[LLDB] libcxx summary formatters for std::string_view

[puremourning]

Summary

When printing a std::string_view, print the referenced string as the
summary. Support string_view, u32string_view, u16string_view and
wstring_view, as we do for std::string and friends.

This is based on the existing fomratter for std::string, and just
extracts the data and length members, pushing them through the existing
string formatter.

In testing this, a "FIXME" was corrected for printing of non-ASCII empty
values. Previously, the "u", 'U" etc. prefixes were not printed for
basic_string<> types that were not char. This is trivial to resolve by
printing the prefix before the "".

[puremourning]

I'm happy to revert/split out the change for empty strings, as this is perhaps contentious (and not exactly minimal for this patch).

Also, I'm only implementing libcxx (for now). We can follow up with libstdc++ in another patch if this is accepted.

This is my first lldb patch, so apologies if I did something out of ordinary.

[teemperor]

In D112222#3077988, @puremourning wrote:

I'm happy to revert/split out the change for empty strings, as this is perhaps contentious (and not exactly minimal for this patch).

I would actually prefer if we could split this into a separate change :) (Sorry!)

Also, I'm only implementing libcxx (for now). We can follow up with libstdc++ in another patch if this is accepted.

Sounds good to me.

This is my first lldb patch, so apologies if I did something out of ordinary.

Nope, I think this is actually looking pretty good. I just have a few nits that I'll try get around today/tomorrow.

[puremourning]

I would actually prefer if we could split this into a separate change :) (Sorry!)

No problem, that was my gut feeling at the time too.

[puremourning]

Remove change to the formatting of empty u16 and u32 strings

[puremourning]

RE-post with clang-format in path

[jingham]

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/string_view/TestDataFormatterLibcxxStringView.py

62

We have lldbtest.expect_var_path for doing this sort of test. It makes these tests easier to read and less likely to be fooled by accidental matches.

[puremourning]

Use expect_var_path rather than just expect in test

[puremourning]

Thanks for the review!

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/string_view/TestDataFormatterLibcxxStringView.py

62

Done. There's s slight difference in this API - the null pointer summary returns "" via this api rather than the output which returns "nullptr", so I've inlaced both in the test.

[shafik]

It looks good to me but can we verify it behaves nicely with undefined behavior cases e.g.:

std::string s = "Hellooooooooooooooo ";
std::string_view sv = s + "World\n";

and a case like the one that was fixed in D108228

I am not expecting any surprises since you are using the underlying string formatter but worth checking.

[puremourning]

Revert some formatting lost in rebase

[puremourning]

In D112222#3078896, @shafik wrote:

It looks good to me but can we verify it behaves nicely with undefined behavior cases e.g.:

std::string s = "Hellooooooooooooooo ";
std::string_view sv = s + "World\n";

Will add some cases, sure.

and a case like the one that was fixed in D108228

Thanks for the pointer! (no pun intended). I will apply the same change/mitigattion to my new code.

I am not expecting any surprises since you are using the underlying string formatter but worth checking.

yes, certainly is, thanks!

[puremourning]

Add some tests for dodgy inputs.
Handle invalid cases more consistently.
Factor out some copy paste code.

[puremourning]

Sorry, but is anything further required from me on this patch ?

[jingham]

In D112222#3141355, @puremourning wrote:

Sorry, but is anything further required from me on this patch ?

You addressed an issue Shafik asked you to, so then he should make sure he's happy with the change and mark the patch accepted. OTOH we're all busy so it's easy to let this sort of thing drop. On your end, you should wait a polite interval then issue a gentle ping in his direction... A week is an okay interval, I think, so now would be appropriate.

[puremourning]

In D112222#3141363, @jingham wrote:

In D112222#3141355, @puremourning wrote:

Sorry, but is anything further required from me on this patch ?

You addressed an issue Shafik asked you to, so then he should make sure he's happy with the change and mark the patch accepted. OTOH we're all busy so it's easy to let this sort of thing drop. On your end, you should wait a polite interval then issue a gentle ping in his direction... A week is an okay interval, I think, so now would be appropriate.

