lein-figwheel expects files with .js extension inside its source
directories to be foreign libraries. And foreign libraries must
declare a namespace. In fact, lein-figwheel assumes it, and if it
doesn't find it and can't map the file back to a source .cljs file, it
bombs out with a NullPointerException when trying to check for its
existance.
This might happen when you put your externs file(s) inside the source
directories (this is in fact the case that led to the discovery of
this issue).
Clearly Duct server.figwheel shouldn't be telling lein-figwheel to
process absolutely all files in source directories (but probably just
those having .cljs/cljc extension or those declared as foreign
libraries[1]).
But on the other hand, lein-figwheel should be more robust and handle
that situation in a more graceful way.
[1] We have opened an issue in Duct server.figwheel regarding this behaviour.
lein-figwheel expects files with .js extension inside its source directories to be foreign libraries. And foreign libraries must declare a namespace. In fact, lein-figwheel assumes it, and if it doesn't find it and can't map the file back to a source .cljs file, it bombs out with a NullPointerException when trying to check for its existance.
This might happen when you put your externs file(s) inside the source directories (this is in fact the case that led to the discovery of this issue).
While lein-figwheel doesn't by default try to process such files on its own, when using Duct server.figwheel it tells lein-figwheel to proccess all files inside the configured source directories (see https://github.com/duct-framework/server.figwheel/blob/master/src/duct/server/figwheel.clj#L54-L55).
Clearly Duct server.figwheel shouldn't be telling lein-figwheel to process absolutely all files in source directories (but probably just those having .cljs/cljc extension or those declared as foreign libraries[1]).
But on the other hand, lein-figwheel should be more robust and handle that situation in a more graceful way.
[1] We have opened an issue in Duct server.figwheel regarding this behaviour.