[PATCH v3] XML reader: improve XML node traversal

[Giuliano Procida <gprocida@google.com>]

Bug 27616: libabigail treats empty and nearly empty XML elements inconsistently

The XML reader uses libxml's Reader API for parsing XML and traverses
high-level XML nodes using reader cursor advancement. Low-level nodes
are read into complete node trees and are traversed following
children, next and (in one instance) parent pointers. Some
intermediate-level nodes can be parsed both ways.

A lot of code cares about node types, typically skipping over
non-element nodes. Unfortunately, in a few places, the tracked "corpus
node" needs to land on text (whitespace) within elements for the XML
reader to work; stripping text nodes out causes some elements to be
skipped. Almost all node tree traversals are very straightforward and
can be expressed using simpler primitves than at present.

This commit changes all the node tree traversals to use two node
iteration primitives consistently. These are "first_child" and
"next_child", both of which automatically skip text nodes. They
replace the existing "advance_to_next_sibling_element" and *all*
direct references to "children" and "next" nodes. The unwanted
dependency on text within elements has been fixed.

For-loops constructed with the new primitives present only element
nodes to the loop body. This allows a lot of redundant checking for
null / non-element nodes to be removed.

These changes have been tested by using abidiff to comparing all
current test XML files with copies where all text has been removed.
One such test case is included in this commit.

	* include/abg-libxml-utils.h
	(advance_to_next_sibling_element): Remove this function.
	(first_child): Add new function.
	(next_child): Likewise. This is simpler than but functionally
	identical to advance_to_next_sibling_element.
	* src/abg-libxml-utils.cc (skip_non_elements): New function to
	skip non-element nodes in a sibling node list.
	(go_to_next_sibling_element_or_stay): Remove this function
	which has been superseded by skip_non_elements.
	(first_child): New function to find the first child element of
	a node.
	(next_child): New function to find the next sibling element of
	a node.
	* src/abg-reader.cc (walk_xml_node_to_map_type_ids): Remove
	redundant node checks. Iterate over children with first_child
	and next_child helpers.
	(read_translation_unit): Likewise.
	(read_translation_unit_from_input): Remove a no-longer-needed
	->next and redundant node checks. Advance "corpus node" after
	reading the translation unit.
	(read_symbol_db_from_input): Remove a no-longer-needed ->next
	and advance "corpus node" at the end of the for-loop.  Remove
	redundant node checks.
	(build_needed): Remove redundant node checks. Iterate over
	children with first_child and next_child.
	(read_elf_needed_from_input): Remove redundant node checks and
	simplify logic. Move to next element node after reading
	elf-needed node.
	(read_corpus_from_input): Remove no-children early return
	which was inhibited by text nodes anyway. Set initial "corpus
	node" using first_child instead of children pointer. Remove
	redundant "corpus node" updates at end of function as the
	caller takes care of this and the node can become null with
	the new primitives.
	(read_corpus_group_from_input): Iterate over children using
	first_child and next child. Set "corpus node" for each corpus,
	not just the first. Incidentally keep going even if one corpus
	parse fails.
	(build_namespace_decl): Remove redundant node checks. Iterate
	over children using first_child and next_child.
	(build_elf_symbol): Remove redundant node checks.
	(build_elf_symbol_db): Iterate over children using first_child
	and next_child.
	(build_function_decl): Remove redundant node checks. Iterate
	over children using first_child and next_child.
	(build_function_type): Likewise.
	(build_array_type_def): Likewise.
	(build_enum_type_decl): Likewise.
	(build_class_decl): Remove redundant node checks. Iterate over
	children using first_child and next_child. Add comment about
	skipping children of declaration-only types
	(build_union_decl): Likewise.
	(build_function_tdecl): Remove redundant node checks. Iterate
	over children using first_child and next_child.
	(build_type_composition): Likewise.
	(build_template_tparameter): Likewise.
	* tests/data/Makefile.am: Add new test files.
	* tests/data/test-abidiff-exit/test-squished-report.txt: Add
	empty diff report.
	* tests/data/test-abidiff-exit/test-squished-v0.abi: Add test
	ABI file, containing all ELF elements.
	* tests/data/test-abidiff-exit/test-squished-v1.abi: Likewise
	and identical, except that all text has been stripped.
	* tests/test-abidiff-exit.cc: Add new test case.

