with-redefs does not work for macros

[Vebjorn Ljosa]

In one of my tests, I was trying to mock something (`clojure.tools.logging/warn`) that happened to be a macro. It had me puzzled for a while until I discovered that `with-redefs` resets the value of the vars after the body is executed, but does not reset the flag that says that the var is a macro:

$ lein repl
Clojure 1.6.0
…
user=> (defmacro foo [] `(prn "I am a macro"))
#'user/foo
user=> (clojure.test/function? 'foo)

false
user=> (with-redefs [foo (fn [] 42)])
nil
user=> (clojure.test/function? foo)
true
user=> (foo)
ArityException Wrong number of args (0) passed to: user/foo clojure.lang.AFn.throwArity (AFn.java:429)
user=> (foo 42 42)
(clojure.core/prn "I am a macro")

Is this a bug?

I looked at the source for `with-redefs-fn`, and the fix appears simple: record for each val whether it's a macro or not, and then call the `(setMacro)` method on the vars that should be macros after resetting their values.

Vebjorn

[Vebjorn Ljosa]

On Monday, April 27, 2015 at 12:34:14 PM UTC-4, Vebjorn Ljosa wrote:

In one of my tests, I was trying to mock something (`clojure.tools.logging/warn`) that happened to be a macro. It had me puzzled for a while until I discovered that `with-redefs` resets the value of the vars after the body is executed, but does not reset the flag that says that the var is a macro:

Granted, using `with-redefs` with a macro rarely makes sense because macroexpansion has to occur within the extent of `with-redefs` for the redefinition to have any effect. (I can't even think of an example where I would want to do that, so maybe `with-redefs` should emit a warning when it's being asked to redefine a macro.) But in any case, an attempt to use `with-redefs` on something that happens to be a macro should not mess up the root binding permanently.

[Tiago Espinha]

Damn it, I got exactly the same thing. In my case when trying to mock the /error fun...ehem...macro :-)

There should definitely be some kind of warning or even an error. It doesn't make sense to mock macros since these are expanded at compile time.

[Beau Fabry]

Not an answer to your question, but I usually just redefine clojure.tools.logging/log* instead for tests.

[Tiago Espinha]

It's definitely good to mention. It's also what I ended up doing but didn't mention it in my answer :)

--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clo...@googlegroups.com
Note that posts from new members are moderated - please be patient with your first post.
To unsubscribe from this group, send email to
clojure+u...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
---
You received this message because you are subscribed to a topic in the Google Groups "Clojure" group.
To unsubscribe from this topic, visit https://groups.google.com/d/topic/clojure/gCDnbREpdSg/unsubscribe.
To unsubscribe from this group and all its topics, send an email to clojure+u...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.