libstdc++: Add pretty printer for std::initializer_list

Re-using the std::span printer, this now shows the contents of the
initializer list instead of the pointer and length members.

Signed-off-by: Philipp Fent <fent@in.tum.de>

libstdc++-v3/ChangeLog:

	* python/libstdcxx/v6/printers.py (StdSpanPrinter._iterator):
	Rename as iterator.
	(StdInitializerListPrinter): Define new printer.
	(build_libstdcxx_dictionary): Register new printer.
	* testsuite/libstdc++-prettyprinters/cxx11.cc: Check printer for
	initializer_list.

libstdc++-v3/python/libstdcxx/v6/printers.py

@@ -1657,7 +1657,7 @@ class StdRegexStatePrinter:
 class StdSpanPrinter:
     "Print a std::span"
 
-    class _iterator(Iterator):
+    class iterator(Iterator):
         def __init__(self, begin, size):
             self.count = 0
             self.begin = begin
@@ -1686,7 +1686,24 @@ class StdSpanPrinter:
         return '%s of length %d' % (self.typename, self.size)
 
     def children(self):
-        return self._iterator(self.val['_M_ptr'], self.size)
+        return self.iterator(self.val['_M_ptr'], self.size)
+
+    def display_hint(self):
+        return 'array'
+
+class StdInitializerListPrinter:
+    "Print a std::initializer_list"
+
+    def __init__(self, typename, val):
+        self.typename = typename
+        self.val = val
+        self.size = val['_M_len']
+
+    def to_string(self):
+        return '%s of length %d' % (self.typename, self.size)
+
+    def children(self):
+        return StdSpanPrinter.iterator(self.val['_M_array'], self.size)
 
     def display_hint(self):
         return 'array'
@@ -2156,6 +2173,9 @@ def build_libstdcxx_dictionary ():
     libstdcxx_printer.add_version('std::tr1::', 'unordered_multiset',
                                   Tr1UnorderedSetPrinter)
 
+    libstdcxx_printer.add_version('std::', 'initializer_list',
+                                  StdInitializerListPrinter)
+
     # std::regex components
     libstdcxx_printer.add_version('std::__detail::', '_State',
                                   StdRegexStatePrinter)

libstdc++-v3/testsuite/libstdc++-prettyprinters/cxx11.cc

@@ -25,6 +25,7 @@
 #include <memory>
 #include <iostream>
 #include <future>
+#include <initializer_list>
 #include "../util/testsuite_allocator.h" // NullablePointer
 
 typedef std::tuple<int, int> ExTuple;
@@ -191,6 +192,11 @@ main()
   std::error_code ecfut0 = std::make_error_code(std::future_errc{});
   // { dg-final { note-test ecfut0 {std::error_code = {"future": 0}} } }
 
+  std::initializer_list<int> emptyIl = {};
+  // { dg-final { note-test emptyIl {std::initializer_list of length 0} } }
+  std::initializer_list<int> il = {3, 4};
+  // { dg-final { note-test il {std::initializer_list of length 2 = {3, 4}} } }
+
   placeholder(""); // Mark SPOT
   use(efl);
   use(fl);