cpptools-srv keeps crashing since 1.31.4 update

[udoprog]

Environment

• OS and Version: Linux Fedora 44
• VS Code Version: 1.115.0
• C/C++ Extension Version: 1.31.4

Bug Summary and Steps to Reproduce

Open anything that starts the language server and it crashes.

core dump

           PID: 16978 (cpptools-srv)
           UID: 1000 (udoprog)
           GID: 1000 (udoprog)
        Signal: 11 (SEGV)
     Timestamp: Thu 2026-04-09 20:18:23 CEST (6s ago)
  Command Line: ~/.vscode/extensions/ms-vscode.cpptools-1.31.4-linux-x64/bin/cpptools-srv 16668 {4D053999-AB07-4B93-84BE-689BAE90B127}
    Executable: ~/.vscode/extensions/ms-vscode.cpptools-1.31.4-linux-x64/bin/cpptools-srv
 Control Group: /user.slice/user-1000.slice/user@1000.service/app.slice/app-org.chromium.Chromium-7449.scope
          Unit: user@1000.service
     User Unit: app-org.chromium.Chromium-7449.scope
         Slice: user-1000.slice
     Owner UID: 1000 (udoprog)
       Boot ID: 993e5437cbca4b9bac8f63a4fe3f463b
    Machine ID: 06cb422986654a4795d2f71c41d640d6
      Hostname: host
       Storage: /var/lib/systemd/coredump/core.cpptools-srv.1000.993e5437cbca4b9bac8f63a4fe3f463b.16978.1775758703000000.zst (present)
  Size on Disk: 68.9M
       Message: Process 16978 (cpptools-srv) of user 1000 dumped core.
                
                Module libc.so without build-id.
                Module libc.so
                Module cpptools-srv without build-id.
                Stack trace of thread 16986:
                #0  0x00007fbdbd85fc39 n/a (libc.so + 0x5fc39)
                #1  0x00000000010818d3 _ZN12_GLOBAL__N_114reraise_signalEiP20crash_handler_data_t (cpptools-srv + 0xc818d3)
                #2  0x0000000001081f19 _Z13crash_handleriP9siginfo_tPv (cpptools-srv + 0xc81f19)
                #3  0x00007fbdbd8605a8 n/a (libc.so + 0x605a8)
                #4  0x0000000000d3902a _Z25add_token_cache_to_stringPK13a_token_cache (cpptools-srv + 0x93902a)
                #5  0x0000000000eabb79 _ZL21extract_member_bodiesP16a_template_cachePP9Dyn_arrayIP24a_template_cache_segment12FE_allocatorEi (cpptools-srv + 0xaabb79)
                #6  0x0000000000edee66 _ZL20template_declarationP17a_tmpl_decl_statePi.constprop.0 (cpptools-srv + 0xadee66)
                #7  0x0000000000ee320d _Z43template_or_specialization_declaration_fullP17a_tmpl_decl_stateiP18a_decl_parse_state (cpptools-srv + 0xae320d)
                #8  0x0000000000ee4026 _ZL38template_or_specialization_declarationP12a_token_kindiP17a_source_positioniP18a_decl_parse_state (cpptools-srv + 0xae4026)
                #9  0x0000000000ee51c5 _Z33template_directive_or_declarationP12a_token_kindiP17a_source_position (cpptools-srv + 0xae51c5)
                #10 0x00000000009e7d2b _Z26scan_nonmember_declarationP18a_decl_parse_stateP14a_source_range (cpptools-srv + 0x5e7d2b)
                #11 0x00000000009eaad5 _Z11declarationiiiiP10a_param_idP14a_source_rangeP18a_decl_parse_state.constprop.0 (cpptools-srv + 0x5eaad5)
                #12 0x00000000009ebb49 _ZL21namespace_declarationP12a_token_kindiiP17a_source_positionPP8a_symbol (cpptools-srv + 0x5ebb49)
                #13 0x00000000009e8c1c _Z26scan_nonmember_declarationP18a_decl_parse_stateP14a_source_range (cpptools-srv + 0x5e8c1c)
                #14 0x00000000009eaad5 _Z11declarationiiiiP10a_param_idP14a_source_rangeP18a_decl_parse_state.constprop.0 (cpptools-srv + 0x5eaad5)
                #15 0x00000000009ef404 _Z16translation_unitv (cpptools-srv + 0x5ef404)
                #16 0x0000000000efe4f5 _Z24process_translation_unitPKciP25an_exported_template_file (cpptools-srv + 0xafe4f5)
                #17 0x0000000000917b10 _Z8cfe_mainiPPc (cpptools-srv + 0x517b10)
                #18 0x0000000000f5adcd _Z26cfe_main_exception_handleriPPc (cpptools-srv + 0xb5adcd)
                #19 0x0000000000917cad _Z8edg_mainiPPc (cpptools-srv + 0x517cad)
                #20 0x0000000000f4fc5e _ZL20invoke_edge_compilerRSt6vectorINSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEESaIS5_EE (cpptools-srv + 0xb4fc5e)
                #21 0x0000000000f5193e _Z18edge_compiler_mainiPPKc (cpptools-srv + 0xb5193e)
                #22 0x00000000007eb2a4 _ZN17a_compiler_thread28compiler_thread_routine_implEPKcPS_ (cpptools-srv + 0x3eb2a4)
                #23 0x0000000001155e3b _ZN4msvc15thread_helper_t12thread_entryEPv (cpptools-srv + 0xd55e3b)
                #24 0x00007fbdbd869047 n/a (libc.so + 0x69047)
                #25 0x00007fbdbd86aa96 n/a (libc.so + 0x6aa96)
                ELF object binary architecture: AMD x86-64

