Add gdb pretty printers for a wide variety of libc++ data structures.

[saugustine]

Summary

Also add a test suite.

[thakis]

libcxx/utils/gdb/libcxx/printers.py

33

(llvm uses pep8 style)

[Eugene.Zelenko]

Please also add installation, since pretty-printers should be shipped with libc++, same as GCC does with libstdc++ and its pretty-printers.

[EricWF]

wow. This is a fantastic amount of work. Thank you. No longer will libc++ accidentally break the pretty printers!

I'm happy to handle the minutiae related to configuring the build and test suite. I check in some code to detect GDB and LLDB shortly.

More review to come shortly...

Thanks again!

libcxx/test/pretty_printers/gdb_pretty_printer_test.sh.cpp

3

Please add the LLVM license header to all new files.

[ldionne]

In D65609#1613721, @EricWF wrote:

wow. This is a fantastic amount of work. Thank you. No longer will libc++ accidentally break the pretty printers!

I want to echo this. This is really cool. I _really_ hope we can get something similar for LLDB.

I'm happy to handle the minutiae related to configuring the build and test suite. I check in some code to detect GDB and LLDB shortly.

We could have a lit feature like has-gdb or something along those lines? And we can then put these pretty-printer tests directly in test/libcxx. WDYT?

[Eugene.Zelenko]

In D65609#1615019, @ldionne wrote:

In D65609#1613721, @EricWF wrote:

wow. This is a fantastic amount of work. Thank you. No longer will libc++ accidentally break the pretty printers!

I want to echo this. This is really cool. I _really_ hope we can get something similar for LLDB.

LLDB has pretty-printers. They are implemented in C++ instead of scripting.

[ldionne]

In D65609#1615069, @Eugene.Zelenko wrote:

In D65609#1615019, @ldionne wrote:

In D65609#1613721, @EricWF wrote:

wow. This is a fantastic amount of work. Thank you. No longer will libc++ accidentally break the pretty printers!

I want to echo this. This is really cool. I _really_ hope we can get something similar for LLDB.

LLDB has pretty-printers. They are implemented in C++ instead of scripting.

Sorry, my point is that we don't have the pretty-printer tests checked into libc++ and part of its test suite, which has been a source of pain in the past. Changing that situation is what I was referring to when I said "I hope we can get something similar for LLDB".

[Eugene.Zelenko]

In D65609#1615072, @ldionne wrote:

In D65609#1615069, @Eugene.Zelenko wrote:

In D65609#1615019, @ldionne wrote:

In D65609#1613721, @EricWF wrote:

wow. This is a fantastic amount of work. Thank you. No longer will libc++ accidentally break the pretty printers!

I want to echo this. This is really cool. I _really_ hope we can get something similar for LLDB.

LLDB has pretty-printers. They are implemented in C++ instead of scripting.

Sorry, my point is that we don't have the pretty-printer tests checked into libc++ and part of its test suite, which has been a source of pain in the past. Changing that situation is what I was referring to when I said "I hope we can get something similar for LLDB".

Sorry for misunderstanding, but may be libc++ developers should run LLDB tests too? Or at least make sure that libc++ changes do force LLDB tests on BuildBot and tests results should be monitored by committer?

[ldionne]

In D65609#1611310, @Eugene.Zelenko wrote:

Please also add installation, since pretty-printers should be shipped with libc++, same as GCC does with libstdc++ and its pretty-printers.

Did these pretty-printers exist for libc++ before this patch? If so, how were they shipped?

libcxx/test/pretty_printers/gdb_pretty_printer_test.py

100

I assume this is a remnant of prior testing?

[Eugene.Zelenko]

In D65609#1615142, @ldionne wrote:

In D65609#1611310, @Eugene.Zelenko wrote:

Please also add installation, since pretty-printers should be shipped with libc++, same as GCC does with libstdc++ and its pretty-printers.

Did these pretty-printers exist for libc++ before this patch? If so, how were they shipped?

There is separate project on GitHub. It was mentioned in libcxx/docs/UsingLibcxx.rst.

GCC ships libstdc++ pretty-printers in <install directory>/share/gcc-<version>/python/libstdcxx/.

[ldionne]

In D65609#1615153, @Eugene.Zelenko wrote:

In D65609#1615142, @ldionne wrote:

In D65609#1611310, @Eugene.Zelenko wrote:

Please also add installation, since pretty-printers should be shipped with libc++, same as GCC does with libstdc++ and its pretty-printers.

Did these pretty-printers exist for libc++ before this patch? If so, how were they shipped?

There is separate project on GitHub. It was mentioned in libcxx/docs/UsingLibcxx.rst.

I had missed that, thanks!

In that case, this patch should update the documentation.

GCC ships libstdc++ pretty-printers in <install directory>/share/gcc-<version>/python/libstdcxx/.

I guess we could start with doing the same for libc++'s pretty-printers.

[saugustine]

• Run a pep8 formatter.
• Address other comments from code review.

[saugustine]

In D65609#1613721, @EricWF wrote:

wow. This is a fantastic amount of work. Thank you. No longer will libc++ accidentally break the pretty printers!

tamur and rdhindsa (cc'd as reviewers) both deserve strong credit for this. It wasn't solely me by a long shot. I will include them in the final commit message.

I'm happy to handle the minutiae related to configuring the build and test suite. I check in some code to detect GDB and LLDB shortly.

Thank you--that will be very helpful.

I've updated the revision to address these comments.

In D65609#1611310, @Eugene.Zelenko wrote:

Please also add installation, since pretty-printers should be shipped with libc++, same as GCC does with libstdc++ and its pretty-printers.

I wanted to discuss how to do that, but I think ericwf is thankfully taking that hassle from me.

In D65609#1615019, @ldionne wrote:

In D65609#1613721, @EricWF wrote:

wow. This is a fantastic amount of work. Thank you. No longer will libc++ accidentally break the pretty printers!

I want to echo this. This is really cool. I _really_ hope we can get something similar for LLDB.

I'm unfamiliar with how lldb handles scripting, but the python script portion of the framework is fairly short and straightforward. The test program itself contains both its inputs and test cases, so lldb could be run against it no problem. Perhaps with an ifdef to use lldb-based comparison strings.

libcxx/test/pretty_printers/gdb_pretty_printer_test.py

100

Rats. Fixed.

[saugustine]

Anyone have any remaining thoughts?

[saugustine]

Would someone please accept this patch, or let me know what else there is to be done?

[echristo]

In D65609#1615158, @ldionne wrote:

In D65609#1615153, @Eugene.Zelenko wrote:

In D65609#1615142, @ldionne wrote:

In D65609#1611310, @Eugene.Zelenko wrote:

Please also add installation, since pretty-printers should be shipped with libc++, same as GCC does with libstdc++ and its pretty-printers.

Did these pretty-printers exist for libc++ before this patch? If so, how were they shipped?

There is separate project on GitHub. It was mentioned in libcxx/docs/UsingLibcxx.rst.

I had missed that, thanks!

In that case, this patch should update the documentation.

GCC ships libstdc++ pretty-printers in <install directory>/share/gcc-<version>/python/libstdcxx/.

I guess we could start with doing the same for libc++'s pretty-printers.

We could check them in for now and then EricWF can do the moving and updating of documentation around when they're happy?

I'm pretty happy with this as is... any objections?

-eric

[echristo]

The concern that ldionne had has been addressed and I think anything else can be done in post - it'd be nice to have these available for people to use while EricWF works up some of the test harness.

