[lldb][DataFormatter] Allow std::string formatters to match against custom allocators #156050

Michael137 · 2025-08-29T16:02:24Z

This came up in #155691.

For std::basic_string our formatter matching logic required the allocator template parameter to be a std::allocator. There is no compelling reason (that I know of) why this would be required for us to apply the existing formatter to the string. We don't check the allocator parameter for other STL containers either. This meant that std::string that used custom allocators wouldn't be formatted. This patch relaxes the regex for basic_string.

…ustom allocators This came up in llvm#155691. For `std::basic_string` our formatter matching logic required the allocator template parameter to be a `std::allocator`. There is no compelling reason (that I know of) why this would be required for us to apply the existing formatter to the string. We don't check the `allocator` parameter for other STL containers either. This meant that `std::string` that used custom allocators wouldn't be formatted. This patch relaxes the regex for `basic_string`.

github-actions · 2025-09-04T12:24:09Z

✅ With the latest revision this PR passed the C/C++ code formatter.

llvmbot · 2025-09-05T06:39:52Z

@llvm/pr-subscribers-lldb

Author: Michael Buch (Michael137)

Changes

This came up in #155691.

For std::basic_string our formatter matching logic required the allocator template parameter to be a std::allocator. There is no compelling reason (that I know of) why this would be required for us to apply the existing formatter to the string. We don't check the allocator parameter for other STL containers either. This meant that std::string that used custom allocators wouldn't be formatted. This patch relaxes the regex for basic_string.

Full diff: https://github.com/llvm/llvm-project/pull/156050.diff

3 Files Affected:

(modified) lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp (+17-33)
(modified) lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/string/TestDataFormatterStdString.py (+6)
(modified) lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/string/main.cpp (+35)

diff --git a/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp b/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
index c39b529f7305a..277de8f444828 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
@@ -749,31 +749,27 @@ static void LoadLibCxxFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
                 lldb_private::formatters::LibcxxStringSummaryProviderASCII,
                 "std::string summary provider",
                 "^std::__[[:alnum:]]+::basic_string<char, "
-                "std::__[[:alnum:]]+::char_traits<char>, "
-                "std::__[[:alnum:]]+::allocator<char> >$",
+                "std::__[[:alnum:]]+::char_traits<char>,.*>$",
                 stl_summary_flags, true);
   AddCXXSummary(cpp_category_sp,
                 lldb_private::formatters::LibcxxStringSummaryProviderASCII,
                 "std::string summary provider",
                 "^std::__[[:alnum:]]+::basic_string<unsigned char, "
-                "std::__[[:alnum:]]+::char_traits<unsigned char>, "
-                "std::__[[:alnum:]]+::allocator<unsigned char> >$",
+                "std::__[[:alnum:]]+::char_traits<unsigned char>,.*>$",
                 stl_summary_flags, true);
 
   AddCXXSummary(cpp_category_sp,
                 lldb_private::formatters::LibcxxStringSummaryProviderUTF16,
                 "std::u16string summary provider",
                 "^std::__[[:alnum:]]+::basic_string<char16_t, "
-                "std::__[[:alnum:]]+::char_traits<char16_t>, "
-                "std::__[[:alnum:]]+::allocator<char16_t> >$",
+                "std::__[[:alnum:]]+::char_traits<char16_t>,.*>$",
                 stl_summary_flags, true);
 
   AddCXXSummary(cpp_category_sp,
                 lldb_private::formatters::LibcxxStringSummaryProviderUTF32,
                 "std::u32string summary provider",
                 "^std::__[[:alnum:]]+::basic_string<char32_t, "
-                "std::__[[:alnum:]]+::char_traits<char32_t>, "
-                "std::__[[:alnum:]]+::allocator<char32_t> >$",
+                "std::__[[:alnum:]]+::char_traits<char32_t>,.*>$",
                 stl_summary_flags, true);
 
   AddCXXSummary(cpp_category_sp,
@@ -784,8 +780,7 @@ static void LoadLibCxxFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
                 lldb_private::formatters::LibcxxWStringSummaryProvider,
                 "std::wstring summary provider",
                 "^std::__[[:alnum:]]+::basic_string<wchar_t, "
-                "std::__[[:alnum:]]+::char_traits<wchar_t>, "
-                "std::__[[:alnum:]]+::allocator<wchar_t> >$",
+                "std::__[[:alnum:]]+::char_traits<wchar_t>,.*>$",
                 stl_summary_flags, true);
 
