Fix infinite recursion when calling to_text on an Atom with lazy field

engine/runtime-integration-tests/src/test/java/org/enso/interpreter/test/DebuggingEnsoTest.java

@@ -862,6 +862,47 @@ public void testSteppingIntoMoreExpressionsOneLine() {
     testStepping(src, "foo", new Object[] {0}, steps, expectedLineNumbers);
   }
 
+  @Test
+  public void testEvaluateLazyField() {
+    var fooFunc =
+        createEnsoMethod(
+            """
+        from Standard.Base.Any import all
+
+        type Generator
+            Value n ~next
+
+        natural =
+            gen n = Generator.Value n (gen n+1)
+            gen 2
+
+        foo x =
+            two = natural
+            three = two.next
+            end = 0
+        """,
+            "foo");
+    try (DebuggerSession session =
+        debugger.startSession(
+            (SuspendedEvent event) -> {
+              switch (event.getSourceSection().getCharacters().toString().strip()) {
+                case "end = 0" -> {
+                  DebugScope scope = event.getTopStackFrame().getScope();
+                  var twoValue = scope.getDeclaredValue("two");
+                  assertThat(twoValue.isReadable(), is(true));
+                  var nProp = twoValue.getProperty("n");
+                  assertThat("n property should be readable", nProp.asInt(), is(2));
+                  var nextProp = twoValue.getProperty("next");
+                  assertThat("next property is readable", nextProp.isReadable(), is(true));
+                }
+              }
+              event.getSession().suspendNextExecution();
+            })) {
+      session.suspendNextExecution();
+      fooFunc.execute(0);
+    }
+  }
+
   private static final class FrameEntry {
     private final String scopeName;
     private final Map<String, String> values = new HashMap<>();

engine/runtime-integration-tests/src/test/java/org/enso/interpreter/test/LazyAtomFieldTest.java

@@ -1,6 +1,7 @@
 package org.enso.interpreter.test;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
 
 import java.io.ByteArrayOutputStream;
 import java.net.URI;
@@ -167,6 +168,28 @@ public void fiveAtomObjectFields() throws Exception {
     """);
   }
 
+  @Test
+  public void toTextOnAtomWithLazyField() throws URISyntaxException {
+    var res =
+        evalCode(
+            """
+        from Standard.Base.Any import all
+
+        type Generator
+            Value n ~next
+
+        natural =
+            gen n = Generator.Value n (gen n+1)
+            gen 2
+
+        main _ =
+            two = natural
+            two.to_text
+        """,
+            "main");
+    assertTrue(res.isString());
+  }
+
   private void checkNumHolder(String typeDefinition) throws Exception {
     var code =
         "polyglot java import java.util.Random as R\n"

engine/runtime-integration-tests/src/test/java/org/enso/interpreter/test/interop/AtomInteropTest.java

@@ -1,5 +1,7 @@
 package org.enso.interpreter.test.interop;
 
+import static org.enso.test.utils.ContextUtils.executeInContext;
+import static org.enso.test.utils.ContextUtils.unwrapValue;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.containsInAnyOrder;
 import static org.hamcrest.Matchers.containsString;
@@ -177,7 +179,7 @@ public void fieldFromPrivateConstructorIsReadable() {
 
         main = My_Type.Cons "a"
         """);
-    ContextUtils.executeInContext(
+    executeInContext(
         ctx,
         () -> {
           var atom = ContextUtils.unwrapValue(ctx, myTypeAtom);
@@ -281,7 +283,7 @@ public void fieldIsInvocable() {
 
         main = My_Type.Cons 1 2
         """);
-    ContextUtils.executeInContext(
+    executeInContext(
         ctx,
         () -> {
           var atom = ContextUtils.unwrapValue(ctx, myTypeAtom);
@@ -305,7 +307,7 @@ public void fieldIsReadable() {
 
