From 2bf827f6009350db145eb7db74af39643b1731e1 Mon Sep 17 00:00:00 2001
From: Brummel <mould@mycelium.de>
Date: Sun, 10 May 2026 01:19:45 +0200
Subject: [PATCH] test: red for mono-pass unknown module prefix on qualified
 xmod reference in class workspace

---
 crates/ail/tests/mono_xmod_qualified_ref.rs  | 90 ++++++++++++++++++++
 examples/test_mono_imports_classmod.ail.json | 59 +++++++++++++
 examples/test_mono_imports_main.ail.json     | 29 +++++++
 3 files changed, 178 insertions(+)
 create mode 100644 crates/ail/tests/mono_xmod_qualified_ref.rs
 create mode 100644 examples/test_mono_imports_classmod.ail.json
 create mode 100644 examples/test_mono_imports_main.ail.json

diff --git a/crates/ail/tests/mono_xmod_qualified_ref.rs b/crates/ail/tests/mono_xmod_qualified_ref.rs
new file mode 100644
index 0000000..4efa515
--- /dev/null
+++ b/crates/ail/tests/mono_xmod_qualified_ref.rs
@@ -0,0 +1,90 @@
+//! Bug regression: the workspace-monomorphisation pass must seed
+//! `env.imports` for the current module before re-running `synth` on
+//! a fn body, otherwise a qualified cross-module reference like
+//! `OtherMod.helper` is rejected with `unknown module prefix` whenever
+//! the workspace also contains a `Def::Class` (which makes the mono
+//! pass actually traverse bodies instead of identity-cloning the
+//! workspace).
+//!
+//! Sibling to commit 13b36cc (`env.globals` seeding for self-recursive
+//! top-level fn) and 5c5180f (`env.types` / `env.ctor_index` seeding for
+//! user ADTs). Same shape: `synth` walks every fn body during the mono
+//! pass and consults env tables that `check_in_workspace` populates
+//! per-module but `mono::build_workspace_env` /
+//! `collect_mono_targets` / `collect_residuals_ordered` do not.
+//!
+//! The qualified-ref synth path lives at `lib.rs:1697`:
+//!
+//! ```ignore
+//! let target_module = match env.imports.get(prefix) {
+//!     Some(m) => m.clone(),
+//!     None => return Err(CheckError::UnknownModule { module: prefix.to_string() }),
+//! };
+//! ```
+//!
+//! `env.imports` is the per-module alias→module-name map populated at
+//! `lib.rs:1147-1152` from `m.imports`. The mono entry points never
+//! seed it, so a body whose synth walk hits a qualified-name reference
+//! errors out — even though the import is declared in the source and
+//! visible to the typechecker.
+
+use std::path::Path;
+use std::process::Command;
+
+fn ail_bin() -> &'static str {
+    env!("CARGO_BIN_EXE_ail")
+}
+
+/// Property: a workspace where module A declares a class+instance and
+/// also a regular top-level fn `helper`, and module B imports A and
+/// calls `A.helper` via a qualified `Term::Var { name: "A.helper" }`,
+/// must build and run end-to-end. The mono pass re-runs `synth` on
+/// every fn body to recover residual class constraints; that env must
+/// agree with the env the main typecheck path used, including
+/// `env.imports` for the current module so the qualified-name lookup
+/// resolves.
+///
+/// Pre-fix: `ail check` passes (typecheck seeds `env.imports` per
+/// module via `check_in_workspace`); `ail build` fails at the mono
+/// pass with `monomorphise_workspace: unknown module prefix
+/// \`test_mono_imports_classmod\` in qualified reference` because
+/// `mono::build_workspace_env` and the per-fn entry points never seed
+/// `env.imports`. `synth`'s qualified-name path (`lib.rs:1697`) thus
+/// falls through to `UnknownModule`.