   AddCXXSummary(cpp_category_sp,
@@ -1301,24 +1296,16 @@ static void RegisterStdStringSummaryProvider(
 
   category_sp->AddTypeSummary(makeSpecifier(string_ty), summary_sp);
 
-  // std::basic_string<char>
   category_sp->AddTypeSummary(
       makeSpecifier(llvm::formatv("std::basic_string<{}>", char_ty).str()),
       summary_sp);
-  // std::basic_string<char,std::char_traits<char>,std::allocator<char> >
-  category_sp->AddTypeSummary(
-      makeSpecifier(llvm::formatv("std::basic_string<{0},std::char_traits<{0}>,"
-                                  "std::allocator<{0}> >",
-                                  char_ty)
-                        .str()),
-      summary_sp);
-  // std::basic_string<char, std::char_traits<char>, std::allocator<char> >
+
   category_sp->AddTypeSummary(
-      makeSpecifier(
-          llvm::formatv("std::basic_string<{0}, std::char_traits<{0}>, "
-                        "std::allocator<{0}> >",
+      std::make_shared<lldb_private::TypeNameSpecifierImpl>(
+          llvm::formatv("^std::basic_string<{0}, ?std::char_traits<{0}>,.*>$",
                         char_ty)
-              .str()),
+              .str(),
+          eFormatterMatchRegex),
       summary_sp);
 }
 
@@ -1363,20 +1350,17 @@ static void LoadLibStdcppFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
   cpp_category_sp->AddTypeSummary("std::__cxx11::string", eFormatterMatchExact,
                                   string_summary_sp);
   cpp_category_sp->AddTypeSummary(
-      "std::__cxx11::basic_string<char, std::char_traits<char>, "
-      "std::allocator<char> >",
-      eFormatterMatchExact, string_summary_sp);
-  cpp_category_sp->AddTypeSummary("std::__cxx11::basic_string<unsigned char, "
-                                  "std::char_traits<unsigned char>, "
-                                  "std::allocator<unsigned char> >",
-                                  eFormatterMatchExact, string_summary_sp);
+      "^std::__cxx11::basic_string<char, std::char_traits<char>,.*>$",
+      eFormatterMatchRegex, string_summary_sp);
+  cpp_category_sp->AddTypeSummary("^std::__cxx11::basic_string<unsigned char, "
+                                  "std::char_traits<unsigned char>,.*>$",
+                                  eFormatterMatchRegex, string_summary_sp);
 
   cpp_category_sp->AddTypeSummary("std::__cxx11::wstring", eFormatterMatchExact,
                                   string_summary_sp);
   cpp_category_sp->AddTypeSummary(
-      "std::__cxx11::basic_string<wchar_t, std::char_traits<wchar_t>, "
-      "std::allocator<wchar_t> >",
-      eFormatterMatchExact, string_summary_sp);
+      "^std::__cxx11::basic_string<wchar_t, std::char_traits<wchar_t>,.*>$",
+      eFormatterMatchRegex, string_summary_sp);
 
   SyntheticChildren::Flags stl_synth_flags;
   stl_synth_flags.SetCascades(true).SetSkipPointers(false).SetSkipReferences(
diff --git a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/string/TestDataFormatterStdString.py b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/string/TestDataFormatterStdString.py
index fec20bae997ef..6a27b5d2f0780 100644
--- a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/string/TestDataFormatterStdString.py
+++ b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/string/TestDataFormatterStdString.py
@@ -80,6 +80,8 @@ def cleanup():
                 '(%s::string) Q = "quite a long std::strin with lots of info inside it"'
                 % ns,
                 "(%s::string *) null_str = nullptr" % ns,
+                '(CustomString) custom_str = "hello!"',
+                '(CustomWString) custom_wstr = L"hello!"',
             ],
         )
 
@@ -143,6 +145,10 @@ def do_test_multibyte(self):
                 '(%s::u16string) u16_empty = u""' % ns,
                 '(%s::u32string) u32_string = U"🍄🍅🍆🍌"' % ns,
                 '(%s::u32string) u32_empty = U""' % ns,
+                '(CustomStringU16) custom_u16 = u"ß水氶"',
+                '(CustomStringU16) custom_u16_empty = u""',
+                '(CustomStringU32) custom_u32 = U"🍄🍅🍆🍌"',
+                '(CustomStringU32) custom_u32_empty = U""',
             ],
         )
 
diff --git a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/string/main.cpp b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/string/main.cpp
index f22c890861d01..577b78e35fc1f 100644
--- a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/string/main.cpp
+++ b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/string/main.cpp
@@ -1,6 +1,33 @@
+#include <cstdlib>
 #include <stdint.h>
 #include <string>
 
