INTRODUCTION

make.py (and the pymake modules that support it) are an implementation of the make tool which are mostly compatible with makefiles written for GNU make.

PURPOSE

The Mozilla project inspired this tool with several goals:

• Improve build speeds, especially on Windows. This can be done by reducing the total number of processes that are launched, especially MSYS shell processes which are expensive.

• Allow writing some complicated build logic directly in Python instead of in shell.

• Allow computing dependencies for special targets, such as members within ZIP files.

• Enable experiments with build system. By writing a makefile parser, we can experiment with converting in-tree makefiles to another build system, such as SCons, waf, ant, …insert your favorite build tool here. Or we could experiment along the lines of makepp, keeping our existing makefiles, but change the engine to build a global dependency graph.

KNOWN INCOMPATIBILITIES

• Order-only prerequisites are not yet supported

• Secondary expansion is not yet supported.

• Target-specific variables behave differently than in GNU make: in pymake, the target-specific variable only applies to the specific target that is mentioned, and does not apply recursively to all dependencies which are remade. This is an intentional change: the behavior of GNU make is neither deterministic nor intuitive.

• $(eval)isonlysupportedduringtheparsephase\mathrm{.}Anyattempttorecursivelyexpandan(eval)\; is\; only\; supported\; during\; the\; parse\; phase.\; Any\; attempt\; to\; recursively\; expand\; an$(eval) function during command execution will fail. This is an intentional incompatibility.

• There is a subtle difference in execution order that can cause unexpected changes in the following circumstance:

• • A file foo.c exists on the VPATH
• • A rule for foo.c exists with a dependency on tool and no commands
• • tool is remade for some other reason earlier in the file In this case, pymake resets the VPATH of foo.c, while GNU make does not. This shouldn’t happen in the real world, since a target found on the VPATH without commands is silly. But mozilla/js/src happens to have a rule, which I’m patching.

• pymake does not implement any of the builtin implicit rules or the related variables. Mozilla only cares because pymake doesn’t implicitly define $(RM), which I’m also fixing in the Mozilla code.

ISSUES

• Speed is a problem.

FUTURE WORK

• implement a new type of command which is implemented in python. This would allow us to replace the current nsinstall binary (and execution costs for the shell and binary) with an in-process python solution.

AUTHOR

Initial code was written by Benjamin Smedberg benjamin@smedbergs.us. For future releases see http://benjamin.smedbergs.us/pymake/

See the LICENSE file for license information (MIT license)