enums

TODO.md

@@ -125,7 +125,14 @@
     floats follow IEEE (`fadd`/`fsub`/`fmul`/`fdiv`, no trap)
   - constant folding (global initializers) covers `-`, `*`, `/` alongside `+`
 
-7. enums (native and c interop) (see below)
+7. enums (native and c interop) (implemented; see below)
+  - native enums are nominal value types with integer runtime representations
+  - unbacked enums are non-empty, dense, zero-based, and use the smallest fitting unsigned backing
+  - explicitly backed enums require an integer type and strictly increasing literal values
+  - enum members support `Type.member`, `package.Type.member`, and contextual `.member`
+  - enum values support storage, calls/returns, and same-type equality/inequality
+  - explicitly backed native enums use their backing ABI in `c_func` signatures and variadic promotion
+  - imported C enum types alias libclang's target-selected integer backing and enumerators import as package constants
 
 8. distinct types (implemented; see below)
   - nominal declarations preserve identity across packages and reuse the backing runtime representation
@@ -255,3 +262,19 @@ Nat :: enum(u8) {
 dog_tag1 Animal :: Animal.dog
 dog_tag2 Animal :: .dog # type inferred
 ```
+
+Unbacked enums cannot assign explicit values. Backed enum values must be decimal integer
+literals, fit the backing type, and increase strictly; gaps are allowed.
+
+Native enum types remain distinct from integers and from other enum types. They support
+`==` and `!=`, but not arithmetic, ordering, casts, or backing-value extraction.
+
+C enums follow C/Zig import semantics rather than native enum semantics:
+
+```
+native :: import "native.h"
+value native.Imported_Enum :: native.IMPORTED_ENUM_VALUE
+```
+
+The imported enum type is an alias of its target-selected C integer backing, and imported
+enumerators are package-level constants.

compiler/ast/ast.odin

@@ -72,6 +72,7 @@ Expr_Kind :: enum u8 {
 	Array,
 	None,
 	Name,
+	Enum_Literal,
 	Address,
 	Deref,
 	Index,

compiler/checker/checker.odin

@@ -636,7 +636,7 @@ mark_expr_imports_used :: proc(checker: ^Checker, expr_id: ast.Expr_Id, file: as
 			append(&stack, expr.left)
 		case .Add, .Sub, .Mul, .Div, .Index, .Orelse, .Eq, .Ne, .Lt, .Le, .Gt, .Ge, .And, .Or, .Range:
 			append(&stack, expr.left, expr.right)
-		case .Invalid, .Integer, .Float, .String, .Bool, .None, .Name:
+		case .Invalid, .Integer, .Float, .String, .Bool, .None, .Name, .Enum_Literal:
 		}
 	}
 }
@@ -879,6 +879,28 @@ validate_type_nodes :: proc(checker: ^Checker) {
 				symbol_text(checker, symbol.Id(item.name)),
 			)
 		}
+		if item.kind == .Enum {
+			if !item.declared || !types.is_concrete_integer(item.child) {
+				source.addf(
+					checker.diagnostics,
+					source.Span{},
+					"enum type '%s' requires a concrete integer backing type",
+					symbol_text(checker, symbol.Id(item.name)),
+				)
+			} else {
+				for member in types.enum_members_for(&checker.module.types, id) {
+					if !fits_integer_type(member.value, item.child, checker.target) {
+						source.addf(
+							checker.diagnostics,
+							source.Span{},
+							"enum value %d does not fit in %s",
+							member.value,
+							types.name(item.child),
+						)
+					}
+				}
+			}
+		}
 		if item.has_sentinel {
 			value := i128(item.sentinel)
 			if types.is_signed(item.child, checker.target) {
@@ -1101,6 +1123,8 @@ infer_compound_expr :: proc(
 		return types.array(store, element, u64(len(expr.args)), false)
 	case .None:
 		return types.INVALID
+	case .Enum_Literal:
+		return types.INVALID
 	case .Address:
 		child := infer_nested_expr(checker, expr.left, locals, pkg, file, demanded)
 		return types.pointer(store, child, false, false)
@@ -1126,6 +1150,10 @@ infer_compound_expr :: proc(
 		preserve := item.has_sentinel && expr.args[1] == ast.INVALID_EXPR
 		return types.slice(store, item.child, item.mutable, preserve, item.sentinel)
 	case .Field:
+		if enum_type, enum_ok := enum_type_from_field_expr(checker, expr, pkg, file); enum_ok {
+			_, member_ok := find_enum_member(checker, enum_type, expr.name)
+			return enum_type if member_ok else types.INVALID
+		}
 		value := infer_nested_expr(checker, expr.left, locals, pkg, file, demanded)
 		field_name := symbol_text(checker, expr.name)
 		item, has_item := types.container(value, store)
@@ -1220,7 +1248,7 @@ infer_expr :: proc(
 				last = types.F64
 				_ = pop(&stack)
 			case .String, .Array, .None, .Address, .Deref, .Index, .Slice,
-			     .Field, .Unwrap, .Orelse, .Struct_Literal, .Keyed,
+			     .Field, .Unwrap, .Orelse, .Struct_Literal, .Keyed, .Enum_Literal,
 			     .Bool, .Not, .Eq, .Ne, .Lt, .Le, .Gt, .Ge, .And, .Or, .Range:
 				last = infer_compound_expr(checker, expr, locals, pkg, file, demanded)
 				_ = pop(&stack)
@@ -1250,6 +1278,14 @@ infer_expr :: proc(
 						}
 					}
 				}
+				if !types.is_valid(last) {
+					if enum_type, enum_ok := enum_type_from_name_expr(checker, expr, pkg, file); enum_ok {
+						_, member_ok := find_enum_member(checker, enum_type, expr.name)
+						if member_ok {
+							last = enum_type
+						}
+					}
+				}
 				if !types.is_valid(last) {
 					target_pkg, available := expr_package(checker, expr, pkg, file)
 					if available {
@@ -1867,7 +1903,7 @@ promote_c_vararg_expr :: proc(checker: ^Checker, expr_id: hir.Expr_Id, span: sou
 		)
 		return invalid_hir_expr(checker, span, id, types.C_INT)
 	}
-	promoted := types.c_vararg_promotion(actual, checker.target)
+	promoted := types.c_vararg_promotion(actual, checker.target, &checker.module.types)
 	if types.equal(actual, promoted) {
 		return expr_id
 	}
@@ -2055,6 +2091,75 @@ find_struct_field :: proc(checker: ^Checker, struct_type: types.Type, name: symb
 	return 0, {}, false
 }
 
+find_enum_member :: proc(checker: ^Checker, enum_type: types.Type, name: symbol.Id) -> (types.Enum_Member, bool) {
+	for member in types.enum_members_for(&checker.module.types, enum_type) {
+		if member.name == u32(name) {
+			return member, true
+		}
+	}
+	return {}, false
+}
+
+enum_type_from_name_expr :: proc(
+	checker: ^Checker,
+	expr: ast.Expr,
+	pkg: ast.Package_Id,
+	file: ast.File_Id,
+) -> (types.Type, bool) {
+	if !symbol.is_valid(expr.qualifier) ||
+	   find_import(checker, file, expr.qualifier) != ast.INVALID_IMPORT {