Reviewed-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Giuliano Procida <gprocida@google.com>
---
 include/abg-libxml-utils.h                    |   5 +-
 src/abg-libxml-utils.cc                       |  47 ++--
 src/abg-reader.cc                             | 260 ++++++------------
 tests/data/Makefile.am                        |   3 +
 .../test-squished-report.txt                  |   0
 .../test-abidiff-exit/test-squished-v0.abi    |  43 +++
 .../test-abidiff-exit/test-squished-v1.abi    |   1 +
 tests/test-abidiff-exit.cc                    |  11 +
 8 files changed, 167 insertions(+), 203 deletions(-)
 create mode 100644 tests/data/test-abidiff-exit/test-squished-report.txt
 create mode 100644 tests/data/test-abidiff-exit/test-squished-v0.abi
 create mode 100644 tests/data/test-abidiff-exit/test-squished-v1.abi

diff --git a/include/abg-libxml-utils.h b/include/abg-libxml-utils.h
index 69e940f6..f87ee5a0 100644
--- a/include/abg-libxml-utils.h
+++ b/include/abg-libxml-utils.h
@@ -82,7 +82,10 @@ int get_xml_node_depth(xmlNodePtr);
   reinterpret_cast<char*>(xml_char_str.get())
 
 xmlNodePtr
-advance_to_next_sibling_element(xmlNodePtr node);
+first_child(xmlNodePtr node);
+
+xmlNodePtr
+next_child(xmlNodePtr node);
 
 void
 escape_xml_string(const std::string& str,
diff --git a/src/abg-libxml-utils.cc b/src/abg-libxml-utils.cc
index a1acff1f..baea25ac 100644
--- a/src/abg-libxml-utils.cc
+++ b/src/abg-libxml-utils.cc
@@ -413,40 +413,39 @@ unescape_xml_comment(const std::string& str)
   return result;
 }
 
-/// Maybe get the next sibling element node of an XML node, or stay to the sam
+/// Skip until we reach an XML element node or run out of (child) nodes.
 ///
-/// If there is no next sibling xml element node, the function returns
-/// the initial node.
+/// @param a pointer to a node.
 ///
-/// @param node the initial node to consider.
-///
-/// @return the next sibling node or the initial node @p node.
-static xmlNodePtr
-go_to_next_sibling_element_or_stay(xmlNodePtr node)
+/// @return a pointer to an XML element node or nil.
+xmlNodePtr
+skip_non_elements(xmlNodePtr node)
 {
-  xmlNodePtr n;
-  for (n = node; n; n = n->next)
-    {
-      if (n->type == XML_ELEMENT_NODE)
-	break;
-    }
-  return n ? n : node;
+  while (node && node->type != XML_ELEMENT_NODE)
+    node = node->next;
+  return node;
 }
 
-/// Get the next sibling element node of an XML node.
+/// Get the first child element of an XML node.
 ///
-/// If there is no next sibling xml element node, the function returns nil.
+/// @param a pointer to the node whose children are to be perused.
 ///
-/// @param node the XML node to consider.
+/// @return a pointer to the first XML element child of @p node or nil.
+xmlNodePtr
+first_child(xmlNodePtr node)
+{
+  return skip_non_elements(node->children);
+}
+
+/// Get the next sibling element of an XML node.
 ///
-/// @return the next sibling element node or nil.
+/// @param a pointer to the XML node whose following siblings are to be perused.
+///
+/// @return a pointer to the next sibling element of @p node or nil.
 xmlNodePtr
-advance_to_next_sibling_element(xmlNodePtr node)
+next_child(xmlNodePtr node)
 {
-  xmlNodePtr n = go_to_next_sibling_element_or_stay(node->next);
-  if (n == 0 || n->type != XML_ELEMENT_NODE)
-    return 0;
-  return n;
+  return skip_non_elements(node->next);
 }
 
 }//end namespace xml
diff --git a/src/abg-reader.cc b/src/abg-reader.cc
index ef0b7d57..f1b08474 100644
--- a/src/abg-reader.cc
+++ b/src/abg-reader.cc
@@ -1333,18 +1333,13 @@ static void
 walk_xml_node_to_map_type_ids(read_context& ctxt,
 			      xmlNodePtr node)
 {
-  xmlNodePtr n = node;
-
-  if (!n || n->type != XML_ELEMENT_NODE)
-    return;
-
-  if (xml_char_sptr s = XML_NODE_GET_ATTRIBUTE(n, "id"))
+  if (xml_char_sptr s = XML_NODE_GET_ATTRIBUTE(node, "id"))
     {
       string id = CHAR_STR(s);
-      ctxt.map_id_and_node(id, n);
+      ctxt.map_id_and_node(id, node);
     }
 
-  for (n = n->children; n; n = n->next)
+  for (xmlNodePtr n = xml::first_child(node); n; n = xml::next_child(n))
     walk_xml_node_to_map_type_ids(ctxt, n);
 }
 
@@ -1386,12 +1381,8 @@ read_translation_unit(read_context& ctxt, translation_unit& tu, xmlNodePtr node)
       || !ctxt.get_corpus())
     walk_xml_node_to_map_type_ids(ctxt, node);
 
-  for (xmlNodePtr n = node->children; n; n = n->next)
-    {
-      if (n->type != XML_ELEMENT_NODE)
-	continue;
-      handle_element_node(ctxt, n, /*add_decl_to_scope=*/true);
-    }
+  for (xmlNodePtr n = xml::first_child(node); n; n = xml::next_child(n))
+    handle_element_node(ctxt, n, /*add_decl_to_scope=*/true);
 
   ctxt.pop_scope_or_abort(tu.get_global_scope());
 
