The most important thing to realize about code generators in abuild is that code generation can be viewed as a just another service that a build item can offer, just like libraries or header files. In many build systems, code generators are problematic because you need to take special steps to make sure generated code appears before compilation or dependency generation begin. With abuild, code generators get run at the correct stage by virtue of appearing in the correct place in the dependency tree.

In order for a make-based build item to provide code generation, it must have a Rules.mk file. The Rules.mk file is a GNU Make fragment that is included by abuild only when explicitly requested. In order to use the rules implemented in one build item's Rules.mk file, you must depend on that build item and also list its name in the BUILD_ITEM_RULES variable in your Abuild.mk file. Any rules defined in Rules.mk are run from the abuild output directory of the build item that is using the rules. That means that if the rules need to refer to files inside the build item that provides the rules, they must do so by either accessing interface variables defined in that build item's Abuild.interface, or prefixing the files with a variable that abuild provides. Specifically, for a build item named build-item, abuild provides variable called abDIR_build-item that can be accessed from a Rules.mk file. Note that abuild only provides these variables for build items in your dependency chain. Also, use of these variables from Abuild.mk files is strongly discouraged as it can cause your build tree to contain path-based dependencies instead of name-based dependencies which would defeat one of the most compelling advantages of abuild. The best practice is to refer to files in your own build item from your own files by using the abuild-provided variable name to find your own path, and to define interface variables for files that you intend for other build items to access. Either way, there are certain things that it are important to keep in mind when writing GNU Make rules for use inside of abuild. For a discussion of this topic, please see Section 27.2, “Guidelines for Make Rule Authors”.