line comment action: correct for the case of embedded part on the line

- when the selected line contains embedded fragment with the other language,
line still can be commented with the wrapping language comment symbols

WEB-29018 vue files with jade/pug as lang - comments not working!

platform/core-api/src/com/intellij/psi/util/PsiTreeUtil.java

@@ -332,11 +332,20 @@ public class PsiTreeUtil {
 
   @Nullable
   public static PsiElement findFirstParent(@Nullable PsiElement element, boolean strict, Condition<PsiElement> condition) {
+    //noinspection unchecked
+    return findFirstParent(element, strict, condition, Condition.FALSE);
+  }
+
+  @Nullable
+  public static PsiElement findFirstParent(@Nullable PsiElement element, boolean strict,
+                                           @NotNull final Condition<PsiElement> condition,
+                                           @NotNull final Condition<PsiElement> stopCondition) {
     if (strict && element != null) {
       element = element.getParent();
     }
 
     while (element != null) {
+      if (stopCondition.value(element)) return null;
       if (condition.value(element)) {
         return element;
       }

platform/lang-api/src/com/intellij/psi/util/PsiUtilBase.java

@@ -133,7 +133,14 @@ public class PsiUtilBase extends PsiUtilCore implements PsiEditorUtil {
           lang = language;
         }
         else if (lang != language) {
-          return null;
+          // correctly process the case when leaf element is a part of embedded fragment, but it is totally contained inside
+          // "parent" language
+          Language finalLang = lang;
+          final TextRange range = new TextRange(start, end);
+          final PsiElement wrappingParent = PsiTreeUtil.findFirstParent(
+            elt, false, element -> file.equals(element.getContainingFile()) && finalLang.equals(element.getLanguage()),
+            element -> element.getTextRange() != null && !range.contains(element.getTextRange()));
+          if (wrappingParent == null) return null;
         }
       }
       TextRange range = elt.getTextRange();