Testing current behavior of if/then/else (#11395)

Related to #9165 work. Let's make sure the current behavior of `if`/`then`/`else` is properly tested by a unit test. Extracting test created as part of #11365 to verify it really describes the current behavior.

engine/runtime-integration-tests/src/test/java/org/enso/compiler/test/IfThenElseTest.java

@@ -0,0 +1,299 @@
+package org.enso.compiler.test;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+import com.oracle.truffle.api.interop.InteropLibrary;
+import com.oracle.truffle.api.interop.TruffleObject;
+import com.oracle.truffle.api.library.ExportLibrary;
+import com.oracle.truffle.api.library.ExportMessage;
+import java.io.ByteArrayOutputStream;
+import org.enso.test.utils.ContextUtils;
+import org.graalvm.polyglot.Context;
+import org.graalvm.polyglot.PolyglotException;
+import org.graalvm.polyglot.Value;
+import org.hamcrest.Matchers;
+import org.hamcrest.core.AllOf;
+import org.junit.After;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.Ignore;
+import org.junit.Test;
+
+public class IfThenElseTest {
+  private static Context ctx;
+  private static final ByteArrayOutputStream MESSAGES = new ByteArrayOutputStream();
+
+  @BeforeClass
+  public static void initEnsoContext() {
+    ctx = ContextUtils.defaultContextBuilder().out(MESSAGES).err(MESSAGES).build();
+    assertNotNull("Enso language is supported", ctx.getEngine().getLanguages().get("enso"));
+  }
+
+  @After
+  public void cleanMessages() {
+    MESSAGES.reset();
+  }
+
+  @AfterClass
+  public static void closeEnsoContext() {
+    ctx.close();
+    ctx = null;
+  }
+
+  @Test
+  public void simpleIfThenElse() throws Exception {
+    var code = """
+    check x = if x then "Yes" else "No"
+    """;
+
+    var check = ContextUtils.getMethodFromModule(ctx, code, "check");
+
+    assertEquals("Yes", check.execute(true).asString());
+    assertEquals("No", check.execute(false).asString());
+  }
+
+  @Test
+  public void simpleIfThen() throws Exception {
+    var code = """
+    check x = if x then "Yes"
+    """;
+
+    var check = ContextUtils.getMethodFromModule(ctx, code, "check");
+
+    assertEquals("Yes", check.execute(true).asString());
+    assertTrue("Expect Nothing", check.execute(false).isNull());
+  }
+
+  @Test
+  public void variableDefinedInThen() throws Exception {
+    var code = """
+    check x = if x then
+        xt = x.to_text
+        "Good:"+xt
+    """;
+
+    var check = ContextUtils.getMethodFromModule(ctx, code, "check");
+
+    assertEquals("Good:True", check.execute(true).asString());
+    assertTrue("Expect Nothing", check.execute(false).isNull());
+  }
+
+  @Test
+  public void variableDefinedInElse() throws Exception {
+    var code =
+        """
+    check x = if x then "OKeyish:"+x.to_text else
+        xt = x.to_text
+        "Bad:"+xt
+    """;
+    var check = ContextUtils.getMethodFromModule(ctx, code, "check");
+
+    assertEquals("OKeyish:True", check.execute(true).asString());
+    assertEquals("Bad:False", check.execute(false).asString());
+  }
+
+  @Test
+  public void variableUsedAfterTheBranch() throws Exception {
+    try {
+      var code =
+          """
+    check x =
+        res = if x then "OKeyish:"+x.to_text else
+            xt = x.to_text
+            "Bad:"+xt
+
+        xt
+    """;
+
+      var check = ContextUtils.getMethodFromModule(ctx, code, "check");
+      fail("Expecting error, but got: " + check);
+    } catch (PolyglotException ex) {
+      assertThat(
+          ex.getMessage(),
+          AllOf.allOf(
+              Matchers.containsString("The name `xt` could not be found"),
+              Matchers.containsString("6:5: error")));
+    }
+  }
+
+  @Test
+  public void conditionMustBeBoolean() throws Exception {
+    var code = """
+    check x = if x then "Yes" else "No"
+    """;
+
+    var check = ContextUtils.getMethodFromModule(ctx, code, "check");
+
+    try {
+      var res = check.execute("Yes").asString();
+      fail("Expecting error, not: " + res);
+    } catch (PolyglotException ex) {
+      assertThat(ex.getMessage(), Matchers.containsString(".Error"));
+    }
+    try {
+      var res = check.execute((Object) null).asString();
