Fix for issue dart-lang/yaml_edit#23 (dart-archive/yaml_edit#34)

* Fix for selecting the correct index in insertion

* Add new test cases

* Add more tests and format corrections

Author: Ishad-M-I-M

pkgs/yaml_edit/lib/src/list_mutations.dart

@@ -117,7 +117,7 @@ SourceEdit _appendToBlockList(
   // Adjusts offset to after the trailing newline of the last entry, if it exists
   if (list.isNotEmpty) {
     final lastValueSpanEnd = list.nodes.last.span.end.offset;
-    final nextNewLineIndex = yaml.indexOf('\n', lastValueSpanEnd);
+    final nextNewLineIndex = yaml.indexOf('\n', lastValueSpanEnd - 1);
     if (nextNewLineIndex == -1) {
       formattedValue = getLineEnding(yaml) + formattedValue;
     } else {

pkgs/yaml_edit/test/append_test.dart

@@ -149,6 +149,99 @@ a:
   2: null
 '''));
     });
+
+    test('block append (1)', () {
+      final yamlEditor = YamlEditor('''
+# comment
+- z:
+    x: 1
+    y: 2
+- z:
+    x: 3
+    y: 4
+''');
+      yamlEditor.appendToList([], {
+        'z': {'x': 5, 'y': 6}
+      });
+
+      expect(yamlEditor.toString(), equals('''
+# comment
+- z:
+    x: 1
+    y: 2
+- z:
+    x: 3
+    y: 4
+- z:
+    x: 5
+    y: 6
+'''));
+    });
+
+    test('block append (2)', () {
+      final yamlEditor = YamlEditor('''
+# comment
+a:
+  - z:
+      x: 1
+      y: 2
+  - z:
+      x: 3
+      y: 4
+b:
+  - w:
+      m: 2
+      n: 4
+''');
+      yamlEditor.appendToList([
+        'a'
+      ], {
+        'z': {'x': 5, 'y': 6}
+      });
+
+      expect(yamlEditor.toString(), equals('''
+# comment
+a:
+  - z:
+      x: 1
+      y: 2
+  - z:
+      x: 3
+      y: 4
+  - z:
+      x: 5
+      y: 6
+b:
+  - w:
+      m: 2
+      n: 4
+'''));
+    });
+
+    test('block append nested and with comments', () {
+      final yamlEditor = YamlEditor('''
+a:
+  b:
+    - c:
+        d: 1
+    - c:
+        d: 2
+# comment
+  e:
+    - g:
+        e: 1
+        f: 2 
+# comment
+''');
+      expect(
+          () => yamlEditor.appendToList([
+                'a',
+                'e'
+              ], {
+                'g': {'e': 3, 'f': 4}
+              }),
+          returnsNormally);
+    });
   });
 
   group('flow list', () {

pkgs/yaml_edit/test/insert_test.dart

@@ -98,6 +98,81 @@ void main() {
 '''));
       expectYamlBuilderValue(doc, [0, 1, 2]);
     });
+
+    for (var i = 0; i < 3; i++) {
+      test('block insert(1) at $i', () {
+        final yamlEditor = YamlEditor('''
+# comment
+- z:
+    x: 1
+    y: 2
+- z:
+    x: 3
+    y: 4
+''');
+        expect(
+            () => yamlEditor.insertIntoList(
+                [],
+                i,
+                {
+                  'z': {'x': 5, 'y': 6}
+                }),
+            returnsNormally);
+      });
+    }
+
+    for (var i = 0; i < 3; i++) {
+      test('block insert(2) at $i', () {
+        final yamlEditor = YamlEditor('''
+a:
+  - z:
+      x: 1
+      y: 2
+  - z:
+      x: 3
+      y: 4
+b:
+  - w:
+      m: 2
+      n: 4
+''');
+        expect(
+            () => yamlEditor.insertIntoList(
+                ['a'],
+                i,
+                {
+                  'z': {'x': 5, 'y': 6}
+                }),
+            returnsNormally);
+      });
+    }
+
+    for (var i = 0; i < 2; i++) {
+      test('block insert nested and with comments at $i', () {
+        final yamlEditor = YamlEditor('''
+a:
+  b:
+    - c:
+        d: 1
+    - c:
+        d: 2
+# comment
+  e:
+    - g:
+        e: 1
+        f: 2 
+# comment
+''');
+        expect(
+            () => yamlEditor.insertIntoList(
+                ['a', 'b'],
+                i,
+                {
+                  'g': {'e': 3, 'f': 4}
+                }),
+            returnsNormally);
+      });
+    }
   });
 
   group('flow list', () {