AILang/crates/ail/tests/mono_xmod_ctor_pattern.rs

//! Regression: the workspace-monomorphisation pass must not mis-resolve
//! a cross-module constructor pattern. The mono pass re-runs `synth` on
//! every fn body to recover residual class constraints; that env is built
//! by `mono::build_workspace_env`, which delegates to `crate::build_check_env`
//! and produces a workspace-flat `ctor_index` and `types` map.
//!
//! Post-ct.2, `Pattern::Ctor` lookup is type-driven — it consults the
//! scrutinee's canonical `Type::Con.name` to find the TypeDef directly
//! in `env.module_types`, then validates the ctor name within it. The
//! mono pass's flat `ctor_index` is no longer consulted by this path;
//! the per-module overlay (lib.rs:1247-1258) is now decorative for the
//! pattern path and remains only for duplicate-type / duplicate-ctor
//! detection at the workspace-build prologue.
//!
//! This test pins the cross-module pattern shape against a minimal
//! 2-module fixture (`test_mono_ctor_main` + `test_mono_ctor_listmod`).
//! Pre-ct.2 the bug surfaced as `PatternTypeMismatch { ctor: "Cons",
//! ty: "test_mono_ctor_listmod.List<Int>" }` because the mono env
//! resolved `Cons` to bare `List` via the flat index. Post-ct.2 the
//! lookup is type-driven and `expected.name == "test_mono_ctor_listmod.List"`
//! directly indexes the right TypeDef.
//!
//! Surfaced by iter 23.2 Task 3, which adds `class Eq a` + Eq Int/Bool/Str
//! instances to `examples/prelude.ail.json`, flipping the
//! `workspace_has_typeclasses` gate so every workspace exercises the
//! mono pass.

use std::path::PathBuf;

fn examples_dir() -> PathBuf {
    let mut d = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
    d.pop();
    d.pop();
    d.join("examples")
}

/// Property: `monomorphise_workspace` must succeed on a workspace that
/// (a) flips the typeclass gate (any `Def::Class` + `Def::Instance` is
/// enough), and (b) contains a fn whose body pattern-matches a
/// constructor whose `Def::Type` lives in an imported module.
///
/// The minimal fixture is two modules:
///
///   * `test_mono_ctor_listmod` — declares `data List a = Nil | Cons a (List a)`.
///   * `test_mono_ctor_main` — imports the listmod, declares
///     `class Trivial a` + `instance Trivial Int` (to flip the
///     `workspace_has_typeclasses` gate), and defines
///     `head_or_zero : test_mono_ctor_listmod.List<Int> -> Int` that
///     matches on `Cons h _ | Nil`.
///
/// Pre-ct.2 repro: `monomorphise_workspace` returned
/// `Err(CheckError::PatternTypeMismatch { ctor: "Cons", ty:
/// "test_mono_ctor_listmod.List<Int>" })`. The same workspace
/// typechecked cleanly because the typecheck pass overlaid a
/// per-module `ctor_index` whose imports-fallback produced the
/// qualified `resolved_type_name`, while the mono pass kept the
/// workspace-flat index whose local hit produced the bare one.
///
/// Post-ct.2 expectation: `monomorphise_workspace` returns `Ok`
/// because the Pattern::Ctor lookup no longer consults
/// `ctor_index` at all — it walks directly from the scrutinee's
/// canonical `Type::Con.name` to its TypeDef in
/// `env.module_types` and validates the ctor by name there.
#[test]
fn mono_pass_handles_xmod_ctor_pattern() {
    let entry = examples_dir().join("test_mono_ctor_main.ail");
    let ws = ailang_surface::load_workspace(&entry).expect("load");

    // Pre-condition: the workspace typechecks cleanly. The bug is
    // localised to the mono pass; the typecheck path does not have it.
    let diags = ailang_check::check_workspace(&ws);
    assert!(
        diags.is_empty(),
        "fixture must typecheck before mono runs: {:?}",
        diags
    );

    // Pin the symptom to the inner cause. Pre-fix this returns Err
    // with the qualified scrutinee type and the bare `Cons` ctor.
    let result = ailang_check::monomorphise_workspace(&ws);
    match result {
        Ok(_) => { /* post-fix: pass */ }
        Err(ailang_check::CheckError::PatternTypeMismatch { ctor, ty }) => {
            panic!(
                "mono pass mis-resolves cross-module ctor pattern: \
                 ctor=`{}` ty=`{}` (expected mono to succeed; the bare \
                 ctor_index in build_workspace_env resolves `Cons` to \
                 the local bare `List` instead of qualified \
                 `test_mono_ctor_listmod.List`)",
                ctor, ty
            );
        }
        Err(other) => {
            panic!(
                "mono pass failed with unexpected error variant: {:?} \
                 (expected PatternTypeMismatch on cross-module Cons)",
                other
            );
        }
    }
}