Configuration and Logs

I don't have a c_cpp_properties.json, or I don't know where it is.

C/C++ Crash Call Stack

A C/C++ extension process has crashed. The crashing process name, date/time, signal, and call stack are below -- it would be helpful to include that in a bug report at https://github.com/Microsoft/vscode-cpptools/issues.

cpptools-srv
4/9/2026, 8:18:23 PM
SIGSEGV
?+282
…
…
template_or_specialization_declaration_full(a_tmpl_decl_state*, int, a_decl_parse_state*)+5837
…
?+213
scan_nonmember_declaration(a_decl_parse_state*, a_source_range*)+5979
…
…
scan_nonmember_declaration(a_decl_parse_state*, a_source_range*)+9804
…
translation_unit()+740
process_translation_unit(char const*, int, an_exported_template_file*)+1525
cfe_main(int, char**)+128
cfe_main_exception_handler(int, char**)+13
edg_main(int, char**)+13
…
edge_compiler_main(int, char const**)+110
a_compiler_thread::compiler_thread_routine_impl(char const*, a_compiler_thread*)+324

Other Extensions

No response

Additional context

No response

[bobbrow]

This is our top crash on linux, but we don't have a repro available to debug. Are you able to isolate this to a source file that reproduces the crash?

[sean-mcmanus]

@udoprog I assume it requires some system includes to repro? Are you able to run a command like g++ -E -dD <source.cpp plus any args> to generate a preprocessed file?

[udoprog]

Sorry! The repo I opened in vscode was https://github.com/Ardour/ardour. I don't use this extension a lot. I don't have a minimal repro.

[sean-mcmanus]

@bobbrow It doesn't appear to be a regression from 1.31.4, but it does seem like a regression from 1.30.5 (EDG 6.8).

[sean-mcmanus]

@udoprog Are you able to provide more repro steps regarding that repo? What setup/configuration steps are required and what file is opened? What compiler is being used? If you run the C/C++: Log Diagnostics command, you can see more info on how the active file is being configured for IntelliSense.

[bobbrow]

Sorry! The repo I opened in vscode was https://github.com/Ardour/ardour. I don't use this extension a lot. I don't have a minimal repro.

That's ok. We don't need a minimal repro. We can do that part. We just need to know the file(s) you were looking at and the configuration (like @sean-mcmanus asked for).

[udoprog]

OK, so the .vscode/c_cpp_configuration.json that (I think) was added automatically looks like this:

{
    "configurations": [
        {
            "name": "Linux",
            "includePath": [
                "${workspaceFolder}/**"
            ],
            "defines": [],
            "compilerPath": "/usr/bin/clang",
            "cStandard": "c17",
            "cppStandard": "c++17",
            "intelliSenseMode": "linux-clang-x64"
        }
    ],
    "version": 4
}

And I've not been able to open any file without it crashing. Like gtk2_ardour/editing_context.cc.

Is that what you wanted?