patch 9.1.0522: Vim9: string(object) hangs for recursive references

Problem:  Vim9: string(object) hangs for recursive references
Solution: Handle recursive objects specifically, add a hang test and a
          compare test (Ernie Rael)

fixes: #15080
closes: #15082

Signed-off-by: Ernie Rael <errael@raelity.com>
Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/eval.c

@@ -6138,6 +6138,58 @@ class_tv2string(typval_T *tv, char_u **tofree)
     return r;
 }
 
+/*
+ * Return a textual representation of an Object in "tv".
+ * If the memory is allocated "tofree" is set to it, otherwise NULL.
+ * When "copyID" is not zero replace recursive object with "...".
+ * When "restore_copyID" is FALSE, repeated items in the object are
+ * replaced with "...".  May return NULL.
+ */
+    static char_u *
+object_tv2string(
+    typval_T	*tv,
+    char_u	**tofree,
+    int		copyID,
+    int		restore_copyID,
+    char_u	*numbuf,
+    int		echo_style,
+    int		composite_val)
+{
+    char_u	*r = NULL;
+
+    object_T	*obj = tv->vval.v_object;
+    if (obj == NULL || obj->obj_class == NULL)
+    {
+	*tofree = NULL;
+	r = (char_u *)"object of [unknown]";
+    }
+    else if (copyID != 0 && obj->obj_copyID == copyID
+            && obj->obj_class->class_obj_member_count != 0)
+    {
+	int n = 25 + strlen((char*)obj->obj_class->class_name);
+	r = alloc(n);
+	if (r != NULL)
+	    (void)vim_snprintf((char*)r, n, "object of %s {...}",
+						obj->obj_class->class_name);
+	*tofree = r;
+    }
+    else
+    {
+	int old_copyID;
+	if (restore_copyID)
+	    old_copyID = obj->obj_copyID;
+
+	obj->obj_copyID = copyID;
+	*tofree = object2string(obj, numbuf, copyID, echo_style,
+				restore_copyID, composite_val);
+	if (restore_copyID)
+	    obj->obj_copyID = old_copyID;
+	r = *tofree;
+    }
+
+    return r;
+}
+
 /*
  * Return a string with the string representation of a variable.
  * If the memory is allocated "tofree" is set to it, otherwise NULL.
@@ -6169,7 +6221,7 @@ echo_string_core(
 	{
 	    // Only give this message once for a recursive call to avoid
 	    // flooding the user with errors.  And stop iterating over lists
-	    // and dicts.
+	    // and dicts and objects.
 	    did_echo_string_emsg = TRUE;
 	    emsg(_(e_variable_nested_too_deep_for_displaying));
 	}
@@ -6227,9 +6279,8 @@ echo_string_core(
 	    break;
 
 	case VAR_OBJECT:
-	    *tofree = r = object2string(tv->vval.v_object, numbuf, copyID,
-					echo_style, restore_copyID,
-					composite_val);
+	    r = object_tv2string(tv, tofree, copyID, restore_copyID,
+					 numbuf, echo_style, composite_val);
 	    break;
 
 	case VAR_FLOAT:

src/testdir/test_vim9_class.vim

@@ -2246,6 +2246,47 @@ def Test_class_object_to_string()
     assert_equal("object of TextPosition {lnum: 1, col: 22}", string(pos))
   END
   v9.CheckSourceSuccess(lines)
+
+  # check string() with object nesting
+  lines =<< trim END
+    vim9script
+    class C
+        var nest1: C
+        var nest2: C
+        def Init(n1: C, n2: C)
+            this.nest1 = n1
+            this.nest2 = n2
+        enddef
+    endclass
+
+    var o1 = C.new()
+    var o2 = C.new()
+    o1.Init(o1, o2)
+    o2.Init(o2, o1)
+
+    # The following previously put's vim into an infinite loop.
+
+    var expect = "object of C {nest1: object of C {...}, nest2: object of C {nest1: object of C {...}, nest2: object of C {...}}}"
+    assert_equal(expect, string(o1))
+  END
+  v9.CheckSourceSuccess(lines)
+
+  lines =<< trim END
+    vim9script
+
+    class B
+    endclass
+
+    class C
+        var b: B
+        var c: C
+    endclass
+
+    var o1 = C.new(B.new(), C.new(B.new()))
+    var expect = "object of C {b: object of B {}, c: object of C {b: object of B {}, c: object of [unknown]}}"
+    assert_equal(expect, string(o1))
+  END
+  v9.CheckSourceSuccess(lines)
 enddef
 
 def Test_interface_basics()
@@ -10516,6 +10557,27 @@ def Test_Object_Compare_With_Recursive_Class_Ref()
     assert_equal(false, result)
   END
   v9.CheckScriptSuccess(lines)
+
+  lines =<< trim END
+    vim9script
+    class C
+        var nest1: C
+        var nest2: C
+        def Init(n1: C, n2: C)
+            this.nest1 = n1
+            this.nest2 = n2
+        enddef
+    endclass
+
+    var o1 = C.new()
+    var o2 = C.new()
+    o1.Init(o1, o2)
+    o2.Init(o2, o1)
+
+    var result = o1 == o2
+    assert_equal(true, result)
+  END
+  v9.CheckScriptSuccess(lines)
 enddef
 