+		return types.INVALID, false
+	}
+	enum_type := types.find_named(&checker.module.types, u32(pkg), u32(expr.qualifier))
+	return enum_type, types.is_enum(enum_type, &checker.module.types)
+}
+
+enum_type_from_field_expr :: proc(
+	checker: ^Checker,
+	expr: ast.Expr,
+	pkg: ast.Package_Id,
+	file: ast.File_Id,
+	mark_used := false,
+) -> (types.Type, bool) {
+	if expr.left == ast.INVALID_EXPR || int(expr.left) >= len(checker.ast_module.exprs) {
+		return types.INVALID, false
+	}
+	base := checker.ast_module.exprs[expr.left]
+	if base.kind != .Name || !symbol.is_valid(base.qualifier) {
+		return types.INVALID, false
+	}
+	target_pkg, available := expr_package(checker, base, pkg, file, mark_used)
+	if !available {
+		return types.INVALID, false
+	}
+	enum_type := types.find_named(&checker.module.types, u32(target_pkg), u32(base.name))
+	return enum_type, types.is_enum(enum_type, &checker.module.types)
+}
+
+enum_member_hir :: proc(
+	checker: ^Checker,
+	enum_type: types.Type,
+	name: symbol.Id,
+	span: source.Span,
+) -> hir.Expr_Id {
+	member, ok := find_enum_member(checker, enum_type, name)
+	if !ok {
+		id := source.addf(checker.diagnostics, span, "unknown enum member '%s'", symbol_text(checker, name))
+		return invalid_hir_expr(checker, span, id, enum_type)
+	}
+	value := i64(member.value) if member.value < 0 else transmute(i64)u64(member.value)
+	return add_hir_expr(checker, hir.Expr{
+		kind=.Integer,
+		span=span,
+		type=enum_type,
+		integer=value,
+		target=hir.INVALID_REF,
+		left=hir.INVALID_EXPR,
+		right=hir.INVALID_EXPR,
+		diagnostic=source.INVALID_DIAGNOSTIC,
+	})
+}
+
 build_function_value :: proc(
 	checker: ^Checker,
 	template: ast.Function_Id,
@@ -2213,6 +2318,17 @@ build_compound_expr :: proc(
 			kind=.None, span=expr.span, type=expected, target=hir.INVALID_REF,
 			left=hir.INVALID_EXPR, right=hir.INVALID_EXPR, diagnostic=source.INVALID_DIAGNOSTIC,
 		})
+	case .Enum_Literal:
+		if !types.is_enum(expected, store) {
+			id := source.addf(
+				checker.diagnostics,
+				expr.span,
+				"'.%s' requires an enum context",
+				symbol_text(checker, expr.name),
+			)
+			return invalid_hir_expr(checker, expr.span, id, expected)
+		}
+		return enum_member_hir(checker, expected, expr.name, expr.span)
 	case .Address:
 		value := build_nested_expr(checker, expr.left, locals, global_reads, calls, types.INVALID, pkg, file)
 		if !hir_is_location(checker, value) {
@@ -2278,6 +2394,9 @@ build_compound_expr :: proc(
 			target=hir.INVALID_REF, right=hir.INVALID_EXPR, diagnostic=source.INVALID_DIAGNOSTIC,
 		})
 	case .Field:
+		if enum_type, enum_ok := enum_type_from_field_expr(checker, expr, pkg, file, true); enum_ok {
+			return enum_member_hir(checker, enum_type, expr.name, expr.span)
+		}
 		base := build_nested_expr(checker, expr.left, locals, global_reads, calls, types.INVALID, pkg, file)
 		base_type := checker.module.exprs[base].type
 		field_name := symbol_text(checker, expr.name)
@@ -2417,7 +2536,15 @@ build_compound_expr :: proc(
 		left_const := eval_constant(checker, expr.left)
 		right_const := eval_constant(checker, expr.right)
 		left, right: hir.Expr_Id
-		if right_const.kind == .Value && left_const.kind != .Value {
+		left_expr := checker.ast_module.exprs[expr.left]
+		right_expr := checker.ast_module.exprs[expr.right]
+		if right_expr.kind == .Enum_Literal && left_expr.kind != .Enum_Literal {
+			left = build_nested_expr(checker, expr.left, locals, global_reads, calls, types.INVALID, pkg, file)
+			right = build_nested_expr(checker, expr.right, locals, global_reads, calls, checker.module.exprs[left].type, pkg, file)
+		} else if left_expr.kind == .Enum_Literal && right_expr.kind != .Enum_Literal {
+			right = build_nested_expr(checker, expr.right, locals, global_reads, calls, types.INVALID, pkg, file)
+			left = build_nested_expr(checker, expr.left, locals, global_reads, calls, checker.module.exprs[right].type, pkg, file)
+		} else if right_const.kind == .Value && left_const.kind != .Value {
 			left = build_nested_expr(checker, expr.left, locals, global_reads, calls, types.INVALID, pkg, file)
 			hint := checker.module.exprs[left].type
 			right = build_nested_expr(checker, expr.right, locals, global_reads, calls, hint, pkg, file)
@@ -2435,7 +2562,13 @@ build_compound_expr :: proc(
 			return invalid_hir_expr(checker, expr.span, expr.diagnostic, types.BOOL)
 		}
 		operand_type := types.INVALID
-		if types.is_bool(left_type) && types.is_bool(right_type) {
+		if types.is_enum(left_type, store) || types.is_enum(right_type, store) {
+			if !types.equal(left_type, right_type) || (expr.kind != .Eq && expr.kind != .Ne) {
+				id := source.add(checker.diagnostics, expr.span, "enum values only support '==' and '!=' with the same enum type")
+				return invalid_hir_expr(checker, expr.span, id, types.BOOL)
+			}
+			operand_type = left_type
+		} else if types.is_bool(left_type) && types.is_bool(right_type) {
 			if expr.kind != .Eq && expr.kind != .Ne {
 				id := source.add(checker.diagnostics, expr.span, "bool values only support '==' and '!='")
 				return invalid_hir_expr(checker, expr.span, id, types.BOOL)
@@ -2617,7 +2750,8 @@ build_expr :: proc(
 			switch expr.kind {
 			case .String, .Array, .None, .Address, .Deref, .Index, .Slice,
 			     .Field, .Unwrap, .Orelse, .Struct_Literal, .Keyed,
-			     .Bool, .Not, .Eq, .Ne, .Lt, .Le, .Gt, .Ge, .And, .Or, .Range:
+			     .Bool, .Not, .Eq, .Ne, .Lt, .Le, .Gt, .Ge, .And, .Or, .Range,
+			     .Enum_Literal:
 				last = build_compound_expr(
 					checker, expr, locals, global_reads, calls, frame.expected, pkg, file,
 				)
@@ -2674,6 +2808,11 @@ build_expr :: proc(
 						})
 					}
 				}
+				if last == hir.INVALID_EXPR {
+					if enum_type, enum_ok := enum_type_from_name_expr(checker, expr, pkg, file); enum_ok {
+						last = enum_member_hir(checker, enum_type, expr.name, expr.span)
+					}
+				}
 				if last == hir.INVALID_EXPR {
 					target_pkg, available := expr_package(checker, expr, pkg, file, true)
 					if !available {

compiler/cimport/libclang.odin

@@ -81,6 +81,9 @@ Api :: struct {
 	get_type_spelling:             proc "c"(CXType) -> CXString,
 	get_typedef_underlying_type:   proc "c"(CXCursor) -> CXType,
 	get_type_declaration:          proc "c"(CXType) -> CXCursor,