[saugustine]

Thanks. Commited as r370551

[saugustine]

Reverted because it broke some buildbots. Looking into why.

libcxx/test/pretty_printers/gdb_pretty_printer_test.py

+#===----------------------------------------------------------------------===##
+#
+# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#
+#===----------------------------------------------------------------------===##
+"""Commands used to automate testing gdb pretty printers.
+
+This script is part of a larger framework to test gdb pretty printers. It
+runs the program, detects test cases, checks them, and prints results.
+
+See gdb_pretty_printer_test.sh.cpp on how to write a test case.
+
+"""
+
+from __future__ import print_function
+import re
+import gdb
+
+test_failures = 0
+
+
+class CheckResult(gdb.Command):
+
+    def __init__(self):
+        super(CheckResult, self).__init__(
+            "print_and_compare", gdb.COMMAND_DATA)
+
+    def invoke(self, arg, from_tty):
+        try:
+            # Stack frame is:
+            # 0. StopForDebugger
+            # 1. ComparePrettyPrintToChars or ComparePrettyPrintToRegex
+            # 2. TestCase
+            compare_frame = gdb.newest_frame().older()
+            testcase_frame = compare_frame.older()
+            test_loc = testcase_frame.find_sal()
+            # Use interactive commands in the correct context to get the pretty
+            # printed version
+
+            value_str = self._get_value_string(compare_frame, testcase_frame)
+
+            # Ignore the convenience variable name and newline
+            value = value_str[value_str.find("= ") + 2:-1]
+            gdb.newest_frame().select()
+
+            expectation_val = compare_frame.read_var("expectation")
+            if "PrettyPrintToRegex" in compare_frame.name():
+                check_literal = expectation_val.string()
+                test_fails = not re.match(check_literal, value)
+            else:
+                check_literal_string = expectation_val.string(encoding="utf-8")
+                check_literal = check_literal_string.encode("utf-8")
+                test_fails = value != check_literal
+
+            if test_fails:
+                global test_failures
+                print("FAIL: " + test_loc.symtab.filename +
+                      ":" + str(test_loc.line))
+                print("GDB printed:")
+                print("   " + value)
+                print("Value should match:")
+                print("   " + check_literal)
+                test_failures += 1
+            else:
+                print("PASS: " + test_loc.symtab.filename +
+                      ":" + str(test_loc.line))
+
+        except RuntimeError as e:
+            # At this point, lots of different things could be wrong, so don't try to
+            # recover or figure it out. Don't exit either, because then it's
+            # impossible debug the framework itself.
+            print("FAIL: Something is wrong in the test framework.")
+            print(str(e))
+            test_failures += 1
+
+    def _get_value_string(self, compare_frame, testcase_frame):
+        compare_frame.select()
+        if "ComparePrettyPrint" in compare_frame.name():
+            return gdb.execute("p value", to_string=True)
+        value_str = str(compare_frame.read_var("value"))
+        clean_expression_str = value_str.strip("'\"")
+        testcase_frame.select()
+        return gdb.execute("p " + clean_expression_str, to_string=True)
+
+
+def exit_handler(event=None):
+    global test_failures
+    if test_failures:
+        print("FAILED %d cases" % test_failures)
+    exit(test_failures)
+
+
+# Start code executed at load time
+
+# Disable terminal paging
+gdb.execute("set height 0")
+gdb.execute("set python print-stack full")
+test_failures = 0
+CheckResult()
+test_bp = gdb.Breakpoint("StopForDebugger")
+test_bp.enabled = True
+test_bp.silent = True
+test_bp.commands = "print_and_compare\ncontinue"
+# "run" won't return if the program exits; ensure the script regains control.
+gdb.events.exited.connect(exit_handler)
+gdb.execute("run")
+# If the program didn't exit, something went wrong, but we don't
+# know what. Fail on exit.
+test_failures += 1
+exit_handler(None)

