From 4b84e781d4b992a3781ad2446fc815c94bc769d6 Mon Sep 17 00:00:00 2001
From: Brummel <mould@mycelium.de>
Date: Sat, 9 May 2026 17:50:29 +0200
Subject: [PATCH] iter 22b.2.3: invalid-superclass-param class-schema
 diagnostic

---
 crates/ail/src/main.rs                        | 19 +++++++
 crates/ailang-core/src/workspace.rs           | 50 +++++++++++++++++++
 ...est_22b2_invalid_superclass_param.ail.json | 42 ++++++++++++++++
 3 files changed, 111 insertions(+)
 create mode 100644 examples/test_22b2_invalid_superclass_param.ail.json

diff --git a/crates/ail/src/main.rs b/crates/ail/src/main.rs
index 4d44f12..12ed1a1 100644
--- a/crates/ail/src/main.rs
+++ b/crates/ail/src/main.rs
@@ -1049,6 +1049,25 @@ fn workspace_error_to_diagnostic(
                 "defining_module": defining_module,
             })),
         ),
+        W::InvalidSuperclassParam {
+            class,
+            superclass,
+            expected_param,
+            got_type,
+        } => Some(
+            ailang_check::Diagnostic::error(
+                "invalid-superclass-param",
+                format!(
+                    "class `{class}` declares superclass `{superclass} {got_type}`, but its own parameter is `{expected_param}` — superclass `type` must equal class `param`"
+                ),
+            )
+            .with_ctx(serde_json::json!({
+                "class": class,
+                "superclass": superclass,
+                "expected_param": expected_param,
+                "got_type": got_type,
+            })),
+        ),
     }
 }
 
diff --git a/crates/ailang-core/src/workspace.rs b/crates/ailang-core/src/workspace.rs
index 98cd5dc..0d5c245 100644
--- a/crates/ailang-core/src/workspace.rs
+++ b/crates/ailang-core/src/workspace.rs
@@ -215,6 +215,21 @@ pub enum WorkspaceLoadError {
         method: String,
         defining_module: String,
     },
+
+    /// Iter 22b.2: class-schema validation. A class's `superclass.type`
+    /// does not equal its own `param`. Decision 11 single-superclass
+    /// model requires the superclass to be applied to the same param
+    /// (e.g. `class Ord a extends Eq a`, not `extends Eq b`).
+    #[error(
+        "class `{class}` declares superclass `{superclass} {got_type}`, but its own parameter is `{expected_param}` \
+        — superclass `type` must equal class `param`"
+    )]
+    InvalidSuperclassParam {
+        class: String,
+        superclass: String,
+        expected_param: String,
+        got_type: String,
+    },
 }
 
 /// Hash over the canonical bytes of a complete module.
@@ -425,6 +440,16 @@ fn validate_classdefs(
                             defining_module: mod_name.clone(),
                         })?;
                 }
+                if let Some(sc) = &c.superclass {
+                    if sc.type_ != c.param {
+                        return Err(WorkspaceLoadError::InvalidSuperclassParam {
+                            class: c.name.clone(),
+                            superclass: sc.class.clone(),
+                            expected_param: c.param.clone(),
+                            got_type: sc.type_.clone(),
+                        });
+                    }
+                }
             }
         }
     }
@@ -806,4 +831,29 @@ mod tests {
             other => panic!("expected KindMismatch, got {other:?}"),
         }
     }
+
+    /// Iter 22b.2: a class whose `superclass.type` differs from its
+    /// own `param` (e.g. `class Ord a extends Eq b`) must fire
+    /// `InvalidSuperclassParam`. Decision 11 axis 1 ("single
+    /// superclass, applied to the same param") makes the only legal
+    /// shape `extends Eq a` when the parent class has `param: "a"`.
+    #[test]
+    fn superclass_with_wrong_param_fires_invalid_superclass_param() {
+        let entry = std::path::PathBuf::from(
+            "../../examples/test_22b2_invalid_superclass_param.ail.json",
+        );
+        let err = load_workspace(&entry)
+            .expect_err("must fire invalid-superclass-param");
+        match err {
+            WorkspaceLoadError::InvalidSuperclassParam {
+                class, superclass, expected_param, got_type,
+            } => {
+                assert_eq!(class, "Ord");
+                assert_eq!(superclass, "Eq");
+                assert_eq!(expected_param, "a");
+                assert_eq!(got_type, "b");
+            }
+            other => panic!("expected InvalidSuperclassParam, got {other:?}"),
+        }
+    }
 }
diff --git a/examples/test_22b2_invalid_superclass_param.ail.json b/examples/test_22b2_invalid_superclass_param.ail.json
new file mode 100644
index 0000000..9aacdb5
--- /dev/null
+++ b/examples/test_22b2_invalid_superclass_param.ail.json
@@ -0,0 +1,42 @@
+{
+  "schema": "ailang/v0",
+  "name": "test_22b2_invalid_superclass_param",
+  "imports": [],
+  "defs": [
+    {
+      "kind": "class", "name": "Eq", "param": "a",
+      "methods": [
+        {
+          "name": "eq",
+          "type": {
+            "k": "fn",
+            "params": [
+              { "k": "var", "name": "a" },
+              { "k": "var", "name": "a" }
+            ],
+            "ret": { "k": "con", "name": "Bool" },
+            "effects": []
+          }
+        }
+      ]
+    },
+    {
+      "kind": "class", "name": "Ord", "param": "a",
+      "superclass": { "class": "Eq", "type": "b" },
+      "methods": [
+        {
+          "name": "lt",
+          "type": {
+            "k": "fn",
+            "params": [
+              { "k": "var", "name": "a" },
+              { "k": "var", "name": "a" }
+            ],
+            "ret": { "k": "con", "name": "Bool" },
+            "effects": []
+          }
+        }
+      ]
+    }
+  ]
+}