Compiler bug with lazy-seq getting quoted

Question

I have encountered a bug when lazy-seq is passed into a quote. Here is an example which causes the issue:

`
user=> (eval `(quote ~(lazy-seq '(1 2 3))))
(1 2 3)

user=> (eval `(quote ~(lazy-seq '())))
Syntax error (UnsupportedOperationException) compiling fn* at (REPL:1:1).
Unknown Collection type

user=> (eval (quote ())) () ``

Answer 1

Is there some scenario where this is relevant?

Comments

Lots of Clojure's methods will return a lazy-seq, so if quote is used on an empty collection, it can cause this issue.  For example: "`(quote ~(map a b))"

I wrote the above example using lazy-seq directly to make a minimal test case

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I’m not aware of anyone running into this ever, so I’m really more interested in when someone (like yourself) might actually have run into it.

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Is there any scenario not involving eval where this causes a problem? Because eval is vanishingly rare in production Clojure code.

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"(defmacro m [] `'~(keep (constantly nil) (range 10)))" has the same issue.

I found that the `Compiler$EmptyExpr` doesn't deal with empty sequences properly other than empty lists. Maybe the Compiler code around here https://github.com/clojure/clojure/blob/6975553804b0f8da9e196e6fb97838ea4e153564/src/jvm/clojure/lang/Compiler.java#L2990-L2991 should handle those cases.

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I had a macro that records some data using quote into a data structure.  This is something like "(defmacro m [x y]  `(swap! global-data assoc ~(foo x)  (quote ~(map bar y))))"
The issue was triggered when "y" was passed an empty vector.

I managed to work around this for now by just casting the mapped lazy seq to a vector:
"(defmacro m [x y]  `(swap! global-data assoc ~(foo x)  (quote ~(vec (map bar y)))))"

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thank you, that's helpful