libcxx/test/pretty_printers/gdb_pretty_printer_test.sh.cpp

+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: system-windows
+
+// RUN: %cxx %flags %s -o %t.exe %compile_flags -g %link_flags
+// Ensure locale-independence for unicode tests.
+// RUN: LC_CTYPE="en_US.UTF-8" gdb -batch -nx -iex "set autoload off" -ex "source %libcxx_src_root/utils/gdb/libcxx/printers.py" -ex "python register_libcxx_printer_loader()" -ex "source %libcxx_src_root/test/pretty_printers/gdb_pretty_printer_test.py" %t.exe
+
+#include <bitset>
+#include <deque>
+#include <list>
+#include <map>
+#include <memory>
+#include <queue>
+#include <set>
+#include <sstream>
+#include <stack>
+#include <string>
+#include <tuple>
+#include <unordered_map>
+#include <unordered_set>
+
+// To write a pretty-printer test:
+//
+// 1. Declare a variable of the type you want to test
+//
+// 2. Set its value to something which will test the pretty printer in an
+//    interesting way.
+//
+// 3. Call ComparePrettyPrintToChars with that variable, and a "const char*"
+//    value to compare to the printer's output.
+//
+//    Or
+//
+//    Call ComparePrettyPrintToChars with that variable, and a "const char*"
+//    *python* regular expression to match against the printer's output.
+//    The set of special characters in a Python regular expression overlaps
+//    with a lot of things the pretty printers print--brackets, for
+//    example--so take care to escape appropriately.
+//
+// Alternatively, construct a string that gdb can parse as an expression,
+// so that printing the value of the expression will test the pretty printer
+// in an interesting way. Then, call CompareExpressionPrettyPrintToChars or
+// CompareExpressionPrettyPrintToRegex to compare the printer's output.
+
+// Avoids setting a breakpoint in every-single instantiation of
+// ComparePrettyPrintTo*.  Also, make sure neither it, nor the
+// variables we need present in the Compare functions are optimized
+// away.
+void StopForDebugger(void *value, void *check) __attribute__((optnone)) { }
+
+// Prevents the compiler optimizing away the parameter in the caller function.
+template <typename Type>
+void MarkAsLive(Type &&t) __attribute__((optnone)) { }
+
+// In all of the Compare(Expression)PrettyPrintTo(Regex/Chars) functions below,
+// the python script sets a breakpoint just before the call to StopForDebugger,
+// compares the result to the expectation.
+//
+// The expectation is a literal string to be matched exactly in
+// *PrettyPrintToChars functions, and is a python regular expression in
+// *PrettyPrintToRegex functions.
+//
+// In ComparePrettyPrint* functions, the value is a variable of any type. In
+// CompareExpressionPrettyPrint functions, the value is a string expression that
+// gdb will parse and print the result.
+//
+// The python script will print either "PASS", or a detailed failure explanation
+// along with the line that has invoke the function. The testing will continue
+// in either case.
+
+template <typename TypeToPrint> void ComparePrettyPrintToChars(
+    TypeToPrint value,
+    const char *expectation) {
+  StopForDebugger(&value, &expectation);
+}
+
+template <typename TypeToPrint> void ComparePrettyPrintToRegex(
+    TypeToPrint value,
+    const char *expectation) {
+  StopForDebugger(&value, &expectation);
+}
+
+void CompareExpressionPrettyPrintToChars(
+    std::string value,
+    const char *expectation) {
+  StopForDebugger(&value, &expectation);
+}
+
+void CompareExpressionPrettyPrintToRegex(
+    std::string value,
+    const char *expectation) {
+  StopForDebugger(&value, &expectation);
+}
+
+namespace example {
+  struct example_struct {
+    int a = 0;
+    int arr[1000];
+  };
+}
+
+// If enabled, the self test will "fail"--because we want to be sure it properly
+// diagnoses tests that *should* fail. Evaluate the output by hand.
+void framework_self_test() {
+#ifdef FRAMEWORK_SELF_TEST
+  // Use the most simple data structure we can.
+  const char a = 'a';
+
+  // Tests that should pass
+  ComparePrettyPrintToChars(a, "97 'a'");
+  ComparePrettyPrintToRegex(a, ".*");
+
+  // Tests that should fail.
+  ComparePrettyPrintToChars(a, "b");
+  ComparePrettyPrintToRegex(a, "b");
+#endif
+}
+
+// A simple pass-through allocator to check that we handle CompressedPair
+// correctly.
+template <typename T> class UncompressibleAllocator : public std::allocator<T> {
+ public:
+  char X;
+};
+
+void string_test() {
+  std::string short_string("kdjflskdjf");
+  // The display_hint "string" adds quotes the printed result.
+  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 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";
+  ComparePrettyPrintToChars(test3,
+                            ("u\"mehmet bizim dostumuz agzi kirik testimiz\""));
+}
+
+void u32string_test() {
+  std::u32string test0 = U"Hello World";
+  ComparePrettyPrintToChars(test0, "U\"Hello World\"");
+  std::u32string test1 =
+      U"\U0001d552\U0001d553\U0001d554\U0001d555\U0001d556\U0001d557";
+  ComparePrettyPrintToChars(
+      test1,
+      ("U\"\U0001d552\U0001d553\U0001d554\U0001d555\U0001d556\U0001d557\""));
+  std::u32string test2 = U"\U00004f60\U0000597d";
+  ComparePrettyPrintToChars(test2, ("U\"\U00004f60\U0000597d\""));
+  std::u32string test3 = U"mehmet bizim dostumuz agzi kirik testimiz";
+  ComparePrettyPrintToChars(test3, ("U\"mehmet bizim dostumuz agzi kirik testimiz\""));
+}
+
+void tuple_test() {
+  std::tuple<int, int, int> test0(2, 3, 4);
+  ComparePrettyPrintToChars(
+      test0,
+      "std::tuple containing = {[1] = 2, [2] = 3, [3] = 4}");
+
+  std::tuple<> test1;
+  ComparePrettyPrintToChars(
+      test1,
+      "empty std::tuple");
+}
+
+void unique_ptr_test() {
+  std::unique_ptr<std::string> matilda(new std::string("Matilda"));
+  ComparePrettyPrintToRegex(
+      std::move(matilda),
+      R"(std::unique_ptr<std::string> containing = {__ptr_ = 0x[a-f0-9]+})");
+  std::unique_ptr<int> forty_two(new int(42));
+  ComparePrettyPrintToRegex(std::move(forty_two),
+      R"(std::unique_ptr<int> containing = {__ptr_ = 0x[a-f0-9]+})");
+
+  std::unique_ptr<int> this_is_null;
+  ComparePrettyPrintToChars(std::move(this_is_null),
+      R"(std::unique_ptr is nullptr)");
+}
+
+void bitset_test() {
+  std::bitset<258> i_am_empty(0);
+  ComparePrettyPrintToChars(i_am_empty, "std::bitset<258>");
+
+  std::bitset<0> very_empty;
+  ComparePrettyPrintToChars(very_empty, "std::bitset<0>");
+
+  std::bitset<15> b_000001111111100(1020);
+  ComparePrettyPrintToChars(b_000001111111100,
+      "std::bitset<15> = {[2] = 1, [3] = 1, [4] = 1, [5] = 1, [6] = 1, "
+      "[7] = 1, [8] = 1, [9] = 1}");
+
+  std::bitset<258> b_0_129_132(0);
+  b_0_129_132[0] = true;
+  b_0_129_132[129] = true;
+  b_0_129_132[132] = true;
+  ComparePrettyPrintToChars(b_0_129_132,
+      "std::bitset<258> = {[0] = 1, [129] = 1, [132] = 1}");
+}
+
+void list_test() {
+  std::list<int> i_am_empty{};
+  ComparePrettyPrintToChars(i_am_empty, "std::list is empty");
+
+  std::list<int> one_two_three {1, 2, 3};