+	get_enum_decl_integer_type:    proc "c"(CXCursor) -> CXType,
+	get_enum_constant_value:       proc "c"(CXCursor) -> i64,
+	get_enum_constant_unsigned:    proc "c"(CXCursor) -> u64,
 	get_canonical_type:            proc "c"(CXType) -> CXType,
 	get_pointee_type:              proc "c"(CXType) -> CXType,
 	get_array_element_type:        proc "c"(CXType) -> CXType,
@@ -119,6 +122,7 @@ CXCursor_VarDecl :: i32(9)
 CXCursor_TypedefDecl :: i32(20)
 CXCursor_MacroDefinition :: i32(501)
 CXCursor_FieldDecl :: i32(6)
+CXCursor_EnumConstantDecl :: i32(7)
 
 CXLinkage_External :: i32(4)
 CXTLS_None :: i32(0)
@@ -201,6 +205,9 @@ load_api_from :: proc(path: string) -> (Api, bool) {
 		load_proc(&api, "clang_getTypeSpelling", &api.get_type_spelling) &&
 		load_proc(&api, "clang_getTypedefDeclUnderlyingType", &api.get_typedef_underlying_type) &&
 		load_proc(&api, "clang_getTypeDeclaration", &api.get_type_declaration) &&
+		load_proc(&api, "clang_getEnumDeclIntegerType", &api.get_enum_decl_integer_type) &&
+		load_proc(&api, "clang_getEnumConstantDeclValue", &api.get_enum_constant_value) &&
+		load_proc(&api, "clang_getEnumConstantDeclUnsignedValue", &api.get_enum_constant_unsigned) &&
 		load_proc(&api, "clang_getCanonicalType", &api.get_canonical_type) &&
 		load_proc(&api, "clang_getPointeeType", &api.get_pointee_type) &&
 		load_proc(&api, "clang_getArrayElementType", &api.get_array_element_type) &&
@@ -468,6 +475,10 @@ translate_type :: proc(ctx: ^Context, value: CXType, preferred_record_name := ""
 		record := add_record(ctx, declaration, preferred_record_name)
 		populate_record(ctx, record, declaration)
 		return add_type(ctx, Type{kind=.Record, child=INVALID_TYPE, record=record})
+	case CXType_Enum:
+		declaration := ctx.api.get_type_declaration(value)
+		backing := ctx.api.get_enum_decl_integer_type(declaration)
+		return translate_type(ctx, backing, preferred_record_name, depth+1)
 	case CXType_FunctionProto:
 		result := translate_type(ctx, ctx.api.get_result_type(value), "", depth+1)
 		if result == INVALID_TYPE {
@@ -508,7 +519,7 @@ translate_type :: proc(ctx: ^Context, value: CXType, preferred_record_name := ""
 			return INVALID_TYPE
 		}
 		return translate_type(ctx, canonical, preferred_record_name, depth+1)
-	case CXType_Enum, CXType_FunctionNoProto,
+	case CXType_FunctionNoProto,
 	     CXType_IncompleteArray, CXType_VariableArray, CXType_DependentSizedArray:
 		return INVALID_TYPE
 	}
@@ -551,6 +562,49 @@ add_alias :: proc(ctx: ^Context, name: string, value: Type_Id, reason := "") {
 	})
 }
 
+enum_backing_unsigned :: proc(value: CXType) -> bool {
+	switch value.kind {
+	case CXType_Char_U, CXType_UChar, CXType_UShort, CXType_UInt, CXType_ULong, CXType_ULongLong:
+		return true
+	}
+	return false
+}
+
+Enum_Constant_Context :: struct {
+	ctx:      ^Context,
+	backing:  Type_Id,
+	unsigned: bool,
+}
+
+visit_enum_constant :: proc "c"(cursor, parent: CXCursor, client_data: rawptr) -> i32 {
+	context = runtime.default_context()
+	enum_ctx := (^Enum_Constant_Context)(client_data)
+	ctx := enum_ctx.ctx
+	if ctx.api.get_cursor_kind(cursor) != CXCursor_EnumConstantDecl {
+		return CXChildVisit_Continue
+	}
+	name := clone_cx_string(ctx.api, ctx.api.get_cursor_spelling(cursor), ctx.allocator)
+	defer delete(name, ctx.allocator)
+	if len(name) == 0 {
+		return CXChildVisit_Continue
+	}
+	value := Macro_Value{kind=.Integer, type=enum_ctx.backing}
+	if enum_ctx.unsigned {
+		value.integer = ctx.api.get_enum_constant_unsigned(cursor)
+	} else {
+		signed := ctx.api.get_enum_constant_value(cursor)
+		value.negative = signed < 0
+		value.integer = u64(-i128(signed)) if signed < 0 else u64(signed)
+	}
+	append(&ctx.result.macros, Macro_Constant{
+		name=fmt.aprintf("%s", name, allocator=ctx.allocator),
+		type=enum_ctx.backing,
+		value=value,
+		reason=fmt.aprintf("", allocator=ctx.allocator),
+	})
+	return CXChildVisit_Continue
+}
+
 is_macro_identifier :: proc(value: string) -> bool {
 	if len(value) == 0 {
 		return false
@@ -1367,7 +1421,19 @@ visit_cursor :: proc "c"(cursor, parent: CXCursor, client_data: rawptr) -> i32 {
 			add_alias(ctx, name, value)
 		}
 	case CXCursor_EnumDecl:
-		add_unsupported(ctx, name, "C enums are not supported")
+		backing_c := ctx.api.get_enum_decl_integer_type(cursor)
+		backing := translate_type(ctx, backing_c)
+		if backing == INVALID_TYPE {
+			add_unsupported(ctx, name, "C enum backing type is not supported")
+			break
+		}
+		add_alias(ctx, name, backing)
+		enum_ctx := Enum_Constant_Context{
+			ctx=ctx,
+			backing=backing,
+			unsigned=enum_backing_unsigned(backing_c),
+		}
+		_ = ctx.api.visit_children(cursor, visit_enum_constant, &enum_ctx)
 	case CXCursor_VarDecl:
 		if len(name) == 0 {
 			return CXChildVisit_Continue

compiler/lexer/lexer.odin

@@ -18,6 +18,7 @@ keyword_kind :: proc(text: string) -> token.Kind {
 	case "c_func":        return .Keyword_C_Func
 	case "struct":        return .Keyword_Struct
 	case "c_struct":      return .Keyword_C_Struct
+	case "enum":          return .Keyword_Enum
 	case "distinct":      return .Keyword_Distinct
 	case "import":        return .Keyword_Import
 	case "return":        return .Keyword_Return

compiler/llvm/llvm.odin

@@ -189,11 +189,16 @@ function_result_type :: proc(function: ir.Function, store: ^types.Store) -> stri
 	return llvm_type(function.result, store)
 }
 
-c_abi_extension :: proc(value: types.Type, selected: target.Target) -> string {
+c_abi_extension :: proc(value: types.Type, store: ^types.Store) -> string {
-	if !types.is_concrete_integer(value) {
+	resolved := types.runtime_representation(value, store)
+	if !types.is_concrete_integer(resolved) {
 		return ""
 	}
-	switch target.c_integer_extension(selected, types.bits(value, selected), types.is_signed(value, selected)) {
+	switch target.c_integer_extension(
+		store.selected,
+		types.bits(resolved, store.selected),
+		types.is_signed(resolved, store.selected),
+	) {
 	case .Sign: return "signext"
 	case .Zero: return "zeroext"
 	case .None: return ""
@@ -203,7 +208,7 @@ c_abi_extension :: proc(value: types.Type, selected: target.Target) -> string {
 
 emit_function_result :: proc(builder: ^strings.Builder, function: ir.Function, store: ^types.Store) {
 	if function.calling_convention == .C {
-		extension := c_abi_extension(function.result, store.selected)
