Expand Gotlin language and tooling

internal/lang/compiler_test.go

@@ -867,6 +867,183 @@ worker Counter {
 	}
 }
 
+func TestGenerateGoRejectsValReassignment(t *testing.T) {
+	src := `
+package demo
+
+fun main() {
+    val count = 0
+    count = 1
+}
+
+`
+
+	prog, err := Parse(src)
+	if err != nil {
+		t.Fatalf("parse failed: %v", err)
+	}
+	_, err = GenerateGo(prog)
+	if err == nil {
+		t.Fatal("expected val reassignment error")
+	}
+	if !strings.Contains(err.Error(), "cannot reassign immutable name count") {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
+func TestGenerateGoDefer(t *testing.T) {
+	src := `
+package demo
+
+import database.sql
+
+fun main() {
+    val rows = sql.Open("postgres", "dsn")
+    defer rows.Close()
+}
+
+`
+	prog, err := Parse(src)
+	if err != nil {
+		t.Fatalf("parse failed: %v", err)
+	}
+	out, err := GenerateGo(prog)
+	if err != nil {
+		t.Fatalf("go generation failed: %v", err)
+	}
+	if !strings.Contains(string(out), "defer rows.Close()") {
+		t.Fatalf("generated Go missing defer:\n%s", out)
+	}
+}
+
+func TestGenerateGoDecimalLiteral(t *testing.T) {
+	src := `
+package demo
+
+fun interest(): Double {
+    return 0.025
+}
+`
+	prog, err := Parse(src)
+	if err != nil {
+		t.Fatalf("parse failed: %v", err)
+	}
+	out, err := GenerateGo(prog)
+	if err != nil {
+		t.Fatalf("go generation failed: %v", err)
+	}
+	for _, want := range []string{"func interest() float64", "return 0.025"} {
+		if !strings.Contains(string(out), want) {
+			t.Fatalf("generated Go missing %q:\n%s", want, out)
+		}
+	}
+}
+
+func TestGenerateGoRejectsMultiValReassignment(t *testing.T) {
+	src := `
+package demo
+
+import database.sql
+
+fun main() {
+    val db, err = sql.Open("postgres", "postgres://localhost/postgres?sslmode=disable")
+    err = nil
+}
+`
+
+	prog, err := Parse(src)
+	if err != nil {
+		t.Fatalf("parse failed: %v", err)
+	}
+	_, err = GenerateGo(prog)
+	if err == nil {
+		t.Fatal("expected multi-val reassignment error")
+	}
+	if !strings.Contains(err.Error(), "cannot reassign immutable name err") {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
+func TestGenerateGoAllowsVarReassignment(t *testing.T) {
+	src := `
+package demo
+
+fun main() {
+    var count = 0
+    count = 1
+    count += 2
+    println(count)
+}
+`
+
+	prog, err := Parse(src)
+	if err != nil {
+		t.Fatalf("parse failed: %v", err)
+	}
+	out, err := GenerateGo(prog)
+	if err != nil {
+		t.Fatalf("go generation failed: %v", err)
+	}
+	code := string(out)
+	for _, want := range []string{
+		`count := 0`,
+		`count = 1`,
+		`count += 2`,
+	} {
+		if !strings.Contains(code, want) {
+			t.Fatalf("generated Go missing %q:\n%s", want, code)
+		}
+	}
+}
+
+func TestGenerateGoRejectsReassignmentToImmutableClassField(t *testing.T) {
+	src := `
+package demo
+
+class Counter(val count: Int, var total: Int) {
+    fun freeze() {
+        count = 1
+    }
+}
+`
+
+	prog, err := Parse(src)
+	if err != nil {
+		t.Fatalf("parse failed: %v", err)
+	}
+	_, err = GenerateGo(prog)
+	if err == nil {
+		t.Fatal("expected immutable class field reassignment error")
+	}
+	if !strings.Contains(err.Error(), "cannot reassign immutable name count") {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
+func TestGenerateGoAllowsReassignmentToMutableClassField(t *testing.T) {
+	src := `
+package demo
+
+class Counter(var count: Int) {
+    fun inc() {
+        count += 1
+    }
+}
+`
+
+	prog, err := Parse(src)
+	if err != nil {
+		t.Fatalf("parse failed: %v", err)
+	}
+	out, err := GenerateGo(prog)
+	if err != nil {
+		t.Fatalf("go generation failed: %v", err)
+	}
+	if !strings.Contains(string(out), `self.count += 1`) {
+		t.Fatalf("generated Go missing mutable field assignment:\n%s", string(out))
+	}
+}
+
 func TestGenerateGoWorkerSyncPanicPropagationScaffolding(t *testing.T) {
 	src := `
 package demo