Add structured coroutines and explicit error handling

internal/lang/nullability_test.go

@@ -0,0 +1,67 @@
+package lang
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestSafeAccessAndNonNullAssertion(t *testing.T) {
+	prog, err := Parse(`package demo
+data class User(var email: String)
+fun safe(user: *User?): String? { return user?.email }
+fun required(user: *User?): String { return user!!.email }`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	out, err := GenerateGo(prog)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, want := range []string{"if value == nil {", "return &result", "non-null assertion failed"} {
+		if !strings.Contains(string(out), want) {
+			t.Fatalf("missing %q:\n%s", want, out)
+		}
+	}
+}
+
+func TestRejectNullableDereference(t *testing.T) {
+	prog, err := Parse(`package demo
+fun unsafe(user: *User?): String { return user.email }`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, err = GenerateGo(prog)
+	if err == nil || !strings.Contains(err.Error(), "requires ?. or !!") {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
+func TestRejectNullForNonNullableTypes(t *testing.T) {
+	for _, source := range []string{
+		`package demo data class User(var email: String) fun main() { val user: *User = null }`,
+		`package demo data class User(var email: String) fun use(user: *User) {} fun main() { use(null) }`,
+		`package demo fun name(): String { return null }`,
+		`package demo fun main() { val value = null }`,
+	} {
+		prog, err := Parse(source)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if _, err = GenerateGo(prog); err == nil {
+			t.Fatalf("expected nullability error for %s", source)
+		}
+	}
+}
+
+func TestNullableSmartCasts(t *testing.T) {
+	prog, err := Parse(`package demo
+data class User(var email: String)
+fun guarded(user: *User?): String { if (user == null) { return "missing" }; return user.email }
+fun branched(user: *User?): String { if (user != null) { return user.email } else { return "missing" } }`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err = GenerateGo(prog); err != nil {
+		t.Fatal(err)
+	}
+}