Mustachio: One tweak to whitespace trimming (#2555)

lib/src/mustachio/parser.dart

@@ -115,7 +115,13 @@ class MustachioParser {
           }
         } else {
           assert(result.type == _TagParseResultType.parsedTag);
-          trimTextRight();
+          if (result.node is Section) {
+            // Trim the right off of the preceding text node, only if a Section
+            // was just parsed. For other tags, like Variables or Partials,
+            // the whitespace may be important, as the tag itself will be
+            // rendered as text.
+            trimTextRight();
+          }
           addTextNode(textStartIndex, textEndIndex);
           children.add(result.node);
           textStartIndex = _index;

test/mustachio/renderer_test.dart

@@ -385,7 +385,8 @@ void main() {
     expect(renderBar(bar, barTemplate), equals('Text Partial hello'));
   });
 
-  test('Parser removes whitespace preceding a tag on its own line', () async {
+  test('Parser removes whitespace preceding a Section tag on its own line',
+      () async {
     var fooTemplateFile = getFile('/project/foo.mustache')
       ..writeAsStringSync('''
 <ol>
@@ -405,6 +406,25 @@ void main() {
 '''));
   });
 
+  test('Parser does not remove whitespace preceding a non-Section tag',
+      () async {
+    var fooTemplateFile = getFile('/project/foo.mustache')
+      ..writeAsStringSync('''
+Hello
+{{ #b1 }}
+{{ s1 }}
+{{ /b1 }}
+''');
+    var fooTemplate = await Template.parse(fooTemplateFile);
+    var foo = Foo()
+      ..b1 = true
+      ..s1 = 'World';
+    expect(renderFoo(foo, fooTemplate), equals('''
+Hello
+World
+'''));
+  });
+
   test('Renderer throws when it cannot resolve a variable key', () async {
     var fooTemplateFile = getFile('/project/foo.mustache')
       ..writeAsStringSync('Text {{s2}}');