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//! Raw, best-effort stderr writing that bypasses `std.Io` entirely.
//!
//! `std.debug.lockStderr` (and everything layered on top of it) routes
//! through `std.Options.debug_io`, whose default implementation is
//! `std.Io.Threaded`. This keeps ~70KB of unreachable code in binaries.
const std = @import("std");
const builtin = @import("builtin");
/// Write bytes to stderr using the most primitive mechanism available
/// for the target. This is best-effort: errors are ignored, since this
/// is only used for diagnostics (logging and panic messages).
///
/// Freestanding targets (e.g. wasm) have no stderr, so this is a no-op
/// there.
pub fn write(bytes: []const u8) void {
switch (builtin.os.tag) {
.freestanding, .other => {},
.windows => {
const windows = std.os.windows;
const handle = windows.peb().ProcessParameters.hStdError;
var iosb: windows.IO_STATUS_BLOCK = undefined;
_ = windows.ntdll.NtWriteFile(
handle,
null, // event
null, // APC routine
null, // APC context
&iosb,
bytes.ptr,
@intCast(bytes.len),
null, // byte offset
null, // key
);
},
else => {
const posix = std.posix;
var i: usize = 0;
while (i < bytes.len) {
const rc = posix.system.write(
posix.STDERR_FILENO,
bytes[i..].ptr,
bytes.len - i,
);
switch (posix.errno(rc)) {
.SUCCESS => i += @as(usize, @intCast(rc)),
.INTR => continue,
else => return,
}
}
},
}
}
test write {
// Smoke test: must not crash. We can't assert on the output without
// capturing stderr, which isn't worth the complexity here.
write("");
}
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