xml-support.c: Use std::string for growing string buffer

This main idea behind this patch is this change to xml-support.c:scope_level

  -  /* Body text accumulation.  This is an owning pointer.  */
  -  struct obstack *body;
  +  /* Body text accumulation.  */
  +  std::string body;

... which allows simplifying other parts of the code.

In target_fetch_description_xml, we want to distinguish between
returning "success + empty std::string" and "no success", and
gdb::optional is a natural fit for that.

gdb/ChangeLog:
2017-04-18  Pedro Alves  <palves@redhat.com>

	* tracefile-tfile.c (tfile_write_tdesc): Adjust to use
	gdb::optional<std::string>.
	* xml-support.c: Include <string>.
	(scope_level::scope_level(scope_level &&))
	(scope_level::~scope_level): Delete.
	(scope_level::body): Now a std::string.
	(gdb_xml_body_text, gdb_xml_end_element): Adjust.
	(xinclude_parsing_data::xinclude_parsing_data): Add 'output'
	parameter.
	(xinclude_parsing_data::~xinclude_parsing_data): Delete.
	(xinclude_parsing_data::output): Now a std::string reference.
	(xinclude_start_include): Adjust.
	(xml_xinclude_default): Adjust.
	(xml_process_xincludes): Add 'output' parameter, and return bool.
	* xml-support.h (xml_process_xincludes): Add 'output' parameter,
	and return bool.
	* xml-tdesc.c: Include <unordered_map> and <string>.
	(tdesc_xml_cache): Delete.
	(tdesc_xml_cache_s): Delete.
	(xml_cache): Now an std::unordered_map.
	(tdesc_parse_xml): Adjust to use std::string and unordered_map.
	(target_fetch_description_xml): Change return type to
	gdb::optional<std::string>, and adjust.
	* xml-tdesc.h: Include "common/gdb_optional.h" and <string>.
	(target_fetch_description_xml): Change return type to
	gdb::optional<std::string>.

1 files changed, 8 insertions, 7 deletions

diff --git a/gdb/xml-support.h b/gdb/xml-support.h
index de685e2..8248a32 100644
--- a/gdb/xml-support.h
+++ b/gdb/xml-support.h
@@ -54,17 +54,18 @@ extern const char *xml_builtin[][2];
 
 typedef char *(*xml_fetch_another) (const char *href, void *baton);
 
-/* Return a new string which is the expansion of TEXT after processing
-   <xi:include> tags.  FETCHER will be called (with FETCHER_BATON) to
-   retrieve any new files.  DEPTH should be zero on the initial call.
+/* Append the expansion of TEXT after processing <xi:include> tags in
+   RESULT.  FETCHER will be called (with FETCHER_BATON) to retrieve
+   any new files.  DEPTH should be zero on the initial call.
 
-   On failure, this function uses NAME in a warning and returns NULL.
+   On failure, this function uses NAME in a warning and returns false.
    It may throw an exception, but does not for XML parsing
    problems.  */
 
-char *xml_process_xincludes (const char *name, const char *text,
-			     xml_fetch_another fetcher, void *fetcher_baton,
-			     int depth);
+bool xml_process_xincludes (std::string &result,
+			    const char *name, const char *text,
+			    xml_fetch_another fetcher, void *fetcher_baton,
+			    int depth);
 
 /* Simplified XML parser infrastructure.  */