iter 23.1.4: E2E fixture — bare LT match via implicit prelude import

crates/ail/tests/e2e.rs

@@ -895,6 +895,19 @@ fn workspace_build_runs_imported_fn() {
     assert_eq!(stdout.trim(), "5", "ws_lib.add(2,3) should print 5");
 }
 
+/// Guards Iter 23.1: `examples/ordering_match.ail.json` pattern-matches
+/// on the prelude `Ordering` ctor `LT` without an explicit prelude import.
+/// End-to-end: typecheck → codegen → link → run → stdout exactly `"1\n"`.
+/// Property: the implicit prelude import wired by `build_check_env` /
+/// `check_in_workspace` (Iter 23.1 Task 3) propagates through codegen so
+/// the bare ctor name `LT` resolves cross-module without an explicit
+/// `imports: ["prelude"]` entry in the source module.
+#[test]
+fn ordering_match_via_prelude_prints_1() {
+    let stdout = build_and_run("ordering_match.ail.json");
+    assert_eq!(stdout, "1\n");
+}
+
 /// Guards Iter 5d: `ail manifest --workspace --json` lists defs from all
 /// modules of the workspace — visible via a `module` field per entry.
 #[test]

crates/ailang-codegen/src/lib.rs

@@ -1639,6 +1639,16 @@ impl<'a> Emitter<'a> {
     /// under a swapped `module_name` (see `emit_specialised_fn`)
     /// resolve its bare ctor references against the *owner* module's
     /// ctor table, not the consumer's.
+    ///
+    /// Iter 23.1: bare-type lookup now falls back to imported modules
+    /// when the ctor is not local — mirroring `lookup_ctor_in_pattern`.
+    /// The typechecker (Iter 23.1 Task 3) already accepts a bare
+    /// `Term::Ctor { type_name, ctor }` whose `type_name` is owned by
+    /// an imported module (the implicit `prelude` import is the
+    /// motivating case: an `Ordering` ctor `LT` written without an
+    /// explicit `imports: ["prelude"]`). Codegen must honour the same
+    /// resolution path so the lockstep `Pattern::Ctor ↔ Term::Ctor ↔
+    /// codegen` is preserved.
     pub(crate) fn lookup_ctor_by_type(
         &self,
         type_name: &str,
@@ -1669,24 +1679,41 @@ impl<'a> Emitter<'a> {
             }
             Ok(cref)
         } else {
-            let cref = self
+            // Local-first: current module's ctor table wins on conflict.
+            if let Some(cref) = self
                 .module_ctor_index
                 .get(self.module_name)
                 .and_then(|m| m.get(ctor_name))
                 .cloned()
-                .ok_or_else(|| {
-                    CodegenError::Internal(format!(
-                        "unknown ctor `{ctor_name}` in module `{}`",
-                        self.module_name
-                    ))
-                })?;
-            if cref.type_name != type_name {
-                return Err(CodegenError::Internal(format!(
-                    "ctor `{ctor_name}` belongs to `{}`, not `{type_name}`",
-                    cref.type_name
-                )));
+            {
+                if cref.type_name != type_name {
+                    return Err(CodegenError::Internal(format!(
+                        "ctor `{ctor_name}` belongs to `{}`, not `{type_name}`",
+                        cref.type_name
+                    )));
+                }
+                return Ok(cref);
             }
-            Ok(cref)
+            // Iter 23.1: fallback — scan other modules for a bare ctor
+            // whose declared `type_name` matches. The typechecker has
+            // already pinned uniqueness (an ambiguous bare type name
+            // is rejected with `CheckError::AmbiguousType`), so the
+            // first hit whose owning type matches the requested
+            // `type_name` is unique. Mirrors `lookup_ctor_in_pattern`.
+            for (mname, ctors) in self.module_ctor_index.iter() {
+                if mname == self.module_name {
+                    continue;
+                }
+                if let Some(cref) = ctors.get(ctor_name).cloned() {
+                    if cref.type_name == type_name {
+                        return Ok(cref);
+                    }
+                }
+            }
+            Err(CodegenError::Internal(format!(
+                "unknown ctor `{ctor_name}` in module `{}`",
+                self.module_name
+            )))
         }
     }
 

examples/ordering_match.ail.json

@@ -0,0 +1,48 @@
+{
+  "schema": "ailang/v0",
+  "name": "ordering_match",
+  "imports": [],
+  "defs": [
+    {
+      "kind": "fn",
+      "name": "main",
+      "type": {
+        "k": "fn",
+        "params": [],
+        "ret": { "k": "con", "name": "Unit" },
+        "effects": ["IO"]
+      },
+      "params": [],
+      "doc": "Iter 23.1 fixture: pattern-match on prelude Ordering ctor without explicit prelude import.",
+      "body": {
+        "t": "do",
+        "op": "io/print_int",
+        "args": [
+          {
+            "t": "match",
+            "scrutinee": {
+              "t": "ctor",
+              "type": "Ordering",
+              "ctor": "LT",
+              "args": []
+            },
+            "arms": [
+              {
+                "pat": { "p": "ctor", "ctor": "LT", "fields": [] },
+                "body": { "t": "lit", "lit": { "kind": "int", "value": 1 } }
+              },
+              {
+                "pat": { "p": "ctor", "ctor": "EQ", "fields": [] },
+                "body": { "t": "lit", "lit": { "kind": "int", "value": 2 } }
+              },
+              {
+                "pat": { "p": "ctor", "ctor": "GT", "fields": [] },
+                "body": { "t": "lit", "lit": { "kind": "int", "value": 3 } }
+              }
+            ]
+          }
+        ]
+      }
+    }
+  ]
+}