structs as errors in fallibles

LANGUAGE.md

@@ -44,7 +44,7 @@ roadmap and milestone history.
 - named native struct fields may declare defaults with `field T = expression`; keyed literals use defaults for omitted fields and explicit initializers override them
 - void-payload tagged-union variants, anonymous struct payloads, contextual `.variant`, `.variant{payload}`, and `.variant{field = value}` construction
 - native sum composition with `A | B` for unbacked enums and tagged unions, optionally grouped as `(A | B)`, using program-global `u16` variant ids
-- fallible channel types `T ! E`, where `E` is a native enum/tagged union or supported sum composition; `void ! E` functions complete successfully on fallthrough, and void-success `catch` handlers may fall through without `yield`
+- fallible channel types `T ! E`, where `E` is a native enum, native struct, tagged union, or supported sum composition; `void ! E` functions complete successfully on fallthrough, and void-success `catch` handlers may fall through without `yield`
 
 #### distinct types
 

compiler/checker/checker.odin

@@ -3976,7 +3976,8 @@ validate_declarations :: proc(checker: ^Checker) {
 		}
 		if types.is_valid(function.error) && !signature_poisoned {
 			error_type := type_from_syntax(checker, function.error, function.pkg, function.file)
-			error_sum := types.is_enum(error_type, &checker.module.types) ||
+			error_channel := types.is_enum(error_type, &checker.module.types) ||
+			                 types.is_struct(error_type, &checker.module.types) ||
 			                 types.is_tagged_union(error_type, &checker.module.types)
 			if function.c_abi {
 				checker.template_diagnostics[function_id] = source.add(
@@ -3984,11 +3985,11 @@ validate_declarations :: proc(checker: ^Checker) {
 					function.span,
 					"fallible functions must use 'func', not 'c_func'",
 				)
-			} else if !error_sum {
+			} else if !error_channel {
 				checker.template_diagnostics[function_id] = source.add(
 					checker.diagnostics,
 					function.span,
-					"fallible function error type must be a native enum or tagged union",
+					"fallible function error type must be a native enum, struct, or tagged union",
 				)
 			}
 		}

compiler/checker/comptime.odin

@@ -4487,6 +4487,19 @@ ct_return_value :: proc(state: ^Ct_State, expr_id: ast.Expr_Id, span: source.Spa
 		if expr.kind == .Enum_Literal && types.sum_has_name(&checker.module.types, error_type, u32(expr.name)) {
 			error_path = true
 			expected = error_type
+		} else if expr.kind == .Struct_Literal {
+			target_pkg, available := expr_package(checker, expr, state.pkg, state.file, true)
+			named := types.find_named(
+				&checker.module.types,
+				u32(target_pkg),
+				u32(expr.name),
+				file=u32(expr_lookup_file(expr, state.file)),
+			) if available else types.INVALID
+			named = types.resolve_alias(named, &checker.module.types)
+			if can_implicitly_convert_type(checker, named, error_type) {
+				error_path = true
+				expected = error_type
+			}
 		} else if expr.kind == .Name && !symbol.is_valid(expr.qualifier) {
 			if index, found := ct_find_binding_index(state, expr.name); found {
 				actual := state.bindings[index].type

