rustlib lldb provider crash
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A-debuggers-lldb
C-bug
needs-triage
- Dominant language
- Rust
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Description
I tried to debug this code:
A breakpoint is set on this line. After the debugger breaks, the lldb crashes after a few seconds. Could be the same as #114137 since some local variables indeed do not display, though they crashed in different places.
Meta
rustc --version --verbose:
rustc 1.95.0 (59807616e 2026-04-14)
binary: rustc
commit-hash: 59807616e1fa2540724bfbac14d7976d7e4a3860
commit-date: 2026-04-14
host: x86_64-pc-windows-msvc
release: 1.95.0
LLVM version: 22.1.2
Backtrace
Traceback (most recent call last):
File "C:\Users/synopses0130/.rustup/toolchains/stable-x86_64-pc-windows-msvc/lib/rustlib/etc\lldb_providers.py", line 784, in MSVCEnumSummaryProvider
name: str = variant_names.enum_members[name_idx].name
~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^
IndexError: list index out of range
Traceback (most recent call last):
File "C:\Users/synopses0130/.rustup/toolchains/stable-x86_64-pc-windows-msvc/lib/rustlib/etc\lldb_providers.py", line 784, in MSVCEnumSummaryProvider
name: str = variant_names.enum_members[name_idx].name
~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^
IndexError: list index out of range
Traceback (most recent call last):
File "C:\Users/synopses0130/.rustup/toolchains/stable-x86_64-pc-windows-msvc/lib/rustlib/etc\lldb_providers.py", line 784, in MSVCEnumSummaryProvider
name: str = variant_names.enum_members[name_idx].name
~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^
IndexError: list index out of range
[26.250 ERROR codelldb::debug_session] error: 'header' is not a valid command.
Traceback (most recent call last):
File "C:\Users/synopses0130/.rustup/toolchains/stable-x86_64-pc-windows-msvc/lib/rustlib/etc\lldb_providers.py", line 784, in MSVCEnumSummaryProvider
name: str = variant_names.enum_members[name_idx].name
~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^
IndexError: list index out of range
Traceback (most recent call last):
File "C:\Users/synopses0130/.rustup/toolchains/stable-x86_64-pc-windows-msvc/lib/rustlib/etc\lldb_providers.py", line 784, in MSVCEnumSummaryProvider
name: str = variant_names.enum_members[name_idx].name
~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^
IndexError: list index out of range
Traceback (most recent call last):
File "C:\Users/synopses0130/.rustup/toolchains/stable-x86_64-pc-windows-msvc/lib/rustlib/etc\lldb_providers.py", line 784, in MSVCEnumSummaryProvider
name: str = variant_names.enum_members[name_idx].name
~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^
IndexError: list index out of range
Debug adapter exit code=3221225477, signal=null.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the crash with the linked codec.rs breakpoint on the Windows MSVC toolchain, then inspect rustlib/etc/lldb_providers.py around MSVCEnumSummaryProvider at line 784. Confirm how an out-of-range enum member index is reached and verify that the debugger no longer crashes while inspecting the reproduced code.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python, rust
- Domain
- devtools, operating-systems
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 48/100