+#[test]
+fn mono_pass_handles_qualified_cross_module_reference() {
+    let manifest_dir = env!("CARGO_MANIFEST_DIR");
+    let workspace = Path::new(manifest_dir).parent().unwrap().parent().unwrap();
+    let src = workspace
+        .join("examples")
+        .join("test_mono_imports_main.ail.json");
+    let tmp = std::env::temp_dir().join(format!(
+        "ailang_mono_xmod_qualified_{}",
+        std::process::id()
+    ));
+    std::fs::create_dir_all(&tmp).unwrap();
+    let out = tmp.join("bin");
+
+    let build = Command::new(ail_bin())
+        .args(["build", src.to_str().unwrap(), "-o"])
+        .arg(&out)
+        .output()
+        .expect("ail build failed to run");
+    assert!(
+        build.status.success(),
+        "ail build failed: stderr={}",
+        String::from_utf8_lossy(&build.stderr)
+    );
+
+    let run = Command::new(&out).output().expect("execute binary");
+    assert!(
+        run.status.success(),
+        "binary {} exited non-zero",
+        out.display()
+    );
+    // helper(42) = 42 + 100 = 142
+    assert_eq!(
+        String::from_utf8(run.stdout).expect("stdout utf8").trim(),
+        "142"
+    );
+}
diff --git a/examples/test_mono_imports_classmod.ail.json b/examples/test_mono_imports_classmod.ail.json
new file mode 100644
index 0000000..4e07dfd
--- /dev/null
+++ b/examples/test_mono_imports_classmod.ail.json
@@ -0,0 +1,59 @@
+{
+  "schema": "ailang/v0",
+  "name": "test_mono_imports_classmod",
+  "imports": [],
+  "defs": [
+    {
+      "kind": "class",
+      "name": "Foo",
+      "param": "a",
+      "methods": [
+        {
+          "name": "foo",
+          "type": {
+            "k": "fn",
+            "params": [{ "k": "var", "name": "a" }],
+            "ret": { "k": "con", "name": "Int" },
+            "effects": []
+          }
+        }
+      ]
+    },
+    {
+      "kind": "instance",
+      "class": "Foo",
+      "type": { "k": "con", "name": "Int" },
+      "methods": [
+        {
+          "name": "foo",
+          "body": {
+            "t": "lam",
+            "params": ["x"],
+            "paramTypes": [{ "k": "var", "name": "a" }],
+            "retType": { "k": "con", "name": "Int" },
+            "body": { "t": "var", "name": "x" }
+          }
+        }
+      ]
+    },
+    {
+      "kind": "fn",
+      "name": "helper",
+      "type": {
+        "k": "fn",
+        "params": [{ "k": "con", "name": "Int" }],
+        "ret": { "k": "con", "name": "Int" },
+        "effects": []
+      },
+      "params": ["n"],
+      "body": {
+        "t": "app",
+        "fn": { "t": "var", "name": "+" },
+        "args": [
+          { "t": "var", "name": "n" },
+          { "t": "lit", "lit": { "kind": "int", "value": 100 } }
+        ]
+      }
+    }
+  ]
+}
diff --git a/examples/test_mono_imports_main.ail.json b/examples/test_mono_imports_main.ail.json
new file mode 100644
index 0000000..99eb6e3
--- /dev/null
+++ b/examples/test_mono_imports_main.ail.json
@@ -0,0 +1,29 @@
+{
+  "schema": "ailang/v0",
+  "name": "test_mono_imports_main",
+  "imports": [{ "module": "test_mono_imports_classmod" }],
+  "defs": [
+    {
+      "kind": "fn",
+      "name": "main",
+      "type": {
+        "k": "fn",
+        "params": [],
+        "ret": { "k": "con", "name": "Unit" },
+        "effects": ["IO"]
+      },
+      "params": [],
+      "body": {
+        "t": "do",
+        "op": "io/print_int",
+        "args": [
+          {
+            "t": "app",
+            "fn": { "t": "var", "name": "test_mono_imports_classmod.helper" },
+            "args": [{ "t": "lit", "lit": { "kind": "int", "value": 42 } }]
+          }
+        ]
+      }
+    }
+  ]
+}