compiler/llvm/llvm.odin

@@ -1050,6 +1050,16 @@ emit_instruction_stream :: proc(
 						fmt.sbprintf(&emitter.builder, "  %%fallible_payload%d = getelementptr i8, ptr %%fallible_slot%d, i64 %d\n", instruction_index, instruction_index, payload_offset)
 						fmt.sbprintf(&emitter.builder, "  call void @llvm.memcpy.p0.p0.i64(ptr %%fallible_payload%d, ptr %%fallible_error_payload%d, i64 %d, i1 false)\n", instruction_index, instruction_index, error_payload_size)
 					}
+				} else if types.is_struct(error_type, &emitter.module.types) {
+					if !valid_value(instructions, instruction.args[0], error_type, &emitter.module.types) {
+						emit_recovery_value(emitter, instruction_index, instruction, "invalid fallible struct error operand")
+						continue
+					}
+					fmt.sbprintf(&emitter.builder, "  store i16 1, ptr %%fallible_slot%d\n", instruction_index)
+					fmt.sbprintf(&emitter.builder, "  %%fallible_payload%d = getelementptr i8, ptr %%fallible_slot%d, i64 %d\n", instruction_index, instruction_index, payload_offset)
+					fmt.sbprintf(&emitter.builder, "  store %s ", llvm_type(error_type, &emitter.module.types))
+					write_operand(&emitter.builder, instructions, instruction.args[0], error_type, &emitter.module.types)
+					fmt.sbprintf(&emitter.builder, ", ptr %%fallible_payload%d\n", instruction_index)
 				}
 				fmt.sbprintf(&emitter.builder, "  %%v%d = load %s, ptr %%fallible_slot%d\n", instruction_index, type_name, instruction_index)
 				continue
@@ -1389,6 +1399,12 @@ emit_instruction_stream :: proc(
 				fmt.sbprintf(&emitter.builder, "  %%v%d = load %s, ptr %%fallible_error_slot%d\n", instruction_index, type_name, instruction_index)
 				continue
 			}
+			if types.is_struct(error_type, &emitter.module.types) {
+				source_offset := types.fallible_payload_offset(channel_type, &emitter.module.types, emitter.module.target)
+				fmt.sbprintf(&emitter.builder, "  %%fallible_error_source%d = getelementptr i8, ptr %%v%d, i64 %d\n", instruction_index, instruction.a, source_offset)
+				fmt.sbprintf(&emitter.builder, "  %%v%d = load %s, ptr %%fallible_error_source%d\n", instruction_index, llvm_type(error_type, &emitter.module.types), instruction_index)
+				continue
+			}
 			emit_recovery_value(emitter, instruction_index, instruction, "unsupported fallible error type")
 		case .Store:
 			if !valid_address(instructions, instruction.a, instruction.type, &emitter.module.types) ||

compiler_tests.odin

@@ -6953,6 +6953,51 @@ main func() i32 {
 	testing.expect_value(t, state.exit_code, 0)
 }
 
+@(test)
+struct_error_channels_compile_and_run_at_runtime_and_comptime :: proc(t: ^testing.T) {
+	text := `ScanError :: struct {
+	code i32
+	start usize
+	end usize
+}
+scan func(fail bool) i32 ! ScanError {
+	if fail {
+		return ScanError { code = 5, start = 7, end = 11 }
+	}
+	return 41
+}
+scan_local func() i32 ! ScanError {
+	err ScanError := ScanError { code = 3, start = 13, end = 17 }
+	return err
+}
+forward func(fail bool) i32 ! ScanError {
+	return try scan(fail)
+}
+score_comptime func() i32 {
+	return scan(true) catch |err| err.code + i32(err.start) + i32(err.end)
+}
+main func() i32 {
+	direct :: scan(true) catch |err| err.code + i32(err.start) + i32(err.end)
+	local :: scan_local() catch |err| err.code + i32(err.start) + i32(err.end)
+	forwarded :: forward(true) catch |err| err.code + i32(err.start) + i32(err.end)
+	success :: forward(false) catch 0
+	comptime_score i32 :: $score_comptime()
+	return direct + local + forwarded + success + comptime_score - 143
+}
+`
+	directory := "/tmp/brolang-test-struct-error-channel"
+	main_path := "/tmp/brolang-test-struct-error-channel/main.bro"
+	output := "/tmp/brolang-test-struct-error-channel-output"
+	_ = os2.remove_all(directory)
+	defer _ = os2.remove_all(directory)
+	defer _ = os.remove(output)
+	testing.expect(t, os.make_directory(directory) == nil)
+	testing.expect(t, os.write_entire_file(main_path, transmute([]byte)text))
+	testing.expect_value(t, compiler_core.compile_package(directory, output), 0)
+	state := run_executable(output)
+	testing.expect_value(t, state.exit_code, 0)
+}
+
 @(test)
 matched_error_residuals_return_at_runtime_and_comptime :: proc(t: ^testing.T) {
 	text := `KeyError :: enum { key_exists }