I'm reporting an issue with printers.py at https://github.com/llvm/llvm-project/blob/main/libcxx/utils/gdb/libcxx/printers.py.

When using GDB's MI mode and enabling pretty-printing, container contents aren't displayed for the following container types when they contain two or more elements:

• std::list
• std::deque
• std::set
• std::unordered_set
• std::map
• std::unordered_map

This issue affects IDEs such as VSCode's C++ extension that use GDB's MI mode. The issue doesn't occur when using GDB in normal mode.

The issue seems to be caused by duplicate keys in printers.py. For example, for std::deque, the key is always an empty string in the following line:
https://github.com/llvm/llvm-project/blob/main/libcxx/utils/gdb/libcxx/printers.py#L479
(Note that in printers.py for libstdc++, sequential numbers with square brackets [0], [1], [2], etc. are used as keys.)

According to GDB's documentation (https://sourceware.org/gdb/onlinedocs/gdb/Pretty-Printing-API.html), duplicate children keys aren't explicitly forbidden, but in MI mode, they don't seem to work as expected.

Here are the steps to reproduce:

1. Build the following code with libc++ with debug info:

#include <list>

int main() {
    std::list<int> l {0, 1, 2};

    return 0;
}

2. Run the following commands in the terminal (the second and subsequent lines are input to GDB):

$ gdb -interpreter=mi ./a.out
-enable-pretty-printing
b a.cpp:6
r
-var-create l * l
-var-list-children l

The expected result should be a list of children. However, the following error is returned instead:

^error,msg="Duplicate variable object name"

Additionally, here is a screenshot of the issue in VSCode. The contents of the std::list is not visible:

Thank you.