//! Gitea #12 RED→GREEN pin — nullary `(app f)` surface acceptance.
//!
//! Pre-fix, `ail build` rejects `examples/nullary_app_smoke.ail`
//! at parse with `parse_app_body`'s "expected at least one
//! argument" error. Post-fix (parse guard dropped), the file
//! builds, runs, and prints `"hello\n"` from the nullary `greet`
//! invoked as `(app greet)`.
//!
//! Two independent fieldtest specs flagged the same gap:
//! `docs/specs/0030-fieldtest-mut-local.md` F3 and
//! `docs/specs/0035-fieldtest-loop-recur.md` spec_gap. The
//! Form-A surface refusing nullary calls had no schema backing —
//! `Term::App.args` is `[Term...]` (zero-or-more), so the parser
//! guard was an unbacked rule.

use std::path::Path;
use std::process::Command;

fn ail_bin() -> &'static str {
    env!("CARGO_BIN_EXE_ail")
}

fn build_and_run(example: &str) -> String {
    let manifest_dir = env!("CARGO_MANIFEST_DIR");
    let workspace = Path::new(manifest_dir).parent().unwrap().parent().unwrap();
    let src = workspace.join("examples").join(example);
    let tmp = std::env::temp_dir().join(format!(
        "ailang_e2e_{}_{}",
        example.replace('.', "_"),
        std::process::id()
    ));
    std::fs::create_dir_all(&tmp).unwrap();
    let out = tmp.join("bin");
    let status = Command::new(ail_bin())
        .args(["build", src.to_str().unwrap(), "-o"])
        .arg(&out)
        .status()
        .expect("ail build failed to run");
    assert!(status.success(), "ail build failed for {example}");
    let output = Command::new(&out).output().expect("execute binary");
    assert!(
        output.status.success(),
        "binary {} exited non-zero",
        out.display()
    );
    String::from_utf8(output.stdout).expect("stdout utf8")
}

/// A nullary user fn called as `(app greet)` builds and runs; the
/// nullary application surface form is the canonical zero-arg
/// shape under the resolution of Gitea #12.
#[test]
fn nullary_app_builds_and_runs() {
    let out = build_and_run("nullary_app_smoke.ail");
    assert_eq!(
        out, "hello\n",
        "nullary `(app greet)` must build, run, and emit `hello\\n`; \
         got `{out}` — pre-fix surface parser rejects empty-args at \
         `parse_app_body` with `expected at least one argument` (see \
         Gitea #12).",
    );
}