<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/75936>75936</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            lldb test TestUniqueTypes4.py now fails on Windows
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          DavidSpickett
      </td>
    </tr>
</table>

<pre>
    `llvm-project\lldb\test\API\lang\cpp\unique-types4\TestUniqueTypes4.py` stopped working on Windows once https://github.com/llvm/llvm-project/commit/dd9587795811ba21e6ca6ad52b4531e17e6babd6 landed.

This patch also changed what the test looked for, so the fact that it was passing before doesn't mean as much as you'd think.

The problem now seems to be that for a program like the following:
```
namespace ns {

template <typename T> struct Foo {
  const static T value;
};

template <class T> const T Foo<T>::value = 99;

using FooDouble = Foo<double>;

} // namespace ns

ns::Foo<double> a;
ns::FooDouble f;

int main() {
  // Set breakpoint here
  return (int)a.value + (int)f.value;
}
```
When compiled with:
```
..\bin\clang++.exe main.cpp -o main.exe -fuse-ld=lld -gdwarf
```
(this results in there being DWARF info in main.exe, with an external PDB, this is expected and presumably supported because the test worked before)

LLDB on Windows cannot print the `::value` member.
```
(lldb) expression ns::FooDouble::value
(ror: Couldn't look up symbols:or <Unknown>...
(ns::Foo<double>::value
```
(there is some text corruption due to a log message mixed in there)

On Linux it works as expected:
```
./bin/clang++ -target aarch64-linux-gnu-eabi /tmp/test.cpp -o /tmp/test.o -gdwarf
```
```
(lldb) expression ns::FooDouble::value
(double) $0 = 0
```

The DWARF info has one maybe significant change.

Do this to get the DWARF if you aren't on Windows:
```
$ ./bin/clang++ -target arm64-pc-windows-msvc /tmp/test.cpp -o /tmp/test.o -gdwarf -c
```

`llvm-dwarfdump` of both shows that "value" is described but Windows uses `DW_TAG_member` and Linux uses `DW_TAG_variable`. However, each has a following `DW_TAG_variable` for "value" also. So maybe this doesn't matter at all.

Windows:
```
0x0000005a:       DW_TAG_member
 DW_AT_name  ("value")
                    DW_AT_type (0x00000085 "double")
                    DW_AT_decl_file ("/tmp/test.cpp")
                    DW_AT_decl_line     (4)
 DW_AT_external      (true)
 DW_AT_declaration   (true)
<...>
0x00000071:     DW_TAG_variable
 DW_AT_specification   (0x0000005a "value")
 DW_AT_location        (DW_OP_addr 0x0)
 DW_AT_linkage_name ("?value@?$Foo@N@ns@@2NA")
```
Linux:
```
0x0000003c: DW_TAG_variable
                    DW_AT_name  ("value")
 DW_AT_type  (0x00000057 "double")
 DW_AT_decl_file     ("/tmp/test.cpp")
 DW_AT_decl_line     (4)
                    DW_AT_external      (true)
 DW_AT_declaration   (true)
<...>
0x0000004d: DW_TAG_variable
                  DW_AT_specification   (0x0000003c "value")
                  DW_AT_location        (DW_OP_addrx 0x2)
 DW_AT_linkage_name ("_ZN2ns3FooIdE5valueE")
```

If I instead generate CodeView on Windows, it gets a bit further.

I wonder if perhaps the Windows build is treating this "value" as some constant that is never materialised, whereas Linux makes it a value we can easily read.

lldb can see information from the DWARF on Windows, just not the bit we want for this test:
```
(lldb) (lldb) p a
(ns::Foo<double>)  {}
(lldb) p f
(ns::FooDouble)  {}
(lldb) image lookup -t ns::FooDouble
Best match found in C:\Work\david.spickett\build\testprog\main.exe:
id = {0x00000066}, name = "ns::FooDouble", byte-size = 1, decl = main.cpp:9, compiler_type = "typedef ns::FooDouble"
     typedef 'ns::FooDouble': id = {0x00000048}, name = "Foo<double>", qualified = "ns::Foo<double>", byte-size = 1, decl = main.cpp:3, compiler_type = "template<> struct Foo<double> {
    static const double value;
}"
```
</pre>
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