<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/118191>118191</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Clang Language Server Crash When Using C++26 and Experimental Compile Options
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang
      </td>
    </tr>

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

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

<pre>
    ### Title: Clang Language Server Crash When Using C++26 and Experimental Compile Options

**Description:**

I encountered a crash with the Clang Language Server while trying to compile a simple C++ project using C++26 and an experimental compile option. Below are the details of my project and the error output that occurred.

**Environment:**
- OS: Windows
- Clangd version: 19.1.4
- CMake version: 3.10
- Visual Studio 2022

**CMakeLists.txt:**
```cmake
cmake_minimum_required(VERSION 3.10)

project(hello_world)

set(CMAKE_CXX_STANDARD 26)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
add_compile_options(-fexperimental-new-constant-interpreter)

add_executable(hello_world main.cpp)
```

**main.cpp:**
```cpp
#include <cstdint>
#include <iostream>
#include <vector>
using namespace std;

using ll = int64_t;
vector<pair<ll,ll>> v[ll(1e5+5)];

int main(){
    cout<<"hello world\n";
}
```

**Error Log:**
During compilation, the Clang Language Server crashed multiple times, outputting the following error:

```
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.      C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.42.34433\include\ppltasks.h:676:124: current parser token ')'
1.      C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.42.34433\include\ppltasks.h:95:1: parsing namespace 'Concurrency'
... [more stack frames]
[Error - 11:13:32] The Clang Language Server server crashed 5 times in the last 3 minutes. The server will not be restarted. See the output for more information.
```

**Steps to Reproduce:**
1. Create a directory and add the above `CMakeLists.txt` and `main.cpp`.
2. Build the project using CMake and initiate the Clang Language Server.
3. Observe the crash and error logs.

**Expected Behavior:**
The Clang Language Server should not crash, and the project should compile successfully.

**Additional Notes:**
- The crash seems related to parsing issues in the `ppltasks.h` header file.
- The issue persists despite using a stable version of Clangd and CMake.

Please let me know if you need further information to investigate this issue. Thank you!

