/zig-debug-symbs

A minimum reproducible error repo for a weird issue where `lldb` debugging in VS Code

Primary LanguageZig

About

This repo demonstrates some strange debugging behavior in VS Code, where precisely not taking a branching statement (like a while loop or if) results in CodeLLDB briefly displaying that the instruction pointer has immediately jumped to the end of the inside of the control flow block.

Steps to reproduce

  1. Use any version of Zig >=0.11.0 (latest test just now was done with 0.12.0-dev.2059+42389cb9c)
  2. In VS Code, ensure CodeLLDB is installed along with Ziglang tools.
  3. zig build
  4. Set a breakpoint on line 8 of src/main.zig.
  5. In debugger view on the left (run button with a bug in bottom left corner), run Zibug.
  6. Step through, observe debugger briefly reports that it is about to execute the last statement inside the while loop, which is strictly impossible for at least two reasons:

  • a) The predicate guarding each block must have evaluated to false, because (0 > 1) == false.

  • b) The last statement of each control flow block is immediately preceded by a print statement. If we were actually about to execute the last statement of the while/if loop, we would have something printed in stdout, but in fact we see nothing.

Example screenshots:

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