Sure, I wasn't nagging, just checking :) I completely understand how these things go. There's no rush.

[shafik]

Apologies, this dropped off my radar it LGTM, thank you!

[puremourning]

In D112222#3143966, @shafik wrote:

Apologies, this dropped off my radar it LGTM, thank you!

Thanks!

Sorry for my ignorance, but what's the next step to land this? Do you want me to rebase it first and push that, or is someone abele land this for me, as I don't have commit rights ?

[puremourning]

Just giving this a gentle nudge again. As I said before, there's no rush, but if there's any action I can take to get this landed, please let me know. Many thanks again, ben.

[puremourning]

Polite ping to get this committed.

I have rebased against main today and run the test, it still passes and the patch applies cleanly.

[puremourning]

Friendly ping to get this landed.

lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp

 //===-- CPlusPlusLanguage.cpp ---------------------------------------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
static void LoadLibCxxFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
   AddCXXSummary(cpp_category_sp,
                 lldb_private::formatters::LibcxxWStringSummaryProvider,
                 "std::wstring summary provider",
                 ConstString("^std::__[[:alnum:]]+::basic_string<wchar_t, "
                             "std::__[[:alnum:]]+::char_traits<wchar_t>, "
                             "std::__[[:alnum:]]+::allocator<wchar_t> >$"),
                 stl_summary_flags, true);
 
+  AddCXXSummary(cpp_category_sp,
+                lldb_private::formatters::LibcxxStringViewSummaryProviderASCII,
+                "std::string_view summary provider",
+                ConstString("^std::__[[:alnum:]]+::string_view$"),
+                stl_summary_flags, true);
+  AddCXXSummary(cpp_category_sp,
+                lldb_private::formatters::LibcxxStringViewSummaryProviderASCII,
+                "std::string_view summary provider",
+                ConstString("^std::__[[:alnum:]]+::basic_string_view<char, "
+                            "std::__[[:alnum:]]+::char_traits<char> >$"),
+                stl_summary_flags, true);
+  AddCXXSummary(
+      cpp_category_sp,
+      lldb_private::formatters::LibcxxStringViewSummaryProviderASCII,
+      "std::string_view summary provider",
+      ConstString("^std::__[[:alnum:]]+::basic_string_view<unsigned char, "
+                  "std::__[[:alnum:]]+::char_traits<unsigned char> >$"),
+      stl_summary_flags, true);
+
+  AddCXXSummary(cpp_category_sp,
+                lldb_private::formatters::LibcxxStringViewSummaryProviderUTF16,
+                "std::u16string_view summary provider",
+                ConstString("^std::__[[:alnum:]]+::basic_string_view<char16_t, "
+                            "std::__[[:alnum:]]+::char_traits<char16_t> >$"),
+                stl_summary_flags, true);
+
+  AddCXXSummary(cpp_category_sp,
+                lldb_private::formatters::LibcxxStringViewSummaryProviderUTF32,
+                "std::u32string_view summary provider",
+                ConstString("^std::__[[:alnum:]]+::basic_string_view<char32_t, "
+                            "std::__[[:alnum:]]+::char_traits<char32_t> >$"),
+                stl_summary_flags, true);
+
+  AddCXXSummary(cpp_category_sp,
+                lldb_private::formatters::LibcxxWStringViewSummaryProvider,
+                "std::wstring_view summary provider",
+                ConstString("^std::__[[:alnum:]]+::wstring_view$"),
+                stl_summary_flags, true);
+  AddCXXSummary(cpp_category_sp,
+                lldb_private::formatters::LibcxxWStringViewSummaryProvider,
+                "std::wstring_view summary provider",
+                ConstString("^std::__[[:alnum:]]+::basic_string_view<wchar_t, "
+                            "std::__[[:alnum:]]+::char_traits<wchar_t> >$"),
+                stl_summary_flags, true);
+
   SyntheticChildren::Flags stl_synth_flags;
   stl_synth_flags.SetCascades(true).SetSkipPointers(false).SetSkipReferences(
       false);
   SyntheticChildren::Flags stl_deref_flags = stl_synth_flags;
   stl_deref_flags.SetFrontEndWantsDereference();
 
