[pango/more-attr-update-fixes: 1/2] Explicitly preserve unlimited attributes

[Matthias Clasen <matthiasc src gnome org>]

commit 887cc68c36f31c5d8796c377919c186870d2b198
Author: Matthias Clasen <mclasen redhat com>
Date:   Sun May 23 21:03:22 2021 -0400

    Explicitly preserve unlimited attributes
    
    When calling pango_attr_list_update(), we must not
    change the limits or attributes that are unlimited.

 pango/pango-attributes.c | 42 ++++++++++++++++++++++++------------------
 1 file changed, 24 insertions(+), 18 deletions(-)
---
diff --git a/pango/pango-attributes.c b/pango/pango-attributes.c
index 8b4b2f7a..0d604f3d 100644
--- a/pango/pango-attributes.c
+++ b/pango/pango-attributes.c
@@ -1760,28 +1760,34 @@ pango_attr_list_update (PangoAttrList *list,
             continue;
           }
 
-        if (attr->start_index >= pos &&
-            attr->start_index < pos + remove)
-          {
-            attr->start_index = pos + add;
-          }
-        else if (attr->start_index >= pos + remove)
+        if (attr->start_index != PANGO_ATTR_INDEX_FROM_TEXT_BEGINNING)
           {
-            attr->start_index += add - remove;
+            if (attr->start_index >= pos &&
+                attr->start_index < pos + remove)
+              {
+                attr->start_index = pos + add;
+              }
+            else if (attr->start_index >= pos + remove)
+              {
+                attr->start_index += add - remove;
+              }
           }
 
-        if (attr->end_index >= pos &&
-            attr->end_index < pos + remove)
-          {
-            attr->end_index = pos;
-          }
-        else if (attr->end_index >= pos + remove)
+        if (attr->end_index != PANGO_ATTR_INDEX_TO_TEXT_END)
           {
-            if (add > remove &&
-                G_MAXUINT - attr->end_index < add - remove)
-              attr->end_index = G_MAXUINT;
-            else
-              attr->end_index += add - remove;
+            if (attr->end_index >= pos &&
+                attr->end_index < pos + remove)
+              {
+                attr->end_index = pos;
+              }
+            else if (attr->end_index >= pos + remove)
+              {
+                if (add > remove &&
+                    G_MAXUINT - attr->end_index < add - remove)
+                  attr->end_index = G_MAXUINT;
+                else
+                  attr->end_index += add - remove;
+              }
           }
       }
 }