Add value-returning match expressions

internal/lang/enum_test.go

@@ -77,3 +77,68 @@ fun main() { println(Status::PendingReservation) }`)
 		}
 	}
 }
+
+func TestGenerateExhaustiveMatchExpression(t *testing.T) {
+	prog, err := Parse(`package demo
+enum AccountType { BASIC, SAVINGS }
+fun interestRate(accountType: AccountType): Double {
+    return match (accountType) {
+        AccountType::BASIC -> 0.0
+        AccountType::SAVINGS -> 0.02
+    }
+}`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	out, err := GenerateGo(prog)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, want := range []string{"func() float64", "case AccountTypeBASIC:", "return 0.0", "case AccountTypeSAVINGS:", "return 0.02", `panic("unreachable exhaustive match")`} {
+		if !strings.Contains(string(out), want) {
+			t.Fatalf("missing %q:\n%s", want, out)
+		}
+	}
+}
+
+func TestGeneratePayloadMatchExpression(t *testing.T) {
+	prog, err := Parse(`package demo
+enum Outcome { Success(String), Failure(String) }
+fun message(outcome: Outcome): String {
+    return match (outcome) {
+        Outcome::Success(value) -> value
+        Outcome::Failure(reason) -> reason
+    }
+}`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	out, err := GenerateGo(prog)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, want := range []string{"switch gotlinMatch", "value := gotlinMatch", "return value", "return reason"} {
+		if !strings.Contains(string(out), want) {
+			t.Fatalf("missing %q:\n%s", want, out)
+		}
+	}
+}
+
+func TestRejectInvalidMatchExpression(t *testing.T) {
+	for _, test := range []struct {
+		source string
+		want   string
+	}{
+		{`package demo enum State { On, Off } fun value(state: State): Int { return match (state) { State::On -> 1 } }`, "missing Off"},
+		{`package demo enum State { On, Off } fun value(state: State): Int { return match (state) { State::On -> 1 State::Off -> "off" } }`, "has type String, expected Int"},
+	} {
+		prog, err := Parse(test.source)
+		if err != nil {
+			t.Fatal(err)
+		}
+		_, err = GenerateGo(prog)
+		if err == nil || !strings.Contains(err.Error(), test.want) {
+			t.Fatalf("expected %q, got %v", test.want, err)
+		}
+	}
+}