   AddCXXSynthetic(
       cpp_category_sp,

lldb/source/Plugins/Language/CPlusPlus/LibCxx.h

 //===-- LibCxx.h ---------------------------------------------------*- 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
 //
 //===----------------------------------------------------------------------===//

 bool LibcxxStringSummaryProviderUTF32(
     ValueObject &valobj, Stream &stream,
     const TypeSummaryOptions &summary_options); // libc++ std::u32string
 
 bool LibcxxWStringSummaryProvider(
     ValueObject &valobj, Stream &stream,
     const TypeSummaryOptions &options); // libc++ std::wstring
 
+bool LibcxxStringViewSummaryProviderASCII(
+    ValueObject &valueObj, Stream &stream,
+    const TypeSummaryOptions &summary_options); // libc++ std::string_view
+
+bool LibcxxStringViewSummaryProviderUTF16(
+    ValueObject &valobj, Stream &stream,
+    const TypeSummaryOptions &summary_options); // libc++ std::u16string_view
+
+bool LibcxxStringViewSummaryProviderUTF32(
+    ValueObject &valobj, Stream &stream,
+    const TypeSummaryOptions &summary_options); // libc++ std::u32string_view
+
+bool LibcxxWStringViewSummaryProvider(
+    ValueObject &valobj, Stream &stream,
+    const TypeSummaryOptions &options); // libc++ std::wstring_view
+
 bool LibcxxOptionalSummaryProvider(
     ValueObject &valobj, Stream &stream,
     const TypeSummaryOptions &options); // libc++ std::optional<>
 
 bool LibcxxSmartPointerSummaryProvider(
     ValueObject &valobj, Stream &stream,
     const TypeSummaryOptions
         &options); // libc++ std::shared_ptr<> and std::weak_ptr<>

lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp

 //===-- LibCxx.cpp --------------------------------------------------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
 #include "LibCxx.h"
 
 #include "lldb/Core/Debugger.h"
 #include "lldb/Core/FormatEntity.h"
 #include "lldb/Core/ValueObject.h"
 #include "lldb/Core/ValueObjectConstResult.h"
 #include "lldb/DataFormatters/FormattersHelpers.h"
 #include "lldb/DataFormatters/StringPrinter.h"
 #include "lldb/DataFormatters/TypeSummary.h"
 #include "lldb/DataFormatters/VectorIterator.h"
 #include "lldb/Target/ProcessStructReader.h"
 #include "lldb/Target/SectionLoadList.h"
 #include "lldb/Target/Target.h"
+#include "lldb/Utility/ConstString.h"
 #include "lldb/Utility/DataBufferHeap.h"
 #include "lldb/Utility/Endian.h"
 #include "lldb/Utility/Status.h"
 #include "lldb/Utility/Stream.h"
 
 #include "Plugins/LanguageRuntime/CPlusPlus/CPPLanguageRuntime.h"
 #include "Plugins/TypeSystem/Clang/TypeSystemClang.h"
 

 /// extract its data payload. Return the size + payload pair.
 static llvm::Optional<std::pair<uint64_t, ValueObjectSP>>
 ExtractLibcxxStringInfo(ValueObject &valobj) {
   ValueObjectSP D(valobj.GetChildAtIndexPath({0, 0, 0, 0}));
   if (!D)
     return {};
 
   ValueObjectSP layout_decider(
       D->GetChildAtIndexPath(llvm::ArrayRef<size_t>({0, 0})));
 
   // this child should exist
   if (!layout_decider)
     return {};
 
   ConstString g_data_name("__data_");
   ConstString g_size_name("__size_");
   bool short_mode = false; // this means the string is in short-mode and the
ExtractLibcxxStringInfo(ValueObject &valobj) {
   const uint64_t capacity =
       capacity_vo->GetValueAsUnsigned(LLDB_INVALID_OFFSET);
   if (size == LLDB_INVALID_OFFSET || capacity == LLDB_INVALID_OFFSET ||
       capacity < size)
     return {};
   return std::make_pair(size, location_sp);
 }
 
