I have written a custom Ant task that compiles a tree of fasm source files, similar to what the javac task does for Java files. If anyone is interested, you can find it here: https://github.com/dykstrom/fasm-ant.

And what javac does for Java files?

Ah, sorry for not being clearer. If one does not live in the Java universe, it may not be obvious what Ant or the javac task does. Ant is a build tool that is built in Java, and is mostly used for building Java projects.

Ant works by running various tasks. Most tasks you will ever use are built-in, but you can also create your own tasks. The built-in javac task recursively finds all Java source files in a directory, invokes the Java compiler on them, and creates a similar tree structure with the compiled files.

What I have done is creating a custom task that recursively finds all assembly source files in a directory, invokes fasm on those files that need to be recompiled, and creates an output tree structure with the compiled files.