Swift Debug

Swift Debug: Semantic Runtime Debugging

Bridge static code context with dynamic runtime state using LLDB extensions.

Setup

Install the LLDB plugin once per environment:

scripts/swift_debug install

This sets up the Python plugin and adds the loader script to ~/.lldbinit.

LLDB Commands (After Install)

Once installed, these commands are available in any LLDB session:

• sz_break "<QUERY>": Set a breakpoint by semantic search (e.g., sz_break "user authentication logic")
• sz_explain: Explain the current execution frame — what this code does and why
• sz_inspect: Capture stacktrace and variable values for semantic analysis

Gotchas

• The plugin must be installed BEFORE debugging — sz_* commands will not exist in LLDB without running install first.
• sz_break uses semantic matching, not line numbers. If the query is too broad, it may set multiple breakpoints — review them with breakpoint list.
• Runtime state captured by sz_inspect is a snapshot — variables may change between inspection and your next step.
• If ~/.lldbinit already exists and is managed by another tool, the install script appends to it. Check for conflicts if LLDB behaves unexpectedly.

Workflow

1. Install: Run scripts/swift_debug install (one-time setup)
2. Locate: Use sz_break "<query>" to set breakpoints semantically
3. Inspect: When hit, use sz_inspect to capture runtime state
4. Understand: Use sz_explain to understand the execution context