AILang/crates/ail/tests/polyfn_dot_qualified_branch_pin.rs

//! Pin for the iter-24.3 FreeFnCall constraint-residual-push
//! invariant (DESIGN.md §"Cross-module references in synthesised
//! bodies" invariant 3).
//!
//! Property protected: bare-name references to polymorphic free fns
//! that resolve through the auto-injected-prelude path AT THE
//! DOT-QUALIFIED SYNTH BRANCH push residuals for the fn's declared
//! constraints. The discharge loop then fires `NoInstance` at
//! typecheck if no instance ships for the unified concrete type.
//!
//! Failure mode this pin catches: a future refactor changes the
//! prelude auto-injection resolution path so that bare-name `print`
//! reaches synth via a different branch (e.g. locals, env.module_globals
//! direct hit) that does NOT push residuals. Without this pin, the
//! regression surfaces as `unknown variable: show` from codegen for
//! the negative case — confusing diagnostic, hard to bisect.

use ailang_check::check_workspace;
use ailang_surface::load_workspace;
use std::path::PathBuf;

fn fixture_path() -> PathBuf {
    PathBuf::from(env!("CARGO_MANIFEST_DIR"))
        .join("../../examples")
        .join("show_no_instance.ail")
}

#[test]
fn bare_name_polyfn_fires_typecheck_no_instance_not_codegen_unknown_var() {
    // The fixture calls `print f` bare-name (no `prelude.` qualifier)
    // where `f : Int -> Int`. The auto-injected-prelude resolution
    // must route this through the dot-qualified synth branch so that
    // the `Show a` declared constraint of `print` produces a residual,
    // and the discharge loop fires `no-instance`.
    let ws = load_workspace(&fixture_path()).expect("workspace loads");
    let diags = check_workspace(&ws);

    // Exactly one `no-instance` diagnostic — proves:
    //   (a) the bare-name `print` resolved (was not "unknown variable")
    //   (b) the resolution reached the dot-qualified synth branch
    //       which pushes the declared-constraint residual
    //   (c) the discharge loop ran with the residual and fired the
    //       NoInstance because no `Show (Int -> Int)` instance exists.
    let no_inst: Vec<_> = diags.iter().filter(|d| d.code == "no-instance").collect();
    assert_eq!(
        no_inst.len(),
        1,
        "expected exactly one 'no-instance' diagnostic — got {} (all diags: {diags:?})",
        no_inst.len()
    );

    // No "unknown variable" or other codegen-grade errors at typecheck:
    // if the residual push did NOT fire, the typecheck would pass
    // silently and the error would only surface at codegen.
    let unknown_vars: Vec<_> = diags
        .iter()
        .filter(|d| {
            d.code == "unknown-variable"
                || d.message.contains("unknown variable")
                || d.code == "internal"
        })
        .collect();
    assert!(
        unknown_vars.is_empty(),
        "expected zero 'unknown variable' or 'internal' diagnostics at typecheck — \
         got {} (all diags: {diags:?}). If this fires, the bare-name `print` \
         resolution bypassed the dot-qualified synth branch and the constraint \
         residual was never pushed.",
        unknown_vars.len()
    );
}