add defer

compiler_tests.odin

@@ -2061,6 +2061,69 @@ missing_return :: func() i32 {
 	testing.expect(t, missing)
 }
 
+@(test)
+defer_compiles_and_runs :: proc(t: ^testing.T) {
+	output := "/tmp/brolang-test-defer"
+	defer _ = os.remove(output)
+	status := compiler_core.compile_package("examples/programs/defer", output)
+	testing.expect_value(t, status, 0)
+	state := run_executable(output)
+	// LIFO, runs on fall-through / break / continue / return (with the return value
+	// captured before defers run), scoped bare blocks, and `defer { ... }` blocks
+	// together produce 42.
+	testing.expect_value(t, state.exit_code, 42)
+}
+
+@(test)
+defer_misuse_is_diagnosed :: proc(t: ^testing.T) {
+	// Deferring control flow that would escape the defer is rejected: `defer return`,
+	// `defer break`, and a `return` inside a `defer { ... }` block.
+	text := `main :: func() i32 {
+	bad_defer_return()
+	bad_defer_break()
+	bad_return_in_defer()
+	return 0
+}
+bad_defer_return :: func() void {
+	defer return
+}
+bad_defer_break :: func() void {
+	for 0..3 |i| {
+		defer break
+		_ = i
+	}
+}
+bad_return_in_defer :: func() void {
+	defer {
+		return
+	}
+}
+`
+	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)
+
+	defer_return := false
+	defer_break := false
+	return_in_defer := false
+	for diagnostic in diagnostics.items {
+		defer_return = defer_return || strings.contains(diagnostic.message, "cannot defer a 'return' statement")
+		defer_break = defer_break || strings.contains(diagnostic.message, "cannot defer a 'break' statement")
+		return_in_defer = return_in_defer || strings.contains(diagnostic.message, "cannot 'return' inside a 'defer'")
+	}
+	testing.expect(t, defer_return)
+	testing.expect(t, defer_break)
+	testing.expect(t, return_in_defer)
+}
+
 @(test)
 foreign_function_links_from_c_source :: proc(t: ^testing.T) {
 	output := "/tmp/brolang-test-foreign-source"