+		extension := c_abi_extension(function.result, store)
 		if len(extension) > 0 {
 			fmt.sbprintf(builder, "%s ", extension)
 		}
@@ -423,7 +428,7 @@ emit_call_args :: proc(
 		            (instructions[arg].type if valid_instruction(instructions, arg) else types.INVALID)
 		fmt.sbprintf(builder, "%s ", llvm_type(arg_type, store))
 		if c_abi && index < len(param_types) {
-			extension := c_abi_extension(arg_type, store.selected)
+			extension := c_abi_extension(arg_type, store)
 			if len(extension) > 0 {
 				fmt.sbprintf(builder, "%s ", extension)
 			}
@@ -1200,11 +1205,12 @@ emit_instruction_stream :: proc(
 			}
 			from_type := instructions[instruction.a].type
 			if types.equal(from_type, instruction.type) ||
-			   !types.equal(types.c_vararg_promotion(from_type, emitter.module.target), instruction.type) {
+			   !types.equal(types.c_vararg_promotion(from_type, emitter.module.target, &emitter.module.types), instruction.type) {
 				emit_recovery_value(emitter, instruction_index, instruction, "invalid C variadic promotion operand")
 				continue
 			}
-			if types.bits(from_type, emitter.module.target) == types.bits(instruction.type, emitter.module.target) {
+			from_repr := types.runtime_representation(from_type, &emitter.module.types)
+			if types.bits(from_repr, emitter.module.target) == types.bits(instruction.type, emitter.module.target) {
 				type_name := llvm_type(instruction.type, &emitter.module.types)
 				fmt.sbprintf(&emitter.builder, "  %%v%d = select i1 true, %s ", instruction_index, type_name)
 				write_operand(&emitter.builder, instructions, instruction.a, from_type, &emitter.module.types)
@@ -1213,8 +1219,8 @@ emit_instruction_stream :: proc(
 				strings.write_string(&emitter.builder, "\n")
 				continue
 			}
-			operation := "fpext" if types.is_float(from_type, emitter.module.target) else
+			operation := "fpext" if types.is_float(from_repr, emitter.module.target) else
-			             ("sext" if types.is_signed(from_type, emitter.module.target) else "zext")
+			             ("sext" if types.is_signed(from_repr, emitter.module.target) else "zext")
 			fmt.sbprintf(&emitter.builder, "  %%v%d = %s %s ", instruction_index, operation, llvm_type(from_type, &emitter.module.types))
 			write_operand(&emitter.builder, instructions, instruction.a, from_type, &emitter.module.types)
 			fmt.sbprintf(&emitter.builder, " to %s\n", llvm_type(instruction.type, &emitter.module.types))
@@ -1367,7 +1373,7 @@ emit_instruction_stream :: proc(
 						            (instructions[arg].type if valid_instruction(instructions, arg) else types.INVALID)
 						if index >= len(param_fields) &&
 						   (!types.is_c_vararg_type(expected, &emitter.module.types) ||
-						    !types.equal(types.c_vararg_promotion(expected, emitter.module.target), expected)) {
+						    !types.equal(types.c_vararg_promotion(expected, emitter.module.target, &emitter.module.types), expected)) {
 							valid_args = false
 							break
 						}
@@ -1409,7 +1415,7 @@ emit_instruction_stream :: proc(
 					strings.write_string(&emitter.builder, "fastcc ")
 				}
 				if function_item.c_abi {
-					extension := c_abi_extension(function_item.child, emitter.module.target)
+					extension := c_abi_extension(function_item.child, &emitter.module.types)
 					if len(extension) > 0 {
 						fmt.sbprintf(&emitter.builder, "%s ", extension)
 					}
@@ -1455,7 +1461,7 @@ emit_instruction_stream :: proc(
 					} else {
 						fmt.sbprintf(&emitter.builder, "%s ", llvm_type(arg_type, &emitter.module.types))
 						if function_item.c_abi && fixed {
-							extension := c_abi_extension(arg_type, emitter.module.target)
+							extension := c_abi_extension(arg_type, &emitter.module.types)
 							if len(extension) > 0 {
 								fmt.sbprintf(&emitter.builder, "%s ", extension)
 							}
@@ -1490,7 +1496,7 @@ emit_instruction_stream :: proc(
 					            (instructions[arg].type if valid_instruction(instructions, arg) else types.INVALID)
 					if index >= len(target.param_types) &&
 					   (!types.is_c_vararg_type(expected, &emitter.module.types) ||
-					    !types.equal(types.c_vararg_promotion(expected, emitter.module.target), expected)) {
+					    !types.equal(types.c_vararg_promotion(expected, emitter.module.target, &emitter.module.types), expected)) {
 						valid_args = false
 						break
 					}
@@ -1572,7 +1578,7 @@ emit_instruction_stream :: proc(
 				} else {
 					fmt.sbprintf(&emitter.builder, "%s ", llvm_type(arg_type, &emitter.module.types))
 					if target.calling_convention == .C && fixed {
-						extension := c_abi_extension(arg_type, emitter.module.target)
+						extension := c_abi_extension(arg_type, &emitter.module.types)
 						if len(extension) > 0 {
 							fmt.sbprintf(&emitter.builder, "%s ", extension)
 						}
@@ -1898,7 +1904,7 @@ emit_functions :: proc(emitter: ^Emitter) {
 			type_name := c_abi_param_type(param_type, &emitter.module.types) if function.calling_convention == .C else llvm_type(param_type, &emitter.module.types)
 			fmt.sbprintf(&emitter.builder, "%s", type_name)
 			if function.calling_convention == .C && !types.is_record(param_type, &emitter.module.types) {
-				extension := c_abi_extension(param_type, emitter.module.target)
+				extension := c_abi_extension(param_type, &emitter.module.types)
 				if len(extension) > 0 {
 					fmt.sbprintf(&emitter.builder, " %s", extension)
 				}

compiler/loader/loader.odin

@@ -1325,6 +1325,11 @@ canonical_type :: proc(
 		module.type_store.nodes[index].child = canonical_type(module, item.child, mapping, visiting)
 		return value
 	}
+	if item.kind == .Enum {
+		mapping[index] = value
+		module.type_store.nodes[index].child = canonical_type(module, item.child, mapping, visiting)
+		return value
+	}
 	if item.kind == .Struct || item.kind == .Union {
 		mapping[index] = value
 		fields := types.fields_for(&module.type_store, value)

compiler/parser/parser.odin

@@ -588,6 +588,21 @@ parse_primary :: proc(parser: ^Parser, nesting: int) -> ast.Expr_Id {
 		})
 	case .Left_Bracket:
 		return parse_array_literal(parser, nesting)
+	case .Dot:
+		start := advance(parser)
+		member := current(parser)
+		if member.kind != .Identifier {
+			return invalid_expr(parser, member.span, "expected an enum member after '.'")
