only resolve module types if we know that the TypeExpr could possibly resolve to a module

ql/ql/src/codeql_ql/ast/Ast.qll

@@ -682,8 +682,17 @@ class TypeExpr extends TType, TypeRef {
     // resolve type
     resolveTypeExpr(this, result)
     or
-    // if it resolves to a module
-    exists(FileOrModule mod | resolveModuleRef(this, mod) | result = mod.toType())
+    // if it resolves to a module,
+    exists(FileOrModule mod | resolveModuleRef(this, mod) | result = mod.toType()) and
+    result instanceof ModuleType and
+    // we can get spurious results in some cases, so we restrict to where it is possible to have a module.
+    (
+      // only possible if this is inside a moduleInstantiation.
+      this = any(ModuleExpr mod).getArgument(_).asType()
+      or
+      // or if it's a parameter to a parameterized module
+      this = any(SignatureExpr sig, Module mod | mod.hasParameter(_, _, sig) | sig).asType()
+    )
   }
 
   override AstNode getAChild(string pred) {

ql/ql/test/queries/style/RedundantCast/Foo.qll

@@ -0,0 +1,11 @@
+class Foo extends string {
+  Foo() { this = "Foo" }
+}
+
+predicate test(Foo f) { f.(Foo).toString() = "X" }
+
+predicate test2(Foo a, Foo b) { a.(Foo) = b }
+
+predicate called(Foo a) { a.toString() = "X" }
+
+predicate test3(string s) { called(s.(Foo)) }

ql/ql/test/queries/style/RedundantCast/RedundantCast.expected

@@ -0,0 +1,3 @@
+| Foo.qll:5:25:5:31 | InlineCast | Redundant cast to $@ | Foo.qll:5:28:5:30 | TypeExpr | Foo |
+| Foo.qll:7:33:7:39 | InlineCast | Redundant cast to $@ | Foo.qll:7:36:7:38 | TypeExpr | Foo |
+| Foo.qll:11:36:11:42 | InlineCast | Redundant cast to $@ | Foo.qll:11:39:11:41 | TypeExpr | Foo |

ql/ql/test/queries/style/RedundantCast/RedundantCast.qlref

@@ -0,0 +1 @@
+queries/style/RedundantCast.ql