Use extern for serialized structs

src/base/CommonEnv.zig

@@ -84,8 +84,9 @@ pub fn serialize(
     return @constCast(offset_self);
 }
 
-/// Serialized representation of ModuleEnv
-pub const Serialized = struct {
+/// Serialized representation of CommonEnv
+/// Uses extern struct to guarantee consistent field layout across optimization levels.
+pub const Serialized = extern struct {
     idents: Ident.Store.Serialized,
     strings: StringLiteral.Store.Serialized,
     exposed_items: ExposedItems.Serialized,

src/base/DataSpan.zig

@@ -1,22 +1,23 @@
 //! Just a small struct to take a span of data in an array
 
-const DataSpan = @This();
+/// DataSpan is used for serialization, so it must be extern struct for consistent layout.
+pub const DataSpan = extern struct {
+    start: u32,
+    len: u32,
 
-start: u32,
-len: u32,
+    /// Creates an empty DataSpan with zero start and zero length.
+    pub fn empty() DataSpan {
+        return DataSpan{ .start = 0, .len = 0 };
+    }
 
-/// Creates an empty DataSpan with zero start and zero length.
-pub fn empty() DataSpan {
-    return DataSpan{ .start = 0, .len = 0 };
-}
+    /// Creates a DataSpan with the specified start position and length.
+    pub fn init(start: u32, len: u32) DataSpan {
+        return DataSpan{ .start = start, .len = len };
+    }
 
-/// Creates a DataSpan with the specified start position and length.
-pub fn init(start: u32, len: u32) DataSpan {
-    return DataSpan{ .start = start, .len = len };
-}
-
-/// Converts this DataSpan into a type that contains a span field.
-/// This is useful for creating wrapper types around DataSpan.
-pub fn as(self: DataSpan, comptime T: type) T {
-    return @as(T, .{ .span = self });
-}
+    /// Converts this DataSpan into a type that contains a span field.
+    /// This is useful for creating wrapper types around DataSpan.
+    pub fn as(self: DataSpan, comptime T: type) T {
+        return @as(T, .{ .span = self });
+    }
+};

src/base/Ident.zig

@@ -105,7 +105,8 @@ pub const Store = struct {
     next_unique_name: u32 = 0,
 
     /// Serialized representation of an Ident.Store
-    pub const Serialized = struct {
+    /// Uses extern struct to guarantee consistent field layout across optimization levels.
+    pub const Serialized = extern struct {
         interner: SmallStringInterner.Serialized,
         attributes: collections.SafeList(Attributes).Serialized,
         next_unique_name: u32,

src/base/PackedDataSpan.zig

@@ -11,7 +11,7 @@
 
 const std = @import("std");
 const testing = std.testing;
-const DataSpan = @import("DataSpan.zig");
+const DataSpan = @import("DataSpan.zig").DataSpan;
 
 /// Configurable packed DataSpan with customizable bit allocation
 pub fn PackedDataSpan(comptime start_bits: u6, comptime length_bits: u6) type {

src/base/Scratch.zig

@@ -2,7 +2,7 @@
 //! when working with recursive operations
 
 const std = @import("std");
-const DataSpan = @import("DataSpan.zig");
+const DataSpan = @import("DataSpan.zig").DataSpan;
 
 /// A stack for easily adding and removing index types when doing recursive operations
 pub fn Scratch(comptime T: type) type {

src/base/SmallStringInterner.zig

@@ -204,7 +204,8 @@ pub fn relocate(self: *SmallStringInterner, offset: isize) void {
 }
 
 /// Serialized representation of a SmallStringInterner
-pub const Serialized = struct {
+/// Uses extern struct to guarantee consistent field layout across optimization levels.
+pub const Serialized = extern struct {
     bytes: collections.SafeList(u8).Serialized,
     hash_table: collections.SafeList(Idx).Serialized,
     entry_count: u32,

src/base/StringLiteral.zig

@@ -97,7 +97,8 @@ pub const Store = struct {
     }
 
     /// Serialized representation of a Store
-    pub const Serialized = struct {
+    /// Uses extern struct to guarantee consistent field layout across optimization levels.
+    pub const Serialized = extern struct {
         buffer: collections.SafeList(u8).Serialized,
 