+		}
+		advance(parser)
+		return add_expr(parser, ast.Expr{
+			kind=.Enum_Literal,
+			span=span_from(start.span, member.span),
+			name=member.symbol,
+			left=ast.INVALID_EXPR,
+			right=ast.INVALID_EXPR,
+			diagnostic=source.INVALID_DIAGNOSTIC,
+		})
 	case .Identifier:
 		first := advance(parser)
 		name := first
@@ -1490,6 +1505,118 @@ parse_distinct :: proc(parser: ^Parser, name: token.Token) {
 	_ = finish_statement(parser)
 }
 
+parse_enum :: proc(parser: ^Parser, name: token.Token) {
+	start := advance(parser)
+	explicit_backing := false
+	backing := types.INVALID
+	if _, ok := allow(parser, .Left_Paren); ok {
+		explicit_backing = true
+		backing = parse_type(parser)
+		if _, close_ok := allow(parser, .Right_Paren); !close_ok {
+			source.add(parser.diagnostics, current(parser).span, "expected ')' after enum backing type")
+		}
+	}
+	skip_newlines(parser)
+	if _, ok := allow(parser, .Left_Brace); !ok {
+		source.add(parser.diagnostics, current(parser).span, "expected '{' after enum declaration")
+		_ = finish_statement(parser)
+		return
+	}
+	members: [dynamic]types.Enum_Member
+	members.allocator = parser.module.allocator
+	defer delete(members)
+	next_value: i128
+	previous_value: i128
+	has_previous := false
+	skip_newlines(parser)
+	for current(parser).kind != .Right_Brace && current(parser).kind != .Eof {
+		if current(parser).kind != .Identifier {
+			source.add(parser.diagnostics, current(parser).span, "expected an enum member name")
+			for current(parser).kind != .Newline &&
+			    current(parser).kind != .Right_Brace &&
+			    current(parser).kind != .Eof {
+				advance(parser)
+			}
+			skip_newlines(parser)
+			continue
+		}
+		member := advance(parser)
+		duplicate := false
+		for existing in members {
+			if existing.name == u32(member.symbol) {
+				duplicate = true
+				break
+			}
+		}
+		if duplicate {
+			source.addf(parser.diagnostics, member.span, "duplicate enum member '%s'", token_text(parser, member))
+		}
+		value := next_value
+		if _, ok := allow(parser, .Equal); ok {
+			if !explicit_backing {
+				source.add(parser.diagnostics, member.span, "explicit enum values require a backing type")
+			}
+			negative := false
+			if _, minus_ok := allow(parser, .Minus); minus_ok {
+				negative = true
+			}
+			literal := current(parser)
+			if literal.kind != .Integer {
+				source.add(parser.diagnostics, literal.span, "expected a decimal integer literal for enum value")
+			} else {
+				advance(parser)
+				magnitude, magnitude_ok := parse_integer_magnitude(token_text(parser, literal))
+				if !magnitude_ok {
+					source.add(parser.diagnostics, literal.span, "enum value magnitude does not fit in u64")
+				} else {
+					value = i128(magnitude)
+					if negative {
+						value = -value
+					}
+				}
+			}
+		}
+		if has_previous && value <= previous_value {
+			source.add(parser.diagnostics, member.span, "enum values must be strictly increasing")
+		}
+		if !duplicate {
+			append(&members, types.Enum_Member{name=u32(member.symbol), value=value})
+		}
+		previous_value = value
+		has_previous = true
+		next_value = value+1
+		if _, ok := allow(parser, .Comma); ok {
+			skip_newlines(parser)
+		} else {
+			_ = finish_statement(parser, true)
+		}
+	}
+	if _, ok := allow(parser, .Right_Brace); !ok {
+		source.add(parser.diagnostics, current(parser).span, "expected '}' after enum members")
+	}
+	if len(members) == 0 {
+		source.add(parser.diagnostics, start.span, "enum declarations require at least one member")
+	}
+	if !explicit_backing {
+		max_value := u64(max(len(members)-1, 0))
+		backing = types.U8
+		if max_value > 0xff {
+			backing = types.U16
+		}
+		if max_value > 0xffff {
+			backing = types.U32
+		}
+		if max_value > 0xffff_ffff {
+			backing = types.U64
+		}
+	}
+	id := types.named(&parser.module.type_store, u32(parser.pkg), u32(name.symbol))
+	if !types.define_enum(&parser.module.type_store, id, backing, members[:], explicit_backing) {
+		source.addf(parser.diagnostics, name.span, "duplicate type declaration '%s'", token_text(parser, name))
+	}
+	_ = finish_statement(parser)
+}
+
 decode_import_path :: proc(parser: ^Parser, tok: token.Token) -> string {
 	text := token_text(parser, tok)
 	if len(text) < 2 {
@@ -1601,6 +1728,10 @@ parse_top_level :: proc(parser: ^Parser) {
 		parse_struct(parser, name, current(parser).kind == .Keyword_C_Struct)
 		return
 	}
+	if operator.kind == .Colon_Colon && current(parser).kind == .Keyword_Enum {
+		parse_enum(parser, name)
+		return
+	}
 	if operator.kind == .Colon_Colon && current(parser).kind == .Keyword_Distinct {
 		parse_distinct(parser, name)
 		return

compiler/token/token.odin

@@ -52,6 +52,7 @@ Kind :: enum u8 {
 	Keyword_C_Func,
 	Keyword_Struct,
 	Keyword_C_Struct,
+	Keyword_Enum,
 	Keyword_Distinct,
 	Keyword_Import,
 	Keyword_Return,

compiler/types/types.odin

@@ -65,6 +65,7 @@ Kind :: enum u8 {
 	Named,
 	Alias,
 	Distinct,
+	Enum,
 	Struct,
 	Union,
 }
@@ -91,6 +92,7 @@ Node :: struct {
 	c_layout:     bool,
 	opaque:       bool,
 	declared:     bool,
+	explicit_backing: bool,
 }
 
 Field :: struct {
@@ -99,9 +101,15 @@ Field :: struct {
 	offset: u64,
 }
 
+Enum_Member :: struct {
+	name:  u32,
+	value: i128,
+}
+
 Store :: struct {
 	nodes:        [dynamic]Node,
 	fields:       [dynamic]Field,
+	enum_members: [dynamic]Enum_Member,
 	selected:     target.Target,
 	allocator:    mem.Allocator,
 }
@@ -110,6 +118,7 @@ init_store :: proc(allocator := context.allocator) -> Store {
 	store: Store
 	store.nodes.allocator = allocator
 	store.fields.allocator = allocator
+	store.enum_members.allocator = allocator
 	store.selected = target.DEFAULT
 	store.allocator = allocator
 	return store
@@ -118,19 +127,21 @@ init_store :: proc(allocator := context.allocator) -> Store {
 destroy_store :: proc(store: ^Store) {
 	delete(store.nodes)
 	delete(store.fields)
+	delete(store.enum_members)
 }
 
 clone_store :: proc(source: ^Store, allocator := context.allocator) -> Store {
 	store := init_store(allocator)
 	append(&store.nodes, ..source.nodes[:])
 	append(&store.fields, ..source.fields[:])
+	append(&store.enum_members, ..source.enum_members[:])
 	store.selected = source.selected
 	return store
 }
 
 intern :: proc(store: ^Store, candidate: Node) -> Type {
 	if candidate.kind != .Struct && candidate.kind != .Union &&
-	   candidate.kind != .Named && candidate.kind != .Distinct {
+	   candidate.kind != .Named && candidate.kind != .Distinct && candidate.kind != .Enum {
 		for existing, index in store.nodes {
 			if existing == candidate {
 				return DYNAMIC_START+Type(index)
@@ -146,7 +157,7 @@ named :: proc(store: ^Store, pkg, name: u32, qualifier: u32 = 0, file: u32 = 0xf
 	normalized_file := file if qualifier != 0 else u32(0)
 	for existing, index in store.nodes {
 		if (existing.kind == .Named || existing.kind == .Alias || existing.kind == .Distinct ||
-		    existing.kind == .Struct || existing.kind == .Union) &&
+		    existing.kind == .Enum || existing.kind == .Struct || existing.kind == .Union) &&