-bool lldb_private::formatters::LibcxxWStringSummaryProvider(
-    ValueObject &valobj, Stream &stream,
-    const TypeSummaryOptions &summary_options) {
-  auto string_info = ExtractLibcxxStringInfo(valobj);
-  if (!string_info)
-    return false;
-  uint64_t size;
-  ValueObjectSP location_sp;
-  std::tie(size, location_sp) = *string_info;
-
+static bool
+LibcxxWStringSummaryProvider(ValueObject &valobj, Stream &stream,
+                             const TypeSummaryOptions &summary_options,
+                             ValueObjectSP location_sp, size_t size) {
   if (size == 0) {
     stream.Printf("L\"\"");
     return true;
   }
   if (!location_sp)
     return false;
 
-
   StringPrinter::ReadBufferAndDumpToStreamOptions options(valobj);
   if (summary_options.GetCapping() == TypeSummaryCapping::eTypeSummaryCapped) {
     const auto max_size = valobj.GetTargetSP()->GetMaximumSizeOfStringSummary();
     if (size > max_size) {
       size = max_size;
       options.SetIsTruncated(true);
     }
   }
LibcxxWStringSummaryProvider(ValueObject &valobj, Stream &stream,
   case 4:
     return StringPrinter::ReadBufferAndDumpToStream<
         lldb_private::formatters::StringPrinter::StringElementType::UTF32>(
         options);
   }
   return false;
 }
 
-template <StringPrinter::StringElementType element_type>
-bool LibcxxStringSummaryProvider(ValueObject &valobj, Stream &stream,
-                                 const TypeSummaryOptions &summary_options,
-                                 std::string prefix_token) {
+bool lldb_private::formatters::LibcxxWStringSummaryProvider(
+    ValueObject &valobj, Stream &stream,
+    const TypeSummaryOptions &summary_options) {
   auto string_info = ExtractLibcxxStringInfo(valobj);
   if (!string_info)
     return false;
   uint64_t size;
   ValueObjectSP location_sp;
   std::tie(size, location_sp) = *string_info;
 
+  return ::LibcxxWStringSummaryProvider(valobj, stream, summary_options,
+                                        location_sp, size);
+}
+
+template <StringPrinter::StringElementType element_type>
+static bool
+LibcxxStringSummaryProvider(ValueObject &valobj, Stream &stream,
+                            const TypeSummaryOptions &summary_options,
+                            std::string prefix_token, ValueObjectSP location_sp,
+                            uint64_t size) {
+
   if (size == 0) {
+    stream << prefix_token;
     stream.Printf("\"\"");
     return true;
   }
 
   if (!location_sp)
     return false;
 
   StringPrinter::ReadBufferAndDumpToStreamOptions options(valobj);
else
     options.SetPrefixToken(prefix_token);
   options.SetQuote('"');
   options.SetSourceSize(size);
   options.SetBinaryZeroIsTerminator(false);
   return StringPrinter::ReadBufferAndDumpToStream<element_type>(options);
 }
 
 template <StringPrinter::StringElementType element_type>
+static bool
+LibcxxStringSummaryProvider(ValueObject &valobj, Stream &stream,
+                            const TypeSummaryOptions &summary_options,
+                            std::string prefix_token) {
+  auto string_info = ExtractLibcxxStringInfo(valobj);
+  if (!string_info)
+    return false;
+  uint64_t size;
+  ValueObjectSP location_sp;
+  std::tie(size, location_sp) = *string_info;
+
+  return LibcxxStringSummaryProvider<element_type>(
+      valobj, stream, summary_options, prefix_token, location_sp, size);
+}
+
+template <StringPrinter::StringElementType element_type>
 static bool formatStringImpl(ValueObject &valobj, Stream &stream,
                              const TypeSummaryOptions &summary_options,
                              std::string prefix_token) {
   StreamString scratch_stream;
   const bool success = LibcxxStringSummaryProvider<element_type>(
       valobj, scratch_stream, summary_options, prefix_token);
   if (success)
     stream << scratch_stream.GetData();