logs
```
[Info  - 11:13:29] Connection to server got closed. Server will restart.
I[11:13:30.032] clangd version 19.1.4
I[11:13:30.032] Features: windows
I[11:13:30.032] PID: 4316
I[11:13:30.033] Working directory: c:\dev\cpp\helloworld
I[11:13:30.033] argv[0]: C:\dev\cpp\clang\bin\clangd.exe
I[11:13:30.041] Starting LSP over stdin/stdout
I[11:13:30.041] <-- initialize(0)
I[11:13:30.042] --> reply:initialize(0) 1 ms
I[11:13:30.044] <-- initialized
I[11:13:30.046] <-- textDocument/didOpen
I[11:13:30.047] Loaded compilation database from c:\dev\cpp\helloworld\build/compile_commands.json
I[11:13:30.047] ASTWorker building file c:\dev\cpp\helloworld\main.cpp version 101 with command 
[C:/dev/cpp/helloworld/build]
"C:\\dev\\cpp\\clang\\bin\\clang++.exe" --driver-mode=g++ -O0 -g -Xclang -gcodeview -D_DEBUG -D_DLL -D_MT -Xclang --dependent-lib=msvcrtd -std=gnu++26 -fexperimental-new-constant-interpreter -o CMakeFiles/hello_world.dir/main.cpp.obj -c "-resource-dir=C:\\dev\\cpp\\clang\\lib\\clang\\19" -- "c:\\dev\\cpp\\helloworld\\main.cpp"
I[11:13:30.048] --> window/workDoneProgress/create(0)
I[11:13:30.048] Enqueueing 1 commands for indexing
I[11:13:30.049] <-- reply(0)
I[11:13:30.049] --> $/progress
I[11:13:30.049] --> $/progress
I[11:13:30.056] <-- textDocument/documentSymbol(1)
I[11:13:30.057] <-- textDocument/codeAction(2)
I[11:13:30.061] --> textDocument/clangd.fileStatus
I[11:13:30.068] <-- textDocument/documentLink(3)
I[11:13:30.068] <-- textDocument/inlayHint(4)
I[11:13:30.161] --> $/progress
I[11:13:30.161] --> $/progress
I[11:13:30.269] <-- textDocument/foldingRange(5)
I[11:13:30.270] --> reply:textDocument/foldingRange(5) 0 ms
I[11:13:30.356] <-- textDocument/documentSymbol(6)
I[11:13:30.361] <-- textDocument/semanticTokens/full(7)
I[11:13:30.685] Built preamble of size 11708152 for file c:\dev\cpp\helloworld\main.cpp version 101 in 0.62 seconds
I[11:13:30.685] --> workspace/semanticTokens/refresh(1)
I[11:13:30.685] --> textDocument/clangd.fileStatus
I[11:13:30.686] Indexing c++23 standard library in the context of c:\dev\cpp\helloworld\main.cpp
I[11:13:30.687] <-- reply(1)
I[11:13:30.819] --> textDocument/publishDiagnostics
I[11:13:30.819] --> textDocument/inactiveRegions
I[11:13:30.819] --> reply:textDocument/documentSymbol(1) 763 ms
I[11:13:30.819] --> reply:textDocument/codeAction(2) 762 ms
I[11:13:30.819] --> reply:textDocument/documentLink(3) 751 ms
I[11:13:30.819] --> reply:textDocument/inlayHint(4) 751 ms
I[11:13:30.820] --> reply:textDocument/documentSymbol(6) 463 ms
I[11:13:30.820] --> reply:textDocument/semanticTokens/full(7) 458 ms
I[11:13:30.820] --> textDocument/clangd.fileStatus
I[11:13:31.296] <-- textDocument/semanticTokens/full/delta(8)
I[11:13:31.296] --> reply:textDocument/semanticTokens/full/delta(8) 0 ms
I[11:13:31.296] --> textDocument/clangd.fileStatus
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.      C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.42.34433\include\ppltasks.h:676:124: current parser token ')'
1.      C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.42.34433\include\ppltasks.h:95:1: parsing namespace 'Concurrency'
2.      C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.42.34433\include\ppltasks.h:156:1: parsing namespace 'Concurrency::details'
3.      C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.42.34433\include\ppltasks.h:671:5: parsing struct/union/class body 'Concurrency::details::_ResultHolder<std::vector<bool>>'
4.      C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.42.34433\include\ppltasks.h:674:9: parsing function body 'Concurrency::details::_ResultHolder<std::vector<bool>>::Set'
5.      C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.42.34433\include\ppltasks.h:674:9: in compound statement ('{}')
