Address review comments

rust/ql/lib/codeql/rust/dataflow/internal/DataFlowImpl.qll

@@ -428,6 +428,9 @@ module RustDataFlow implements InputSig<Location> {
   private Function getStaticTargetExt(Call c) {
     result = c.getStaticTarget()
     or
+    // If the static target of an overloaded operation cannot be resolved, we fall
+    // back to the trait method as the target. This ensures that the flow models
+    // still apply.
     not exists(c.getStaticTarget()) and
     exists(TraitItemNode t, string methodName |
       c.(Operation).isOverloaded(t, methodName, _) and

rust/ql/lib/codeql/rust/dataflow/internal/Node.qll

@@ -554,6 +554,8 @@ newtype TNode =
     e.hasEnclosingCfgScope() and
     (
       isArgumentForCall(e, _, _) and
+      // For compound assignments into variables like `x += y`, we do not want flow into
+      // `[post] x`, as that would create spurious flow when `x` is a parameter.
       not (e = any(CompoundAssignmentExpr cae).getLhs() and e instanceof VariableAccess)
       or
       lambdaCallExpr(_, _, e)