 }
 
 bool lldb_private::formatters::LibcxxStringSummaryProviderUTF32(
     ValueObject &valobj, Stream &stream,
     const TypeSummaryOptions &summary_options) {
   return formatStringImpl<StringPrinter::StringElementType::UTF32>(
       valobj, stream, summary_options, "U");
 }
+
+template <StringPrinter::StringElementType element_type>
+static bool formatStringViewImpl(ValueObject &valobj, Stream &stream,
+                                 const TypeSummaryOptions &summary_options,
+                                 std::string prefix_token) {
+
+  // extract the size/location from the string_view object
+  ConstString g_data_name("__data");
+  ConstString g_size_name("__size");
+  auto dataobj = valobj.GetChildMemberWithName(g_data_name, true);
+  auto sizeobj = valobj.GetChildMemberWithName(g_size_name, true);
+
+  if (!dataobj || !sizeobj)
+    return false;
+
+  uint64_t size = sizeobj->GetValueAsUnsigned(0);
+
+  return LibcxxStringSummaryProvider<element_type>(
+      valobj, stream, summary_options, prefix_token, dataobj, size);
+}
+
+bool lldb_private::formatters::LibcxxStringViewSummaryProviderASCII(
+    ValueObject &valobj, Stream &stream,
+    const TypeSummaryOptions &summary_options) {
+  return formatStringViewImpl<StringPrinter::StringElementType::ASCII>(
+      valobj, stream, summary_options, "");
+}
+
+bool lldb_private::formatters::LibcxxStringViewSummaryProviderUTF16(
+    ValueObject &valobj, Stream &stream,
+    const TypeSummaryOptions &summary_options) {
+  return formatStringViewImpl<StringPrinter::StringElementType::UTF16>(
+      valobj, stream, summary_options, "u");
+}
+
+bool lldb_private::formatters::LibcxxStringViewSummaryProviderUTF32(
+    ValueObject &valobj, Stream &stream,
+    const TypeSummaryOptions &summary_options) {
+  return formatStringViewImpl<StringPrinter::StringElementType::UTF32>(
+      valobj, stream, summary_options, "U");
+}
+
+bool lldb_private::formatters::LibcxxWStringViewSummaryProvider(
+    ValueObject &valobj, Stream &stream,
+    const TypeSummaryOptions &summary_options) {
+
+  ConstString g_data_name("__data");
+  ConstString g_size_name("__size");
+  auto dataobj = valobj.GetChildMemberWithName(g_data_name, true);
+  auto sizeobj = valobj.GetChildMemberWithName(g_size_name, true);
+
+  if (!dataobj || !sizeobj)
+    return false;
+
+  uint64_t size = sizeobj->GetValueAsUnsigned(0);
+
+  return ::LibcxxWStringSummaryProvider(valobj, stream, summary_options,
+                                        dataobj, size);
+}

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/string/TestDataFormatterLibcxxString.py

def test_with_run_command(self):
                 '(const wchar_t *) mazeltov = 0x',
                 'L"מזל טוב"',
                 '(%s::string) empty = ""'%ns,
                 '(%s::string) q = "hello world"'%ns,
                 '(%s::string) Q = "quite a long std::strin with lots of info inside it"'%ns,
                 '(%s::string) IHaveEmbeddedZeros = "a\\0b\\0c\\0d"'%ns,
                 '(%s::wstring) IHaveEmbeddedZerosToo = L"hello world!\\0てざ ル゜䋨ミ㠧槊 きゅへ狦穤襩 じゃ馩リョ 䤦監"'%ns,
                 '(%s::u16string) u16_string = u"ß水氶"'%ns,
-                # FIXME: This should have a 'u' prefix.
-                '(%s::u16string) u16_empty = ""'%ns,
+                '(%s::u16string) u16_empty = u""'%ns,
                 '(%s::u32string) u32_string = U"🍄🍅🍆🍌"'%ns,
-                # FIXME: This should have a 'U' prefix.
-                '(%s::u32string) u32_empty = ""'%ns,
+                '(%s::u32string) u32_empty = U""'%ns,
                 '(%s::basic_string<unsigned char, %s::char_traits<unsigned char>, '
                 '%s::allocator<unsigned char> >) uchar = "aaaaa"'%(ns,ns,ns),
                 '(%s::string *) null_str = nullptr'%ns,
         ])
 
         self.runCmd("n")
 