+  ComparePrettyPrintToChars(one_two_three,
+      "std::list with 3 elements = {1, 2, 3}");
+
+  std::list<std::string> colors {"red", "blue", "green"};
+  ComparePrettyPrintToChars(colors,
+      R"(std::list with 3 elements = {"red", "blue", "green"})");
+}
+
+void deque_test() {
+  std::deque<int> i_am_empty{};
+  ComparePrettyPrintToChars(i_am_empty, "std::deque is empty");
+
+  std::deque<int> one_two_three {1, 2, 3};
+  ComparePrettyPrintToChars(one_two_three,
+      "std::deque with 3 elements = {1, 2, 3}");
+
+  std::deque<example::example_struct> bfg;
+  for (int i = 0; i < 10; ++i) {
+    example::example_struct current;
+    current.a = i;
+    bfg.push_back(current);
+  }
+  for (int i = 0; i < 3; ++i) {
+    bfg.pop_front();
+  }
+  for (int i = 0; i < 3; ++i) {
+    bfg.pop_back();
+  }
+  ComparePrettyPrintToRegex(bfg,
+      "std::deque with 4 elements = {"
+      "{a = 3, arr = {[^}]+}}, "
+      "{a = 4, arr = {[^}]+}}, "
+      "{a = 5, arr = {[^}]+}}, "
+      "{a = 6, arr = {[^}]+}}}");
+}
+
+void map_test() {
+  std::map<int, int> i_am_empty{};
+  ComparePrettyPrintToChars(i_am_empty, "std::map is empty");
+
+  std::map<int, std::string> one_two_three;
+  one_two_three.insert({1, "one"});
+  one_two_three.insert({2, "two"});
+  one_two_three.insert({3, "three"});
+  ComparePrettyPrintToChars(one_two_three,
+      "std::map with 3 elements = "
+      R"({[1] = "one", [2] = "two", [3] = "three"})");
+
+  std::map<int, example::example_struct> bfg;
+  for (int i = 0; i < 4; ++i) {
+    example::example_struct current;
+    current.a = 17 * i;
+    bfg.insert({i, current});
+  }
+  ComparePrettyPrintToRegex(bfg,
+      R"(std::map with 4 elements = {)"
+      R"(\[0\] = {a = 0, arr = {[^}]+}}, )"
+      R"(\[1\] = {a = 17, arr = {[^}]+}}, )"
+      R"(\[2\] = {a = 34, arr = {[^}]+}}, )"
+      R"(\[3\] = {a = 51, arr = {[^}]+}}})");
+}
+
+void multimap_test() {
+  std::multimap<int, int> i_am_empty{};
+  ComparePrettyPrintToChars(i_am_empty, "std::multimap is empty");
+
+  std::multimap<int, std::string> one_two_three;
+  one_two_three.insert({1, "one"});
+  one_two_three.insert({3, "three"});
+  one_two_three.insert({1, "ein"});
+  one_two_three.insert({2, "two"});
+  one_two_three.insert({2, "zwei"});
+  one_two_three.insert({1, "bir"});
+
+  ComparePrettyPrintToChars(one_two_three,
+      "std::multimap with 6 elements = "
+      R"({[1] = "one", [1] = "ein", [1] = "bir", )"
+      R"([2] = "two", [2] = "zwei", [3] = "three"})");
+}
+
+void queue_test() {
+  std::queue<int> i_am_empty;
+  ComparePrettyPrintToChars(i_am_empty,
+      "std::queue wrapping = {std::deque is empty}");
+
+  std::queue<int> one_two_three(std::deque<int>{1, 2, 3});
+    ComparePrettyPrintToChars(one_two_three,
+        "std::queue wrapping = {"
+        "std::deque with 3 elements = {1, 2, 3}}");
+}
+
+void priority_queue_test() {
+  std::priority_queue<int> i_am_empty;
+  ComparePrettyPrintToChars(i_am_empty,
+      "std::priority_queue wrapping = {std::vector of length 0, capacity 0}");
+
+  std::priority_queue<int> one_two_three;
+  one_two_three.push(11111);
+  one_two_three.push(22222);
+  one_two_three.push(33333);
+
+  ComparePrettyPrintToRegex(one_two_three,
+      R"(std::priority_queue wrapping = )"
+      R"({std::vector of length 3, capacity 3 = {33333)");
+
+  ComparePrettyPrintToRegex(one_two_three, ".*11111.*");
+  ComparePrettyPrintToRegex(one_two_three, ".*22222.*");
+}
+
+void set_test() {
+  std::set<int> i_am_empty;
+  ComparePrettyPrintToChars(i_am_empty, "std::set is empty");
+
+  std::set<int> one_two_three {3, 1, 2};
+  ComparePrettyPrintToChars(one_two_three,
+      "std::set with 3 elements = {1, 2, 3}");
+
+  std::set<std::pair<int, int>> prime_pairs {
+      std::make_pair(3, 5), std::make_pair(5, 7), std::make_pair(3, 5)};
+
+  ComparePrettyPrintToChars(prime_pairs,
+      "std::set with 2 elements = {"
+      "{first = 3, second = 5}, {first = 5, second = 7}}");
+}
+
+void stack_test() {
+  std::stack<int> test0;
+  ComparePrettyPrintToChars(test0,
+                            "std::stack wrapping = {std::deque is empty}");
+  test0.push(5);
+  test0.push(6);
+  ComparePrettyPrintToChars(
+      test0, "std::stack wrapping = {std::deque with 2 elements = {5, 6}}");
+  std::stack<bool> test1;
+  test1.push(true);
+  test1.push(false);
+  ComparePrettyPrintToChars(
+      test1,
+      "std::stack wrapping = {std::deque with 2 elements = {true, false}}");
+
+  std::stack<std::string> test2;
+  test2.push("Hello");
+  test2.push("World");
+  ComparePrettyPrintToChars(test2,
+                            "std::stack wrapping = {std::deque with 2 elements "
+                            "= {\"Hello\", \"World\"}}");
+}
+
+void multiset_test() {
+  std::multiset<int> i_am_empty;
+  ComparePrettyPrintToChars(i_am_empty, "std::multiset is empty");
+
+  std::multiset<std::string> one_two_three {"1:one", "2:two", "3:three", "1:one"};
+  ComparePrettyPrintToChars(one_two_three,
+      "std::multiset with 4 elements = {"
+      R"("1:one", "1:one", "2:two", "3:three"})");
+}
+
+void vector_test() {
+  std::vector<bool> test0 = {true, false};
+  ComparePrettyPrintToChars(test0,
+                            "std::vector<bool> of "
+                            "length 2, capacity 64 = {1, 0}");
+  for (int i = 0; i < 31; ++i) {
+    test0.push_back(true);
+    test0.push_back(false);
+  }
+  ComparePrettyPrintToRegex(
+      test0,
+      "std::vector<bool> of length 64, "
+      "capacity 64 = {1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, "
+      "0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, "
+      "0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0}");
+  test0.push_back(true);
+  ComparePrettyPrintToRegex(
+      test0,
+      "std::vector<bool> of length 65, "
+      "capacity 128 = {1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, "
+      "1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, "
+      "1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1}");
+
+  std::vector<int> test1;
+  ComparePrettyPrintToChars(test1, "std::vector of length 0, capacity 0");
+
+  std::vector<int> test2 = {5, 6, 7};
+  ComparePrettyPrintToChars(test2,
+                            "std::vector of length "
+                            "3, capacity 3 = {5, 6, 7}");
+
+  std::vector<int, UncompressibleAllocator<int>> test3({7, 8});
+  ComparePrettyPrintToChars(std::move(test3),
+                            "std::vector of length "
+                            "2, capacity 2 = {7, 8}");
+}
+
+void set_iterator_test() {
+  std::set<int> one_two_three {1111, 2222, 3333};
+  auto it = one_two_three.find(2222);
+  MarkAsLive(it);
+  CompareExpressionPrettyPrintToRegex("it",
+      R"(std::__tree_const_iterator  = {\[0x[a-f0-9]+\] = 2222})");
+
+  auto not_found = one_two_three.find(1234);
+  MarkAsLive(not_found);
+  // Because the end_node is not easily detected, just be sure it doesn't crash.
+  CompareExpressionPrettyPrintToRegex("not_found",
+      R"(std::__tree_const_iterator  = {\[0x[a-f0-9]+\] = .*})");
+}
+
