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Some compiler exceptions wrapped in new CompilerException

Description

Clojure error reporting changed in CLJ-1169 to wrap exceptions thrown during macro evaluation in CompilerException to give more input:

Clojure 1.6

(defmacro demo [] (throw (ex-info "fail" {}))) (demo) ExceptionInfo fail clojure.core/ex-info (core.clj:4403) (class *e) => clojure.lang.ExceptionInfo

Clojure 1.7.0-alpha2 to 1.7.0-RC1

(defmacro demo [] (throw (ex-info "fail" {}))) (demo) ExceptionInfo fail clojure.core/ex-info (core.clj:4403) ;; NOTE: lein repl will instead print: CompilerException clojure.lang.ExceptionInfo: fail {}, compiling:(form-init8304622754337237403.clj:1:1) (class *e) => clojure.lang.Compiler$CompilerException

This change has caused some breakage for users that throw exceptions in macros and expect to see the same exception at the top of the exception chain, not wrapped in a CompilerException. This change is somewhat masked in the Clojure REPL because clojure.main/root-cause unwraps CompilerException wrappers and prints the root cause when an exception occurs.

More background can be found in some messages on:
https://groups.google.com/d/msg/clojure/ccZuKTYKDPc/xpaz44UDqYwJ

Approach: The attached patch rolls back most of the change for CLJ-1169, specifically the part that wraps exceptions in CompilerException and the tests that were affected by this change (good examples of the kind of breakage others are seeing). I left the parts of CLJ-1169 that added quotes in the error message and those equivalent tests.

Patch: clj-1745.patch

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  • 05 Jun 2015, 10:36 PM

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Alex Miller June 5, 2015 at 10:36 PM

I went back and looked at CLJ-1169 and while I think the intentions are good there, I do think that wrapping exceptions that happen to be thrown out of macro bodies like this does create unexpected (certainly different) behavior. I've attached a patch that rolls back most of the CLJ-1169 change.

Alex Miller June 5, 2015 at 10:02 PM

There is one confusing factor in replicating this re lein vs Clojure. The Clojure REPL will unpeel CompilerExceptions (see clojure.main/root-cause) so the repl actually prints the same in 1.7 as in 1.6 (but the exception chain and class are wrapped in one more CompilerException than before). Leiningen's repl will actually show the full structure.

Alex Miller June 5, 2015 at 1:50 PM

Pulling this into 1.7 just for tracking discussion.

Stuart Halloway June 5, 2015 at 1:15 AM

All the stuff about lein in this ticket is just noise, and I am removing it. (Please don't use the phrase "small reproducing case" for anything that includes lein.) Clojure's behavior changed: improved error reporting. Code that explicitly relied on less-good error reporting broke.

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Created June 4, 2015 at 6:09 PM
Updated June 17, 2015 at 4:58 PM
Resolved June 17, 2015 at 4:58 PM

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