+template <typename T> struct CustomAlloc {
+  using value_type = T;
+  using pointer = value_type *;
+  using const_pointer = const value_type *;
+  using size_type = std::size_t;
+
+  pointer allocate(size_type n) { return (T *)malloc(n * sizeof(T)); }
+
+  void deallocate(pointer p, size_type) {
+    if (p)
+      free(p);
+  }
+};
+
+using CustomString =
+    std::basic_string<char, std::char_traits<char>, CustomAlloc<char>>;
+
+using CustomWString =
+    std::basic_string<wchar_t, std::char_traits<wchar_t>, CustomAlloc<wchar_t>>;
+
+using CustomStringU16 = std::basic_string<char16_t, std::char_traits<char16_t>,
+                                          CustomAlloc<char16_t>>;
+
+using CustomStringU32 = std::basic_string<char32_t, std::char_traits<char32_t>,
+                                          CustomAlloc<char32_t>>;
+
 size_t touch_string(std::string &in_str) {
   return in_str.size(); // Break here to look at bad string
 }
@@ -99,8 +126,16 @@ int main() {
   std::string *pq = &q;
   std::string *pQ = &Q;
 
+  CustomString custom_str("hello!");
+  CustomWString custom_wstr(L"hello!");
+  CustomStringU16 custom_u16(u16_string.c_str());
+  CustomStringU16 custom_u16_empty(u"");
+  CustomStringU32 custom_u32(u32_string.c_str());
+  CustomStringU32 custom_u32_empty(U"");
+
   S.assign(L"!!!!!"); // Set break point at this line.
   std::string *not_a_string = (std::string *)0x0;
   touch_string(*not_a_string);
+
   return 0;
 }

labath

We could potentially also drop the char_traits thingy.

Michael137 · 2025-09-05T08:24:41Z

We could potentially also drop the char_traits thingy.

Yea was thinking the same. Might do that as a follow-up. That seems like a more niche use-case, but probably something people do

Michael137 · 2025-09-05T08:25:15Z

/cherry-pick 4b362f1

llvmbot · 2025-09-05T08:31:45Z

/pull-request #157048

…ustom allocators (llvm#156050) This came up in llvm#155691. For `std::basic_string` our formatter matching logic required the allocator template parameter to be a `std::allocator`. There is no compelling reason (that I know of) why this would be required for us to apply the existing formatter to the string. We don't check the `allocator` parameter for other STL containers either. This meant that `std::string` that used custom allocators wouldn't be formatted. This patch relaxes the regex for `basic_string`. (cherry picked from commit 4b362f1)

Michael137 mentioned this pull request Aug 29, 2025

Xcode and Android lldb don't find correct formatter if type is in C++ struct/class #155691

Open

Michael137 force-pushed the lldb/custom-string-alloc-formats branch from 88ec358 to af0f77f Compare September 1, 2025 12:23

fixup! fix test compilation with libstdc++

a509c8c

Michael137 force-pushed the lldb/custom-string-alloc-formats branch from ca0d7c8 to a509c8c Compare September 4, 2025 14:56

fixup! fix test compilation with libstdc++

1ef9645

Michael137 marked this pull request as ready for review September 5, 2025 06:39

Michael137 requested a review from JDevlieghere as a code owner September 5, 2025 06:39

llvmbot added the lldb label Sep 5, 2025

Michael137 requested review from adrian-prantl and labath September 5, 2025 06:39

labath approved these changes Sep 5, 2025

View reviewed changes

Michael137 merged commit 4b362f1 into llvm:main Sep 5, 2025
12 checks passed

Michael137 deleted the lldb/custom-string-alloc-formats branch September 5, 2025 08:24

Michael137 added this to the LLVM 21.x Release milestone Sep 5, 2025

github-project-automation bot added this to LLVM Release Status Sep 5, 2025

github-project-automation bot moved this to Needs Triage in LLVM Release Status Sep 5, 2025

llvmbot moved this from Needs Triage to Done in LLVM Release Status Sep 5, 2025

dwblaikie mentioned this pull request Sep 16, 2025

port 5b4819e to release #159209

Open

jhuber6 mentioned this pull request Sep 17, 2025

[LLVM] Update CUDA ELF flags for their new ABI #159451

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