+void map_iterator_test() {
+  std::map<int, std::string> one_two_three;
+  one_two_three.insert({1, "one"});
+  one_two_three.insert({2, "two"});
+  one_two_three.insert({3, "three"});
+  auto it = one_two_three.begin();
+  MarkAsLive(it);
+  CompareExpressionPrettyPrintToRegex("it",
+      R"(std::__map_iterator  = )"
+      R"({\[0x[a-f0-9]+\] = {first = 1, second = "one"}})");
+
+  auto not_found = one_two_three.find(7);
+  MarkAsLive(not_found);
+  CompareExpressionPrettyPrintToRegex("not_found",
+      R"(std::__map_iterator  = {\[0x[a-f0-9]+\] =  end\(\)})");
+}
+
+void unordered_set_test() {
+  std::unordered_set<int> i_am_empty;
+  ComparePrettyPrintToChars(i_am_empty, "std::unordered_set is empty");
+
+  std::unordered_set<int> numbers {12345, 67890, 222333, 12345};
+  numbers.erase(numbers.find(222333));
+  ComparePrettyPrintToRegex(numbers, "std::unordered_set with 2 elements = ");
+  ComparePrettyPrintToRegex(numbers, ".*12345.*");
+  ComparePrettyPrintToRegex(numbers, ".*67890.*");
+
+  std::unordered_set<std::string> colors {"red", "blue", "green"};
+  ComparePrettyPrintToRegex(colors, "std::unordered_set with 3 elements = ");
+  ComparePrettyPrintToRegex(colors, R"(.*"red".*)");
+  ComparePrettyPrintToRegex(colors, R"(.*"blue".*)");
+  ComparePrettyPrintToRegex(colors, R"(.*"green".*)");
+}
+
+void unordered_multiset_test() {
+  std::unordered_multiset<int> i_am_empty;
+  ComparePrettyPrintToChars(i_am_empty, "std::unordered_multiset is empty");
+
+  std::unordered_multiset<int> numbers {12345, 67890, 222333, 12345};
+  ComparePrettyPrintToRegex(numbers,
+                            "std::unordered_multiset with 4 elements = ");
+  ComparePrettyPrintToRegex(numbers, ".*12345.*12345.*");
+  ComparePrettyPrintToRegex(numbers, ".*67890.*");
+  ComparePrettyPrintToRegex(numbers, ".*222333.*");
+
+  std::unordered_multiset<std::string> colors {"red", "blue", "green", "red"};
+  ComparePrettyPrintToRegex(colors,
+                            "std::unordered_multiset with 4 elements = ");
+  ComparePrettyPrintToRegex(colors, R"(.*"red".*"red".*)");
+  ComparePrettyPrintToRegex(colors, R"(.*"blue".*)");
+  ComparePrettyPrintToRegex(colors, R"(.*"green".*)");
+}
+
+void unordered_map_test() {
+  std::unordered_map<int, int> i_am_empty;
+  ComparePrettyPrintToChars(i_am_empty, "std::unordered_map is empty");
+
+  std::unordered_map<int, std::string> one_two_three;
+  one_two_three.insert({1, "one"});
+  one_two_three.insert({2, "two"});
+  one_two_three.insert({3, "three"});
+  ComparePrettyPrintToRegex(one_two_three,
+                            "std::unordered_map with 3 elements = ");
+  ComparePrettyPrintToRegex(one_two_three, R"(.*\[1\] = "one".*)");
+  ComparePrettyPrintToRegex(one_two_three, R"(.*\[2\] = "two".*)");
+  ComparePrettyPrintToRegex(one_two_three, R"(.*\[3\] = "three".*)");
+}
+
+void unordered_multimap_test() {
+  std::unordered_multimap<int, int> i_am_empty;
+  ComparePrettyPrintToChars(i_am_empty, "std::unordered_multimap is empty");
+
+  std::unordered_multimap<int, std::string> one_two_three;
+  one_two_three.insert({1, "one"});
+  one_two_three.insert({2, "two"});
+  one_two_three.insert({3, "three"});
+  one_two_three.insert({2, "two"});
+  ComparePrettyPrintToRegex(one_two_three,
+                            "std::unordered_multimap with 4 elements = ");
+  ComparePrettyPrintToRegex(one_two_three, R"(.*\[1\] = "one".*)");
+  ComparePrettyPrintToRegex(one_two_three, R"(.*\[2\] = "two".*\[2\] = "two")");
+  ComparePrettyPrintToRegex(one_two_three, R"(.*\[3\] = "three".*)");
+}
+
+void unordered_map_iterator_test() {
+  std::unordered_map<int, int> ones_to_eights;
+  ones_to_eights.insert({1, 8});
+  ones_to_eights.insert({11, 88});
+  ones_to_eights.insert({111, 888});
+
+  auto ones_to_eights_begin = ones_to_eights.begin();
+  MarkAsLive(ones_to_eights_begin);
+  CompareExpressionPrettyPrintToRegex("ones_to_eights_begin",
+      R"(std::__hash_map_iterator  = {\[1+\] = 8+})");
+
+  auto not_found = ones_to_eights.find(5);
+  MarkAsLive(not_found);
+  CompareExpressionPrettyPrintToRegex("not_found",
+      R"(std::__hash_map_iterator = end\(\))");
+}
+
+void unordered_set_iterator_test() {
+  std::unordered_set<int> ones;
+  ones.insert(111);
+  ones.insert(1111);
+  ones.insert(11111);
+
+  auto ones_begin = ones.begin();
+  MarkAsLive(ones_begin);
+  CompareExpressionPrettyPrintToRegex("ones_begin",
+      R"(std::__hash_const_iterator  = {1+})");
+
+  auto not_found = ones.find(5);
+  MarkAsLive(not_found);
+  CompareExpressionPrettyPrintToRegex("not_found",
+      R"(std::__hash_const_iterator = end\(\))");
+}
+
+// Check that libc++ pretty printers do not handle pointers.
+void pointer_negative_test() {
+  int abc = 123;
+  int *int_ptr = &abc;
+  // Check that the result is equivalent to "p/r int_ptr" command.
+  ComparePrettyPrintToRegex(int_ptr, R"(\(int \*\) 0x[a-f0-9]+)");
+}
+
+void shared_ptr_test() {
+  // Shared ptr tests while using test framework call another function
+  // due to which there is one more count for the pointer. Hence, all the
+  // following tests are testing with expected count plus 1.
+  std::shared_ptr<const int> test0 = std::make_shared<const int>(5);
+  ComparePrettyPrintToRegex(
+      test0,
+      R"(std::shared_ptr<int> count 2, weak 0 containing = {__ptr_ = 0x[a-f0-9]+})");
+
+  std::shared_ptr<const int> test1(test0);
+  ComparePrettyPrintToRegex(
+      test1,
+      R"(std::shared_ptr<int> count 3, weak 0 containing = {__ptr_ = 0x[a-f0-9]+})");
+
+  {
+    std::weak_ptr<const int> test2 = test1;
+    ComparePrettyPrintToRegex(
+        test0,
+        R"(std::shared_ptr<int> count 3, weak 1 containing = {__ptr_ = 0x[a-f0-9]+})");
+  }
+
+  ComparePrettyPrintToRegex(
+      test0,
+      R"(std::shared_ptr<int> count 3, weak 0 containing = {__ptr_ = 0x[a-f0-9]+})");
+
+  std::shared_ptr<const int> test3;
+  ComparePrettyPrintToChars(test3, "std::shared_ptr is nullptr");
+}
+
+void streampos_test() {
+  std::streampos test0 = 67;
+  ComparePrettyPrintToChars(
+      test0, "std::fpos with stream offset:67 with state: {count:0 value:0}");
+  std::istringstream input("testing the input stream here");
+  std::streampos test1 = input.tellg();
+  ComparePrettyPrintToChars(
+      test1, "std::fpos with stream offset:0 with state: {count:0 value:0}");
+  std::unique_ptr<char[]> buffer(new char[5]);
+  input.read(buffer.get(), 5);
+  test1 = input.tellg();
+  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();
+
+  u32string_test();
+  tuple_test();
+  unique_ptr_test();
+  shared_ptr_test();
+  bitset_test();
+  list_test();
+  deque_test();
+  map_test();
+  multimap_test();
+  queue_test();
+  priority_queue_test();
+  stack_test();
+  set_test();
+  multiset_test();
+  vector_test();
+  set_iterator_test();
+  map_iterator_test();
+  unordered_set_test();
+  unordered_multiset_test();
+  unordered_map_test();
+  unordered_multimap_test();
+  unordered_map_iterator_test();
+  unordered_set_iterator_test();
+  pointer_negative_test();
+  streampos_test();
+  return 0;
+}