@@ -1485,16 +1476,9 @@ read_translation_unit_from_input(read_context&	ctxt)
   else
     {
       node = 0;
-      for (xmlNodePtr n = ctxt.get_corpus_node()->next; n; n = n->next)
-	{
-	  if (!n
-	      || n->type != XML_ELEMENT_NODE)
-	    continue;
-	  if (!xmlStrEqual(n->name, BAD_CAST("abi-instr")))
-	    return nil;
-	  node = n;
-	  break;
-	}
+      xmlNodePtr n = ctxt.get_corpus_node();
+      if (n && xmlStrEqual(n->name, BAD_CAST("abi-instr")))
+	node = n;
     }
 
   if (node == 0)
@@ -1507,9 +1491,9 @@ read_translation_unit_from_input(read_context&	ctxt)
   // case, after that unexpected call to read_translation_unit(), the
   // current corpus node of the context is going to point to that
   // translation unit that has been read under the hood.  Let's set
-  // the corpus node to the one we initially called
+  // the corpus node to just after the one we initially called
   // read_translation_unit() on here.
-  ctxt.set_corpus_node(node);
+  ctxt.set_corpus_node(xml::next_child(node));
   return tu;
 }
 
@@ -1583,32 +1567,32 @@ read_symbol_db_from_input(read_context&		 ctxt,
 	xmlTextReaderNext(reader.get());
       }
   else
-    for (xmlNodePtr n = ctxt.get_corpus_node()->next; n; n = n->next)
-      {
-	if (!n || n->type != XML_ELEMENT_NODE)
-	  continue;
-
-	bool has_fn_syms = false, has_var_syms = false;
-	if (xmlStrEqual(n->name, BAD_CAST("elf-function-symbols")))
-	  has_fn_syms = true;
-	else if (xmlStrEqual(n->name, BAD_CAST("elf-variable-symbols")))
-	  has_var_syms = true;
-	else
-	  break;
-	ctxt.set_corpus_node(n);
-	if (has_fn_syms)
-	  {
-	    fn_symdb = build_elf_symbol_db(ctxt, n, true);
-	    found = true;
-	  }
-	else if (has_var_syms)
-	  {
-	    var_symdb = build_elf_symbol_db(ctxt, n, false);
-	    found = true;
-	  }
-	else
-	  break;
-      }
+    {
+      xmlNodePtr n = ctxt.get_corpus_node();
+      for (; n; n = xml::next_child(n))
+	{
+	  bool has_fn_syms = false, has_var_syms = false;
+	  if (xmlStrEqual(n->name, BAD_CAST("elf-function-symbols")))
+	    has_fn_syms = true;
+	  else if (xmlStrEqual(n->name, BAD_CAST("elf-variable-symbols")))
+	    has_var_syms = true;
+	  else
+	    break;
+	  if (has_fn_syms)
+	    {
+	      fn_symdb = build_elf_symbol_db(ctxt, n, true);
+	      found = true;
+	    }
+	  else if (has_var_syms)
+	    {
+	      var_symdb = build_elf_symbol_db(ctxt, n, false);
+	      found = true;
+	    }
+	  else
+	    break;
+	}
+      ctxt.set_corpus_node(n);
+    }
 
   return found;
 }
@@ -1626,16 +1610,12 @@ read_symbol_db_from_input(read_context&		 ctxt,
 static bool
 build_needed(xmlNode* node, vector<string>& needed)
 {
-  if (!node)
-    return false;
-
-  if (!node || !xmlStrEqual(node->name,BAD_CAST("elf-needed")))
+  if (!xmlStrEqual(node->name,BAD_CAST("elf-needed")))
     return false;
 
-  for (xmlNodePtr n = node->children; n; n = n->next)
+  for (xmlNodePtr n = xml::first_child(node); n; n = xml::next_child(n))
     {
-      if (n->type != XML_ELEMENT_NODE
-	  || !xmlStrEqual(n->name, BAD_CAST("dependency")))
+      if (!xmlStrEqual(n->name, BAD_CAST("dependency")))
 	continue;
 
       string name;
@@ -1683,27 +1663,19 @@ read_elf_needed_from_input(read_context&	ctxt,
 	return false;
 
       node = xmlTextReaderExpand(reader.get());
-      if (!node)
-	return false;
     }
   else
     {
-      for (xmlNodePtr n = ctxt.get_corpus_node()->next; n; n = n->next)
-	{
-	  if (!n || n->type != XML_ELEMENT_NODE)
-	    continue;
-	  if (!xmlStrEqual(n->name, BAD_CAST("elf-needed")))
-	    return false;
-	  node = n;
-	  break;
-	}
+      xmlNodePtr n = ctxt.get_corpus_node();
+      if (n && xmlStrEqual(n->name, BAD_CAST("elf-needed")))
+	node = n;
     }
 
   bool result = false;
   if (node)
     {
       result = build_needed(node, needed);
-      ctxt.set_corpus_node(node);
+      ctxt.set_corpus_node(xml::next_child(node));
     }
 
   return result;
@@ -1907,10 +1879,7 @@ read_corpus_from_input(read_context& ctxt)
 	corp.set_soname(reinterpret_cast<char*>(soname_str.get()));
     }
 
