Clojure JIRA

[CLJ-270] defn-created fns inherit old metadata from the Var they are assigned to

Tue, 24 Aug 2010 06:23:00 -0500

What (small set of) steps will reproduce the problem?

user> (def #^{:foo "bar"} x 5)
#'user/x
user> (meta #'x)
{:ns #<Namespace user>, :name x, :file "NO_SOURCE_FILE", :line 1, :foo "bar"}
user> (defn x [] 5)
#'user/x
user> (meta #'x)
{:ns #<Namespace user>, :name x, :file "NO_SOURCE_FILE", :line 1, :arglists ([])}
user> (meta x)
{:ns #<Namespace user>, :name x, :file "NO_SOURCE_FILE", :line 1, :foo "bar"}

What is the expected output? What do you see instead?

I expect (meta #'x) to evaluate to the value of the final (meta x) in the above.

What version are you using?

Current master (commit 61202d2ff6925002400a9843e8fbd080f3bef3a5).

Was this discussed on the group? If so, please provide a link to the discussion.

http://groups.google.com/group/clojure/browse_thread/thread/4c7151aa9c4d919c/d1b033ef5a13dd89?lnk=gst&q=off-by-one#d1b033ef5a13dd89

Prompted by discussion at

http://groups.google.com/group/clojure/browse_thread/thread/6553d48c981019eb/3c55b0bd43a5d8e9?lnk=gst&q=off-by-one#3c55b0bd43a5d8e9

Initial attempt at a diagnosis:

I think this is due to DefExpr's eval method binding the Var to init.eval() first and attaching the supplied metadata to the Var later – see Compiler.java lines 341-352. (Note the Var is always already in place when init.eval() is called, regardless of whether it existed prior to the evaluation of the def / defn.) Thus the init expression supplied by defn sees the old (and wrong) metadata on the Var.

[CLJ-273] def with a function value returns meta {:macro false}, but def itself doesn't have meta

Tue, 24 Aug 2010 09:32:00 -0500

On the master (1.2) branch, if you create a def with an initial function value, {:macro false} is added to the metadata of the return value for def. However, if you look again at the metadata on the var itself, the {:macro false} is not present! This breaks the use of contrib's defalias when aliasing macros, because the new alias is marked as {:macro false}.

The code below demonstrates the issue, which was introduced in http://github.com/richhickey/clojure/commit/430dd4fa711d0008137d7a82d4b4cd27b6e2d6d1, "metadata for fns."

;; all running on 1.2, DIFF noted in comments

(defmacro foo [])
-> #'user/foo

(meta (def bar (.getRoot #'foo)))
-> {:macro false, :ns #<Namespace user>, :name bar, :file "NO_SOURCE_PATH", :line 83}
;; DIFF: where did that :macro false come from??

(def bar (.getRoot #'foo))
-> #'user/bar

(meta #'bar)
-> {:ns #<Namespace user>, :name bar, :file "NO_SOURCE_PATH", :line 84}
;; LIKE 1.1, but really weird: now the :macro false is gone again!

[CLJ-2] Scopes

Thu, 8 Mar 2012 04:01:38 -0600

Add the scope system for dealing with resource lifetime management

[CLJ-84] GC Issue 81: compile gen-class fail when class returns self

Fri, 10 Dec 2010 09:30:52 -0600

Reported by davidhaub, Feb 14, 2009

When attempting to compile the following program, clojure fails with a
ClassNotFoundException.  It occurs because one of the methods returns the
same class that is being generated.  If the returnMe method below is
changed to return an Object, the compile succeeds.

Beware when testing! If the classpath contains a class file (say from a
prior successful build when the returnMe method was changed to return an
object), the compile will succeed.  Always clear out the
clojure.compile.path prior to compiling.

;badgenclass.clj
(ns badgenclass
  (:gen-class
     :state state
     :methods
     [[returnMe [] badgenclass]]
     :init init))
(defn -init []
  [[] nil])

(defn -returnMe [this]
  this)

#!/bin/sh
rm -rf classes
mkdir classes
java -cp lib/clojure.jar:classes:. -Dclojure.compile.path=classes \
clojure.lang.Compile badgenclass


Comment 1 by chouser, Mar 07, 2009

Attached is a patch that accepts strings or symbols for parameter and return class
names, and generates the appropriate bytecode without calling Class/forName.  It
fixes this issue, but because 'ns' doesn't resolve :gen-class's arguments, class
names aren't checked as early anymore.  :gen-class-created classes with invalid
parameter or return types can even be instantiated, and no error will be reported
until the broken method is called.

One possible alternative would be to call Class/forName on any symbols given, but
allow strings to use the method given by this patch.  To return your own type, you'd
need a method defined like:

  [returnMe [] "badgenclass"]

Any thoughts?