libcxx/utils/gdb/libcxx/printers.py

+#===----------------------------------------------------------------------===##
+#
+# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#
+#===----------------------------------------------------------------------===##
+"""GDB pretty-printers for libc++.
+
+These should work for objects compiled when _LIBCPP_ABI_UNSTABLE is defined
+and when it is undefined.
+"""
+
+from __future__ import print_function
+
+import re
+import gdb
+
+# One under-documented feature of the gdb pretty-printer API
+# is that clients can call any other member of the API
+# before they call to_string.
+# Therefore all self.FIELDs must be set in the pretty-printer's
+# __init__ function.
+
+_void_pointer_type = gdb.lookup_type("void").pointer()
+
+
+_long_int_type = gdb.lookup_type("unsigned long long")
+
+
+def addr_as_long(addr):
+    return int(addr.cast(_long_int_type))
+
+
+# The size of a pointer in bytes.
+_pointer_size = _void_pointer_type.sizeof
+
+
+def _remove_cxx_namespace(typename):
+    """Removed libc++ specific namespace from the type.
+
+    Arguments:
+      typename(string): A type, such as std::__u::something.
+
+    Returns:
+      A string without the libc++ specific part, such as std::something.
+    """
+
+    return re.sub("std::__.*?::", "std::", typename)
+
+
+def _remove_generics(typename):
+    """Remove generics part of the type. Assumes typename is not empty.
+
+    Arguments:
+      typename(string): A type such as std::my_collection<element>.
+
+    Returns:
+      The prefix up to the generic part, such as std::my_collection.
+    """
+
+    match = re.match("^([^<]+)", 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"),
+]
+
+
+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.
+
+    Returns:
+      A string, without type_defs, libc++ namespaces, and common substitutions
+      applied.
+    """
+
+    type_without_typedefs = gdb_type.strip_typedefs()
+    typename = type_without_typedefs.name or type_without_typedefs.tag or \
+        str(type_without_typedefs)
+    result = _remove_cxx_namespace(typename)
+    for find_str, subst_str in _common_substitutions:
+        result = re.sub(find_str, subst_str, result)
+    return result
+
+
+def _typename_for_nth_generic_argument(gdb_type, n):
+    """Returns a pretty string for the nth argument of the given type.
+
+    Arguments:
+      gdb_type(gdb.Type): A type object, such as the one for std::map<int, int>
+      n: The (zero indexed) index of the argument to return.
+
+    Returns:
+      A string for the nth argument, such a "std::string"
+    """
+    element_type = gdb_type.template_argument(n)
+    return _prettify_typename(element_type)
+
+
+def _typename_with_n_generic_arguments(gdb_type, n):
+    """Return a string for the type with the first n (1, ...) generic args."""
+
+    base_type = _remove_generics(_prettify_typename(gdb_type))
+    arg_list = [base_type]
+    template = "%s<"
+    for i in range(n):
+        arg_list.append(_typename_for_nth_generic_argument(gdb_type, i))
+        template += "%s, "
+    result = (template[:-2] + ">") % tuple(arg_list)
+    return result
+
+
+def _typename_with_first_generic_argument(gdb_type):
+    return _typename_with_n_generic_arguments(gdb_type, 1)
+
+
+class StdTuplePrinter(object):
+    """Print a std::tuple."""
+
+    class _Children(object):
+        """Class to iterate over the tuple's children."""
+
+        def __init__(self, val):
+            self.val = val
+            self.child_iter = iter(self.val["__base_"].type.fields())
+            self.count = 0
+
+        def __iter__(self):
+            return self
+
+        def next(self):
+            # child_iter raises StopIteration when appropriate.
+            field_name = self.child_iter.next()
+            child = self.val["__base_"][field_name]["__value_"]
+            self.count += 1
+            return ("[%d]" % self.count, child)
+
+    def __init__(self, val):
+        self.val = val
+
+    def to_string(self):
+        typename = _remove_generics(_prettify_typename(self.val.type))
+        if not self.val.type.fields():
+            return "empty %s" % typename
+        return "%s containing" % typename
+
+    def children(self):
+        if not self.val.type.fields():
+            return iter(())
+        return self._Children(self.val)
+
+
+def _get_base_subobject(child_class_value, index=0):
+    """Returns the object's value in the form of the parent class at index.
+
+    This function effectively casts the child_class_value to the base_class's
+    type, but the type-to-cast to is stored in the field at index, and once
+    we know the field, we can just return the data.
+
+    Args:
+      child_class_value: the value to cast
+      index: the parent class index
+
+    Raises:
+      Exception: field at index was not a base-class field.
+    """
+
+    field = child_class_value.type.fields()[index]
+    if not field.is_base_class:
+        raise Exception("Not a base-class field.")
+    return child_class_value[field]
+
+
+def _value_of_pair_first(value):
+    """Convenience for _get_base_subobject, for the common case."""
+    return _get_base_subobject(value, 0)["__value_"]
+
+
+class StdStringPrinter(object):
+    """Print a std::string."""
+
+    def _get_short_size(self, short_field, short_size):
+        """Short size depends on both endianness and a compile-time define."""
+
+        # If the padding field is present after all this indirection, then string
+        # was compiled with _LIBCPP_ABI_ALTERNATE_STRING_LAYOUT defined.
+        field = short_field.type.fields()[1].type.fields()[0]
+        libcpp_abi_alternate_string_layout = field.name and "__padding" in field.name
+
+        # Strictly, this only tells us the current mode, not how libcxx was
+        # compiled.
+        libcpp_big_endian = "big endian" in gdb.execute("show endian",
+                                                        to_string=True)
+
+        # This logical structure closely follows the original code (which is clearer
+        # in C++).  Keep them parallel to make them easier to compare.
+        if libcpp_abi_alternate_string_layout:
+            if libcpp_big_endian:
+                return short_size >> 1
+            else:
+                return short_size
+        elif libcpp_big_endian:
+            return short_size
+        else:
+            return short_size >> 1
+
+    def __init__(self, val):
+        self.val = val
+
+    def to_string(self):
+        """Build a python string from the data whether stored inline or separately."""
+
+        value_field = _value_of_pair_first(self.val["__r_"])
+        short_field = value_field["__s"]
+        short_size = short_field["__size_"]
+        if short_size == 0:
+            return ""
+        short_mask = self.val["__short_mask"]
+        # Counter intuitive to compare the size and short_mask to see if the string
+        # is long, but that's the way the implementation does it. Note that
+        # __is_long() doesn't use get_short_size in C++.
+        is_long = short_size & short_mask
+        if is_long:
+            long_field = value_field["__l"]
+            data = long_field["__data_"]
+            size = long_field["__size_"]
+        else:
+            data = short_field["__data_"]
+            size = self._get_short_size(short_field, short_size)
+        if hasattr(data, "lazy_string"):
+            return data.lazy_string(length=size)
+        return data.string(length=size)
+
+    def display_hint(self):
+        return "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)
+
+    def to_string(self):
+        typename = _remove_generics(_prettify_typename(self.val.type))
+        if not self.addr:
+            return "%s is nullptr" % typename
+        return ("%s<%s> containing" %
+                (typename,
+                 _remove_generics(_prettify_typename(self.pointee_type))))
+
+    def __iter__(self):
+        if self.addr:
+            yield "__ptr_", self.addr.cast(self.pointee_type.pointer())
+
+    def children(self):
+        return self
+
+
+class StdSharedPointerPrinter(object):
+    """Print a std::shared_ptr."""
+
+    def __init__(self, val):
+        self.val = val
+        self.addr = self.val["__ptr_"]
+
+    def to_string(self):
+        """Returns self as a string."""
+        typename = _remove_generics(_prettify_typename(self.val.type))
+        pointee_type = _remove_generics(
+            _prettify_typename(self.val.type.template_argument(0)))
+        if not self.addr:
+            return "%s is nullptr" % typename
+        refcount = self.val["__cntrl_"]
+        if refcount != 0:
+            usecount = refcount["__shared_owners_"] + 1
+            weakcount = refcount["__shared_weak_owners_"]
+            if usecount == 0:
+                state = "expired, weak %d" % weakcount
+            else:
+                state = "count %d, weak %d" % (usecount, weakcount)
+        return "%s<%s> %s containing" % (typename, pointee_type, state)
+
+    def __iter__(self):
+        if self.addr:
+            yield "__ptr_", self.addr
+
+    def children(self):
+        return self
+
+
+class StdVectorPrinter(object):
+    """Print a std::vector."""
+
+    class _VectorBoolIterator(object):
+        """Class to iterate over the bool vector's children."""
+
+        def __init__(self, begin, size, bits_per_word):
+            self.item = begin
+            self.size = size
+            self.bits_per_word = bits_per_word
+            self.count = 0
+            self.offset = 0
+
+        def __iter__(self):
+            return self
+
+        def next(self):
+            """Retrieve the next element."""
+
+            self.count += 1
+            if self.count > self.size:
+                raise StopIteration
+            entry = self.item.dereference()
+            if entry & (1 << self.offset):
+                outbit = 1
+            else:
+                outbit = 0
+            self.offset += 1
+            if self.offset >= self.bits_per_word:
+                self.item += 1
+                self.offset = 0
+            return ("[%d]" % self.count, outbit)
+
+    class _VectorIterator(object):
+        """Class to iterate over the non-bool vector's children."""
+
+        def __init__(self, begin, end):
+            self.item = begin
+            self.end = end
+            self.count = 0
+
+        def __iter__(self):
+            return self
+
+        def next(self):
+            self.count += 1
+            if self.item == self.end:
+                raise StopIteration
+            entry = self.item.dereference()
+            self.item += 1
+            return ("[%d]" % self.count, entry)
+
+    def __init__(self, val):
+        """Set val, length, capacity, and iterator for bool and normal vectors."""
+        self.val = val
+        self.typename = _remove_generics(_prettify_typename(val.type))
+        begin = self.val["__begin_"]
+        if self.val.type.template_argument(0).code == gdb.TYPE_CODE_BOOL:
+            self.typename += "<bool>"
+            self.length = self.val["__size_"]
+            bits_per_word = self.val["__bits_per_word"]