-  if (!node->children)
-    return nil;
-
-  ctxt.set_corpus_node(node->children);
+  ctxt.set_corpus_node(xml::first_child(node));
 
   corpus& corp = *ctxt.get_corpus();
 
@@ -1976,17 +1945,6 @@ read_corpus_from_input(read_context& ctxt)
       // call at the beginning of the function.
       xmlTextReaderNext(reader.get());
     }
-  else
-    {
-      node = ctxt.get_corpus_node();
-      node = xml::advance_to_next_sibling_element(node);
-      if (!node)
-	{
-	  node = ctxt.get_corpus_node();
-	  node = xml::advance_to_next_sibling_element(node->parent);
-	}
-      ctxt.set_corpus_node(node);
-    }
 
   return ctxt.get_corpus();
 }
@@ -2036,13 +1994,13 @@ read_corpus_group_from_input(read_context& ctxt)
   if (!node)
     return nil;
 
-  //node = xml::get_first_element_sibling_if_text(node->children);
-  node = xml::advance_to_next_sibling_element(node->children);
-  ctxt.set_corpus_node(node);
-
-  corpus_sptr corp;
-  while ((corp = read_corpus_from_input(ctxt)))
-    ctxt.get_corpus_group()->add_corpus(corp);
+  for (xmlNodePtr n = xml::first_child(node); n; n = xml::next_child(n))
+    {
+      ctxt.set_corpus_node(n);
+      corpus_sptr corp = read_corpus_from_input(ctxt);
+      if (corp)
+	ctxt.get_corpus_group()->add_corpus(corp);
+    }
 
   xmlTextReaderNext(reader.get());
 
@@ -2728,12 +2686,8 @@ build_namespace_decl(read_context&	ctxt,
   ctxt.push_decl_to_current_scope(decl, add_to_current_scope);
   ctxt.map_xml_node_to_decl(node, decl);
 
-  for (xmlNodePtr n = node->children; n; n = n->next)
-    {
-      if (n->type != XML_ELEMENT_NODE)
-	continue;
-      handle_element_node(ctxt, n, /*add_to_current_scope=*/true);
-    }
+  for (xmlNodePtr n = xml::first_child(node); n; n = xml::next_child(n))
+    handle_element_node(ctxt, n, /*add_to_current_scope=*/true);
 
   ctxt.pop_scope_or_abort(decl);
 
@@ -2757,9 +2711,7 @@ build_elf_symbol(read_context& ctxt, const xmlNodePtr node,
 {
   elf_symbol_sptr nil;
 
-  if (!node
-      || node->type != XML_ELEMENT_NODE
-      || !xmlStrEqual(node->name, BAD_CAST("elf-symbol")))
+  if (!xmlStrEqual(node->name, BAD_CAST("elf-symbol")))
     return nil;
 
   string name;
@@ -2918,7 +2870,7 @@ build_elf_symbol_db(read_context& ctxt,
   xml_node_ptr_elf_symbol_sptr_map_type xml_node_ptr_elf_symbol_map;
 
   elf_symbol_sptr sym;
-  for (xmlNodePtr n = node->children; n; n = n->next)
+  for (xmlNodePtr n = xml::first_child(node); n; n = xml::next_child(n))
     {
       if ((sym = build_elf_symbol(ctxt, n, /*drop_if_suppress=*/true)))
 	{
@@ -3084,12 +3036,9 @@ build_function_decl(read_context&	ctxt,
   std::vector<function_decl::parameter_sptr> parms;
   type_base_sptr return_type = env->get_void_type();
 
-  for (xmlNodePtr n = node->children; n ; n = n->next)
+  for (xmlNodePtr n = xml::first_child(node); n; n = xml::next_child(n))
     {
-      if (n->type != XML_ELEMENT_NODE)
-	continue;
-
-      else if (xmlStrEqual(n->name, BAD_CAST("parameter")))
+      if (xmlStrEqual(n->name, BAD_CAST("parameter")))
 	{
 	  if (function_decl::parameter_sptr p =
 	      build_function_parameter(ctxt, n))
@@ -3779,12 +3728,9 @@ build_function_type(read_context&	ctxt,
   ctxt.get_translation_unit()->bind_function_type_life_time(fn_type);
   ctxt.key_type_decl(fn_type, id);
 
-  for (xmlNodePtr n = node->children; n ; n = n->next)
+  for (xmlNodePtr n = xml::first_child(node); n; n = xml::next_child(n))
     {
-      if (n->type != XML_ELEMENT_NODE)
-	continue;
-
-      else if (xmlStrEqual(n->name, BAD_CAST("parameter")))
+      if (xmlStrEqual(n->name, BAD_CAST("parameter")))
 	{
 	  if (function_decl::parameter_sptr p =
 	      build_function_parameter(ctxt, n))
@@ -4015,12 +3961,9 @@ build_array_type_def(read_context&	ctxt,
   read_location(ctxt, node, loc);
   array_type_def::subranges_type subranges;
 
