Fix handling of ::keywords using aliases

This patch introduces namespace tracking to Marginalia's parser: ns,
in-ns, require, use and alias forms are now evaluated in the proper
namespace at read-time. This is necessary to handle ::keywords in full
generality, since ::foo/bar is a valid token iff the symbol 'foo can
be resolved to a namespace at read time:

    (in-ns 'test)

    ::foo/bar
    ; => invalid token results in read-time error

    (require '[some.namespace :as foo])
    ::foo/bar
    ; => :some.namespace/foo

NB. only top-level #{ns in-ns require use alias} forms are recognized.

src/marginalia/parser.clj

@@ -15,6 +15,9 @@
 (def top-level-comments (atom []))
 (def sub-level-comments (atom []))
 
+(def user-ns (the-ns 'user))
+(def current-namespace (atom user-ns))
+
 (def *comments* nil)
 
 (defn read-comment [reader semicolon]
@@ -49,6 +52,14 @@
           (recur (.read rdr))
           :else (.unread rdr c))))
 
+(defn maybe-change-namespace [form]
+  (when (and (seq? form)
+             ('#{ns in-ns require use alias} (first form)))
+    (binding [*ns* @current-namespace]
+      (eval form))
+    (when ('#{ns in-ns} (first form))
+      (reset! current-namespace (the-ns (second form))))))
+
 (defn parse* [reader]
   (take-while
    :form
@@ -58,12 +69,14 @@
        (binding [*comments* top-level-comments]
          (skip-spaces-and-comments reader))
        (let [start (.getLineNumber reader)
-             form (binding [*comments* sub-level-comments]
+             form (binding [*comments* sub-level-comments
+                            *ns*       @current-namespace]
                     (. clojure.lang.LispReader
                        (read reader false nil false)))
              end (.getLineNumber reader)
              code {:form form :start start :end end}
              comments @top-level-comments]
+         (maybe-change-namespace form)
          (swap! top-level-comments (constantly []))
          (if (empty? comments)
            [code]

test/marginalia/test/parse.clj

@@ -8,4 +8,5 @@
   ;(is (= (count (marginalia.parser/parse "(ns test)\n123")) 1)) still failing
   (is (= (count (marginalia.parser/parse "(ns test)\n123\n")) 1))
   (is (= (count (marginalia.parser/parse "(ns test)\n\"string\"")) 1))
-  (is (= (count (marginalia.parser/parse "(ns test)\n\"some string\"")) 1)))
+  (is (= (count (marginalia.parser/parse "(ns test)\n\"some string\"")) 1))
+  (is (= (count (marginalia.parser/parse "(ns test (:require [marginalia.parser :as parser]))\n(defn foo [] ::parser/foo)")) 1)))