         /// Serialize a Store into this Serialized struct, appending data to the writer

src/base/mod.zig

@@ -13,7 +13,7 @@ pub const SmallStringInterner = @import("SmallStringInterner.zig");
 pub const safe_memory = @import("safe_memory.zig");
 
 pub const target = @import("target.zig");
-pub const DataSpan = @import("DataSpan.zig");
+pub const DataSpan = @import("DataSpan.zig").DataSpan;
 pub const PackedDataSpan = @import("PackedDataSpan.zig").PackedDataSpan;
 pub const FunctionArgs = @import("PackedDataSpan.zig").FunctionArgs;
 pub const SmallCollections = @import("PackedDataSpan.zig").SmallCollections;

src/canonicalize/CIR.zig

@@ -75,7 +75,7 @@ pub const BuiltinIndices = struct {
 /// Represents a definition (binding of a pattern to an expression) in the CIR
 pub const Def = struct {
     pub const Idx = enum(u32) { _ };
-    pub const Span = struct { span: base.DataSpan };
+    pub const Span = extern struct { span: base.DataSpan };
 
     pattern: Pattern.Idx,
     expr: Expr.Idx,
@@ -134,7 +134,7 @@ pub const Def = struct {
 /// Represents a type header (e.g., 'Maybe a' or 'Try err ok') in type annotations
 pub const TypeHeader = struct {
     pub const Idx = enum(u32) { _ };
-    pub const Span = struct { start: u32, len: u32 };
+    pub const Span = extern struct { start: u32, len: u32 };
 
     name: base.Ident.Idx,
     args: TypeAnno.Span,
@@ -170,7 +170,7 @@ pub const TypeHeader = struct {
 /// Represents a where clause constraint in type definitions
 pub const WhereClause = union(enum) {
     pub const Idx = enum(u32) { _ };
-    pub const Span = struct { span: base.DataSpan };
+    pub const Span = extern struct { span: base.DataSpan };
 
     w_method: struct {
         var_: TypeAnno.Idx,
@@ -293,7 +293,7 @@ pub const Annotation = struct {
 /// Represents an item exposed by a module's interface
 pub const ExposedItem = struct {
     pub const Idx = enum(u32) { _ };
-    pub const Span = struct { span: base.DataSpan };
+    pub const Span = extern struct { span: base.DataSpan };
 
     name: base.Ident.Idx,
     alias: ?base.Ident.Idx,
@@ -321,7 +321,7 @@ pub const ExposedItem = struct {
 /// Represents a field in a record pattern for pattern matching
 pub const PatternRecordField = struct {
     pub const Idx = enum(u32) { _ };
-    pub const Span = struct { start: u32, len: u32 };
+    pub const Span = extern struct { start: u32, len: u32 };
 };
 
 /// Represents an arbitrary precision smallish decimal value
@@ -678,10 +678,11 @@ pub const Import = struct {
             self.imports.relocate(offset);
         }
 
-        pub const Serialized = struct {
+        /// Uses extern struct to guarantee consistent field layout across optimization levels.
+        pub const Serialized = extern struct {
             // Placeholder to match Store size - not serialized
             // Reserve space for hashmap (3 pointers for unmanaged hashmap internals)
-            map: [3]u64 = undefined,
+            map: [3]u64,
             imports: collections.SafeList(base.StringLiteral.Idx).Serialized,
 
             /// Serialize a Store into this Serialized struct, appending data to the writer
@@ -730,7 +731,7 @@ pub const Import = struct {
 /// Represents a field in a record expression
 pub const RecordField = struct {
     pub const Idx = enum(u32) { _ };
-    pub const Span = struct { span: base.DataSpan };
+    pub const Span = extern struct { span: base.DataSpan };
 
     name: base.Ident.Idx,
     value: Expr.Idx,
@@ -761,7 +762,7 @@ pub const ExternalDecl = struct {
     region: Region,
 
     pub const Idx = enum(u32) { _ };
-    pub const Span = struct { span: base.DataSpan };
+    pub const Span = extern struct { span: base.DataSpan };
     /// A safe list of external declarations
     pub const SafeList = collections.SafeList(ExternalDecl);
 

src/canonicalize/Diagnostic.zig

@@ -252,7 +252,7 @@ pub const Diagnostic = union(enum) {
     },
 
     pub const Idx = enum(u32) { _ };
-    pub const Span = struct { span: base.DataSpan };
+    pub const Span = extern struct { span: base.DataSpan };
 