-  for (xmlNodePtr n = node->children; n ; n = n->next)
+  for (xmlNodePtr n = xml::first_child(node); n; n = xml::next_child(n))
     {
-      if (n->type != XML_ELEMENT_NODE)
-	continue;
-
-      else if (xmlStrEqual(n->name, BAD_CAST("subrange")))
+      if (xmlStrEqual(n->name, BAD_CAST("subrange")))
 	{
 	  if (array_type_def::subrange_sptr s =
 	      build_subrange_type(ctxt, n))
@@ -4173,11 +4116,8 @@ build_enum_type_decl(read_context&	ctxt,
 
   string base_type_id;
   enum_type_decl::enumerators enums;
-  for (xmlNodePtr n = node->children; n; n = n->next)
+  for (xmlNodePtr n = xml::first_child(node); n; n = xml::next_child(n))
     {
-      if (n->type != XML_ELEMENT_NODE)
-	continue;
-
       if (xmlStrEqual(n->name, BAD_CAST("underlying-type")))
 	{
 	  xml_char_sptr a = xml::build_sptr(xmlGetProp(n, BAD_CAST("type-id")));
@@ -4544,11 +4484,11 @@ build_class_decl(read_context&		ctxt,
       decl->set_naming_typedef(naming_typedef);
     }
 
-  for (xmlNodePtr n = node->children; !is_decl_only && n; n = n->next)
+  for (xmlNodePtr n = xml::first_child(node); n; n = xml::next_child(n))
     {
-      if (n->type != XML_ELEMENT_NODE)
-	continue;
-
+      // See https://sourceware.org/bugzilla/show_bug.cgi?id=26591#c7.
+      if (is_decl_only)
+        continue;
       if (xmlStrEqual(n->name, BAD_CAST("base-class")))
 	{
 	  access_specifier access =
@@ -4595,11 +4535,8 @@ build_class_decl(read_context&		ctxt,
 
 	  ctxt.map_xml_node_to_decl(n, decl);
 
-	  for (xmlNodePtr p = n->children; p; p = p->next)
+	  for (xmlNodePtr p = xml::first_child(n); p; p = xml::next_child(p))
 	    {
-	      if (p->type != XML_ELEMENT_NODE)
-		continue;
-
 	      if (type_base_sptr t =
 		  build_type(ctxt, p, /*add_to_current_scope=*/true))
 		{
@@ -4633,11 +4570,8 @@ build_class_decl(read_context&		ctxt,
 	  bool is_static = false;
 	  read_static(n, is_static);
 
-	  for (xmlNodePtr p = n->children; p; p = p->next)
+	  for (xmlNodePtr p = xml::first_child(n); p; p = xml::next_child(p))
 	    {
-	      if (p->type != XML_ELEMENT_NODE)
-		continue;
-
 	      if (var_decl_sptr v =
 		  build_var_decl(ctxt, p, /*add_to_cur_scope=*/false))
 		{
@@ -4691,11 +4625,8 @@ build_class_decl(read_context&		ctxt,
 	  bool is_ctor = false, is_dtor = false, is_const = false;
 	  read_cdtor_const(n, is_ctor, is_dtor, is_const);
 
-	  for (xmlNodePtr p = n->children; p; p = p->next)
+	  for (xmlNodePtr p = xml::first_child(n); p; p = xml::next_child(p))
 	    {
-	      if (p->type != XML_ELEMENT_NODE)
-		continue;
-
 	      if (function_decl_sptr f =
 		  build_function_decl_if_not_suppressed(ctxt, p, decl,
 							/*add_to_cur_sc=*/true))
@@ -4730,11 +4661,8 @@ build_class_decl(read_context&		ctxt,
 	  bool is_ctor = false, is_dtor = false, is_const = false;
 	  read_cdtor_const(n, is_ctor, is_dtor, is_const);
 
-	  for (xmlNodePtr p = n->children; p; p = p->next)
+	  for (xmlNodePtr p = xml::first_child(n); p; p = xml::next_child(p))
 	    {
-	      if (p->type != XML_ELEMENT_NODE)
-		continue;
-
 	      if (shared_ptr<function_tdecl> f =
 		  build_function_tdecl(ctxt, p,
 				       /*add_to_current_scope=*/true))
@@ -4944,11 +4872,11 @@ build_union_decl(read_context& ctxt,
   ctxt.map_xml_node_to_decl(node, decl);
   ctxt.key_type_decl(decl, id);
 
-  for (xmlNodePtr n = node->children; !is_decl_only && n; n = n->next)
+  for (xmlNodePtr n = xml::first_child(node); n; n = xml::next_child(n))
     {
-      if (n->type != XML_ELEMENT_NODE)
-	continue;
-
+      // See https://sourceware.org/bugzilla/show_bug.cgi?id=26591#c7.
+      if (is_decl_only)
+        continue;
       if (xmlStrEqual(n->name, BAD_CAST("member-type")))
 	{
 	  access_specifier access = private_access;
@@ -4956,11 +4884,8 @@ build_union_decl(read_context& ctxt,
 
 	  ctxt.map_xml_node_to_decl(n, decl);
 
