Bind *ns* to file's ns during read

Commit 54cba5c introduced a method of
detecting unqualified, unquoted symbols within syntax quotes that are
consumed in-namespace.

From the commit message:

> We can avoid this situation by walking the body and de-qualifying only
> the symbols that have been qualified in the current ns. This should
> not be problematic since unknown symbols are qualified in the current
> ns by default.

Now, the "current ns" is determined by the reader to be the value of
the *ns* var. When using Slamhound from an editor plugin, it can be
assumed that *ns* is set to the namespace of the current open buffer.
Unfortunately, when using Slamhound from a command line, *ns* is
actually set to the `user` ns.

This causes symbols that we expect to be qualified as `my.ns/foo` to
actually be qualified as `user/foo`. There have been scattered reports
of slamhound attempting to alias namespaces as `user`¹. In at least some
of these cases, this problem is likely to blame.

¹ #65 comes to mind

src/slam/hound/asplode.clj

@@ -216,6 +216,20 @@
           stripped-ns (-> (apply dissoc ns-map ns-clauses)
                           (assoc :old old-ns)
                           (merge (preserve-ns-references old-ns)))
-          body (take-while #(not= ::done %)
-                           (repeatedly #(read rdr false ::done)))]
-      [stripped-ns (doall body)])))
+          ;; All unqualified, unquoted symbols are qualified to *ns* by the
+          ;; reader during syntax-quote expansion, so we must be sure that
+          ;; *ns* is set to the file's namespace in order for the regrow step
+          ;; to work properly.
+          ;;
+          ;; Unfortunately, this means we are introducing the potentially
+          ;; surprising side effect of creating a namespace on read. This
+          ;; cannot be helped, as there is no way of creating a Namespace
+          ;; object that is not added to the global map of namespaces.
+          ;;
+          ;; In practice, however, this is unlikely to be a problem;
+          ;; slam.hound/regrow loads all namespaces on the classpath anyway.
+          body (binding [*ns* (create-ns (:name ns-map))]
+                 (doall
+                   (take-while #(not= ::done %)
+                               (repeatedly #(read rdr false ::done)))))]
+      [stripped-ns body])))

test/slam/hound/asplode_test.clj

@@ -196,4 +196,9 @@
             :exclude {clojure.core #{test compile}}
             :meta {:doc "Testing some things going on here."}
             :name slamhound.sample}
-           ((do something))])))
+           ((do something))]))
+  (testing "output is constant regardless of *ns*"
+    (let [buf "(ns slamhound.sample) (eval `foo)"]
+      (is (= (asplode (StringReader. buf))
+             (binding [*ns* (find-ns 'user)]
+               (asplode (StringReader. buf))))))))