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[LLDB] Fix MS STL variant with non-trivial types #171489

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[LLDB] Fix MS STL variant with non-trivial types #171489

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3860c0b
[LLDB] Fix MS STL `variant` with non-trivial types and PDB
Nerixyz Nov 6, 2025
ae5ecea
fix: comments
Nerixyz Dec 10, 2025
0ccc47b
Merge remote-tracking branch 'upstream/main' into fix/ms-stl-variant
Nerixyz Dec 11, 2025
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16 changes: 11 additions & 5 deletions lldb/source/Plugins/Language/CPlusPlus/MsvcStlVariant.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -67,12 +67,18 @@ std::optional<int64_t> GetIndexValue(ValueObject &valobj) {
ValueObjectSP GetNthStorage(ValueObject &outer, int64_t index) {
// We need to find the std::_Variant_storage base class.

// -> std::_SMF_control (typedef to std::_Variant_base)
ValueObjectSP container_sp = outer.GetSP()->GetChildAtIndex(0);
if (!container_sp)
// Navigate "down" to std::_Variant_base by finding the holder of "_Which".
// This might be down a few levels if a variant member isn't trivially
// destructible/copyable/etc.
ValueObjectSP which_sp = outer.GetChildMemberWithName("_Which");
Comment on lines +70 to +73
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@Michael137 Michael137 Dec 11, 2025

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Is this related to making it run with PDB? Or is this about handling more kinds of variant layouts in general? Is that where the additional test-case comes from? If it's the latter I'd prefer it if we split it into a separate PR

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@Michael137 Michael137 Dec 11, 2025

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Oh the title of this PR answers my question. Yea probably better to do the two changes separately

if (!which_sp)
return nullptr;
ValueObject *parent = which_sp->GetParent();
if (!parent)
return nullptr;
// -> std::_Variant_storage
container_sp = container_sp->GetChildAtIndex(0);

// Now go to std::_Variant_storage.
ValueObjectSP container_sp = parent->GetChildAtIndex(0);
if (!container_sp)
return nullptr;

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21 changes: 21 additions & 0 deletions ...nalities/data-formatter/data-formatter-stl/generic/variant/TestDataFormatterStdVariant.py
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Expand Up @@ -50,6 +50,14 @@ def cleanup():
],
)

self.expect_expr(
"v4",
result_summary=" Active Type = int ",
result_children=[
ValueCheck(name="Value", value="4"),
],
)

lldbutil.continue_to_breakpoint(self.process, bkpt)

self.expect(
Expand All @@ -69,6 +77,19 @@ def cleanup():
substrs=["v3 = Active Type = char {", "Value = 'A'", "}"],
)

string_name = (
"std::basic_string<char, std::char_traits<char>, std::allocator<char>>"
if self.getDebugInfo() == "pdb"
else "std::basic_string<char>"
)
self.expect_expr(
"v4",
result_summary=f" Active Type = {string_name} ",
result_children=[
ValueCheck(name="Value", summary='"a string"'),
],
)

self.expect("frame variable v_valueless", substrs=["v_valueless = No Value"])

self.expect(
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5 changes: 5 additions & 0 deletions lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/variant/main.cpp
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Expand Up @@ -49,6 +49,8 @@ int main() {
S>
v_300_types_valueless;

std::variant<int, bool, std::string> v4 = 4;

v_valueless = 5;
v_300_types_valueless.emplace<0>(10);

Expand All @@ -70,6 +72,9 @@ int main() {
// state when we change its value.
v1 = 2.0;
d = std::get<double>(v1);

v4 = "a string";

printf("%f\n", d); // break here

try {
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