+            self.capacity = _value_of_pair_first(
+                self.val["__cap_alloc_"]) * bits_per_word
+            self.iterator = self._VectorBoolIterator(
+                begin, self.length, bits_per_word)
+        else:
+            end = self.val["__end_"]
+            self.length = end - begin
+            self.capacity = _get_base_subobject(
+                self.val["__end_cap_"])["__value_"] - begin
+            self.iterator = self._VectorIterator(begin, end)
+
+    def to_string(self):
+        return ("%s of length %d, capacity %d" %
+                (self.typename, self.length, self.capacity))
+
+    def children(self):
+        return self.iterator
+
+    def display_hint(self):
+        return "array"
+
+
+class StdBitsetPrinter(object):
+    """Print a std::bitset."""
+
+    def __init__(self, val):
+        self.val = val
+        self.n_words = int(self.val["__n_words"])
+        self.bits_per_word = int(self.val["__bits_per_word"])
+        if self.n_words == 1:
+            self.values = [int(self.val["__first_"])]
+        else:
+            self.values = [int(self.val["__first_"][index])
+                           for index in range(self.n_words)]
+
+    def to_string(self):
+        typename = _prettify_typename(self.val.type)
+        return "%s" % typename
+
+    def _byte_it(self, value):
+        index = -1
+        while value:
+            index += 1
+            will_yield = value % 2
+            value /= 2
+            if will_yield:
+                yield index
+
+    def _list_it(self):
+        for word_index in range(self.n_words):
+            current = self.values[word_index]
+            if current:
+                for n in self._byte_it(current):
+                    yield ("[%d]" % (word_index * self.bits_per_word + n), 1)
+
+    def __iter__(self):
+        return self._list_it()
+
+    def children(self):
+        return self
+
+
+class StdDequePrinter(object):
+    """Print a std::deque."""
+
+    def __init__(self, val):
+        self.val = val
+        self.size = int(_value_of_pair_first(val["__size_"]))
+        self.start_ptr = self.val["__map_"]["__begin_"]
+        self.first_block_start_index = int(self.val["__start_"])
+        self.node_type = self.start_ptr.type
+        self.block_size = self._calculate_block_size(
+            val.type.template_argument(0))
+
+    def _calculate_block_size(self, element_type):
+        """Calculates the number of elements in a full block."""
+        size = element_type.sizeof
+        # Copied from struct __deque_block_size implementation of libcxx.
+        return 4096 / size if size < 256 else 16
+
+    def _bucket_it(self, start_addr, start_index, end_index):
+        for i in range(start_index, end_index):
+            yield i, (start_addr.dereference() + i).dereference()
+
+    def _list_it(self):
+        """Primary iteration worker."""
+        num_emitted = 0
+        current_addr = self.start_ptr
+        start_index = self.first_block_start_index
+        while num_emitted < self.size:
+            end_index = min(start_index + self.size -
+                            num_emitted, self.block_size)
+            for _, elem in self._bucket_it(current_addr, start_index, end_index):
+                yield "", elem
+            num_emitted += end_index - start_index
+            current_addr = gdb.Value(addr_as_long(current_addr) + _pointer_size) \
+                              .cast(self.node_type)
+            start_index = 0
+
+    def to_string(self):
+        typename = _remove_generics(_prettify_typename(self.val.type))
+        if self.size:
+            return "%s with %d elements" % (typename, self.size)
+        return "%s is empty" % typename
+
+    def __iter__(self):
+        return self._list_it()
+
+    def children(self):
+        return self
+
+    def display_hint(self):
+        return "array"
+
+
+class StdListPrinter(object):
+    """Print a std::list."""
+
+    def __init__(self, val):
+        self.val = val
+        size_alloc_field = self.val["__size_alloc_"]
+        self.size = int(_value_of_pair_first(size_alloc_field))
+        dummy_node = self.val["__end_"]
+        self.nodetype = gdb.lookup_type(
+            re.sub("__list_node_base", "__list_node",
+                   str(dummy_node.type.strip_typedefs()))).pointer()
+        self.first_node = dummy_node["__next_"]
+
+    def to_string(self):
+        typename = _remove_generics(_prettify_typename(self.val.type))
+        if self.size:
+            return "%s with %d elements" % (typename, self.size)
+        return "%s is empty" % typename
+
+    def _list_iter(self):
+        current_node = self.first_node
+        for _ in range(self.size):
+            yield "", current_node.cast(self.nodetype).dereference()["__value_"]
+            current_node = current_node.dereference()["__next_"]
+
+    def __iter__(self):
+        return self._list_iter()
+
+    def children(self):
+        return self if self.nodetype else iter(())
+
+    def display_hint(self):
+        return "array"
+
+
+class StdQueueOrStackPrinter(object):
+    """Print a std::queue or std::stack."""
+
+    def __init__(self, val):
+        self.val = val
+        self.underlying = val["c"]
+
+    def to_string(self):
+        typename = _remove_generics(_prettify_typename(self.val.type))
+        return "%s wrapping" % typename
+
+    def children(self):
+        return iter([("", self.underlying)])
+
+    def display_hint(self):
+        return "array"
+
+
+class StdPriorityQueuePrinter(object):
+    """Print a std::priority_queue."""
+
+    def __init__(self, val):
+        self.val = val
+        self.underlying = val["c"]
+
+    def to_string(self):
+        # TODO(tamur): It would be nice to print the top element. The technical
+        # difficulty is that, the implementation refers to the underlying
+        # container, which is a generic class. libstdcxx pretty printers do not
+        # print the top element.
+        typename = _remove_generics(_prettify_typename(self.val.type))
+        return "%s wrapping" % typename
+
+    def children(self):
+        return iter([("", self.underlying)])
+
+    def display_hint(self):
+        return "array"
+
+
+class RBTreeUtils(object):
+    """Utility class for std::(multi)map, and std::(multi)set and iterators."""
+
+    def __init__(self, cast_type, root):
+        self.cast_type = cast_type
+        self.root = root
+
+    def left_child(self, node):
+        result = node.cast(self.cast_type).dereference()["__left_"]
+        return result
+
+    def right_child(self, node):
+        result = node.cast(self.cast_type).dereference()["__right_"]
+        return result
+
+    def parent(self, node):
+        """Return the parent of node, if it exists."""
+        # If this is the root, then from the algorithm's point of view, it has no
+        # parent.
+        if node == self.root:
+            return None
+
+        # We don't have enough information to tell if this is the end_node (which
+        # doesn't have a __parent_ field), or the root (which doesn't have a parent
+        # from the algorithm's point of view), so cast_type may not be correct for
+        # this particular node. Use heuristics.
+
+        # The end_node's left child is the root. Note that when printing interators
+        # in isolation, the root is unknown.
+        if self.left_child(node) == self.root:
+            return None
+
+        parent = node.cast(self.cast_type).dereference()["__parent_"]
+        # If the value at the offset of __parent_ doesn't look like a valid pointer,
+        # then assume that node is the end_node (and therefore has no parent).
+        # End_node type has a pointer embedded, so should have pointer alignment.
+        if addr_as_long(parent) % _void_pointer_type.alignof:
+            return None
+        # This is ugly, but the only other option is to dereference an invalid
+        # pointer.  0x8000 is fairly arbitrary, but has had good results in
+        # practice.  If there was a way to tell if a pointer is invalid without
+        # actually dereferencing it and spewing error messages, that would be ideal.
+        if parent < 0x8000:
+            return None
+        return parent
+
+    def is_left_child(self, node):
+        parent = self.parent(node)
+        return parent is not None and self.left_child(parent) == node
+
+    def is_right_child(self, node):
+        parent = self.parent(node)
+        return parent is not None and self.right_child(parent) == node
+
+
+class AbstractRBTreePrinter(object):
+    """Abstract super class for std::(multi)map, and std::(multi)set."""
+
+    def __init__(self, val):
+        self.val = val
+        tree = self.val["__tree_"]
+        self.size = int(_value_of_pair_first(tree["__pair3_"]))
+        dummy_root = tree["__pair1_"]
+        root = _value_of_pair_first(dummy_root)["__left_"]
+        cast_type = self._init_cast_type(val.type)
+        self.util = RBTreeUtils(cast_type, root)
+
+    def _get_key_value(self, node):
+        """Subclasses should override to return a list of values to yield."""
+        raise NotImplementedError
+
+    def _traverse(self):
+        """Traverses the binary search tree in order."""
+        current = self.util.root
+        skip_left_child = False
+        while True:
+            if not skip_left_child and self.util.left_child(current):
+                current = self.util.left_child(current)
+                continue
+            skip_left_child = False
+            for key_value in self._get_key_value(current):
+                yield "", key_value
+            right_child = self.util.right_child(current)
+            if right_child:
+                current = right_child
+                continue
+            while self.util.is_right_child(current):
+                current = self.util.parent(current)
+            if self.util.is_left_child(current):
+                current = self.util.parent(current)
+                skip_left_child = True
+                continue
+            break
+
+    def __iter__(self):
+        return self._traverse()
+
+    def children(self):
+        return self if self.util.cast_type and self.size > 0 else iter(())
+
+    def to_string(self):
+        typename = _remove_generics(_prettify_typename(self.val.type))
+        if self.size:
+            return "%s with %d elements" % (typename, self.size)
+        return "%s is empty" % typename
+
+
+class StdMapPrinter(AbstractRBTreePrinter):
+    """Print a std::map or std::multimap."""
+
+    def _init_cast_type(self, val_type):
+        map_it_type = gdb.lookup_type(
+            str(val_type) + "::iterator").strip_typedefs()
+        tree_it_type = map_it_type.template_argument(0)
+        node_ptr_type = tree_it_type.template_argument(1)
+        return node_ptr_type
+
+    def display_hint(self):
+        return "map"
+
+    def _get_key_value(self, node):
+        key_value = node.cast(self.util.cast_type).dereference()[
+            "__value_"]["__cc"]
+        return [key_value["first"], key_value["second"]]
+
+