     /// Helper to extract the region from any diagnostic variant
     pub fn toRegion(self: Diagnostic) Region {

src/canonicalize/Expression.zig

@@ -429,7 +429,7 @@ pub const Expr = union(enum) {
     };
 
     pub const Idx = enum(u32) { _ };
-    pub const Span = struct { span: DataSpan };
+    pub const Span = extern struct { span: DataSpan };
 
     /// A single branch of an if expression.
     /// Contains a condition expression and the body to execute if the condition is true.
@@ -446,7 +446,7 @@ pub const Expr = union(enum) {
         body: Expr.Idx,
 
         pub const Idx = enum(u32) { _ };
-        pub const Span = struct { span: base.DataSpan };
+        pub const Span = extern struct { span: base.DataSpan };
     };
 
     /// A closure, which is a lambda expression that captures variables
@@ -1151,7 +1151,7 @@ pub const Expr = union(enum) {
         exhaustive: TypeVar,
 
         pub const Idx = enum(u32) { _ };
-        pub const Span = struct { span: base.DataSpan };
+        pub const Span = extern struct { span: base.DataSpan };
 
         /// A single branch within a match expression.
         /// Contains patterns to match against, an optional guard condition,
@@ -1210,7 +1210,7 @@ pub const Expr = union(enum) {
             }
 
             pub const Idx = enum(u32) { _ };
-            pub const Span = struct { span: DataSpan };
+            pub const Span = extern struct { span: DataSpan };
         };
 
         /// A pattern within a match branch, which may be part of an OR pattern.
@@ -1233,7 +1233,7 @@ pub const Expr = union(enum) {
             degenerate: bool,
 
             pub const Idx = enum(u32) { _ };
-            pub const Span = struct { span: base.DataSpan };
+            pub const Span = extern struct { span: base.DataSpan };
         };
 
         pub fn pushToSExprTree(self: *const @This(), ir: *const ModuleEnv, tree: *SExprTree, region: Region) std.mem.Allocator.Error!void {
@@ -1267,6 +1267,6 @@ pub const Expr = union(enum) {
         scope_depth: u32,
 
         pub const Idx = enum(u32) { _ };
-        pub const Span = struct { span: base.DataSpan };
+        pub const Span = extern struct { span: base.DataSpan };
     };
 };

src/canonicalize/ExternalDecl.zig

@@ -19,7 +19,7 @@ type_idx: ?u32,
 /// Index type for referencing external declarations in storage.
 pub const Idx = enum(u32) { _ };
 /// A span of external declarations stored contiguously in memory.
-pub const Span = struct { span: DataSpan };
+pub const Span = extern struct { span: DataSpan };
 
 /// Converts this external declaration to an S-expression tree representation for debugging
 pub fn pushToSExprTree(self: *const ExternalDecl, cir: anytype, tree: anytype) !void {

src/canonicalize/ModuleEnv.zig

@@ -1655,8 +1655,8 @@ pub fn getSourceLine(self: *const Self, region: Region) ![]const u8 {
 }
 
