Add POSIX regex wrapper functions.

libabigail code uses the POSIX regex library consistently:

    - compile std::string to regex, with the flag REG_EXTENDED
    - store regex using a shared pointer wrapper
    - check match of regex against std::string

All the C string / std::string logic and so on is repeated at every
call site. This patch introduces wrapper functions to take care of
this logic.

There are no behavioural changes.

	* include/abg-regex.h (compile): Declare new function.
	(match): Declare new function.
	* src/abg-regex.cc (compile): Add new function wrapping
	regcomp. (match): Add new function wrapping regexec.

Reviewed-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Giuliano Procida <gprocida@google.com>

include/abg-regex.h

@@ -71,6 +71,12 @@ operator<<(std::ostream& os, const escape& esc);
 std::string
 generate_from_strings(const std::vector<std::string>& strs);
 
+regex_t_sptr
+compile(const std::string& str);
+
+bool
+match(const regex_t_sptr& r, const std::string& str);
+
 }// end namespace regex
 
 namespace sptr_utils

src/abg-regex.cc

@@ -23,12 +23,22 @@
 /// Some specialization for shared pointer utility templates.
 ///
 
+#include "config.h"
+
 #include <sstream>
 #include <ostream>
 
+#include "abg-internal.h"
+
+// <headers defining libabigail's API go under here>
+ABG_BEGIN_EXPORT_DECLARATIONS
+
 #include "abg-regex.h"
 #include "abg-sptr-utils.h"
 
+ABG_END_EXPORT_DECLARATIONS
+// </headers defining libabigail's API>
+
 namespace abigail
 {
 
@@ -104,6 +114,36 @@ generate_from_strings(const std::vector<std::string>& strs)
   return os.str();
 }
 
+/// Compile a regex from a string.
+///
+/// The result is held in a shared pointer. This will be null if regex
+/// compilation fails.
+///
+/// @param str the string representation of the regex.
+///
+/// @return shared pointer holder of a compiled regex object.
+regex_t_sptr
+compile(const std::string& str)
+{
+  regex_t_sptr r = sptr_utils::build_sptr(new regex_t);
+  if (regcomp(r.get(), str.c_str(), REG_EXTENDED))
+    r.reset();
+  return r;
+}
+
+/// See if a string matches a regex.
+///
+/// @param r a shared pointer holder of a compiled regex object.
+///
+/// @param str a string.
+///
+/// @return whether there was a match.
+bool
+match(const regex_t_sptr& r, const std::string& str)
+{
+  return !regexec(r.get(), str.c_str(), 0, NULL, 0);
+}
+
 }//end namespace regex
 
 }//end namespace abigail