-	  for (xmlNodePtr p = n->children; p; p = p->next)
+	  for (xmlNodePtr p = xml::first_child(n); p; p = xml::next_child(p))
 	    {
-	      if (p->type != XML_ELEMENT_NODE)
-		continue;
-
 	      if (type_base_sptr t =
 		  build_type(ctxt, p, /*add_to_current_scope=*/true))
 		{
@@ -4988,11 +4913,8 @@ build_union_decl(read_context& ctxt,
 	  bool is_static = false;
 	  read_static(n, is_static);
 
-	  for (xmlNodePtr p = n->children; p; p = p->next)
+	  for (xmlNodePtr p = xml::first_child(n); p; p = xml::next_child(p))
 	    {
-	      if (p->type != XML_ELEMENT_NODE)
-		continue;
-
 	      if (var_decl_sptr v =
 		  build_var_decl(ctxt, p, /*add_to_cur_scope=*/false))
 		{
@@ -5030,11 +4952,8 @@ build_union_decl(read_context& ctxt,
 	  bool is_ctor = false, is_dtor = false, is_const = false;
 	  read_cdtor_const(n, is_ctor, is_dtor, is_const);
 
-	  for (xmlNodePtr p = n->children; p; p = p->next)
+	  for (xmlNodePtr p = xml::first_child(n); p; p = xml::next_child(p))
 	    {
-	      if (p->type != XML_ELEMENT_NODE)
-		continue;
-
 	      if (function_decl_sptr f =
 		  build_function_decl_if_not_suppressed(ctxt, p, decl,
 							/*add_to_cur_sc=*/true))
@@ -5063,11 +4982,8 @@ build_union_decl(read_context& ctxt,
 	  bool is_ctor = false, is_dtor = false, is_const = false;
 	  read_cdtor_const(n, is_ctor, is_dtor, is_const);
 
-	  for (xmlNodePtr p = n->children; p; p = p->next)
+	  for (xmlNodePtr p = xml::first_child(n); p; p = xml::next_child(p))
 	    {
-	      if (p->type != XML_ELEMENT_NODE)
-		continue;
-
 	      if (function_tdecl_sptr f =
 		  build_function_tdecl(ctxt, p,
 				       /*add_to_current_scope=*/true))
@@ -5142,11 +5058,8 @@ build_function_tdecl(read_context& ctxt,
   ctxt.push_decl_to_current_scope(fn_tmpl_decl, add_to_current_scope);
 
   unsigned parm_index = 0;
-  for (xmlNodePtr n = node->children; n; n = n->next)
+  for (xmlNodePtr n = xml::first_child(node); n; n = xml::next_child(n))
     {
-      if (n->type != XML_ELEMENT_NODE)
-	continue;
-
       if (template_parameter_sptr parm =
 	  build_template_parameter(ctxt, n, parm_index, fn_tmpl_decl))
 	{
@@ -5206,11 +5119,8 @@ build_class_tdecl(read_context&	ctxt,
   ctxt.push_decl_to_current_scope(class_tmpl, add_to_current_scope);
 
   unsigned parm_index = 0;
-  for (xmlNodePtr n = node->children; n; n = n->next)
+  for (xmlNodePtr n = xml::first_child(node); n; n = xml::next_child(n))
     {
-      if (n->type != XML_ELEMENT_NODE)
-	continue;
-
       if (template_parameter_sptr parm=
 	  build_template_parameter(ctxt, n, parm_index, class_tmpl))
 	{
@@ -5325,11 +5235,8 @@ build_type_composition(read_context&		ctxt,
   ctxt.push_decl_to_current_scope(dynamic_pointer_cast<decl_base>(result),
 				  /*add_to_current_scope=*/true);
 
-  for (xmlNodePtr n = node->children; n; n = n->next)
+  for (xmlNodePtr n = xml::first_child(node); n; n = xml::next_child(n))
     {
-      if (n->type != XML_ELEMENT_NODE)
-	continue;
-
       if ((composed_type =
 	   build_pointer_type_def(ctxt, n,
 				  /*add_to_current_scope=*/true))
@@ -5455,11 +5362,8 @@ build_template_tparameter(read_context&	ctxt,
 
