index out of bounds in build Step zigProcessUpdate beginning in 0.14.0-dev.544+7aaebd177

[scheibo]

Zig Version

0.14.0-dev.564+75cf7fca9

Steps to Reproduce and Observed Behavior

$ git clone https://github.com/scheibo/zigpkg.git
$ cd zigpkg/examples/zig
$ zig build --summary all -Dadd run -- 40

/Users/kjs/Downloads/zigpkg/examples/zig
thread 11744183 panic: index out of bounds: index 0, len 0
/Users/kjs/Code/src/github.com/scheibo/zig/build/zig-macos-aarch64-0.14.0-dev.564+75cf7fca9/lib/std/Build/Step.zig:549:103: 0x102f8787f in zigProcessUpdate (build)
                    const prefix_index: std.zig.Server.Message.PathPrefix = @enumFromInt(prefixed_path[0] - 1);
                                                                                                      ^
/Users/kjs/Code/src/github.com/scheibo/zig/build/zig-macos-aarch64-0.14.0-dev.564+75cf7fca9/lib/std/Build/Step.zig:441:40: 0x102f8a8d3 in evalZigProcess (build)
    const result = try zigProcessUpdate(s, zp, watch);
                                       ^
/Users/kjs/Code/src/github.com/scheibo/zig/build/zig-macos-aarch64-0.14.0-dev.564+75cf7fca9/lib/std/Build/Step/Compile.zig:1762:54: 0x102f33a0f in make (build)
    const maybe_output_bin_path = step.evalZigProcess(
                                                     ^
/Users/kjs/Code/src/github.com/scheibo/zig/build/zig-macos-aarch64-0.14.0-dev.564+75cf7fca9/lib/std/Build/Step.zig:231:13: 0x102ed7b7f in make (build)
    s.makeFn(s, options) catch |err| switch (err) {
            ^
/Users/kjs/Code/src/github.com/scheibo/zig/build/zig-macos-aarch64-0.14.0-dev.564+75cf7fca9/lib/compiler/build_runner.zig:1045:31: 0x102ea0197 in workerMakeOneStep (build)
    const make_result = s.make(.{
                              ^
/Users/kjs/Code/src/github.com/scheibo/zig/build/zig-macos-aarch64-0.14.0-dev.564+75cf7fca9/lib/std/Thread/Pool.zig:115:39: 0x102ea0adf in runFn (build)
            @call(.auto, func, closure.arguments);
                                      ^
/Users/kjs/Code/src/github.com/scheibo/zig/build/zig-macos-aarch64-0.14.0-dev.564+75cf7fca9/lib/std/Thread/Pool.zig:291:32: 0x102f0284b in worker (build)
            run_node.data.runFn(&run_node.data, id);
                               ^
/Users/kjs/Code/src/github.com/scheibo/zig/build/zig-macos-aarch64-0.14.0-dev.564+75cf7fca9/lib/std/Thread.zig:409:13: 0x102ed641f in callFn__anon_14792 (build)
            @call(.auto, f, args);
            ^
/Users/kjs/Code/src/github.com/scheibo/zig/build/zig-macos-aarch64-0.14.0-dev.564+75cf7fca9/lib/std/Thread.zig:678:30: 0x102e9f7a3 in entryFn (build)
                return callFn(f, args_ptr.*);
                             ^
???:?:?: 0x1993f2f93 in ??? (libsystem_pthread.dylib)
???:?:?: 0x8c330001993edd33 in ??? (???)
error: the following build command crashed:
/Users/kjs/Downloads/zigpkg/examples/zig/.zig-cache/o/d52ae6637c08cac9ed90d95a1031dfaf/build /Users/kjs/Code/src/github.com/scheibo/zig/build/zig-macos-aarch64-0.14.0-dev.564+75cf7fca9/zig /Users/kjs/Code/src/github.com/scheibo/zig/build/zig-macos-aarch64-0.14.0-dev.564+75cf7fca9/lib /Users/kjs/Downloads/zigpkg/examples/zig /Users/kjs/Downloads/zigpkg/examples/zig/.zig-cache /Users/kjs/.cache/zig --seed 0x2dba4e0a -Ze9407efbbf133562 --summary all -Dadd run -- 40
make: *** [zig-example] Error 1

Expected Behavior

42
Build Summary: 6/6 steps succeeded
run success
+- run example success 467us MaxRSS:1M
   +- zig build-exe example Debug native success 1s MaxRSS:179M
   |  +- options success
   +- install success
      +- install example success
         +- zig build-exe example Debug native (+1 more reused dependencies)

This works on 0.14.0-dev.367+a57479afc and started failing on 0.14.0-dev.544+7aaebd177, though still repros in the latest nightly (0.14.0-dev.564+75cf7fca9)

[Vexu]

Looks like #20713

[scheibo]

oof yes, thank you. I'll close this as a dupe and reopen if the fix for that doesn't also fix this issue.