 /// Serialized representation of ModuleEnv.
-/// NOTE: Field order matters for cross-platform compatibility! Keep `module_kind` at the end.
-pub const Serialized = struct {
+/// Uses extern struct to guarantee consistent field layout across optimization levels.
+pub const Serialized = extern struct {
     gpa: [2]u64, // Reserve space for allocator (vtable ptr + context ptr), provided during deserialization
     common: CommonEnv.Serialized,
     types: TypeStore.Serialized,
@@ -1670,7 +1670,7 @@ pub const Serialized = struct {
     module_name_idx_reserved: u32, // Reserved space for module_name_idx field (interned during deserialization)
     diagnostics: CIR.Diagnostic.Span,
     store: NodeStore.Serialized,
-    module_kind: ModuleKind,
+    module_kind: [2]u32, // Serialized ModuleKind (tag + optional payload), decoded via decodeModuleKind
     evaluation_order_reserved: u64, // Reserved space for evaluation_order field (required for in-place deserialization cast)
     from_int_digits_ident_reserved: u32, // Reserved space for from_int_digits_ident field (interned during deserialization)
     from_dec_digits_ident_reserved: u32, // Reserved space for from_dec_digits_ident field (interned during deserialization)
@@ -1680,7 +1680,7 @@ pub const Serialized = struct {
     plus_ident_reserved: u32, // Reserved space for plus_ident field (interned during deserialization)
     minus_ident_reserved: u32, // Reserved space for minus_ident field (interned during deserialization)
     times_ident_reserved: u32, // Reserved space for times_ident field (interned during deserialization)
-    div_by_ident_reserved: u32, // Reserved space for div_by_ident field (interned during deserialization)
+    div_by_ident_reserved: u32, // Reserved space for div_by_ field (interned during deserialization)
     div_trunc_by_ident_reserved: u32, // Reserved space for div_trunc_by_ident field (interned during deserialization)
     rem_by_ident_reserved: u32, // Reserved space for rem_by_ident field (interned during deserialization)
     negate_ident_reserved: u32, // Reserved space for negate_ident field (interned during deserialization)
@@ -1704,7 +1704,7 @@ pub const Serialized = struct {
         try self.types.serialize(&env.types, allocator, writer);
 
         // Copy simple values directly
-        self.module_kind = env.module_kind;
+        self.module_kind = encodeModuleKind(env.module_kind);
         self.all_defs = env.all_defs;
         self.all_statements = env.all_statements;
         self.exports = env.exports;
@@ -1714,7 +1714,6 @@ pub const Serialized = struct {
         try self.imports.serialize(&env.imports, allocator, writer);
 
         self.diagnostics = env.diagnostics;
-        self.module_kind = env.module_kind;
 
         // Serialize NodeStore
         try self.store.serialize(&env.store, allocator, writer);
@@ -1772,7 +1771,7 @@ pub const Serialized = struct {
             .gpa = gpa,
             .common = common,
             .types = self.types.deserialize(offset, gpa).*,
-            .module_kind = self.module_kind,
+            .module_kind = decodeModuleKind(self.module_kind),
             .all_defs = self.all_defs,
             .all_statements = self.all_statements,
             .exports = self.exports,
@@ -1809,6 +1808,35 @@ pub const Serialized = struct {
 
         return env;
     }
+
+    /// Encode a ModuleKind to a serializable [2]u32 representation
+    pub fn encodeModuleKind(kind: ModuleKind) [2]u32 {
+        return switch (kind) {
+            .type_module => |idx| .{ 0, @bitCast(idx) },
+            .default_app => .{ 1, 0 },
+            .app => .{ 2, 0 },
+            .package => .{ 3, 0 },
+            .platform => .{ 4, 0 },
+            .hosted => .{ 5, 0 },
+            .deprecated_module => .{ 6, 0 },
+            .malformed => .{ 7, 0 },
+        };
+    }
+
+    /// Decode a [2]u32 representation back to a ModuleKind
+    pub fn decodeModuleKind(encoded: [2]u32) ModuleKind {
+        return switch (encoded[0]) {
+            0 => .{ .type_module = @bitCast(encoded[1]) },
+            1 => .default_app,
+            2 => .app,
+            3 => .package,
+            4 => .platform,
+            5 => .hosted,
+            6 => .deprecated_module,
+            7 => .malformed,
+            else => unreachable,
+        };
+    }
 };
 
 /// Convert a type into a node index

src/canonicalize/NodeStore.zig

@@ -3399,7 +3399,8 @@ pub fn matchBranchPatternSpanFrom(store: *NodeStore, start: u32) Allocator.Error
 }
 
 /// Serialized representation of NodeStore
-pub const Serialized = struct {
+/// Uses extern struct to guarantee consistent field layout across optimization levels.
+pub const Serialized = extern struct {
     gpa: [2]u64, // Reserve enough space for 2 64-bit pointers
     nodes: Node.List.Serialized,
     regions: Region.List.Serialized,

src/canonicalize/Pattern.zig

@@ -231,7 +231,7 @@ pub const Pattern = union(enum) {
     },
 
     pub const Idx = enum(u32) { _ };
-    pub const Span = struct { span: base.DataSpan };
+    pub const Span = extern struct { span: base.DataSpan };
 