 		   existing.pkg == pkg && existing.name == name && existing.qualifier == qualifier &&
 		   existing.file == normalized_file {
 			return DYNAMIC_START+Type(index)
@@ -158,7 +169,7 @@ named :: proc(store: ^Store, pkg, name: u32, qualifier: u32 = 0, file: u32 = 0xf
 find_named :: proc(store: ^Store, pkg, name: u32, qualifier: u32 = 0) -> Type {
 	for existing, index in store.nodes {
 		if (existing.kind == .Named || existing.kind == .Alias || existing.kind == .Distinct ||
-		    existing.kind == .Struct || existing.kind == .Union) &&
+		    existing.kind == .Enum || existing.kind == .Struct || existing.kind == .Union) &&
 		   existing.pkg == pkg && existing.name == name && existing.qualifier == qualifier {
 			return DYNAMIC_START+Type(index)
 		}
@@ -190,6 +201,22 @@ define_distinct :: proc(store: ^Store, id, child: Type) -> bool {
 	return true
 }
 
+define_enum :: proc(store: ^Store, id, backing: Type, members: []Enum_Member, explicit_backing: bool) -> bool {
+	existing, ok := node(store, id)
+	if !ok || existing.kind != .Named || existing.declared {
+		return false
+	}
+	index := int(id-DYNAMIC_START)
+	store.nodes[index].kind = .Enum
+	store.nodes[index].child = backing
+	store.nodes[index].field_start = u32(len(store.enum_members))
+	store.nodes[index].field_count = u32(len(members))
+	store.nodes[index].explicit_backing = explicit_backing
+	store.nodes[index].declared = true
+	append(&store.enum_members, ..members)
+	return true
+}
+
 define_record :: proc(
 	store: ^Store,
 	id: Type,
@@ -247,6 +274,19 @@ params_for :: proc(store: ^Store, value: Type) -> []Field {
 	return store.fields[start:end]
 }
 
+enum_members_for :: proc(store: ^Store, value: Type) -> []Enum_Member {
+	item, ok := node(store, value)
+	if !ok || item.kind != .Enum {
+		return nil
+	}
+	start := int(item.field_start)
+	end := start+int(item.field_count)
+	if start < 0 || end > len(store.enum_members) {
+		return nil
+	}
+	return store.enum_members[start:end]
+}
+
 kind :: proc(value: Type, store: ^Store = nil) -> Kind {
 	switch value {
 	case INVALID:
@@ -409,7 +449,8 @@ is_concrete_scalar :: proc(value: Type) -> bool {
 is_concrete :: proc(value: Type, store: ^Store = nil) -> bool {
 	value_kind := kind(value, store)
 	if value_kind == .Scalar || value_kind == .Array || value_kind == .Pointer ||
-	   value_kind == .Slice || value_kind == .Range || value_kind == .Optional {
+	   value_kind == .Slice || value_kind == .Range || value_kind == .Optional ||
+	   value_kind == .Enum {
 		return true
 	}
 	if value_kind == .Struct || value_kind == .Union {
@@ -460,6 +501,10 @@ is_distinct :: proc(value: Type, store: ^Store) -> bool {
 	return kind(value, store) == .Distinct
 }
 
+is_enum :: proc(value: Type, store: ^Store) -> bool {
+	return kind(value, store) == .Enum
+}
+
 resolve_alias :: proc(value: Type, store: ^Store, depth := 0) -> Type {
 	if depth > 64 {
 		return INVALID
@@ -486,6 +531,9 @@ is_c_record_field_type :: proc(value: Type, store: ^Store, depth := 0) -> bool {
 	if !ok {
 		return false
 	}
+	if item.kind == .Enum {
+		return item.explicit_backing && is_concrete_integer(item.child)
+	}
 	if item.kind == .Array {
 		return item.count > 0 && !item.has_sentinel && !item.inferred_count &&
 		       is_c_record_field_type(item.child, store, depth+1)
@@ -524,7 +572,7 @@ is_runtime_value :: proc(value: Type, store: ^Store, depth := 0) -> bool {
 		item, ok := node(store, value)
 		return ok && item.declared && !item.opaque && (!item.c_layout || item.field_count > 0)
 	}
-	if value_kind == .Distinct {
+	if value_kind == .Distinct || value_kind == .Enum {
 		item, ok := node(store, value)
 		return ok && item.declared && is_runtime_value(item.child, store, depth+1)
 	}
@@ -541,7 +589,7 @@ runtime_representation :: proc(value: Type, store: ^Store, depth := 0) -> Type {
 		return INVALID
 	}
 	item, ok := node(store, value)
-	if !ok || item.kind != .Distinct {
+	if !ok || (item.kind != .Distinct && item.kind != .Enum) {
 		return value
 	}
 	return runtime_representation(item.child, store, depth+1)
@@ -585,6 +633,9 @@ is_c_signature_type :: proc(value: Type, store: ^Store, allow_void := false) ->
 	if contains_distinct(value, store) {
 		return false
 	}
+	if item, ok := node(store, value); ok && item.kind == .Enum {
+		return item.explicit_backing && is_concrete_integer(item.child)
+	}
 	return is_concrete_scalar(value) || is_pointer(value, store) || is_optional_pointer(value, store) ||
 	       (is_c_struct(value, store) && is_runtime_value(value, store))
 }
@@ -621,7 +672,12 @@ is_c_integer_promotion_candidate :: proc(value: Type) -> bool {
 	return value >= C_CHAR && value <= C_USHORT
 }
 
-c_vararg_promotion :: proc(value: Type, selected := target.DEFAULT) -> Type {
+c_vararg_promotion :: proc(value: Type, selected := target.DEFAULT, store: ^Store = nil) -> Type {
+	if store != nil {
+		if item, ok := node(store, value); ok && item.kind == .Enum {
+			return c_vararg_promotion(item.child, selected, store)
+		}
+	}
 	if !is_concrete_scalar(value) {
 		return value
 	}
@@ -642,6 +698,9 @@ c_vararg_promotion :: proc(value: Type, selected := target.DEFAULT) -> Type {
 }
 
 is_c_vararg_type :: proc(value: Type, store: ^Store) -> bool {
+	if item, ok := node(store, value); ok && item.kind == .Enum {
+		return item.explicit_backing && is_concrete_integer(item.child)
+	}
 	return is_concrete_scalar(value) || is_pointer(value, store) || is_optional_pointer(value, store)
 }
 
@@ -909,7 +968,7 @@ size :: proc(value: Type, store: ^Store, selected := target.DEFAULT) -> u64 {
 		return ((child_size+1+child_align-1)/child_align)*child_align
 	case .Function:
 		return 0
-	case .Distinct:
+	case .Distinct, .Enum:
 		return size(child_type(value, store), store, selected)
 	case .Struct:
 		item, _ := node(store, value)
@@ -952,7 +1011,7 @@ alignment_of :: proc(value: Type, store: ^Store, selected := target.DEFAULT) ->
 		return alignment_of(child_type(value, store), store, selected)
 	case .Function:
 		return 1
-	case .Distinct:
+	case .Distinct, .Enum:
 		return alignment_of(child_type(value, store), store, selected)
 	case .Struct:
 		item, _ := node(store, value)

compiler_tests.odin

@@ -2379,6 +2379,42 @@ libclang_import_preserves_external_object_and_final_macro_semantics :: proc(t: ^
 	testing.expect(t, result.available)
 	testing.expect_value(t, result.error_message, "")
 
+	enum_alias_type := cimport.INVALID_TYPE
+	for alias in result.aliases {
+		if alias.name == "Imported_Enum" {
+			enum_alias_type = alias.type
+			break
+		}
+	}
+	testing.expect(t, enum_alias_type != cimport.INVALID_TYPE)
+	if enum_alias_type != cimport.INVALID_TYPE {
+		testing.expect_value(t, result.types[enum_alias_type].kind, cimport.Type_Kind.C_Int)
+	}
+	enum_negative, found_enum_negative := find_cimport_macro(&result, "IMPORTED_ENUM_NEGATIVE")
+	enum_same, found_enum_same := find_cimport_macro(&result, "IMPORTED_ENUM_SAME")
