IDEA-173600 Provide public API to get changed document lines

platform/core-api/src/com/intellij/openapi/editor/Document.java

@@ -141,6 +141,13 @@ public interface Document extends UserDataHolder {
   @Contract(pure=true)
   int getLineEndOffset(int line);
 
+  /**
+   * @return whether the line with the given index has been modified since the document has been saved
+   */
+  default boolean isLineModified(int line) {
+    return false;
+  }
+
   /**
    * Inserts the specified text at the specified offset in the document. Line breaks in
    * the inserted text must be normalized as \n.

platform/core-impl/src/com/intellij/openapi/editor/impl/DocumentImpl.java

@@ -180,6 +180,12 @@ public class DocumentImpl extends UserDataHolderBase implements DocumentEx {
     return stripTrailingSpaces(project, inChangedLinesOnly, true, new int[0]);
   }
 
+  @Override
+  public boolean isLineModified(int line) {
+    LineSet lineSet = myLineSet;
+    return lineSet != null && lineSet.isModified(line);
+  }
+
   /**
    * @return true if stripping was completed successfully, false if the document prevented stripping by e.g. caret(s) being in the way
    */

platform/lang-impl/src/com/intellij/injected/editor/DocumentWindowImpl.java

@@ -518,6 +518,11 @@ public class DocumentWindowImpl extends UserDataHolderBase implements Disposable
     }
   }
 
+  @Override
+  public boolean isLineModified(int line) {
+    return myDelegate.isLineModified(injectedToHostLine(line));
+  }
+
   @Override
   @NotNull
   public Segment[] getHostRanges() {