[libcxx-commits] [libcxx] [lldb] Make std::pair pretty-printer ABI-independent (PR #201768)

[via libcxx-commits]

https://github.com/aokblast created https://github.com/llvm/llvm-project/pull/201768

std::pair is printed explicitly instead of relying on GDB's default struct formatting to keep output stable across ABI configurations.

With _LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR (default on some platforms, e.g. FreeBSD), std::pair gains an empty __non_trivially_copyable_base base class. GDB would otherwise render this as <...__non_trivially_copyable_base<...>> = {<No data fields>}, which makes output ABI-dependent.

Only first and second are meaningful, so print them directly.

>From b6f30f72a8b7f67c8555e9b12c3f7cf13d7175b9 Mon Sep 17 00:00:00 2001
From: aokblast <aokblast at FreeBSD.org>
Date: Fri, 5 Jun 2026 15:26:41 +0800
Subject: [PATCH] [lldb] Make std::pair pretty-printer ABI-independent

std::pair is printed explicitly instead of relying on GDB's default
struct formatting to keep output stable across ABI configurations.

With _LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR (default on
some platforms, e.g. FreeBSD), std::pair gains an empty
__non_trivially_copyable_base base class. GDB would otherwise render
this as <...__non_trivially_copyable_base<...>> = {<No data fields>},
which makes output ABI-dependent.

Only first and second are meaningful, so print them directly.
---
 libcxx/utils/gdb/libcxx/printers.py | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/libcxx/utils/gdb/libcxx/printers.py b/libcxx/utils/gdb/libcxx/printers.py
index ccaa6e9a019e8..9c9ecb245271a 100644
--- a/libcxx/utils/gdb/libcxx/printers.py
+++ b/libcxx/utils/gdb/libcxx/printers.py
@@ -182,6 +182,25 @@ def children(self):
             return iter(())
         return self._Children(self.val)
 
+class StdPairPrinter(object):
+    """Print a std::pair.
+
+    Print std::pair explicitly instead of relying on GDB's default struct
+    formatting. Some ABI configurations (e.g.
+    _LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR, enabled by default on
+    FreeBSD) add an empty __non_trivially_copyable_base base class to
+    std::pair. GDB renders this implementation detail as
+    '<...__non_trivially_copyable_base<...>> = {<No data fields>}', which makes
+    the output ABI-dependent. Only 'first' and 'second' are meaningful, so
+    print just those members.
+    """
+
+    def __init__(self, val):
+        self.val = val
+
+    def children(self):
+        return iter([("first", self.val["first"]), ("second", self.val["second"])])
+
 class StdStringPrinter(object):
     """Print a std::string."""
 
@@ -901,6 +920,7 @@ def __init__(self, name):
             "basic_string": StdStringPrinter,
             "string": StdStringPrinter,
             "string_view": StdStringViewPrinter,
+            "pair": StdPairPrinter,
             "tuple": StdTuplePrinter,
             "unique_ptr": StdUniquePtrPrinter,
             "shared_ptr": StdSharedPointerPrinter,