+	enum_value, found_enum_value := find_cimport_macro(&result, "IMPORTED_ENUM_VALUE")
+	enum_back, found_enum_back := find_cimport_macro(&result, "IMPORTED_ENUM_BACK")
+	enum_anon, found_enum_anon := find_cimport_macro(&result, "IMPORTED_ANON_ENUM")
+	testing.expect(t, found_enum_negative && found_enum_same && found_enum_value && found_enum_back && found_enum_anon)
+	if found_enum_negative {
+		testing.expect(t, enum_negative.value.negative)
+		testing.expect_value(t, enum_negative.value.integer, u64(2))
+	}
+	if found_enum_same {
+		testing.expect(t, enum_same.value.negative)
+		testing.expect_value(t, enum_same.value.integer, u64(2))
+	}
+	if found_enum_value {
+		testing.expect(t, !enum_value.value.negative)
+		testing.expect_value(t, enum_value.value.integer, u64(7))
+	}
+	if found_enum_back {
+		testing.expect_value(t, enum_back.value.integer, u64(3))
+	}
+	if found_enum_anon {
+		testing.expect_value(t, enum_anon.value.integer, u64(9))
+	}
+
 	tls, found_tls := find_cimport_variable(&result, "imported_tls_global")
 	testing.expect(t, found_tls)
 	if found_tls {
@@ -5409,3 +5445,208 @@ distinct_types_compile_and_run_across_packages :: proc(t: ^testing.T) {
 	state := run_executable(output)
 	testing.expect_value(t, state.exit_code, 0)
 }
+
+@(test)
+native_enums_preserve_identity_members_and_integer_representation :: proc(t: ^testing.T) {
+	text := `Animal :: enum {
+	dog
+	cat
+	bird
+}
+Nat :: enum(u16) {
+	one = 1
+	two
+	five = 5
+}
+global Animal :: Animal.dog
+take :: func(value Animal) Animal {
+	return value
+}
+identity :: c_func(value Nat) Nat {
+	return value
+}
+variadic :: c_func(marker c_int, ...) c_int
+main :: func() i32 {
+	value Animal = .cat
+	values [2]Animal :: [.dog, Animal.bird]
+	number Nat = identity(.two)
+	_ = variadic(0, number)
+	if take(value) == Animal.cat and values[0] != values[1] and number == Nat.two {
+		return 0
+	}
+	return 1
+}
+`
+	source_file := source.Source{path="test.bro", text=text}
+	diagnostics := source.init_diagnostics(&source_file)
+	defer source.destroy_diagnostics(&diagnostics)
+	symbols := symbol.init_table()
+	defer symbol.destroy_table(&symbols)
+	stream := lexer.lex(&source_file, &diagnostics, &symbols)
+	defer delete(stream.items)
+	ast_module := parser.parse(&stream, &source_file, &diagnostics)
+	defer ast.destroy_module(&ast_module)
+	hir_module := checker.check(&ast_module, &diagnostics, &symbols)
+	defer hir.destroy_module(&hir_module)
+	ir_module := lower.lower(&hir_module)
+	defer ir.destroy_module(&ir_module)
+	llvm_text := llvm.emit(&ir_module, &diagnostics, &symbols)
+	defer delete(llvm_text)
+
+	animal := types.find_named(&ast_module.type_store, 0, u32(symbol.intern(&symbols, "Animal")))
+	nat := types.find_named(&ast_module.type_store, 0, u32(symbol.intern(&symbols, "Nat")))
+	animal_node, animal_ok := types.node(&ast_module.type_store, animal)
+	nat_node, nat_ok := types.node(&ast_module.type_store, nat)
+	animal_members := types.enum_members_for(&ast_module.type_store, animal)
+	nat_members := types.enum_members_for(&ast_module.type_store, nat)
+
+	testing.expect_value(t, len(diagnostics.items), 0)
+	testing.expect(t, animal_ok && nat_ok)
+	testing.expect(t, types.is_enum(animal, &ast_module.type_store))
+	testing.expect_value(t, animal_node.child, types.U8)
+	testing.expect(t, !animal_node.explicit_backing)
+	testing.expect_value(t, nat_node.child, types.U16)
+	testing.expect(t, nat_node.explicit_backing)
+	testing.expect_value(t, len(animal_members), 3)
+	testing.expect_value(t, animal_members[0].value, i128(0))
+	testing.expect_value(t, animal_members[2].value, i128(2))
+	testing.expect_value(t, nat_members[0].value, i128(1))
+	testing.expect_value(t, nat_members[1].value, i128(2))
+	testing.expect_value(t, nat_members[2].value, i128(5))
+	testing.expect_value(t, types.runtime_representation(animal, &ast_module.type_store), types.U8)
+	testing.expect_value(t, types.size(animal, &ast_module.type_store), u64(1))
+	testing.expect(t, hir_module.globals[0].is_static)
+	testing.expect_value(t, hir_module.globals[0].static_value, i64(0))
+	testing.expect(t, strings.contains(llvm_text, "@bro.g.0 = internal constant i8 0"))
+	found_promotion := false
+	for function in ir_module.functions {
+		for instruction in function.instructions {
+			found_promotion = found_promotion || instruction.op == .C_Vararg_Promote
+		}
+	}
+	testing.expect(t, found_promotion)
+}
+
+@(test)
+unbacked_enum_selects_the_smallest_fitting_unsigned_backing :: proc(t: ^testing.T) {
+	builder := strings.builder_make()
+	defer strings.builder_destroy(&builder)
+	strings.write_string(&builder, "Large :: enum {\n")
+	for index in 0..<257 {
+		fmt.sbprintf(&builder, "value_%d\n", index)
+	}
+	strings.write_string(&builder, "}\nmain :: func() void {}\n")
+	source_file := source.Source{path="test.bro", text=strings.to_string(builder)}
+	diagnostics := source.init_diagnostics(&source_file)
+	defer source.destroy_diagnostics(&diagnostics)
+	symbols := symbol.init_table()
+	defer symbol.destroy_table(&symbols)
+	stream := lexer.lex(&source_file, &diagnostics, &symbols)
+	defer delete(stream.items)
+	module := parser.parse(&stream, &source_file, &diagnostics)
+	defer ast.destroy_module(&module)
+
+	large := types.find_named(&module.type_store, 0, u32(symbol.intern(&symbols, "Large")))
+	item, ok := types.node(&module.type_store, large)
+	testing.expect_value(t, len(diagnostics.items), 0)
+	testing.expect(t, ok)
+	testing.expect_value(t, item.child, types.U16)
+	testing.expect_value(t, len(types.enum_members_for(&module.type_store, large)), 257)
+}
+
+@(test)
+native_enum_invalid_declarations_and_operations_are_diagnosed :: proc(t: ^testing.T) {
+	text := `Empty :: enum {}
+Dense :: enum {
+	zero = 0
+	one
+}
+BadBacking :: enum(f32) {
+	value
+}
+Duplicate :: enum(u8) {
+	value
+	value
+}
+Jumbled :: enum(i8) {
+	second = 2
+	first = 1
+}
+Overflow :: enum(u8) {
+	value = 256
+}
+Other :: enum {
+	value
+}
+foreign :: c_func(value Dense) void
+allowed :: c_func(value Overflow) Overflow
+main :: func() void {
+	dense Dense = Other.value
+	_ = Dense.zero + Dense.one
+	_ = Dense.zero < Dense.one
+	_ = Dense.missing
+	_ = .zero
+	_ = dense
+}
+`
+	source_file := source.Source{path="test.bro", text=text}
+	diagnostics := source.init_diagnostics(&source_file)
+	defer source.destroy_diagnostics(&diagnostics)
+	symbols := symbol.init_table()
+	defer symbol.destroy_table(&symbols)
+	stream := lexer.lex(&source_file, &diagnostics, &symbols)
+	defer delete(stream.items)
+	ast_module := parser.parse(&stream, &source_file, &diagnostics)
+	defer ast.destroy_module(&ast_module)
+	hir_module := checker.check(&ast_module, &diagnostics, &symbols)
+	defer hir.destroy_module(&hir_module)
+
+	found_empty := false
+	found_unbacked_value := false
+	found_backing := false
+	found_duplicate := false
+	found_order := false
+	found_overflow := false
+	found_foreign := false
+	found_conversion := false
+	found_arithmetic := false
+	found_comparison := false
+	found_member := false