         TheVeryLongOne = self.frame().FindVariable("TheVeryLongOne")
def test_with_run_command(self):
                 '(const wchar_t *) mazeltov = 0x',
                 'L"מזל טוב"',
                 '(%s::string) q = "hello world"'%ns,
                 '(%s::string) Q = "quite a long std::strin with lots of info inside it"'%ns,
                 '(%s::string) IHaveEmbeddedZeros = "a\\0b\\0c\\0d"'%ns,
                 '(%s::wstring) IHaveEmbeddedZerosToo = L"hello world!\\0てざ ル゜䋨ミ㠧槊 きゅへ狦穤襩 じゃ馩リョ 䤦監"'%ns,
                 '(%s::u16string) u16_string = u"ß水氶"'%ns,
                 '(%s::u32string) u32_string = U"🍄🍅🍆🍌"'%ns,
-                '(%s::u32string) u32_empty = ""'%ns,
+                '(%s::u32string) u32_empty = U""'%ns,
                 '(%s::basic_string<unsigned char, %s::char_traits<unsigned char>, '
                 '%s::allocator<unsigned char> >) uchar = "aaaaa"'%(ns,ns,ns),
                 '(%s::string *) null_str = nullptr'%ns,
         ])
 
         # The test assumes that std::string is in its cap-size-data layout.
         is_alternate_layout = ('arm' in self.getArchitecture()) and self.platformIsDarwin()
         if is_64_bit and not is_alternate_layout:
             self.expect("frame variable garbage1", substrs=['garbage1 = Summary Unavailable'])
             self.expect("frame variable garbage2", substrs=[r'garbage2 = "\xfa\xfa\xfa\xfa"'])
             self.expect("frame variable garbage3", substrs=[r'garbage3 = "\xf0\xf0"'])
             self.expect("frame variable garbage4", substrs=['garbage4 = Summary Unavailable'])
             self.expect("frame variable garbage5", substrs=['garbage5 = Summary Unavailable'])

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/string_view/Makefile

+CXX_SOURCES := main.cpp
+
+USE_LIBCPP := 1
+
+CXXFLAGS_EXTRAS := -std=c++11 -O0
+include Makefile.rules

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/string_view/TestDataFormatterLibcxxStringView.py

 # coding=utf8
 """
 Test lldb data formatter subsystem.
 """
 
 
 
 import lldb
 from lldbsuite.test.decorators import *
 from lldbsuite.test.lldbtest import *
 from lldbsuite.test import lldbutil
 
 
-class LibcxxStringDataFormatterTestCase(TestBase):
+class LibcxxStringViewDataFormatterTestCase(TestBase):
 
     mydir = TestBase.compute_mydir(__file__)
 
     def setUp(self):
         # Call super's setUp().
         TestBase.setUp(self)
         # Find the line number to break at.
         self.line = line_number('main.cpp', '// Set break point at this line.')
def test_with_run_command(self):
                 check=False)
 
