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Inherit stdout when it is a TTY so interactive apps keep terminal support #235

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Inherit stdout when it is a TTY so interactive apps keep terminal support #235

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21 changes: 15 additions & 6 deletions src/erlang_launcher.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -100,15 +100,24 @@ pub fn launch(io: Io, install_dir: []const u8, env_map: *std.process.Environ.Map
}
}

// On Unix: pipe child stdout through us so we can detect EPIPE from
// the downstream consumer (e.g. `app cmd | head -5`). When the consumer
// exits and breaks the pipe, the copy thread kills the BEAM child.
// On Windows: inherit stdout directly — std.c.read blocks on Windows
// On Unix, when stdout is NOT a tty (piped/redirected): pipe child
// stdout through us so we can detect EPIPE from the downstream consumer
// (e.g. `app cmd | head -5`). When the consumer exits and breaks the
// pipe, the copy thread kills the BEAM child.
//
// When stdout IS a tty, inherit it directly: the BEAM's prim_tty needs
// both stdin and stdout to be TTYs for raw mode, ANSI detection, and
// keyboard input to work (interactive/TUI apps), and the EPIPE hang
// cannot occur on a tty.
//
// On Windows: always inherit stdout — std.c.read blocks on Windows
// pipes, and the EPIPE group-leader hang is Unix-specific anyway.
const stdout_is_tty = Io.File.stdout().isTty(io) catch false;

var child: std.process.Child = undefined;
var copy_thread: ?std.Thread = null;

if (builtin.os.tag != .windows) {
if (builtin.os.tag != .windows and !stdout_is_tty) {
child = try std.process.spawn(io, .{
.argv = final_args,
.environ_map = env_map,
Expand All @@ -124,7 +133,7 @@ pub fn launch(io: Io, install_dir: []const u8, env_map: *std.process.Environ.Map

const term = if (builtin.os.tag != .windows)
child.wait(io) catch {
copy_thread.?.join();
if (copy_thread) |t| t.join();
std.process.exit(0);
}
else
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