
     pub fields: Vec<FieldDef>,
@@ -42,11 +43,13 @@ pub struct StructDef {
 
 impl StructDef {
     /// Create new [`StructDef`].
+    #[expect(clippy::too_many_arguments)]
     pub fn new(
         id: TypeId,
         name: String,
         plural_name: Option<String>,
         has_lifetime: bool,
+        is_foreign: bool,
         file_id: FileId,
         generated_derives: Derives,
         fields: Vec<FieldDef>,
@@ -56,6 +59,7 @@ impl StructDef {
             name,
             plural_name,
             has_lifetime,
+            is_foreign,
             file_id,
             generated_derives,
             fields,