     /// Represents the destructuring of a single field within a record pattern.
     /// Each record destructure specifies how to extract a field from a record.
@@ -247,7 +247,7 @@ pub const Pattern = union(enum) {
         kind: Kind,
 
         pub const Idx = enum(u32) { _ };
-        pub const Span = struct { span: base.DataSpan };
+        pub const Span = extern struct { span: base.DataSpan };
 
         /// The kind of record field destructuring pattern.
         pub const Kind = union(enum) {

src/canonicalize/Statement.zig

@@ -178,7 +178,7 @@ pub const Statement = union(enum) {
     },
 
     pub const Idx = enum(u32) { _ };
-    pub const Span = struct { span: DataSpan };
+    pub const Span = extern struct { span: DataSpan };
 
     pub fn pushToSExprTree(self: *const @This(), env: *const ModuleEnv, tree: *SExprTree, stmt_idx: Statement.Idx) std.mem.Allocator.Error!void {
         switch (self.*) {

src/canonicalize/TypeAnnotation.zig

@@ -97,7 +97,7 @@ pub const TypeAnno = union(enum) {
     },
 
     pub const Idx = enum(u32) { _ };
-    pub const Span = struct { span: DataSpan };
+    pub const Span = extern struct { span: DataSpan };
 
     pub fn pushToSExprTree(self: *const @This(), ir: *const ModuleEnv, tree: *SExprTree, type_anno_idx: TypeAnno.Idx) std.mem.Allocator.Error!void {
         switch (self.*) {
@@ -325,7 +325,7 @@ pub const TypeAnno = union(enum) {
         ty: TypeAnno.Idx,
 
         pub const Idx = enum(u32) { _ };
-        pub const Span = struct { span: DataSpan };
+        pub const Span = extern struct { span: DataSpan };
     };
 
     /// Either a locally declare type, or an external type

src/check/test/TestEnv.zig

@@ -73,7 +73,7 @@ fn loadCompiledModule(gpa: std.mem.Allocator, bin_data: []const u8, module_name:
         .gpa = gpa,
         .common = common,
         .types = serialized_ptr.types.deserialize(@as(i64, @intCast(base_ptr)), gpa).*, // Pass gpa to types deserialize
-        .module_kind = serialized_ptr.module_kind,
+        .module_kind = ModuleEnv.Serialized.decodeModuleKind(serialized_ptr.module_kind),
         .all_defs = serialized_ptr.all_defs,
         .all_statements = serialized_ptr.all_statements,
         .exports = serialized_ptr.exports,

src/collections/ExposedItems.zig

@@ -106,7 +106,8 @@ pub const ExposedItems = struct {
     }
 
     /// Serialized representation of ExposedItems
-    pub const Serialized = struct {
+    /// Uses extern struct to guarantee consistent field layout across optimization levels.
+    pub const Serialized = extern struct {
         items: SortedArrayBuilder(IdentIdx, u16).Serialized,
 
         /// Serialize an ExposedItems into this Serialized struct, appending data to the writer

src/collections/SortedArrayBuilder.zig

@@ -272,7 +272,8 @@ pub fn SortedArrayBuilder(comptime K: type, comptime V: type) type {
         }
 
         /// Serialized representation of SortedArrayBuilder
-        pub const Serialized = struct {
+        /// Uses extern struct to guarantee consistent field layout across optimization levels.
+        pub const Serialized = extern struct {
             entries_offset: i64,
             entries_len: u64,
             entries_capacity: u64,

src/collections/safe_list.zig

@@ -112,7 +112,8 @@ pub fn SafeList(comptime T: type) type {
         };
 
         /// Serialized representation of a SafeList
-        pub const Serialized = struct {
+        /// Uses extern struct to guarantee consistent field layout across optimization levels.
+        pub const Serialized = extern struct {
             offset: i64,
             len: u64,
             capacity: u64,
@@ -592,7 +593,8 @@ pub fn SafeMultiList(comptime T: type) type {
         }
 
         /// Serialized representation of a SafeMultiList
-        pub const Serialized = struct {
+        /// Uses extern struct to guarantee consistent field layout across optimization levels.
+        pub const Serialized = extern struct {
             offset: i64,
             len: u64,
             capacity: u64,
@@ -905,7 +907,7 @@ test "SafeList edge cases serialization" {
 
             const Self = @This();
 
