Made FindDLine fully match its header description.

1 files changed, 30 insertions, 3 deletions

diff --git a/generic/tkTextDisp.c b/generic/tkTextDisp.c
index d45ac73..4d41134 100644
--- a/generic/tkTextDisp.c
+++ b/generic/tkTextDisp.c
@@ -6590,6 +6590,7 @@ FindDLine(
     CONST TkTextIndex *indexPtr)/* Index of desired character. */
 {
     DLine *dlPtrPrev;
+    TkTextIndex indexPtr2;
 
     if (dlPtr == NULL) {
 	return NULL;
@@ -6614,7 +6615,6 @@ FindDLine(
         dlPtrPrev = dlPtr;
         dlPtr = dlPtr->nextPtr;
         if (dlPtr == NULL) {
-            TkTextIndex indexPtr2;
             /*
              * We're past the last display line, either because the desired
              * index lies past the visible text, or because the desired index
@@ -6632,14 +6632,41 @@ FindDLine(
             } else {
                 /*
                  * The desired index is past the visible text. There is no
-                 * display line displaying something at the desired index
+                 * display line displaying something at the desired index.
                  * --> return NULL.
                  */
             }
             break;
         }
         if (TkTextIndexCmp(&dlPtr->index,indexPtr) > 0) {
-            dlPtr = dlPtrPrev;
+            /*
+             * If we're here then we would normally expect that:
+             *   dlPtrPrev->index  <=  indexPtr  <  dlPtr->index
+             * i.e. we have found the searched display line being dlPtr.
+             * However it is possible that some DLines were unlinked
+             * previously, leading to a situation where going through
+             * the list of display lines skips display lines that did
+             * exist just a moment ago.
+             */
+            indexPtr2 = dlPtrPrev->index;
+            TkTextIndexForwBytes(textPtr, &indexPtr2, dlPtrPrev->byteCount,
+                    &indexPtr2);
+            if (TkTextIndexCmp(&indexPtr2,indexPtr) > 0) {
+                /*
+                 * Confirmed:
+                 *   dlPtrPrev->index  <=  indexPtr  <  dlPtr->index
+                 * --> return dlPtrPrev.
+                 */
+                dlPtr = dlPtrPrev;
+            } else {
+                /*
+                 * The last (rightmost) index shown by dlPtrPrev is still
+                 * before the desired index. This may be because there was
+                 * previously a display line between dlPtrPrev and dlPtr
+                 * and this display line has been unlinked.
+                 * --> return dlPtr.
+                 */
+            }
             break;
         }
     }