6.      C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.42.34433\include\algorithm:3734:21: instantiating function definition 'std::transform<std::_Vb_const_iterator<std::_Wrap_alloc<std::allocator<unsigned int>>>, std::_Vector_iterator<std::_Vector_val<std::_Simple_types<char>>>, (lambda at C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.42.34433\include\ppltasks.h:676:75)>'
[Error - 11:13:32] The Clang Language Server server crashed 5 times in the last 3 minutes. The server will not be restarted. See the output for more information.
```
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzsWltv4ziy_jXMS8GCRFm-POTBlu0zjZO-nDjT3TgvBi2VbU4oUkNSTjK_fkFSduy0lc70zqJnsQsIsS2Sxa8uX1VRCjOGbyXiNcmmJJtdscbulL7-f3v79fZqrcqna0LTcMEdtwJJOoFcMLmFGya3DdsiLFHvUUOumdnBlx1K-NVwuYWc0CmhUzoAJkuYP9aoeYXSMgG5qmouED7WlitpSDxxF3XXDE2hub9P0vZeGH8HKAvVSIsaS2BQ-A0fuN2B3WEHqoed28fqJ4fIKijanRkYXtUCDyih1uo3LCw0F7AzCXgK_yBEeZgRTFGoB2AaPZASLePCgNpA9XSU6-S4UdRaaVCNrRsLdscsqKJotMYyOjXDXO65VtJteGqGHnxcOhd84bJUD8bf8YqXsEdtgtEgGUdJ1A-D79k9no6lURL7kc_cNEzA0jYlV0BjSk_39-tuuLEmso9nEMggDldRsXsk8cR_riouedVUK42_N1xjSejo8_x2-e7jh7AlHQfxrT0IHe1QCLV6UFqUx1GDbiR_P_nf-Sr_-nW1vJt8mE1uZ0AHYU7XhNXt_P9-fXc7n8HHD2EmK8tV66iVauOMjnqbU0_2JD70CiWNZdL2uAutWqNFfQTkpOAjFo1la4HnqKFiXEZFXbezD4Y5teNxykUL1rWfmHJZiKZEIGleGFty5_T5N0NcGauRVZfG9lhYpcNICGHJKjQ1KxCMLUk6DajCmBBA0hlwaQf9lQ2DBwl5zbj7EIJQ9yedk3QOe5JN3Z1Rghmh08ypnM2OYrm03hqEjtzI0N0GAChUY0mau4tSbzoIDs9ySSht1w9nXeabe7bcqO2p_WaNdkoE5zKfKWj-Sg7wiQJLqBphueO85RUatybQ0PrcsEPYKCHUg_vlWer2jCcvoH26mU-WczDNuuIWGKybLWislbYuveysrY3HuiB0seV216yjQlWELoTYHz56RxIsuDGNw7LwCeLgUAcmpLc1K-6tZgW67LC0rLiHsqnqAC2OSDzO3fcs_6TVVrMKFlygIVn-nhdaGbWx50QnWe6pnuW5qqpGcvtEsvxzTrL8TinhVy79z6Qf9WmU9vtpSrK8RUayvK6FZebeRDuSTgbDAUknCe271OLTmLRQM21Qg1X3KIHQoYsIOiTxJPnpeMeZg-vAOpDnNCF0mCsZlCieAuIoioBk00ppRyNn_Y12C1zsxxOSTUOA9iBxQpOUpJOUkmwGd53RaM6DMgvRCFx6rwtmLKRQcdlYNJGX06544EKAVBbWCBqNZdpiGcESQ7y0JWWjNHi4XG6Urjw9oi56LS3WxsXtLdZalU2BpzxLIsg1MuuqZcm1zw9PoSCWoZixtdojkEH8olwMYj-NDOJj_hu4YJ3QCKYNF2H1i5LrK1VgAbfcbdtJaScqjeDj2pvmhC5ueaiwQm3NeUV9rLGwWMIUd2zPA70Pqr7irp1qROnt7rdwaeNQyw8KtHMObYFpigKN2TRCPJ1BmJQld_5gAj4oi-a8st8dtTCIlQGNgjm8Vh2DNWSLQ6yQQXwS3IMYdshK1LDhwqeLINKvgdp1AMYaKNHU3GJrdOaiei2OHYJrWtp-winpfdKq8EkgMwgCLVQI91I9AN_Ak2pAIpawabTdoT4NO4ecyz0ay7fBndwEOC6umbx3qwlNgnznsJdxmk3fyY2CM375wgO5khKLwy4tQ7bOSUKZQItn0rRscYq8I9n0hKtxFAe-FmdN1HMH1TV_gcw22rsQHo7NWNfsT-9mbmI_TQaXZ6Vu1hel751TjlzzSTWkyxL3JMsdkbLc19FQRruFMb11NTv2VXoC-bdivMoky9dcHn6VET7iRaH9xAldOjM6iDfLT6A8PVy3QujC2NKV-u6lJM17vZbagv_hWqm2Kbywwhut13ONh8ZaOEN8sxISqC7bvN-_tOFlY_UHz3MtPtqZKhrfdNNFycuPNcrLy4Zu2Y1iJZanjQiUzLK148lGq-o7zsvytcuFhC4OfWqhqorJ0kS_GfXaxpPlnQsW1OAlOI840n93v0M2fo7zOAknqHZnCKzLQwvj5NCFb3AXJ3LoIuAONZDSNraOGx_3PgmyY5wd7_kDlo83SqHXKzXfo-5VqkSSztph6H2MobeF3le_BnrbQpW45_gAvdlqNp_--j_-y82N-3h_9zyxV2KNskRpe4KvSTqrzL7QtoSe74ZnW9kcj3hvPBNAT4WEGFqW1iThKBCVXBO6ONg3UuvfoFcAobSn0ahGF9hzU9LZG43lQL-8l4yDqZzY4hUxZy4_8TrxR7wLMTV6plvIZYQuHpS-nymJvk9D4_QtfDPwKnG9pLn8vcEGXVQmh8AyvjHhssRHLreXF4-fqRhY_9pO42fMhPYJXdQHoH_B9OyVrNB-XT5Va-UPRF0Qs2GnEBfFkyKcXEa0S8AgeQb9UkDI1o70S8tsc1mNwei7atxweU_oKO3E0C2CS8GefnFnVTrqd6xPTnX4vuH_5HQ6GHei2yifF2-Z3LqQzToA0mH8ba35viiIO4pP-mdCZ9ABKh0knUIMVkxaXty505VjpWszCR0NO2QNRpmT5bpuC7VGVrl2T23A8D8QkmQYj5KMenb-eAnhEuJoQMFgoWR50TAtjjbLKH3vD12XFNK40ega7U5qncn6EWYMRt5L79p0BEVbC1LXDsuS6RIEX2umnw69dqGk28gZ7q0Wurzx8Nsk16XmKBl3qlk3a8HNbsbZVipjeXFRz9ckcMkKy_d4i9v2GezryzvIcTEfwnCQdhDkLTK_SY8wHNB_Qt6FZAfDrKt_fIvEl7nvNXH0-xnmYmaAfrcR3yDztUQB_Wz0FtF_nltJRMfdGbAD06JEYRmho9FFJhxl_oi-Z7I70vaLDd6g9X-fAv4nPQWkPx1xkg3eDDmdkHTSvoQK-NOfjn8wdNizU_zG6sYHfyN9onc8MwbWqnx6VSP_Y3WLphH2FyVK1CTN_aHODRzfYqyVat9dBBv0_wY2cPwYn9pg08jwDOtfoLUfWKIN6md_J_W59M9MVCNL13BZdJkW_LujIRlOyXDW5ot4MvgZuJnYKs3trnLFYZg63DQJwP1TAc7smfdK3PjnTMonuqNXrGbSbJSuTl21-rxe-acLK25Rs-C259EvmtUrJoQqTm_7G-3cRvpX9q5M2IOr54TmcLKFD4fLG7RjeybObi_92_CVfarRkDQvdkyfCSd0JFi1LhkwC3-DYjP0B7oDuf8tX8RclddpOU7H7Aqvk2GaxjSNs_hqd93fxP112h8U4_643x-mdFSm6wFmBbJRVqTxFb-mMe0nNE7iNBm6A2ORDZGOh5TFxbqfFaQfY8W4iFyfESm9vfIdxnWSjJJxciXYGoXx__NBafs0zhnrSl_7xmTdbA3px8K_zzmKsNwKvP7L__njqtHi-sc7plal_TX9RwAAAP__wzKLRg">