<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/62340>62340</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [libc++] Pretty printing not working for some containers in GDB's MI mode and IDEs
        </td>
    </tr>

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

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

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

<pre>
    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](https://sourceware.org/gdb/onlinedocs/gdb/GDB_002fMI.html) 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:

```c++
#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
-break-insert a.cpp:6
-exec-run
-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.
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJy8VtuO47gR_Rr6pSBBoizZevCDL-PdAbLBIFkkjwtKLFtMU6SWl3b774OS5Et7ZzYIAgRouG1SVWKdc-oUhffqbBA3rNyx8rAQMXTWbTrlRBBeLBorr5uvjK96cDhYF5Q5gzCgvI8IFxU6YFU2OGUCOp8OV1ZlIAJ0IQyeFVvGj4wfzyp0sUlb2zN-1Pr99i8ZnP0XtoHxY6Ntw_ixF8rQpmrajw_GjzEo7SmDbJ6Xn16YsuzAsu30-c8ODURPh_zpsGN85YGVu1--Qm8lsvLA-PrzybyNrsWLcJhad76_yBqtDErbPt7902H3W5bx0y9f0y70mvEahJGARjSa3jc4DOGajCdT5sz4HlprglAG3fgNTfAgHBrGVwGk8oMWV5Rwsg5Ch3CyWtsLpXrEheuAHi5UVejwetuBcLFgHfTWIaDGnnJTTU9QJESMD5KWi61WPrAq-96WxN8j_mDP44-iorFOokP524-f6cXwH6Ofn5k-f-2Un_UlTidsg4evhy8efGw7EB7-8fc9kUnc7hnfMb4D_AhovLKEkggQPd7pn7lP4dcO56zSop9IsG0b3QTvXTSgDBjreqGnwM9Hu-XwiL2HYKFBaEX0KKG5goyDVq0ICG949ZTpD82RwtE6wA_RDxpJJET_d-ng-1EWb3gF5UHoi7h6aj3sh3AFHxwdWJkX7ZBu70r4_3Uh48Vflqt6Bouv_2oDTmR8D4SpaL5lfKtV44NsJyKnJarcEwomKKHBxL5B5yez8b9H4RAaJ9o3DJ5Ss3KXUWtPkE0L-esCfyxgaFPqQxhZE37kKmW8fmZ627bWSQI02LuWpG0jtZoIJLX_wUu-TV7xbfaKZPvtbip0woeM2k5p6dBMerqbB37QAyroKyHZKClpYw9NHPG--d2koCtIO4WRaKmei3VvVDh-DNgGlJ80_jM6HOEhXfmAwyhzh4OzMrb44jJ5CruotPyDg8l5OpBY5i4df0tsIsn2ZF8yETvj300Ls5QKZVodJQIr9qOLFV-ew5QJMMl1TZbMVnMgfLa-Yq8MhYKmR0Yd5PTB2erAit1zRgAAhyE6A9lja3V4OeZzCE_hb_G1E1vb98JIf-vRgK5XRmgSzogtttbIcYj42MyCH_t3ZBqUGWK4y69-wPVyAr6Es2wgGRuMphA6Vhx6BSnjR5HaGGYHHkcVJq-DatpsHIq3RBmPLoBI22Fgxba6RX5gm7ho5p_vwiWtQxIoVbMF_bRBcCd33eo_QY3c9CZBcOijDuA7G7UkVxVAmcCe7k2Qws_2gu_obtb4wBqds45sciIOJSjjAwr5Q9TKL2MM4_ven1lxYJwf7m33LpwirMA2ZIxgRI-M8z-pZSulIlcQWl_peB11Edk2-NYhGt_ZsZZwnyDKzJNsGk33G8L80Cf5UiZjA7wrrxr91IM8Z-VO9eL83ctN9OiScdenk_nTyvymeQ4UVZbxvKoYP_JimVdFna8TXNd1K-tTIk-rMlkWZZ4IrIrklNfFulmKU7VepQNdcurPhArzBlcb04XcFLIuarHATV6teVHndV4tus2KV_W6bJq6zKv1Kq9P69WpEAUv2tWyyYrlQm14xotsycusyMq8Stt6ndVlVuFyfVrnecOWGfZC6ZRGFxntYsRzU_FimS20aFD78TbLucHLBDZxVx4WbjOOuyaePVtmBKx_ZAkq6PEa_HAsVh5gsmq4dctIA_knfacp5m2Pjwvb2OwvV4-xw-kGs4hOb_7rkTwWQKNjLPDfAQAA__-8rKZH">