         main = My_Type.Cons 1
         """);
-    ContextUtils.executeInContext(
+    executeInContext(
         ctx,
         () -> {
           var atom = ContextUtils.unwrapValue(ctx, myTypeAtom);
@@ -369,4 +371,33 @@ public void typeMembersAreConstructors() {
         myType.getMember("Cons_1").canInstantiate(),
         is(true));
   }
+
+  @Test
+  public void invokeLazyField_DoesNotCauseStackOverflow() {
+    var atom =
+        ContextUtils.evalModule(
+            ctx,
+            """
+        from Standard.Base.Any import all
+
+        type Generator
+            Value n ~next
+
+        natural =
+            gen n = Generator.Value n (gen n+1)
+            gen 2
+
+        main =
+            natural
+        """);
+    executeInContext(
+        ctx,
+        () -> {
+          var atomUnwrapped = unwrapValue(ctx, atom);
+          var interop = InteropLibrary.getUncached();
+          var next = interop.invokeMember(atomUnwrapped, "next");
+          assertThat("Returns next atom", interop.hasMembers(next), is(true));
+          return null;
+        });
+  }
 }

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/text/AnyToTextNode.java

@@ -64,21 +64,18 @@ private Text consName(AtomConstructor constructor) {
 
   @CompilerDirectives.TruffleBoundary
   private Text doComplexAtom(Atom atom) {
-    var interop = InteropLibrary.getUncached();
     var structs = StructsLibrary.getUncached();
     Text res = Text.create("(", consName(atom.getConstructor()));
-    res = Text.create(res, " ");
-    try {
-      res = Text.create(res, showObject(structs.getField(atom, 0)));
-    } catch (UnsupportedMessageException e) {
-      res = Text.create(res, structs.getField(atom, 0).toString());
-    }
-    for (int i = 1; i < atom.getConstructor().getArity(); i++) {
+    for (int i = 0; i < atom.getConstructor().getArity(); i++) {
       res = Text.create(res, " ");
-      try {
-        res = Text.create(res, showObject(structs.getField(atom, i)));
-      } catch (UnsupportedMessageException e) {
-        res = Text.create(res, structs.getField(atom, i).toString());
+      if (isFieldSuspended(i, atom)) {
+        res = Text.create(res, "~" + fieldName(i, atom));
+      } else {
+        try {
+          res = Text.create(res, showObject(structs.getField(atom, i)));
+        } catch (UnsupportedMessageException e) {
+          res = Text.create(res, structs.getField(atom, i).toString());
+        }
       }
     }
     res = Text.create(res, ")");
@@ -99,4 +96,15 @@ private String showObject(Object child) throws UnsupportedMessageException {
       return interop.asString(interop.toDisplayString(child));
     }
   }
+
+  private static boolean isFieldSuspended(int i, Atom atom) {
+    assert 0 <= i && i < atom.getConstructor().getArity();
+    var fieldDef = atom.getConstructor().getFields()[i];
+    return fieldDef.isSuspended();
+  }
+
+  private static String fieldName(int i, Atom atom) {
+    assert 0 <= i && i < atom.getConstructor().getArity();
+    return atom.getConstructor().getFields()[i].getName();
+  }
 }

test/Base_Tests/src/Runtime/Lazy_Spec.enso

@@ -11,6 +11,10 @@ type Lazy
     new ~computation = Lazy.Value computation
     new_eager computation = Lazy.Value computation
 
+type Generator
+    Value n ~next
+
+
 add_specs suite_builder = suite_builder.group "Lazy" group_builder->
     group_builder.specify "should compute the result only once" <|
         ref = Ref.new 0
@@ -96,6 +100,15 @@ add_specs suite_builder = suite_builder.group "Lazy" group_builder->
         Test.expect_panic_with matcher=Illegal_Argument <|
             Lazy.new_eager (Panic.throw (Illegal_Argument.Error "FOO"))
 
+    group_builder.specify "to_text does not evaluate first lazy field" <|
+        atom = Lazy.new (1+1)
+        atom.to_text . should_equal "(Lazy.Value ~get)"
+
+    group_builder.specify "to_text does not evaluate second lazy field" <|
+        gen n = Generator.Value n (gen n+1)
+        two = gen 2
+        two.to_text . should_equal "(Generator.Value 2 ~next)"
+
 main filter=Nothing =
     suite = Test.build suite_builder->
         add_specs suite_builder