[lldb][DataFormatters] Support pretty printing std::string when built with -funsigned-char.

Summary:
When built w/ `-funsigned-char`, `std::string` becomes equivalent to `std::basic_string<unsigned char>`, causing these formatters to not match. This patch adds overloads for both libstdc++ and libc++ string formatters that accepts unsigned char.

Motivated by the following example:

```
$ cat pretty_print.cc

template <typename T>
void print_val(T s) {
  std::cerr << s << '\n';  // Set a breakpoint here!
}

int main() {
  std::string val = "hello";
  print_val(val);
  return 0;
}
$ clang++ -stdlib=libc++ -funsigned-char -fstandalone-debug -g pretty_print.cc
$ lldb ./a.out -b -o 'b pretty_print.cc:6' -o r -o 'fr v'
...
(lldb) fr v
(std::__1::basic_string<unsigned char, std::__1::char_traits<unsigned char>, std::__1::allocator<unsigned char> >) s = {
  __r_ = {
    std::__1::__compressed_pair_elem<std::__1::basic_string<unsigned char, std::__1::char_traits<unsigned char>, std::__1::allocator<unsigned char> >::__rep, 0, false> = {
      __value_ = {
         = {
          __l = (__cap_ = 122511465736202, __size_ = 0, __data_ = 0x0000000000000000)
          __s = {
             = (__size_ = '\n', __lx = '\n')
            __data_ = {
              [0] = 'h'
              [1] = 'e'
              [2] = 'l'
              [3] = 'l'
              [4] = 'o'
              [5] = '\0'
...
```

Reviewers: labath, JDevlieghere, shafik

Subscribers: christof, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D70517

Author: rupprecht

lldb/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/string/TestDataFormatterLibcxxString.py

@@ -74,8 +74,10 @@ def cleanup():
                 '(%s::u16string) u16_empty = ""'%ns,
                 '(%s::u32string) u32_string = U"🍄🍅🍆🍌"'%ns,
                 # FIXME: This should have a 'U' prefix.
-                '(%s::u32string) u32_empty = ""'%ns
-])
+                '(%s::u32string) u32_empty = ""'%ns,
+                '(%s::basic_string<unsigned char, %s::char_traits<unsigned char>, '
+                '%s::allocator<unsigned char> >) uchar = "aaaaa"'%(ns,ns,ns),
+        ])
 
         self.runCmd("n")
 
@@ -107,4 +109,8 @@ def cleanup():
                 '(%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_string = U"🍄🍅🍆🍌"'%ns,
+                '(%s::u32string) u32_empty = ""'%ns,
+                '(%s::basic_string<unsigned char, %s::char_traits<unsigned char>, '
+                '%s::allocator<unsigned char> >) uchar = "aaaaa"'%(ns,ns,ns),
+        ])

lldb/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/string/main.cpp

@@ -16,6 +16,7 @@ int main()
     std::u16string u16_empty(u"");
     std::u32string u32_string(U"🍄🍅🍆🍌");
     std::u32string u32_empty(U"");
+    std::basic_string<unsigned char> uchar(5, 'a');
     S.assign(L"!!!!!"); // Set break point at this line.
     return 0;
 }

lldb/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libstdcpp/string/TestDataFormatterStdString.py

@@ -59,26 +59,28 @@ def cleanup():
         var_empty = self.frame().FindVariable('empty')
         var_q = self.frame().FindVariable('q')
         var_Q = self.frame().FindVariable('Q')
+        var_uchar = self.frame().FindVariable('uchar')
 
         # TODO: This is currently broken
-        # self.assertTrue(var_wempty.GetSummary() == 'L""', "wempty summary wrong")
-        self.assertTrue(
-            var_s.GetSummary() == 'L"hello world! מזל טוב!"',
+        # self.assertEqual(var_wempty.GetSummary(), 'L""', "wempty summary wrong")
+        self.assertEqual(
+            var_s.GetSummary(), 'L"hello world! מזל טוב!"',
             "s summary wrong")
-        self.assertTrue(var_S.GetSummary() == 'L"!!!!"', "S summary wrong")
-        self.assertTrue(
-            var_mazeltov.GetSummary() == 'L"מזל טוב"',
+        self.assertEqual(var_S.GetSummary(), 'L"!!!!"', "S summary wrong")
+        self.assertEqual(
+            var_mazeltov.GetSummary(), 'L"מזל טוב"',
             "mazeltov summary wrong")
-        self.assertTrue(var_empty.GetSummary() == '""', "empty summary wrong")
-        self.assertTrue(
-            var_q.GetSummary() == '"hello world"',
+        self.assertEqual(var_empty.GetSummary(), '""', "empty summary wrong")
+        self.assertEqual(
+            var_q.GetSummary(), '"hello world"',
             "q summary wrong")
-        self.assertTrue(
-            var_Q.GetSummary() == '"quite a long std::strin with lots of info inside it"',
+        self.assertEqual(
+            var_Q.GetSummary(), '"quite a long std::strin with lots of info inside it"',
             "Q summary wrong")
+        self.assertEqual(var_uchar.GetSummary(), '"aaaaa"', "u summary wrong")
 
         self.runCmd("next")
 
-        self.assertTrue(
-            var_S.GetSummary() == 'L"!!!!!"',
+        self.assertEqual(
+            var_S.GetSummary(), 'L"!!!!!"',
             "new S summary wrong")

lldb/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libstdcpp/string/main.cpp

@@ -9,6 +9,7 @@ int main()
     std::string empty("");
     std::string q("hello world");
     std::string Q("quite a long std::strin with lots of info inside it");
+    std::basic_string<unsigned char> uchar(5, 'a');
     S.assign(L"!!!!!"); // Set break point at this line.
     return 0;
 }

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

@@ -425,6 +425,13 @@ static void LoadLibCxxFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
                             "std::__[[:alnum:]]+::char_traits<char>, "
                             "std::__[[:alnum:]]+::allocator<char> >$"),
                 stl_summary_flags, true);
+  AddCXXSummary(cpp_category_sp,
+                lldb_private::formatters::LibcxxStringSummaryProviderASCII,
+                "std::string summary provider",
+                ConstString("^std::__[[:alnum:]]+::basic_string<unsigned char, "
+                            "std::__[[:alnum:]]+::char_traits<unsigned char>, "
+                            "std::__[[:alnum:]]+::allocator<unsigned char> >$"),
+                stl_summary_flags, true);
 
   AddCXXSummary(cpp_category_sp,
                 lldb_private::formatters::LibcxxStringSummaryProviderUTF16,
@@ -723,6 +730,10 @@ static void LoadLibStdcppFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
       ConstString("std::__cxx11::basic_string<char, std::char_traits<char>, "
                   "std::allocator<char> >"),
       cxx11_string_summary_sp);
+  cpp_category_sp->GetTypeSummariesContainer()->Add(
+      ConstString("std::__cxx11::basic_string<unsigned char, std::char_traits<unsigned char>, "
+                  "std::allocator<unsigned char> >"),
+      cxx11_string_summary_sp);
 
   // making sure we force-pick the summary for printing wstring (_M_p is a
   // wchar_t*)