[libcxx] Add a std::string_view pretty printer for libcxx.

[tamur]

Summary

This adds a std::string_view pretty printer for libcxx and updates the gdb pretty printer test.

[EricWF]

LGTM. But I would also like the opinion of Sterling, since they work in this code most often.

libcxx/utils/gdb/libcxx/printers.py

935

Should we have a basic_string_view printer as well?

[saugustine]

libcxx/utils/gdb/libcxx/printers.py

935

Yes we should, but otherwise looks good.

[EricWF]

Committed as: b4c911eccc4cccdd8cb536dc003ff9d4eb3bdc70

Please follow up with the additional basic_string_view tests.

libcxx/test/pretty_printers/gdb_pretty_printer_test.sh.cpp

void string_test() {
   ComparePrettyPrintToChars(short_string, "\"kdjflskdjf\"");
 
   std::basic_string<char, std::char_traits<char>, UncompressibleAllocator<char>>
       long_string("mehmet bizim dostumuz agzi kirik testimiz");
   ComparePrettyPrintToChars(long_string,
                             "\"mehmet bizim dostumuz agzi kirik testimiz\"");
 }
 
+void string_view_test() {
+  std::string_view i_am_empty;
+  ComparePrettyPrintToChars(i_am_empty, "std::string_view of length 0: \"\"");
+
+  std::string source_string("to be or not to be");
+  std::string_view to_be(source_string);
+  ComparePrettyPrintToChars(
+      to_be, "std::string_view of length 18: \"to be or not to be\"");
+
+  const char char_arr[] = "what a wonderful world";
+  std::string_view wonderful(&char_arr[7], 9);
+  ComparePrettyPrintToChars(
+      wonderful, "std::string_view of length 9: \"wonderful\"");
+}
+
 void u16string_test() {
   std::u16string test0 = u"Hello World";
   ComparePrettyPrintToChars(test0, "u\"Hello World\"");
   std::u16string test1 = u"\U00010196\u20AC\u00A3\u0024";
   ComparePrettyPrintToChars(test1, "u\"\U00010196\u20AC\u00A3\u0024\"");
   std::u16string test2 = u"\u0024\u0025\u0026\u0027";
   ComparePrettyPrintToChars(test2, "u\"\u0024\u0025\u0026\u0027\"");
   std::u16string test3 = u"mehmet bizim dostumuz agzi kirik testimiz";
void streampos_test() {
   ComparePrettyPrintToChars(
       test1, "std::fpos with stream offset:5 with state: {count:0 value:0}");
 }
 
 int main(int argc, char* argv[]) {
   framework_self_test();
 
   string_test();
+  string_view_test();
 
   u32string_test();
   tuple_test();
   unique_ptr_test();
   shared_ptr_test();
   bitset_test();
   list_test();
   deque_test();

libcxx/utils/gdb/libcxx/printers.py

def _remove_generics(typename):
     return match.group(1)
 
 
 # Some common substitutions on the types to reduce visual clutter (A user who
 # wants to see the actual details can always use print/r).
 _common_substitutions = [
     ("std::basic_string<char, std::char_traits<char>, std::allocator<char> >",
      "std::string"),
+    ("std::basic_string_view<char, std::char_traits<char> >",
+     "std::string_view"),
 ]
 
 
 def _prettify_typename(gdb_type):
     """Returns a pretty name for the type, or None if no name can be found.
 
     Arguments:
       gdb_type(gdb.Type): A type object.
def to_string(self):
         if hasattr(data, "lazy_string"):
             return data.lazy_string(length=size)
         return data.string(length=size)
 
     def display_hint(self):
         return "string"
 
 
+class StdStringViewPrinter(object):
+    """Print a std::string_view."""
+
+    def __init__(self, val):
+      self.val = val
+
+    def to_string(self):  # pylint: disable=g-bad-name
+      """GDB calls this to compute the pretty-printed form."""
+
+      ptr = self.val["__data"]
+      length = self.val["__size"]
+      print_length = length
+      # We print more than just a simple string (i.e. we also print
+      # "of length %d").  Thus we can't use the "string" display_hint,
+      # and thus we have to handle "print elements" ourselves.
+      # For reference sake, gdb ensures limit == None or limit > 0.
+      limit = gdb.parameter("print elements")
+      if limit is not None:
+        print_length = min(print_length, limit)
+      # FIXME: Passing ISO-8859-1 here isn't always correct.
+      string = ptr.string("ISO-8859-1", "ignore", print_length)
+      if length > print_length:
+        string += "..."
+      return "std::string_view of length %d: \"%s\"" % (length, string)
+
+
 class StdUniquePtrPrinter(object):
     """Print a std::unique_ptr."""
 
     def __init__(self, val):
         self.val = val
         self.addr = _value_of_pair_first(self.val["__ptr_"])
         self.pointee_type = self.val.type.template_argument(0)
 
class LibcxxPrettyPrinter(object):
     def __init__(self, name):
         super(LibcxxPrettyPrinter, self).__init__()
         self.name = name
         self.enabled = True
 
         self.lookup = {
             "basic_string": StdStringPrinter,
             "string": StdStringPrinter,
+            "string_view": StdStringViewPrinter,
             "tuple": StdTuplePrinter,
             "unique_ptr": StdUniquePtrPrinter,
             "shared_ptr": StdSharedPointerPrinter,
             "weak_ptr": StdSharedPointerPrinter,
             "bitset": StdBitsetPrinter,
             "deque": StdDequePrinter,
             "list": StdListPrinter,
             "queue": StdQueueOrStackPrinter,