From edb694fdceea883d785504b95399b415bc2dc634 Mon Sep 17 00:00:00 2001
From: Brummel <mould@mycelium.de>
Date: Mon, 11 May 2026 09:16:20 +0200
Subject: [PATCH] iter ct.2.2-doctidy: refresh stale doc-comments on
 UnknownCtorInPattern and mono_xmod_ctor_pattern

---
 crates/ail/tests/mono_xmod_ctor_pattern.rs | 15 ++++++++++-----
 crates/ailang-check/src/lib.rs             |  7 +++++--
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/crates/ail/tests/mono_xmod_ctor_pattern.rs b/crates/ail/tests/mono_xmod_ctor_pattern.rs
index e2c374e..9f96170 100644
--- a/crates/ail/tests/mono_xmod_ctor_pattern.rs
+++ b/crates/ail/tests/mono_xmod_ctor_pattern.rs
@@ -48,14 +48,19 @@ fn examples_dir() -> PathBuf {
 ///     `head_or_zero : test_mono_ctor_listmod.List<Int> -> Int` that
 ///     matches on `Cons h _ | Nil`.
 ///
-/// Pre-fix repro: `monomorphise_workspace` returns
+/// Pre-ct.2 repro: `monomorphise_workspace` returned
 /// `Err(CheckError::PatternTypeMismatch { ctor: "Cons", ty:
 /// "test_mono_ctor_listmod.List<Int>" })`. The same workspace
-/// typechecks cleanly because `check_in_workspace` clears the flat
-/// `ctor_index` before running `Pattern::Ctor` resolution.
+/// 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-fix expectation: `monomorphise_workspace` returns `Ok` and the
-/// `head_or_zero` fn body's match arm types correctly.
+/// 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.json");
diff --git a/crates/ailang-check/src/lib.rs b/crates/ailang-check/src/lib.rs
index b724984..4095b2d 100644
--- a/crates/ailang-check/src/lib.rs
+++ b/crates/ailang-check/src/lib.rs
@@ -345,8 +345,11 @@ pub enum CheckError {
     #[error("type `{ty}` has no constructor `{ctor}`")]
     UnknownCtor { ty: String, ctor: String },
 
-    /// A pattern referenced a ctor not in [`Env::ctor_index`]. Code:
-    /// `unknown-ctor-in-pattern`.
+    /// A pattern referenced a ctor that does not exist in the
+    /// scrutinee's resolved [`TypeDef`]. The Pattern::Ctor lookup
+    /// is type-driven (post-ct.2): it walks `td.ctors` for the
+    /// `expected` Type::Con's TypeDef and reports this code when
+    /// no ctor of that name is present. Code: `unknown-ctor-in-pattern`.
     #[error("unknown constructor `{0}` in pattern")]
     UnknownCtorInPattern(String),