   // Go parse template parameters that are children nodes
   int parm_index = 0;
-  for (xmlNodePtr n = node->children; n; n = n->next)
+  for (xmlNodePtr n = xml::first_child(node); n; n = xml::next_child(n))
     {
-      if (n->type != XML_ELEMENT_NODE)
-	continue;
-
       if (shared_ptr<template_parameter> p =
 	  build_template_parameter(ctxt, n, parm_index, result))
 	{
diff --git a/tests/data/Makefile.am b/tests/data/Makefile.am
index 0b406f3b..a844a309 100644
--- a/tests/data/Makefile.am
+++ b/tests/data/Makefile.am
@@ -197,6 +197,9 @@ test-abidiff-exit/test-non-leaf-array-v0.o \
 test-abidiff-exit/test-non-leaf-array-v1.c \
 test-abidiff-exit/test-non-leaf-array-v1.o \
 test-abidiff-exit/test-non-leaf-array-report.txt \
+test-abidiff-exit/test-squished-v0.abi \
+test-abidiff-exit/test-squished-v1.abi \
+test-abidiff-exit/test-squished-report.txt \
 \
 test-diff-dwarf/test0-v0.cc		\
 test-diff-dwarf/test0-v0.o			\
diff --git a/tests/data/test-abidiff-exit/test-squished-report.txt b/tests/data/test-abidiff-exit/test-squished-report.txt
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/data/test-abidiff-exit/test-squished-v0.abi b/tests/data/test-abidiff-exit/test-squished-v0.abi
new file mode 100644
index 00000000..6b3d0460
--- /dev/null
+++ b/tests/data/test-abidiff-exit/test-squished-v0.abi
@@ -0,0 +1,43 @@
+<abi-corpus version='2.0' path='data/test-read-dwarf/test6.so'>
+  <elf-needed>
+    <dependency name='libstdc++.so.6'/>
+    <dependency name='libm.so.6'/>
+    <dependency name='libgcc_s.so.1'/>
+    <dependency name='libc.so.6'/>
+  </elf-needed>
+  <elf-function-symbols>
+    <elf-symbol name='_Z3barv' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
+    <elf-symbol name='_Z4blehv' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
+    <elf-symbol name='_ZN1B3fooEv' type='func-type' binding='weak-binding' visibility='default-visibility' is-defined='yes'/>
+    <elf-symbol name='_fini' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
+    <elf-symbol name='_init' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
+  </elf-function-symbols>
+  <elf-variable-symbols>
+    <elf-symbol name='_ZN1CIiE3barE' size='4' type='object-type' binding='gnu-unique-binding' visibility='default-visibility' is-defined='yes'/>
+    <elf-symbol name='_ZZN1B3fooEvE1a' size='4' type='object-type' binding='gnu-unique-binding' visibility='default-visibility' is-defined='yes'/>
+  </elf-variable-symbols>
+  <abi-instr address-size='64' path='test6.cc' comp-dir-path='/home/skumari/Tasks/source_repo/dodji/libabigail/tests/data/test-read-dwarf' language='LANG_C_plus_plus'>
+    <type-decl name='int' size-in-bits='32' id='type-id-1'/>
+    <class-decl name='B' size-in-bits='8' is-struct='yes' visibility='default' filepath='/home/skumari/Tasks/source_repo/dodji/libabigail/tests/data/test-read-dwarf/test6.cc' line='9' column='1' id='type-id-2'>
+      <member-function access='public'>
+        <function-decl name='foo' mangled-name='_ZN1B3fooEv' filepath='/home/skumari/Tasks/source_repo/dodji/libabigail/tests/data/test-read-dwarf/test6.cc' line='11' column='1' visibility='default' binding='global' size-in-bits='64' elf-symbol-id='_ZN1B3fooEv'>
+          <parameter type-id='type-id-3' name='this' is-artificial='yes'/>
+          <return type-id='type-id-1'/>
+        </function-decl>
+      </member-function>
+    </class-decl>
+    <class-decl name='C&lt;int&gt;' size-in-bits='8' is-struct='yes' visibility='default' filepath='/home/skumari/Tasks/source_repo/dodji/libabigail/tests/data/test-read-dwarf/test6.cc' line='26' column='1' id='type-id-4'>
+      <data-member access='public' static='yes'>
+        <var-decl name='bar' type-id='type-id-1' mangled-name='_ZN1CIiE3barE' visibility='default' filepath='/home/skumari/Tasks/source_repo/dodji/libabigail/tests/data/test-read-dwarf/test6.cc' line='31' column='1' elf-symbol-id='_ZN1CIiE3barE'/>
+      </data-member>
+    </class-decl>
+    <pointer-type-def type-id='type-id-2' size-in-bits='64' id='type-id-5'/>
+    <qualified-type-def type-id='type-id-5' const='yes' id='type-id-3'/>
+    <function-decl name='bar' mangled-name='_Z3barv' filepath='/home/skumari/Tasks/source_repo/dodji/libabigail/tests/data/test-read-dwarf/test6.cc' line='19' column='1' visibility='default' binding='global' size-in-bits='64' elf-symbol-id='_Z3barv'>
+      <return type-id='type-id-1'/>
+    </function-decl>
