[Lldb-commits] [lldb] [lldb][test] Fix libstdc++ std::variant formatter for empty variant (PR #147283)

[Michael Buch via lldb-commits]

https://github.com/Michael137 updated https://github.com/llvm/llvm-project/pull/147283

>From be3eb2431b0649ce2730a4cf832dc474e262f49e Mon Sep 17 00:00:00 2001
From: Michael Buch <michaelbuch12 at gmail.com>
Date: Mon, 7 Jul 2025 12:40:37 +0100
Subject: [PATCH 1/2] [lldb][test] Fix libstdc++ std::variant formatter for
 empty variant

Instead of using the byte-size to make a guess at what the
`std::variant_npos` value is, just look it up in debug-info.

Unblocks https://github.com/llvm/llvm-project/pull/147253
---
 lldb/examples/synthetic/gnu_libstdcpp.py            | 13 ++++---------
 .../variant/TestDataFormatterLibStdcxxVariant.py    |  5 -----
 .../data-formatter-stl/libstdcpp/variant/main.cpp   |  1 +
 3 files changed, 5 insertions(+), 14 deletions(-)

diff --git a/lldb/examples/synthetic/gnu_libstdcpp.py b/lldb/examples/synthetic/gnu_libstdcpp.py
index 20b9488af5597..96b11322db775 100644
--- a/lldb/examples/synthetic/gnu_libstdcpp.py
+++ b/lldb/examples/synthetic/gnu_libstdcpp.py
@@ -889,17 +889,12 @@ def VariantSummaryProvider(valobj, dict):
     if not (index_obj and index_obj.IsValid() and data_obj and data_obj.IsValid()):
         return "<Can't find _M_index or _M_u>"
 
-    def get_variant_npos_value(index_byte_size):
-        if index_byte_size == 1:
-            return 0xFF
-        elif index_byte_size == 2:
-            return 0xFFFF
-        else:
-            return 0xFFFFFFFF
+    npos = valobj.GetTarget().FindFirstGlobalVariable("std::variant_npos")
+    if not npos:
+        return "<Can't find std::variant_npos sentinel>"
 
-    npos_value = get_variant_npos_value(index_obj.GetByteSize())
     index = index_obj.GetValueAsUnsigned(0)
-    if index == npos_value:
+    if index == npos.GetValueAsUnsigned(0):
         return " No Value"
 
     # Strip references and typedefs.
diff --git a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libstdcpp/variant/TestDataFormatterLibStdcxxVariant.py b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libstdcpp/variant/TestDataFormatterLibStdcxxVariant.py
index 394e221809f7c..c3325c9e73cb9 100644
--- a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libstdcpp/variant/TestDataFormatterLibStdcxxVariant.py
+++ b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libstdcpp/variant/TestDataFormatterLibStdcxxVariant.py
@@ -2,7 +2,6 @@
 Test lldb data formatter for LibStdC++ std::variant.
 """
 
-
 import lldb
 from lldbsuite.test.decorators import *
 from lldbsuite.test.lldbtest import *
@@ -62,9 +61,6 @@ def test_with_run_command(self):
             "frame variable v3",
             substrs=["v3 =  Active Type = char  {", "Value = 'A'", "}"],
         )
-        """
-        TODO: temporarily disable No Value tests as they seem to fail on ubuntu/debian
-        bots. Pending reproduce and investigation.
 
         self.expect("frame variable v_no_value", substrs=["v_no_value =  No Value"])
 
@@ -72,7 +68,6 @@ def test_with_run_command(self):
             "frame variable v_many_types_no_value",
             substrs=["v_many_types_no_value =  No Value"],
         )
-        """
 
     @add_test_categories(["libstdcxx"])
     def test_invalid_variant_index(self):
diff --git a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libstdcpp/variant/main.cpp b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libstdcpp/variant/main.cpp
index 36e0f74f831f8..acb07d5700b8a 100644
--- a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libstdcpp/variant/main.cpp
+++ b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libstdcpp/variant/main.cpp
@@ -49,6 +49,7 @@ int main() {
   v1 = 12; // v contains int
   v1_typedef = v1;
   v_v1 = v1;
+  v1_typedef = v1;
   int i = std::get<int>(v1);
   printf("%d\n", i); // break here
 

>From 59518c7f14a6beeb29ebdc8b33eeede9176418b3 Mon Sep 17 00:00:00 2001
From: Michael Buch <michaelbuch12 at gmail.com>
Date: Mon, 7 Jul 2025 12:47:28 +0100
Subject: [PATCH 2/2] fixup! revert redundant test change

---
 .../data-formatter/data-formatter-stl/libstdcpp/variant/main.cpp | 1 -
 1 file changed, 1 deletion(-)

diff --git a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libstdcpp/variant/main.cpp b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libstdcpp/variant/main.cpp
index acb07d5700b8a..36e0f74f831f8 100644
--- a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libstdcpp/variant/main.cpp
+++ b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libstdcpp/variant/main.cpp
@@ -49,7 +49,6 @@ int main() {
   v1 = 12; // v contains int
   v1_typedef = v1;
   v_v1 = v1;
-  v1_typedef = v1;
   int i = std::get<int>(v1);
   printf("%d\n", i); // break here