         is_64_bit = self.process().GetAddressByteSize() == 8
 
         # Execute the cleanup function during test case tear down.
         self.addTearDownHook(cleanup)
 
         ns = self.namespace
         self.expect(
             "frame variable",
             substrs=[
-                '(%s::wstring) wempty = L""'%ns,
-                '(%s::wstring) s = L"hello world! מזל טוב!"'%ns,
-                '(%s::wstring) S = L"!!!!"'%ns,
-                '(const wchar_t *) mazeltov = 0x',
-                'L"מזל טוב"',
-                '(%s::string) empty = ""'%ns,
-                '(%s::string) q = "hello world"'%ns,
-                '(%s::string) Q = "quite a long std::strin with lots of info inside it"'%ns,
-                '(%s::string) IHaveEmbeddedZeros = "a\\0b\\0c\\0d"'%ns,
-                '(%s::wstring) IHaveEmbeddedZerosToo = L"hello world!\\0てざ ル゜䋨ミ㠧槊 きゅへ狦穤襩 じゃ馩リョ 䤦監"'%ns,
-                '(%s::u16string) u16_string = u"ß水氶"'%ns,
-                # FIXME: This should have a 'u' prefix.
-                '(%s::u16string) u16_empty = ""'%ns,
-                '(%s::u32string) u32_string = U"🍄🍅🍆🍌"'%ns,
-                # FIXME: This should have a 'U' prefix.
-                '(%s::u32string) u32_empty = ""'%ns,
+                '(%s::wstring_view) wempty = L""'%ns,
+                '(%s::wstring_view) s = L"hello world! מזל טוב!"'%ns,
+                '(%s::wstring_view) S = L"!!!!"'%ns,
+                '(%s::string_view) empty = ""'%ns,
+                '(%s::string) q_source = "hello world"'%ns,
+                '(%s::string_view) q = "hello world"'%ns,
+                '(%s::string_view) Q = "quite a long std::strin with lots of info inside it"'%ns,
+                '(%s::string_view) IHaveEmbeddedZeros = "a\\0b\\0c\\0d"'%ns,
+                '(%s::wstring_view) IHaveEmbeddedZerosToo = L"hello world!\\0てざ ル゜䋨ミ㠧槊 きゅへ狦穤襩 じゃ馩リョ 䤦監"'%ns,
+                '(%s::u16string_view) u16_string = u"ß水氶"'%ns,
+                '(%s::u16string_view) u16_empty = u""'%ns,
+                '(%s::u32string_view) u32_string = U"🍄🍅🍆🍌"'%ns,
+                '(%s::u32string_view) u32_empty = U""'%ns,
                 '(%s::basic_string<unsigned char, %s::char_traits<unsigned char>, '
-                '%s::allocator<unsigned char> >) uchar = "aaaaa"'%(ns,ns,ns),
-                '(%s::string *) null_str = nullptr'%ns,
+                '%s::allocator<unsigned char> >) uchar_source = "aaaaaaaaaa"'%(ns,ns,ns),
+                '(%s::basic_string_view<unsigned char, %s::char_traits<unsigned char> >) uchar = "aaaaa"'%(ns,ns),
+                '(%s::string_view *) null_str = nullptr'%ns,
         ])
 
         self.runCmd("n")
 
         TheVeryLongOne = self.frame().FindVariable("TheVeryLongOne")
         summaryOptions = lldb.SBTypeSummaryOptions()
         summaryOptions.SetCapping(lldb.eTypeSummaryUncapped)
         uncappedSummaryStream = lldb.SBStream()
         TheVeryLongOne.GetSummary(uncappedSummaryStream, summaryOptions)
         uncappedSummary = uncappedSummaryStream.GetData()
         self.assertTrue(uncappedSummary.find("someText") > 0,
                         "uncappedSummary does not include the full string")
         summaryOptions.SetCapping(lldb.eTypeSummaryCapped)
         cappedSummaryStream = lldb.SBStream()
         TheVeryLongOne.GetSummary(cappedSummaryStream, summaryOptions)
         cappedSummary = cappedSummaryStream.GetData()
         self.assertTrue(
             cappedSummary.find("someText") <= 0,
             "cappedSummary includes the full string")
 
-        self.expect_expr("s", result_type=ns+"::wstring", result_summary='L"hello world! מזל טוב!"')
+        self.expect_expr("s", result_type=ns+"::wstring_view", result_summary='L"hello world! מזל טוב!"')
 