+	found_context := false
+	for diagnostic in diagnostics.items {
+		found_empty = found_empty || strings.contains(diagnostic.message, "require at least one member")
+		found_unbacked_value = found_unbacked_value || strings.contains(diagnostic.message, "explicit enum values require a backing type")
+		found_backing = found_backing || strings.contains(diagnostic.message, "requires a concrete integer backing type")
+		found_duplicate = found_duplicate || strings.contains(diagnostic.message, "duplicate enum member")
+		found_order = found_order || strings.contains(diagnostic.message, "strictly increasing")
+		found_overflow = found_overflow || strings.contains(diagnostic.message, "does not fit in u8")
+		found_foreign = found_foreign || strings.contains(diagnostic.message, "requires concrete parameter types")
+		found_conversion = found_conversion || strings.contains(diagnostic.message, "cannot implicitly convert")
+		found_arithmetic = found_arithmetic || strings.contains(diagnostic.message, "arithmetic requires compatible numeric operands")
+		found_comparison = found_comparison || strings.contains(diagnostic.message, "enum values only support")
+		found_member = found_member || strings.contains(diagnostic.message, "unknown enum member")
+		found_context = found_context || strings.contains(diagnostic.message, "requires an enum context")
+	}
+	testing.expect(t, found_empty)
+	testing.expect(t, found_unbacked_value)
+	testing.expect(t, found_backing)
+	testing.expect(t, found_duplicate)
+	testing.expect(t, found_order)
+	testing.expect(t, found_overflow)
+	testing.expect(t, found_foreign)
+	testing.expect(t, found_conversion)
+	testing.expect(t, found_arithmetic)
+	testing.expect(t, found_comparison)
+	testing.expect(t, found_member)
+	testing.expect(t, found_context)
+}
+
+@(test)
+native_enums_compile_and_run_across_packages :: proc(t: ^testing.T) {
+	output := "/tmp/brolang-test-enums"
+	defer _ = os.remove(output)
+	status := compiler_core.compile_package("examples/programs/enums", output)
+	testing.expect_value(t, status, 0)
+	state := run_executable(output)
+	testing.expect_value(t, state.exit_code, 0)
+}

examples/interop/header/app/main.bro

@@ -12,6 +12,10 @@ call_mapper :: func(mapper native.Imported_Mapper) c_int {
 	return mapper?(21)
 }
 
+enum_identity :: c_func(value native.Imported_Enum) native.Imported_Enum {
+	return value
+}
+
 main :: func() void {
 	_ = native.imported_add(pass_alias(20), 22)
 	_ = native.imported_scalar(3, 4)
@@ -19,6 +23,14 @@ main :: func() void {
 	_ = native.imported_read(native.imported_handle()?)
 	_ = native.imported_string("hello")
 	_ = native.imported_apply(double_value, 21)
+	enum_value native.Imported_Enum :: native.IMPORTED_ENUM_NEGATIVE
+	enum_same native.Imported_Enum :: native.IMPORTED_ENUM_SAME
+	_ = native.imported_enum_check(enum_value, native.IMPORTED_ENUM_VALUE)
+	_ = native.imported_enum_variadic(-2, enum_same)
+	enum_record native.Imported_Enum_Record :: native.Imported_Enum_Record { value = native.IMPORTED_ENUM_BACK }
+	_ = native.imported_enum_record(enum_record)
+	_ = native.imported_enum_apply(enum_identity, native.imported_enum_global)
+	_ = native.IMPORTED_ANON_ENUM
 	_ = call_mapper(double_value)
 	_ = native.configured_value(9)
 	_ = native.IMPORTED_SHADOW_OBJECT

examples/interop/header/include/native.h

@@ -80,8 +80,18 @@ typedef struct Imported_Anonymous {
 	};
 } Imported_Anonymous;
 typedef enum Imported_Enum {
-	IMPORTED_ENUM_VALUE,
+	IMPORTED_ENUM_NEGATIVE = -2,
+	IMPORTED_ENUM_SAME = -2,
+	IMPORTED_ENUM_VALUE = 7,
+	IMPORTED_ENUM_BACK = 3,
 } Imported_Enum;
+enum {
+	IMPORTED_ANON_ENUM = 9,
+};
+typedef struct Imported_Enum_Record {
+	Imported_Enum value;
+} Imported_Enum_Record;
+typedef Imported_Enum (*Imported_Enum_Callback)(Imported_Enum value);
 
 int imported_add(imported_int_alias left, int right);
 unsigned long imported_scalar(unsigned char value, unsigned long extra);
@@ -89,6 +99,10 @@ Imported_Handle *imported_handle(void);
 int imported_read(const Imported_Handle *handle);
 int imported_string(const char *value);
 int imported_apply(Imported_Mapper mapper, int value);
+int imported_enum_check(Imported_Enum first, Imported_Enum second);
+int imported_enum_variadic(int expected, ...);
+Imported_Enum_Record imported_enum_record(Imported_Enum_Record value);
+Imported_Enum imported_enum_apply(Imported_Enum_Callback callback, Imported_Enum value);
 Imported_Value imported_by_value(Imported_Value value);
 int imported_check_state(
 	Imported_Color color,
@@ -126,6 +140,7 @@ extern int imported_redeclared_array[4];
 extern Imported_Value imported_record_global;
 extern const Imported_Array_Record imported_const_array_record;
 extern Imported_Array_Record imported_mutable_array_record;
+extern Imported_Enum imported_enum_global;
 extern _Thread_local int imported_tls_global;
 extern int IMPORTED_SHADOW_OBJECT;
 int IMPORTED_SHADOW_FUNCTION(void);

examples/interop/header/native.c

@@ -16,6 +16,7 @@ int imported_redeclared_array[4] = {13, 14, 15, 16};
 Imported_Value imported_record_global = {40};
 const Imported_Array_Record imported_const_array_record = {{20, 21}};
 Imported_Array_Record imported_mutable_array_record = {{0, 1}};
+Imported_Enum imported_enum_global = IMPORTED_ENUM_VALUE;
 int child_shared_global = 0;
 
 int child_value(int value) {
@@ -56,6 +57,38 @@ int imported_apply(Imported_Mapper mapper, int value) {
 	return result;
 }
 
+int imported_enum_check(Imported_Enum first, Imported_Enum second) {
+	if (!(first == IMPORTED_ENUM_NEGATIVE && second == IMPORTED_ENUM_VALUE)) {
+		abort();
+	}
+	return 0;
+}
+
+int imported_enum_variadic(int expected, ...) {
+	va_list args;
+	va_start(args, expected);
+	int value = va_arg(args, int);
+	va_end(args);
+	if (value != expected) {
+		abort();
+	}
+	return 0;
+}
+
+Imported_Enum_Record imported_enum_record(Imported_Enum_Record value) {
+	if (value.value != IMPORTED_ENUM_BACK) {
+		abort();
+	}
+	return value;
+}
+
+Imported_Enum imported_enum_apply(Imported_Enum_Callback callback, Imported_Enum value) {
+	if (callback == NULL || callback(value) != value) {
+		abort();
+	}
+	return value;
+}
+
 int imported_check_state(
 	Imported_Color color,
 	int macro_value,

examples/programs/enums/animals/animals.bro

@@ -0,0 +1,8 @@
+Animal :: enum {
+	dog
+	cat
+}
+
+favorite :: func() Animal {
+	return .cat
+}

examples/programs/enums/main.bro

@@ -0,0 +1,30 @@
+animals :: import "./animals"
+
+State :: enum(u16) {
+	started = 10
+	running
+	stopped = 20
+}
+
+initial State :: State.started
+
+same :: func(left State, right State) bool {
+	return left == right
+}
+
+identity :: c_func(value State) State {
+	return value
+}
+
+main :: func() i32 {
+	state State = identity(.running)
+	values [2]State :: [.started, State.stopped]
+	animal animals.Animal :: animals.Animal.dog
+	if same(state, .running) and
+	   values[0] != values[1] and
+	   animal != animals.favorite() and
+	   initial == State.started {
+		return 0
+	}
+	return 1
+}