 " Test for using a compound operator from a lambda function in an object method

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    522,
 /**/
     521,
 /**/

src/vim9class.c

@@ -3873,7 +3873,9 @@ object_equal(
 }
 
 /*
- * Return a textual representation of object "obj"
+ * Return a textual representation of object "obj".
+ * "obj" must not be NULL.
+ * May return NULL.
  */
     char_u *
 object2string(
@@ -3890,47 +3892,58 @@ object2string(
 								== OK
 					&& rettv.vval.v_string != NULL)
 	return rettv.vval.v_string;
+
+    int		ok = OK;
+    class_T	*cl = obj->obj_class;
+    garray_T	ga;
+    ga_init2(&ga, 1, 50);
+
+    if (cl != NULL && IS_ENUM(cl))
+    {
+	ga_concat(&ga, (char_u *)"enum ");
+	ga_concat(&ga, cl->class_name);
+	char_u *enum_name = ((typval_T *)(obj + 1))->vval.v_string;
+	ga_concat(&ga, (char_u *)".");
+	ga_concat(&ga, enum_name);
+    }
     else
     {
-	garray_T ga;
-	ga_init2(&ga, 1, 50);
-
-	class_T *cl = obj == NULL ? NULL : obj->obj_class;
-	if (cl != NULL && IS_ENUM(cl))
-	{
-	    ga_concat(&ga, (char_u *)"enum ");
-	    ga_concat(&ga, cl->class_name);
-	    char_u *enum_name = ((typval_T *)(obj + 1))->vval.v_string;
-	    ga_concat(&ga, (char_u *)".");
-	    ga_concat(&ga, enum_name);
-	}
-	else
-	{
-	    ga_concat(&ga, (char_u *)"object of ");
-	    ga_concat(&ga, cl == NULL ? (char_u *)"[unknown]"
-		    : cl->class_name);
-	}
-	if (cl != NULL)
-	{
-	    ga_concat(&ga, (char_u *)" {");
-	    for (int i = 0; i < cl->class_obj_member_count; ++i)
-	    {
-		if (i > 0)
-		    ga_concat(&ga, (char_u *)", ");
-		ocmember_T *m = &cl->class_obj_members[i];
-		ga_concat(&ga, m->ocm_name);
-		ga_concat(&ga, (char_u *)": ");
-		char_u *tf = NULL;
-		ga_concat(&ga, echo_string_core(
-			    (typval_T *)(obj + 1) + i,
-			    &tf, numbuf, copyID, echo_style,
-			    restore_copyID, composite_val));
-		vim_free(tf);
-	    }
-	    ga_concat(&ga, (char_u *)"}");
-	}
-	return ga.ga_data;
+	ga_concat(&ga, (char_u *)"object of ");
+	ga_concat(&ga, cl == NULL ? (char_u *)"[unknown]"
+		: cl->class_name);
     }
+    if (cl != NULL)
+    {
+	ga_concat(&ga, (char_u *)" {");
+	for (int i = 0; i < cl->class_obj_member_count; ++i)
+	{
+	    if (i > 0)
+		ga_concat(&ga, (char_u *)", ");
+	    ocmember_T *m = &cl->class_obj_members[i];
+	    ga_concat(&ga, m->ocm_name);
+	    ga_concat(&ga, (char_u *)": ");
+	    char_u *tf = NULL;
+	    char_u *s = echo_string_core((typval_T *)(obj + 1) + i,
+					 &tf, numbuf, copyID, echo_style,
+					 restore_copyID, composite_val);
+	    if (s != NULL)
+		ga_concat(&ga, s);
+	    vim_free(tf);
+	    if (s == NULL || did_echo_string_emsg)
+	    {
+		ok = FAIL;
+		break;
+	    }
+	    line_breakcheck();
+	}
+	ga_concat(&ga, (char_u *)"}");
+    }
+    if (ok == FAIL)
+    {
+	vim_free(ga.ga_data);
+	return NULL;
+    }
+    return (char_u *)ga.ga_data;
 }
 
 /*