+    <function-decl name='bleh' mangled-name='_Z4blehv' filepath='/home/skumari/Tasks/source_repo/dodji/libabigail/tests/data/test-read-dwarf/test6.cc' line='34' column='1' visibility='default' binding='global' size-in-bits='64' elf-symbol-id='_Z4blehv'>
+      <return type-id='type-id-1'/>
+    </function-decl>
+  </abi-instr>
+</abi-corpus>
diff --git a/tests/data/test-abidiff-exit/test-squished-v1.abi b/tests/data/test-abidiff-exit/test-squished-v1.abi
new file mode 100644
index 00000000..3ffa272b
--- /dev/null
+++ b/tests/data/test-abidiff-exit/test-squished-v1.abi
@@ -0,0 +1 @@
+<abi-corpus version='2.0' path='data/test-read-dwarf/test6.so'><elf-needed><dependency name='libstdc++.so.6'/><dependency name='libm.so.6'/><dependency name='libgcc_s.so.1'/><dependency name='libc.so.6'/></elf-needed><elf-function-symbols><elf-symbol name='_Z3barv' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/><elf-symbol name='_Z4blehv' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/><elf-symbol name='_ZN1B3fooEv' type='func-type' binding='weak-binding' visibility='default-visibility' is-defined='yes'/><elf-symbol name='_fini' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/><elf-symbol name='_init' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/></elf-function-symbols><elf-variable-symbols><elf-symbol name='_ZN1CIiE3barE' size='4' type='object-type' binding='gnu-unique-binding' visibility='default-visibility' is-defined='yes'/><elf-symbol name='_ZZN1B3fooEvE1a' size='4' type='object-type' binding='gnu-unique-binding' visibility='default-visibility' is-defined='yes'/></elf-variable-symbols><abi-instr address-size='64' path='test6.cc' comp-dir-path='/home/skumari/Tasks/source_repo/dodji/libabigail/tests/data/test-read-dwarf' language='LANG_C_plus_plus'><type-decl name='int' size-in-bits='32' id='type-id-1'/><class-decl name='B' size-in-bits='8' is-struct='yes' visibility='default' filepath='/home/skumari/Tasks/source_repo/dodji/libabigail/tests/data/test-read-dwarf/test6.cc' line='9' column='1' id='type-id-2'><member-function access='public'><function-decl name='foo' mangled-name='_ZN1B3fooEv' filepath='/home/skumari/Tasks/source_repo/dodji/libabigail/tests/data/test-read-dwarf/test6.cc' line='11' column='1' visibility='default' binding='global' size-in-bits='64' elf-symbol-id='_ZN1B3fooEv'><parameter type-id='type-id-3' name='this' is-artificial='yes'/><return type-id='type-id-1'/></function-decl></member-function></class-decl><class-decl name='C&lt;int&gt;' size-in-bits='8' is-struct='yes' visibility='default' filepath='/home/skumari/Tasks/source_repo/dodji/libabigail/tests/data/test-read-dwarf/test6.cc' line='26' column='1' id='type-id-4'><data-member access='public' static='yes'><var-decl name='bar' type-id='type-id-1' mangled-name='_ZN1CIiE3barE' visibility='default' filepath='/home/skumari/Tasks/source_repo/dodji/libabigail/tests/data/test-read-dwarf/test6.cc' line='31' column='1' elf-symbol-id='_ZN1CIiE3barE'/></data-member></class-decl><pointer-type-def type-id='type-id-2' size-in-bits='64' id='type-id-5'/><qualified-type-def type-id='type-id-5' const='yes' id='type-id-3'/><function-decl name='bar' mangled-name='_Z3barv' filepath='/home/skumari/Tasks/source_repo/dodji/libabigail/tests/data/test-read-dwarf/test6.cc' line='19' column='1' visibility='default' binding='global' size-in-bits='64' elf-symbol-id='_Z3barv'><return type-id='type-id-1'/></function-decl><function-decl name='bleh' mangled-name='_Z4blehv' filepath='/home/skumari/Tasks/source_repo/dodji/libabigail/tests/data/test-read-dwarf/test6.cc' line='34' column='1' visibility='default' binding='global' size-in-bits='64' elf-symbol-id='_Z4blehv'><return type-id='type-id-1'/></function-decl></abi-instr></abi-corpus>
\ No newline at end of file
diff --git a/tests/test-abidiff-exit.cc b/tests/test-abidiff-exit.cc
index 4283e145..f1526b9e 100644
--- a/tests/test-abidiff-exit.cc
+++ b/tests/test-abidiff-exit.cc
@@ -392,6 +392,17 @@ InOutSpec in_out_specs[] =
     "data/test-abidiff-exit/test-non-leaf-array-report.txt",
     "output/test-abidiff-exit/test-non-leaf-array-report.txt"
   },
+  {
+    "data/test-abidiff-exit/test-squished-v0.abi",
+    "data/test-abidiff-exit/test-squished-v1.abi",
+    "",
+    "",
+    "",
+    "--harmless",
+    abigail::tools_utils::ABIDIFF_OK,
+    "data/test-abidiff-exit/test-squished-report.txt",
+    "output/test-abidiff-exit/test-squished-report.txt"
+  },
   {0, 0, 0 ,0, 0, 0, abigail::tools_utils::ABIDIFF_OK, 0, 0}
 };
 
-- 
2.31.0.208.g409f899ff0-goog