-            pub const Serialized = struct {
+            pub const Serialized = extern struct {
                 list_u32: SafeList(u32).Serialized,
                 list_u8: SafeList(u8).Serialized,
 

src/compile/test/module_env_test.zig

@@ -90,7 +90,7 @@ test "ModuleEnv.Serialized roundtrip" {
         .gpa = gpa,
         .common = common,
         .types = deserialized_ptr.types.deserialize(@as(i64, @intCast(@intFromPtr(buffer.ptr))), gpa).*,
-        .module_kind = deserialized_ptr.module_kind,
+        .module_kind = ModuleEnv.Serialized.decodeModuleKind(deserialized_ptr.module_kind),
         .all_defs = deserialized_ptr.all_defs,
         .all_statements = deserialized_ptr.all_statements,
         .exports = deserialized_ptr.exports,

src/eval/builtin_loading.zig

@@ -65,7 +65,7 @@ pub fn loadCompiledModule(gpa: std.mem.Allocator, bin_data: []const u8, module_n
         .gpa = gpa,
         .common = common,
         .types = serialized_ptr.types.deserialize(@as(i64, @intCast(base_ptr)), gpa).*, // Pass gpa to types deserialize
-        .module_kind = serialized_ptr.module_kind,
+        .module_kind = ModuleEnv.Serialized.decodeModuleKind(serialized_ptr.module_kind),
         .all_defs = serialized_ptr.all_defs,
         .all_statements = serialized_ptr.all_statements,
         .exports = serialized_ptr.exports,

src/playground_wasm/main.zig

@@ -949,7 +949,7 @@ fn compileSource(source: []const u8) !CompilerStageData {
                 .gpa = gpa,
                 .common = common,
                 .types = serialized_ptr.types.deserialize(@as(i64, @intCast(base_ptr)), gpa).*,
-                .module_kind = serialized_ptr.module_kind,
+                .module_kind = ModuleEnv.Serialized.decodeModuleKind(serialized_ptr.module_kind),
                 .all_defs = serialized_ptr.all_defs,
                 .all_statements = serialized_ptr.all_statements,
                 .exports = serialized_ptr.exports,

src/repl/repl_test.zig

@@ -76,7 +76,7 @@ fn loadCompiledModule(gpa: std.mem.Allocator, bin_data: []const u8, module_name:
         .gpa = gpa,
         .common = common,
         .types = serialized_ptr.types.deserialize(@as(i64, @intCast(base_ptr)), gpa).*, // Pass gpa to types deserialize
-        .module_kind = serialized_ptr.module_kind,
+        .module_kind = ModuleEnv.Serialized.decodeModuleKind(serialized_ptr.module_kind),
         .all_defs = serialized_ptr.all_defs,
         .all_statements = serialized_ptr.all_statements,
         .exports = serialized_ptr.exports,

src/types/store.zig

@@ -720,7 +720,8 @@ pub const Store = struct {
     // serialization //
 
     /// Serialized representation of types store
-    pub const Serialized = struct {
+    /// Uses extern struct to guarantee consistent field layout across optimization levels.
+    pub const Serialized = extern struct {
         gpa: [2]u64, // Reserve space for allocator (vtable ptr + context ptr), provided during deserialization
         slots: SlotStore.Serialized,
         descs: DescStore.Serialized,
@@ -922,7 +923,8 @@ const SlotStore = struct {
     }
 
     /// Serialized representation of SlotStore
-    pub const Serialized = struct {
+    /// Uses extern struct to guarantee consistent field layout across optimization levels.
+    pub const Serialized = extern struct {
         backing: collections.SafeList(Slot).Serialized,
 
         /// Serialize a SlotStore into this Serialized struct, appending data to the writer
@@ -1024,7 +1026,8 @@ const DescStore = struct {
     }
 
     /// Serialized representation of DescStore
-    pub const Serialized = struct {
+    /// Uses extern struct to guarantee consistent field layout across optimization levels.
+    pub const Serialized = extern struct {
         backing: DescSafeMultiList.Serialized,
 
         /// Serialize a DescStore into this Serialized struct, appending data to the writer