AILang/crates/ailang-check/tests/structural_recursion_pin.rs

//! Iter it.2: pin tests for the structural-recursion guardedness
//! pass + the it.2-only `tail:true` grandfather + the first real
//! `Diverge` effect injection.
//!
//! Spec: `docs/specs/2026-05-15-iteration-discipline.md`. Mirrors the
//! it.1 `loop_recur_pin.rs` harness verbatim (same inline
//! `check_fixture` helper, no `mod common`).

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

fn examples_dir() -> PathBuf {
    let manifest = env!("CARGO_MANIFEST_DIR");
    PathBuf::from(manifest)
        .parent().expect("CARGO_MANIFEST_DIR has a parent (crates/ailang-check)")
        .parent().expect("CARGO_MANIFEST_DIR has a grandparent (crates/)")
        .join("examples")
}

/// Load the named fixture under `examples/`, run check_workspace, and
/// return the diagnostic code list (one entry per Diagnostic).
fn check_fixture(fixture_name: &str) -> Vec<String> {
    let path = examples_dir().join(fixture_name);
    let ws = load_workspace(&path)
        .unwrap_or_else(|e| panic!("workspace `{fixture_name}` must load: {e:?}"));
    let diags = check_workspace(&ws);
    diags.iter().map(|d| d.code.clone()).collect()
}

#[test]
fn structural_list_len_is_clean() {
    // Plain non-tail recursion on a Cons sub-component typechecks
    // clean: structurally guarded ⇒ pure + total, no diagnostics.
    assert!(
        check_fixture("struct_rec_list_len.ail").is_empty(),
        "expected zero diagnostics for structural list length"
    );
}

#[test]
fn foldl_accumulator_is_structural_and_clean() {
    // A foldl-shape accumulator walk (structural on the tail,
    // unconstrained accumulator) classifies as structural recursion
    // and stays clean + Diverge-free (spec D1).
    assert!(
        check_fixture("struct_rec_foldl_sum.ail").is_empty(),
        "expected zero diagnostics for foldl-shape accumulator walk"
    );
}

#[test]
fn non_structural_self_call_is_rejected() {
    // A self-call passing the un-decreased parameter at every
    // candidate position, not `tail`-marked, fires
    // `non-structural-recursion`.
    assert!(
        check_fixture("test_non_structural_recursion.ail.json")
            .contains(&"non-structural-recursion".to_string()),
        "expected non-structural-recursion diagnostic"
    );
}

#[test]
fn tree_forest_mutual_is_clean() {
    // Mutual tree/forest recursion over one ADT family (the
    // cross-reference edge unions {Tree, Forest}) classifies as a
    // mutual structural group: clean, Diverge-free.
    assert!(
        check_fixture("struct_rec_tree_forest.ail").is_empty(),
        "expected zero diagnostics for same-family mutual recursion"
    );
}

#[test]
fn mutual_cross_family_is_rejected() {
    // Mutual recursion whose members' structural params lie in two
    // unrelated ADT families is not a valid mutual structural group
    // (DD-3): the cross-call is an unguarded recursive call.
    assert!(
        check_fixture("test_mutual_cross_family.ail.json")
            .contains(&"non-structural-recursion".to_string()),
        "expected non-structural-recursion for cross-family mutual recursion"
    );
}

#[test]
fn loop_fn_declaring_diverge_is_clean() {
    // A loop-bearing fn that declares `!Diverge` in its effect row
    // reconciles clean (DD-4 / D2).
    assert!(
        check_fixture("loop_needs_diverge.ail").is_empty(),
        "expected zero diagnostics for loop fn declaring !Diverge"
    );
}

#[test]
fn loop_fn_missing_diverge_is_rejected() {
    // A loop-bearing fn missing `!Diverge` raises the existing
    // `undeclared-effect` (no new diagnostic variant; DD-4).
    assert!(
        check_fixture("test_loop_missing_diverge.ail.json")
            .contains(&"undeclared-effect".to_string()),
        "expected undeclared-effect for loop fn missing !Diverge"
    );
}

#[test]
fn structural_recursion_is_diverge_free() {
    // Structural recursion injects no effect: a structural list walk
    // with no `loop` and no declared `!Diverge` stays clean.
    assert!(
        check_fixture("struct_rec_list_len.ail").is_empty(),
        "structural recursion must be Diverge-free"
    );
}

#[test]
fn non_structural_recursion_code_is_registered() {
    // A CheckError::NonStructuralRecursion must map to the kebab code.
    // This step only pins the code() arm exists and returns the exact
    // string; fixture-level behaviour is pinned in Task 2+.
    use ailang_check::CheckError;
    let e = CheckError::NonStructuralRecursion {
        callee: "f".into(),
        arg: "n".into(),
    };
    assert_eq!(e.code(), "non-structural-recursion");
}