sx/examples/1025-errors-trace-format.sx

// Error return-trace formatting (ERR step E3.3). `library/modules/std/trace.sx`
// reads the trace buffer (E3.1, populated by E3.2's raise/try push wiring) and
// renders it. `trace.print_current()` writes the trace to stderr; the catch
// handler sees the full chain because the absorption clear fires at handler
// EXIT, not entry. Frame locations are placeholders until DWARF (ERR E3.0)
// resolves PCs to file:line; the count + ordering are already meaningful.
//
// Note: the trace goes to stderr. The test runner merges stderr+stdout, so the
// snapshot shows the trace lines interleaved with the `print` (stdout) lines.

#import "modules/std.sx";
trace :: #import "modules/std/trace.sx";

// Buffer length probe (the runtime symbol; public read API is the trace module).
sx_trace_len :: () -> u32 extern;

E :: error { BadInput, Overflow }

leaf :: (n: i32) -> !E {
    if n < 0 { raise error.BadInput; }   // pushes frame 0
    return;
}

mid :: (n: i32) -> !E {
    try leaf(n);                          // propagation pushes frame 1
    return;
}

main :: () -> i32 {
    mid(-1) catch (e) {
        print("[stdout] caught {}\n", e);   // tag name via the always-linked table
        trace.print_current();               // [stderr] the 2-frame trace
    };
    print("[stdout] recovered; trace buffer now empty (len {})\n", sx_trace_len());
    return 0;
}