fix(semantic): avoid broad lookup for exact missing keys

Exact name and integer keys already have a direct member lookup. When
that misses, returning FieldNotFound avoids scanning every broad
compatible member and unioning unrelated signatures.

Assisted-by: Codex

Author: lewis6991

crates/emmylua_code_analysis/src/compilation/test/member_infer_test.rs

@@ -36,6 +36,24 @@ mod test {
         assert_eq!(c_ty, union_type);
     }
 
+    #[test]
+    fn test_exact_missing_table_key_does_not_scan_broad_members() {
+        let mut ws = VirtualWorkspace::new_with_init_std_lib();
+
+        ws.def(
+            r#"
+        local t = {
+            a = 1,
+            b = "b",
+        }
+
+        value = t["missing"]
+        "#,
+        );
+
+        assert_eq!(ws.expr_ty("value"), LuaType::Nil);
+    }
+
     #[test]
     fn test_issue_314_generic_inheritance() {
         let mut ws = VirtualWorkspace::new_with_init_std_lib();

crates/emmylua_code_analysis/src/semantic/infer/infer_index/mod.rs

@@ -348,6 +348,11 @@ fn infer_table_member(
         return member_item.resolve_type(db);
     }
 
+    if matches!(key, LuaMemberKey::Name(_) | LuaMemberKey::Integer(_)) {
+        // Exact keys already missed above. The matching scan is only for broad keys.
+        return Err(InferFailReason::FieldNotFound);
+    }
+
     if let Some(result_type) = infer_type_key_member_type(db, key_type, &owner) {
         return Ok(result_type);
     }
@@ -386,7 +391,10 @@ fn infer_custom_type_member(
         return member_item.resolve_type(db);
     }
 
-    if let Some(result_type) = infer_type_key_member_type(db, &lookup.key_type, &owner) {
+    // Exact keys may still resolve through super types below; only broad keys need key-type matching here.
+    if !matches!(lookup.key, LuaMemberKey::Name(_) | LuaMemberKey::Integer(_))
+        && let Some(result_type) = infer_type_key_member_type(db, &lookup.key_type, &owner)
+    {
         return Ok(result_type);
     }