+class StdSetPrinter(AbstractRBTreePrinter):
+    """Print a std::set."""
+
+    def _init_cast_type(self, val_type):
+        set_it_type = gdb.lookup_type(
+            str(val_type) + "::iterator").strip_typedefs()
+        node_ptr_type = set_it_type.template_argument(1)
+        return node_ptr_type
+
+    def display_hint(self):
+        return "array"
+
+    def _get_key_value(self, node):
+        key_value = node.cast(self.util.cast_type).dereference()["__value_"]
+        return [key_value]
+
+
+class AbstractRBTreeIteratorPrinter(object):
+    """Abstract super class for std::(multi)map, and std::(multi)set iterator."""
+
+    def _initialize(self, val, typename):
+        self.typename = typename
+        self.val = val
+        self.addr = self.val["__ptr_"]
+        cast_type = self.val.type.template_argument(1)
+        self.util = RBTreeUtils(cast_type, None)
+        if self.addr:
+            self.node = self.addr.cast(cast_type).dereference()
+
+    def _is_valid_node(self):
+        if not self.util.parent(self.addr):
+            return False
+        return self.util.is_left_child(self.addr) or \
+            self.util.is_right_child(self.addr)
+
+    def to_string(self):
+        if not self.addr:
+            return "%s is nullptr" % self.typename
+        return "%s " % self.typename
+
+    def _get_node_value(self, node):
+        raise NotImplementedError
+
+    def __iter__(self):
+        addr_str = "[%s]" % str(self.addr)
+        if not self._is_valid_node():
+            yield addr_str, " end()"
+        else:
+            yield addr_str, self._get_node_value(self.node)
+
+    def children(self):
+        return self if self.addr else iter(())
+
+
+class MapIteratorPrinter(AbstractRBTreeIteratorPrinter):
+    """Print a std::(multi)map iterator."""
+
+    def __init__(self, val):
+        self._initialize(val["__i_"],
+                         _remove_generics(_prettify_typename(val.type)))
+
+    def _get_node_value(self, node):
+        return node["__value_"]["__cc"]
+
+
+class SetIteratorPrinter(AbstractRBTreeIteratorPrinter):
+    """Print a std::(multi)set iterator."""
+
+    def __init__(self, val):
+        self._initialize(val, _remove_generics(_prettify_typename(val.type)))
+
+    def _get_node_value(self, node):
+        return node["__value_"]
+
+
+class StdFposPrinter(object):
+    """Print a std::fpos or std::streampos."""
+
+    def __init__(self, val):
+        self.val = val
+
+    def to_string(self):
+        typename = _remove_generics(_prettify_typename(self.val.type))
+        offset = self.val["__off_"]
+        state = self.val["__st_"]
+        count = state["__count"]
+        value = state["__value"]["__wch"]
+        return "%s with stream offset:%s with state: {count:%s value:%s}" % (
+            typename, offset, count, value)
+
+
+class AbstractUnorderedCollectionPrinter(object):
+    """Abstract super class for std::unordered_(multi)[set|map]."""
+
+    def __init__(self, val):
+        self.val = val
+        self.table = val["__table_"]
+        self.sentinel = self.table["__p1_"]
+        self.size = int(_value_of_pair_first(self.table["__p2_"]))
+        node_base_type = self.sentinel.type.template_argument(0)
+        self.cast_type = node_base_type.template_argument(0)
+
+    def _list_it(self, sentinel_ptr):
+        next_ptr = _value_of_pair_first(sentinel_ptr)["__next_"]
+        while str(next_ptr.cast(_void_pointer_type)) != "0x0":
+            next_val = next_ptr.cast(self.cast_type).dereference()
+            for key_value in self._get_key_value(next_val):
+                yield "", key_value
+            next_ptr = next_val["__next_"]
+
+    def to_string(self):
+        typename = _remove_generics(_prettify_typename(self.val.type))
+        if self.size:
+            return "%s with %d elements" % (typename, self.size)
+        return "%s is empty" % typename
+
+    def _get_key_value(self, node):
+        """Subclasses should override to return a list of values to yield."""
+        raise NotImplementedError
+
+    def children(self):
+        return self if self.cast_type and self.size > 0 else iter(())
+
+    def __iter__(self):
+        return self._list_it(self.sentinel)
+
+
+class StdUnorderedSetPrinter(AbstractUnorderedCollectionPrinter):
+    """Print a std::unordered_(multi)set."""
+
+    def _get_key_value(self, node):
+        return [node["__value_"]]
+
+    def display_hint(self):
+        return "array"
+
+
+class StdUnorderedMapPrinter(AbstractUnorderedCollectionPrinter):
+    """Print a std::unordered_(multi)map."""
+
+    def _get_key_value(self, node):
+        key_value = node["__value_"]["__cc"]
+        return [key_value["first"], key_value["second"]]
+
+    def display_hint(self):
+        return "map"
+
+
+class AbstractHashMapIteratorPrinter(object):
+    """Abstract class for unordered collection iterators."""
+
+    def _initialize(self, val, addr):
+        self.val = val
+        self.typename = _remove_generics(_prettify_typename(self.val.type))
+        self.addr = addr
+        if self.addr:
+            self.node = self.addr.cast(self.cast_type).dereference()
+
+    def _get_key_value(self):
+        """Subclasses should override to return a list of values to yield."""
+        raise NotImplementedError
+
+    def to_string(self):
+        if not self.addr:
+            return "%s = end()" % self.typename
+        return "%s " % self.typename
+
+    def children(self):
+        return self if self.addr else iter(())
+
+    def __iter__(self):
+        for key_value in self._get_key_value():
+            yield "", key_value
+
+
+class StdUnorderedSetIteratorPrinter(AbstractHashMapIteratorPrinter):
+    """Print a std::(multi)set iterator."""
+
+    def __init__(self, val):
+        self.cast_type = val.type.template_argument(0)
+        self._initialize(val, val["__node_"])
+
+    def _get_key_value(self):
+        return [self.node["__value_"]]
+
+    def display_hint(self):
+        return "array"
+
+
+class StdUnorderedMapIteratorPrinter(AbstractHashMapIteratorPrinter):
+    """Print a std::(multi)map iterator."""
+
+    def __init__(self, val):
+        self.cast_type = val.type.template_argument(0).template_argument(0)
+        self._initialize(val, val["__i_"]["__node_"])
+
+    def _get_key_value(self):
+        key_value = self.node["__value_"]["__cc"]
+        return [key_value["first"], key_value["second"]]
+
+    def display_hint(self):
+        return "map"
+
+
+def _remove_std_prefix(typename):
+    match = re.match("^std::(.+)", typename)
+    return match.group(1) if match is not None else ""
+
+
+class LibcxxPrettyPrinter(object):
+    """PrettyPrinter object so gdb-commands like 'info pretty-printers' work."""
+
+    def __init__(self, name):
+        super(LibcxxPrettyPrinter, self).__init__()
+        self.name = name
+        self.enabled = True
+
+        self.lookup = {
+            "basic_string": StdStringPrinter,
+            "string": StdStringPrinter,
+            "tuple": StdTuplePrinter,
+            "unique_ptr": StdUniquePtrPrinter,
+            "shared_ptr": StdSharedPointerPrinter,
+            "weak_ptr": StdSharedPointerPrinter,
+            "bitset": StdBitsetPrinter,
+            "deque": StdDequePrinter,
+            "list": StdListPrinter,
+            "queue": StdQueueOrStackPrinter,
+            "stack": StdQueueOrStackPrinter,
+            "priority_queue": StdPriorityQueuePrinter,
+            "map": StdMapPrinter,
+            "multimap": StdMapPrinter,
+            "set": StdSetPrinter,
+            "multiset": StdSetPrinter,
+            "vector": StdVectorPrinter,
+            "__map_iterator": MapIteratorPrinter,
+            "__map_const_iterator": MapIteratorPrinter,
+            "__tree_iterator": SetIteratorPrinter,
+            "__tree_const_iterator": SetIteratorPrinter,
+            "fpos": StdFposPrinter,
+            "unordered_set": StdUnorderedSetPrinter,
+            "unordered_multiset": StdUnorderedSetPrinter,
+            "unordered_map": StdUnorderedMapPrinter,
+            "unordered_multimap": StdUnorderedMapPrinter,
+            "__hash_map_iterator": StdUnorderedMapIteratorPrinter,
+            "__hash_map_const_iterator": StdUnorderedMapIteratorPrinter,
+            "__hash_iterator": StdUnorderedSetIteratorPrinter,
+            "__hash_const_iterator": StdUnorderedSetIteratorPrinter,
+        }
+
+        self.subprinters = []
+        for name, subprinter in self.lookup.items():
+            # Subprinters and names are used only for the rarely used command "info
+            # pretty" (and related), so the name of the first data structure it prints
+            # is a reasonable choice.
+            if subprinter not in self.subprinters:
+                subprinter.name = name
+                self.subprinters.append(subprinter)
+
+    def __call__(self, val):
+        """Return the pretty printer for a val, if the type is supported."""
+
+        # Do not handle any type that is not a struct/class.
+        if val.type.strip_typedefs().code != gdb.TYPE_CODE_STRUCT:
+            return None
+
+        # Don't attempt types known to be inside libstdcxx.
+        typename = val.type.name or val.type.tag or str(val.type)
+        match = re.match("^std::(__.*?)::", typename)
+        if match is None or match.group(1) in ["__cxx1998",
+                                               "__debug",
+                                               "__7",
+                                               "__g"]:
+            return None
+
+        # Handle any using declarations or other typedefs.
+        typename = _prettify_typename(val.type)
+        if not typename:
+            return None
+        without_generics = _remove_generics(typename)
+        lookup_name = _remove_std_prefix(without_generics)
+        if lookup_name in self.lookup:
+            return self.lookup[lookup_name](val)
+        return None
+
+
+_libcxx_printer_name = "libcxx_pretty_printer"
+
+
+# These are called for every binary object file, which could be thousands in
+# certain pathological cases. Limit our pretty printers to the progspace.
+def _register_libcxx_printers(event):
+    progspace = event.new_objfile.progspace
+    if not getattr(progspace, _libcxx_printer_name, False):
+        print("Loading libc++ pretty-printers.")
+        gdb.printing.register_pretty_printer(
+            progspace, LibcxxPrettyPrinter(_libcxx_printer_name))
+        setattr(progspace, _libcxx_printer_name, True)
+
+
+def _unregister_libcxx_printers(event):
+    progspace = event.progspace
+    if getattr(progspace, _libcxx_printer_name, False):
+        for printer in progspace.pretty_printers:
+            if getattr(printer, "name", "none") == _libcxx_printer_name:
+                progspace.pretty_printers.remove(printer)
+                setattr(progspace, _libcxx_printer_name, False)
+                break
+
+
+def register_libcxx_printer_loader():
+    """Register event handlers to load libc++ pretty-printers."""
+    gdb.events.new_objfile.connect(_register_libcxx_printers)
+    gdb.events.clear_objfiles.connect(_unregister_libcxx_printers)