sx/library/modules/trace.sx

#import "std.sx";

// =====================================================================
// trace.sx — error return-trace formatting (ERR step E3.3).
//
// Reads the thread-local return-trace buffer (ERR E3.1, populated by the
// push/clear wiring in E3.2) and renders it. A `raise` / propagating `try`
// pushes a frame; an absorbing site (`catch` / `or value` / destructure)
// clears the buffer. So at format time the buffer holds exactly the frames
// of failures that escaped to where you're formatting — typically inside a
// `catch` handler (the clear fires when the handler completes, so the body
// still sees the chain) or the (future) failable-`main` wrapper.
//
// Frame resolution (ERR E3.0 slice 3a): in compiled code a frame is a pointer
// to an interned `TraceFrame` the compiler stamped in at the push site, so the
// location resolves in-process with no DWARF and no symbolizer. (The comptime
// path — a packed `(func_id, ir_offset)` resolved via the interpreter's IR
// tables — lands with slice 3b.)
// =====================================================================

libc :: #library "c";

// The compiled return-trace frame. Named `TraceFrame` (not `Frame`) so it never
// collides with a UI / geometry `Frame` a consumer flat-imports — same-name
// types are now distinct nominal identities (issue 0105), so a bare `Frame` must
// resolve unambiguously to the consumer's own. Layout MUST match
// `getFrameStructType` in src/ir/emit_llvm.zig and `SxFrame` in
// library/vendors/sx_trace_runtime/sx_trace.c.
TraceFrame :: struct {
    file: string;
    line: s32;
    col: s32;
    func: string;
    line_text: string;    // the source line, for the snippet + caret
}

// `n` spaces — used to position the `^` caret under a column.
spaces :: (n: s32) -> string {
    s := "";
    i : s32 = 0;
    while i < n {
        s = concat(s, " ");
        i = i + 1;
    }
    s
}

// The error-trace buffer C API (library/vendors/sx_trace_runtime/sx_trace.c),
// linked in for the JIT and auto-injected for AOT when traces are used.
// `frame_at` returns the raw stored `u64`; `__trace_resolve_frame` turns it
// into a `TraceFrame` — by reinterpreting the stamped `*TraceFrame` in compiled code, or
// by resolving the packed `(func_id, span.start)` in the comptime interpreter.
sx_trace_len       :: () -> u32 #foreign;
sx_trace_truncated :: () -> u32 #foreign;
sx_trace_frame_at  :: (i: u32) -> u64 #foreign;

write :: (fd: s32, buf: [*]u8, count: usize) -> isize #foreign libc;

// Render the current trace buffer to a string (allocated from
// context.allocator). Empty buffer → "" so callers can cheaply skip output.
to_string :: () -> string {
    n := sx_trace_len();
    if n == 0 { return ""; }

    result := "error return trace (most recent call last):\n";
    if sx_trace_truncated() != 0 {
        result = concat(result, "  ... older frames omitted (buffer full)\n");
    }

    i : u32 = 0;
    while i < n {
        f := __trace_resolve_frame(sx_trace_frame_at(i));
        result = concat(result, format("  {} at {}:{}:{}\n", f.func, f.file, f.line, f.col));
        if f.line_text.len > 0 {
            result = concat(result, format("    {}\n", f.line_text));
            result = concat(result, concat("    ", concat(spaces(f.col - 1), "^\n")));
        }
        i = i + 1;
    }
    result
}

// Write the current trace to stderr (fd 2). No-op when the buffer is empty.
print_current :: () {
    s := to_string();
    if s.len > 0 {
        write(2, s.ptr, xx s.len);
    }
}

// Dump the comptime (`#run`) interpreter call-frame chain (ERR E4.1). At
// comptime the interpreter walks its active sx frames and appends them to the
// build output; in compiled code this folds to nothing (there is no
// interpreter stack — the only caller is a dead `is_comptime()` branch).
// Frame source locations await IR-offset resolution, so only names print today.
print_interpreter_frames :: () {
    __interp_print_frames();
}