Build inputs to the ClojureScript compiler determine what ClojureScript source files get compiled. Figwheel follows a simple heuristic for determining the build inputs based on your configuration.You can determine the build inputs explicitly with the
Understanding how build inputs change the ClojureScript compiler’s behavior can be very helpful depending on your compilation goals.
When you supply a directory like
src to the compiler, it will find
all the ClojureScript files (
.cljc) and use them
directly as the initial sources for compilation. All of these
initial sources will be compiled regardless of their relationship to
:main. When a namespaces is required but not present in these
initial sources, the compiler will then attempt to find it on the
If you provide a single file to the compiler like
src/example/core.cljs only that file will in the intial sources and
all it’s depedencies will be resovled via the classpath.
This behavior has various trade-offs that need to be understood in the context of compiling for development and production.
One could not be blamed for coming to the conclusion that it is always better to supply the compiler with a single build input that represents the root namespace of your application. This way the final code base will only include code that is needed by the application.
Its a temptingly simple heuristic that works for many cases. But let me make an argument why it is better to pass a directory or set of directories to the compiler during developement when you are using a hot reloading workflow.
The biggest reason to have all you files under watch while you are developing them is so that you receive feedback on files that are not currently included in the application. I.E you can work and prototype them and Figwheel will give you feedback on how well they are compiling. This feedback is not to be underestimated as it parallels the feedback that every decent IDE gives you about your code’s syntax.
Another major reason to pass your source directories as your build inputs is to support the extra mains feature. If you are simply compiling from a single root namespace, files that you need for your extra main entry point will possibly not be compiled.
When you are developing with
:none any extra
source files that are being worked on but are not required by the
running application will not be loaded in the running application. The
cost of supplying a directory of source files to the compiler will
only be high if it is expensive when the unrequired source files have
a long initial compile time, which is a very rare situation. Even if
that situation occurs the cost is paid only once during the initial
It is for the above reasons that both
supply the watched directories to the compiler. They are being watched
so there is an expectation of feedback, when there is no feedback on
can mistakely assume that the code one is writing has no syntax
Now when we leave development mode the priority changes. We normally
do not want to include extra source files in a deployed artifact and
we have no need for feedback on files that are not getting
deployed. When we compile one big artifact with in
:whitespace we don’t want it contain unneeded namespaces.
figwheel.main uses the file containing your
:main namespace as the
single build input when you are not in
contains code that is being depended on.
This is less of a problem when you use the
:advanced level as it
will perfom dead code elimination from the final artifact.
Overriding build inputs
Now that you understand the trade-offs you can safely use the
:build-inputs config option] to override the default sources passed
to the compile by Figwheel.
Only sending the main namespace
This will probably be the most common build inputs override.
You can accomplish this with the following config:
:main keyword will be replaced by the main namespaces.
Only sending the watched directories
:watch-dirs keyword will be replaced by the watched directories.
Compiling a directory that you don’t want to watch
./src-no-watch is a source directory that you want to
compile but don’t want to watch.
:build-inputs [:watch-dirs "src-no-watch"]
A string is assumed to be a file or a directory.
Watched directories and a specific namespace
:build-inputs [:watch-dirs example.tool.extra]
A symbol is assume to be a ClojureScript namespace.