Zen

Focusing compilation.

Levels:

Zen has different levels that can be set project-wide, for specific source files, or individual code blocks.

• Disable: Disables Zen for this source file or block; any change to the source will trigger a rebuild of dependant objects.
• Shallow: Prevents changes in comments and whitespace from triggering rebuilds of dependant objects.
• Deep: (WIP) Only changes to types (namespaces, classes, functions, and macros) actually used by compiled objects will trigger a rebuild. For example: modifying the class declaration of Foo will only trigger a rebuild of dependant objects if they actually use Foo.

Project Assumptions:

In order to effectively optimize compilation, Zen makes a number of assumptions about the structure of a project.

• Definitions in header files will not be linked to. Zen assumes that if a definition is in a header file, then it will be included by any source files that require it.
• Zen assumes that all definitions in .cc / .cpp source files are useful, and should cause recompilation should they change, while all declarations and definitions in header files exist purely to be used within the compilation units that #include them. Therefore, if a declaration or definition within a header file is not used within the the current compilation unit (directly or indirectly) then any changes made to it should not cause a rebuild of that unit.
• Headers and source from outside the project do not change.

Unsupported code features:

Some features of valid C++ code are not supported by Zen, and are not intended to ever be supported.

These include:

• #include statements anywhere but in the global scope.
• Cross-file code blocks, IE: a code block that begins in one file, and ends in another, via abuse of #include preprocessor macros.
• Macros that act as anything but a pseudo-function. For example: macros such as SWAP(a, b) are acceptable, however a macro that expands to the declaration of a function is not supported, and a macro that contains only the beginning or only the end of a code block are certainly not supported. If you must have such things in your code, the surrounding code block containing the macro should be marked with // ZEN(disable)

Todo:

• Test + ensure correct operation of shallow mode
• Implement deep mode
  • Consider operator overload functions to be used whenever their class is, since they are called without their name being used.
  • Obey ZEN() tags within comments - Disable / Shallow / Deep
  • Test on large codebase(s) to find bugs.