         self.expect(
             "frame variable",
             substrs=[
-                '(%s::wstring) S = L"!!!!!"'%ns,
-                '(const wchar_t *) mazeltov = 0x',
-                'L"מזל טוב"',
-                '(%s::string) q = "hello world"'%ns,
-                '(%s::string) Q = "quite a long std::strin with lots of info inside it"'%ns,
-                '(%s::string) IHaveEmbeddedZeros = "a\\0b\\0c\\0d"'%ns,
-                '(%s::wstring) IHaveEmbeddedZerosToo = L"hello world!\\0てざ ル゜䋨ミ㠧槊 きゅへ狦穤襩 じゃ馩リョ 䤦監"'%ns,
-                '(%s::u16string) u16_string = u"ß水氶"'%ns,
-                '(%s::u32string) u32_string = U"🍄🍅🍆🍌"'%ns,
-                '(%s::u32string) u32_empty = ""'%ns,
+                '(%s::wstring_view) S = L"!!!!"'%ns,
+                '(%s::string) q_source = "Hello world"'%ns,
+                '(%s::string_view) q = "Hello world"'%ns,
+                '(%s::string_view) Q = "quite a long std::strin with lots of info inside it"'%ns,
+                '(%s::string_view) IHaveEmbeddedZeros = "a\\0b\\0c\\0d"'%ns,
+                '(%s::wstring_view) IHaveEmbeddedZerosToo = L"hello world!\\0てざ ル゜䋨ミ㠧槊 きゅへ狦穤襩 じゃ馩リョ 䤦監"'%ns,
+                '(%s::u16string_view) u16_string = u"ß水氶"'%ns,
+                '(%s::u32string_view) u32_string = U"🍄🍅🍆🍌"'%ns,
+                '(%s::u32string_view) u32_empty = U""'%ns,
                 '(%s::basic_string<unsigned char, %s::char_traits<unsigned char>, '
-                '%s::allocator<unsigned char> >) uchar = "aaaaa"'%(ns,ns,ns),
-                '(%s::string *) null_str = nullptr'%ns,
+                '%s::allocator<unsigned char> >) uchar_source = "aaaaaaaaaa"'%(ns,ns,ns),
+                '(%s::basic_string_view<unsigned char, %s::char_traits<unsigned char> >) uchar = "aaaaa"'%(ns,ns),
+                '(%s::string_view *) null_str = nullptr'%ns,
         ])
-
-        # The test assumes that std::string is in its cap-size-data layout.
-        is_alternate_layout = ('arm' in self.getArchitecture()) and self.platformIsDarwin()
-        if is_64_bit and not is_alternate_layout:
-            self.expect("frame variable garbage1", substrs=['garbage1 = Summary Unavailable'])
-            self.expect("frame variable garbage2", substrs=[r'garbage2 = "\xfa\xfa\xfa\xfa"'])
-            self.expect("frame variable garbage3", substrs=[r'garbage3 = "\xf0\xf0"'])
-            self.expect("frame variable garbage4", substrs=['garbage4 = Summary Unavailable'])
-            self.expect("frame variable garbage5", substrs=['garbage5 = Summary Unavailable'])

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/string_view/main.cpp

+#include <string>
+#include <stdint.h>
+#include <string_view>
+
+int main()
+{
+    std::wstring_view wempty(L"");
+    std::wstring_view s(L"hello world! מזל טוב!");
+    std::wstring_view S(L"!!!!");
+    std::string_view empty("");
+    std::string q_source = "hello world";
+    std::string_view q(q_source);
+    std::string_view Q("quite a long std::strin with lots of info inside it");
+    std::string_view TheVeryLongOne("1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890someText1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890");
+    std::string_view IHaveEmbeddedZeros("a\0b\0c\0d",7);
+    std::wstring_view IHaveEmbeddedZerosToo(L"hello world!\0てざ ル゜䋨ミ㠧槊 きゅへ狦穤襩 じゃ馩リョ 䤦監", 38);
+    std::u16string_view u16_string(u"ß水氶");
+    std::u16string_view u16_empty(u"");
+    std::u32string_view u32_string(U"🍄🍅🍆🍌");
+    std::u32string_view u32_empty(U"");
+    std::basic_string<unsigned char> uchar_source(10, 'a');
+    std::basic_string_view<unsigned char> uchar(uchar_source.data(), 5);
+    std::string_view *null_str = nullptr;
+    
+    q_source[0] = 'H'; // Set break point at this line.
+    return 0;
+}