+      fail("Expecting error, not: " + res);
+    } catch (PolyglotException ex) {
+      assertThat(ex.getMessage(), Matchers.containsString(".Error"));
+    }
+  }
+
+  @Test
+  public void javaScriptBooleanIsSupported() throws Exception {
+    var code =
+        """
+    foreign js toBool txt = '''
+      if (txt == "Ano") return true;
+      if (txt == "Ne") return false;
+      throw "What do you mean by: " + txt;
+
+    check x = if toBool x then "Yes" else "No"
+    """;
+
+    var check = ContextUtils.getMethodFromModule(ctx, code, "check");
+
+    assertEquals("Yes", check.execute("Ano").asString());
+    assertEquals("No", check.execute("Ne").asString());
+  }
+
+  @Ignore
+  @Test
+  public void truffleObjectConvertibleToBooleanIsSupported() throws Exception {
+    var code =
+        """
+    from Standard.Base import all
+
+    check x = if x then "Yes" else "No"
+    """;
+
+    var check = ContextUtils.getMethodFromModule(ctx, code, "check");
+
+    var t = new BoolObject(true);
+    var f = new BoolObject(false);
+
+    assertEquals("Yes", check.execute(t).asString());
+    assertEquals("No", check.execute(f).asString());
+  }
+
+  @ExportLibrary(InteropLibrary.class)
+  static final class BoolObject implements TruffleObject {
+    private final boolean value;
+
+    public BoolObject(boolean value) {
+      this.value = value;
+    }
+
+    @ExportMessage
+    boolean isBoolean() {
+      return true;
+    }
+
+    @ExportMessage
+    boolean asBoolean() {
+      return value;
+    }
+  }
+
+  @Test
+  public void warningsAndIfThenElse() throws Exception {
+    var code =
+        """
+    from Standard.Base import all
+
+    check x = if x then "Yes" else "No"
+    """;
+
+    var check = ContextUtils.getMethodFromModule(ctx, code, "check");
+
+    var warnCode = """
+    from Standard.Base import all
+
+    warn w v = Warning.attach w v
+    """;
+    var warn = ContextUtils.getMethodFromModule(ctx, warnCode, "warn");
+
+    var t = warn.execute("Maybe", true);
+    var f = warn.execute("Maybe not", false);
+
+    var yes = check.execute(t);
+    var no = check.execute(f);
+
+    assertEquals("Yes", yes.asString());
+    assertWarning("Maybe", yes);
+    assertEquals("No", no.asString());
+    assertWarning("Maybe not", no);
+  }
+
+  @Test
+  public void warningsInThenOrElse() throws Exception {
+    var code = """
+    from Standard.Base import all
+
+    check x y n = if x then y else n
+    """;
+
+    var check = ContextUtils.getMethodFromModule(ctx, code, "check");
+
+    var warnCode = """
+    from Standard.Base import all
+
+    warn w v = Warning.attach w v
+    """;
+    var warn = ContextUtils.getMethodFromModule(ctx, warnCode, "warn");
+
+    var y = warn.execute("Good", "Yes");
+    var n = warn.execute("Bad", "No");
+
+    var yes = check.execute(true, y, n);
+    var no = check.execute(false, y, n);
+
+    assertEquals("Yes", yes.asString());
+    assertWarning("Good", yes);
+    assertEquals("No", no.asString());
+    assertWarning("Bad", no);
+  }
+
+  @Test
+  public void warningsInCondAndThenOrElse() throws Exception {
+    var code = """
+    from Standard.Base import all
+
+    check x y n = if x then y else n
+    """;
+
+    var check = ContextUtils.getMethodFromModule(ctx, code, "check");
+
+    var warnCode = """
+    from Standard.Base import all
+
+    warn w v = Warning.attach w v
+    """;
+    var warn = ContextUtils.getMethodFromModule(ctx, warnCode, "warn");
+
+    var y = warn.execute("Good", "Yes");
+    var n = warn.execute("Bad", "No");
+    var t = warn.execute("Maybe", true);
+    var f = warn.execute("Maybe not", false);
+
+    var yes = check.execute(t, y, n);
+    var no = check.execute(f, y, n);
+
+    assertEquals("Yes", yes.asString());
+    assertWarning("GoodMaybe", yes);
+    assertEquals("No", no.asString());
+    assertWarning("BadMaybe not", no);
+  }
+
+  private static void assertWarning(String txt, Value v) {
+    assertTrue("Value " + v + " should be an exceptional", v.isException());
+    try {
+      throw v.throwException();
+    } catch (PolyglotException ex) {
+      assertEquals(txt, ex.getMessage());
+    }
+  }
+}