Put anywhere in bad_line_number.clj, run with clj -J-Dclojure.main.report=stderr -Sdeps '{:paths ["."]}' -M -m bad-line-number from the same dir.
(ns bad-line-number)
(defn returns-a-tuple []
[{1 2} :wrapped])
(defn should-also-return-a-tuple-but-doesnt [data]
{data :unwrapped})
(defn -main []
(let [[a fmt] (returns-a-tuple)
data
(try
(should-also-return-a-tuple-but-doesnt a)
(catch Throwable _
(println "Unable to create a map")
[3 4]))
[x y]
(case fmt
:wrapped data
:unwrapped [data nil])]
[x y]))
Running that code results in
{:clojure.main/message
"Execution error (UnsupportedOperationException) at bad-line-number/-main (bad_line_number.clj:10).\nnth not supported on this type: PersistentArrayMap\n",
:clojure.main/triage
{:clojure.error/class java.lang.UnsupportedOperationException,
:clojure.error/line 10,
:clojure.error/cause
"nth not supported on this type: PersistentArrayMap",
:clojure.error/symbol bad-line-number/-main,
:clojure.error/source "bad_line_number.clj",
:clojure.error/phase :execution},
:clojure.main/trace
{:via
[{:type java.lang.UnsupportedOperationException,
:message "nth not supported on this type: PersistentArrayMap",
:at [clojure.lang.RT nthFrom "RT.java" 992]}],
:trace
[[clojure.lang.RT nthFrom "RT.java" 992]
[clojure.lang.RT nth "RT.java" 940]
[bad_line_number$_main invokeStatic "bad_line_number.clj" 10]
[bad_line_number$_main invoke "bad_line_number.clj" 9]
[clojure.lang.AFn applyToHelper "AFn.java" 152]
[clojure.lang.AFn applyTo "AFn.java" 144]
[clojure.lang.Var applyTo "Var.java" 705]
[clojure.core$apply invokeStatic "core.clj" 667]
[clojure.main$main_opt invokeStatic "main.clj" 514]
[clojure.main$main_opt invoke "main.clj" 510]
[clojure.main$main invokeStatic "main.clj" 664]
[clojure.main$main doInvoke "main.clj" 616]
[clojure.lang.RestFn applyTo "RestFn.java" 137]
[clojure.lang.Var applyTo "Var.java" 705]
[clojure.main main "main.java" 40]],
:cause "nth not supported on this type: PersistentArrayMap"}}
Execution error (UnsupportedOperationException) at bad-line-number/-main (bad_line_number.clj:10).
nth not supported on this type: PersistentArrayMap
As you can see, it refers to line 10, which has (let [[a fmt] (returns-a-tuple), so naturally the first line of thinking is "returns-a-tuple somehow returns a map, and that's what I need to investigate".
Just spent a few hours chasing that goose when it's actually should-also-return-a-tuple-but-doesnt that's to blame.
