Apply suggestions from code review

Co-authored-by: Rasmus Wriedt Larsen <rasmuswriedtlarsen@gmail.com>

python/ql/src/semmle/python/functions/ModificationOfParameterWithDefaultCustomizations.qll

@@ -53,7 +53,7 @@ module ModificationOfParameterWithDefault {
   }
 
   /**
-   * A source of remote user input, considered as a flow source.
+   * A mutable default value for a parameter, considered as a flow source.
    */
   class MutableDefaultValue extends Source {
     boolean nonEmpty;
@@ -120,6 +120,9 @@ module ModificationOfParameterWithDefault {
     }
   }
 
+  /** 
+   * An expression that is checked directly in an `if`, possibly with `not`, such as `if x:` or `if not x:`.
+   */
   private class IdentityGuarded extends Expr {
     boolean inverted;
 
@@ -136,6 +139,9 @@ module ModificationOfParameterWithDefault {
       )
     }
 
+    /** 
+     * Whether this guard has been inverted. For `if x:` the result is `false`, and for `if not x:` the result is `true`.
+     */
     boolean isInverted() { result = inverted }
   }
 

python/ql/test/query-tests/Functions/ModificationOfParameterWithDefault/test.py

@@ -15,7 +15,7 @@ def list_del(l = [0]):
 
 # Not OK
 def append_op(l = []):
-    l += 1  #$ modification=l
+    l += [1, 2, 3]  #$ modification=l
     return l
 
 # Not OK
@@ -123,6 +123,6 @@ def dict_update_op_nochange(d = {}):
 
 # OK
 def sanitizer(l = []):
-    if not l == []:
+    if l:
         l.append(1)  #$ SPURIOUS: modification=l
     return l