[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.

Clojure JIRA

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