[libxml2] Fix error reporting with xi:fallback

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 2c747129779be9e3ce84a2f98ce5052a68d41098
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Mon Aug 17 00:54:12 2020 +0200

    Fix error reporting with xi:fallback
    
    When reporting errors, don't use href of xi:include if xi:fallback
    was used. I think this can only be reproduced with
    "xmllint --postvalid", see the original bug report:
    
    https://bugzilla.gnome.org/show_bug.cgi?id=152623

 error.c    | 22 +++++++++++-----------
 xinclude.c |  4 ++++
 2 files changed, 15 insertions(+), 11 deletions(-)
---
diff --git a/error.c b/error.c
index 3e41e173b..9ff1c2ba4 100644
--- a/error.c
+++ b/error.c
@@ -557,6 +557,7 @@ __xmlRaiseError(xmlStructuredErrorFunc schannel,
         * of the usual "base" (doc->URL) for the node (bug 152623).
         */
         xmlNodePtr prev = baseptr;
+        char *href = NULL;
        int inclcount = 0;
        while (prev != NULL) {
            if (prev->prev == NULL)
@@ -564,21 +565,20 @@ __xmlRaiseError(xmlStructuredErrorFunc schannel,
            else {
                prev = prev->prev;
                if (prev->type == XML_XINCLUDE_START) {
-                   if (--inclcount < 0)
-                       break;
+                   if (inclcount > 0) {
+                        --inclcount;
+                    } else {
+                        href = (char *) xmlGetProp(prev, BAD_CAST "href");
+                        if (href != NULL)
+                           break;
+                    }
                } else if (prev->type == XML_XINCLUDE_END)
                    inclcount++;
            }
        }
-       if (prev != NULL) {
-           if (prev->type == XML_XINCLUDE_START) {
-               prev->type = XML_ELEMENT_NODE;
-               to->file = (char *) xmlGetProp(prev, BAD_CAST "href");
-               prev->type = XML_XINCLUDE_START;
-           } else {
-               to->file = (char *) xmlGetProp(prev, BAD_CAST "href");
-           }
-       } else
+        if (href != NULL)
+            to->file = href;
+       else
 #endif
            to->file = (char *) xmlStrdup(baseptr->doc->URL);
        if ((to->file == NULL) && (node != NULL) && (node->doc != NULL)) {
diff --git a/xinclude.c b/xinclude.c
index 9a65ee5a4..2423a9385 100644
--- a/xinclude.c
+++ b/xinclude.c
@@ -61,6 +61,7 @@ struct _xmlXIncludeRef {
     int                 count; /* how many refs use that specific doc */
     xmlXPathObjectPtr    xptr; /* the xpointer if needed */
     int                         skip; /* skip in case of errors */
+    int                     fallback; /* fallback was loaded */
 };
 
 struct _xmlXIncludeCtxt {
@@ -2007,6 +2008,7 @@ xmlXIncludeLoadFallback(xmlXIncludeCtxtPtr ctxt, xmlNodePtr fallback, int nr) {
     } else {
         ctxt->incTab[nr]->inc = NULL;
     }
+    ctxt->incTab[nr]->fallback = 1;
     return(ret);
 }
 
@@ -2266,6 +2268,8 @@ xmlXIncludeIncludeNode(xmlXIncludeCtxtPtr ctxt, int nr) {
         * Change the current node as an XInclude start one, and add an
         * XInclude end one
         */
+        if (ctxt->incTab[nr]->fallback)
+            xmlUnsetProp(cur, BAD_CAST "href");
        cur->type = XML_XINCLUDE_START;
        end = xmlNewDocNode(cur->doc, cur->ns, cur->name, NULL);
        if (end == NULL) {