unified: Ensure parameter defaults resolve correctly

Author: asgerf

unified/ql/lib/codeql/unified/internal/LocalNameBinding.qll

@@ -203,8 +203,17 @@ private module LocalNameBindingInput implements LocalNameBindingInputSig<Locatio
         declaration = func
       )
       or
-      exists(Parameter param |
-        scope = param.getDeclaringCallable() and
+      exists(Parameter param, Callable callable |
+        callable = param.getDeclaringCallable() and
+        (
+          // Scope to the body so parameter defaults cannot see the parameter list
+          // TODO: Use a plugin for languages where parameter defaults can reference earlier parameters
+          scope = callable.getBody()
+          or
+          // For bodyless functions, choose an arbitrary scope
+          not exists(callable.getBody()) and
+          scope = param
+        ) and
         pattern = param.getPattern() and
         declaration = param
       )

unified/ql/test/library-tests/local-name-binding/test.swift

@@ -397,9 +397,9 @@ func t41() {
     // This function and its parameter have the same name
     // The parameter default value must resolve to the outer name (the function)
     // swift-format-ignore
-    func foo(  // name=foo1
+    func foo(  // $ captured=foo1 // name=foo1
         _ foo: Any = // name=foo2
-            foo  // $ MISSING: access=foo1 SPURIOUS: access=foo2
+            foo  // $ access=foo1
     ) {
         foo  // $ access=foo2
     }