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    1 INTRODUCTION
    2 
    3 make.py (and the pymake modules that support it) are an implementation of the make tool
    4 which are mostly compatible with makefiles written for GNU make.
    5 
    6 PURPOSE
    7 
    8 The Mozilla project inspired this tool with several goals:
    9 
   10 * Improve build speeds, especially on Windows. This can be done by reducing the total number
   11   of processes that are launched, especially MSYS shell processes which are expensive.
   12 
   13 * Allow writing some complicated build logic directly in Python instead of in shell.
   14 
   15 * Allow computing dependencies for special targets, such as members within ZIP files.
   16 
   17 * Enable experiments with build system. By writing a makefile parser, we can experiment
   18   with converting in-tree makefiles to another build system, such as SCons, waf, ant, ...insert
   19   your favorite build tool here. Or we could experiment along the lines of makepp, keeping
   20   our existing makefiles, but change the engine to build a global dependency graph.
   21 
   22 KNOWN INCOMPATIBILITIES
   23 
   24 * Order-only prerequisites are not yet supported
   25 
   26 * Secondary expansion is not yet supported.
   27 
   28 * Target-specific variables behave differently than in GNU make: in pymake, the target-specific
   29   variable only applies to the specific target that is mentioned, and does not apply recursively
   30   to all dependencies which are remade. This is an intentional change: the behavior of GNU make
   31   is neither deterministic nor intuitive.
   32 
   33 * $(eval) is only supported during the parse phase. Any attempt to recursively expand
   34   an $(eval) function during command execution will fail. This is an intentional incompatibility.
   35 
   36 * There is a subtle difference in execution order that can cause unexpected changes in the
   37   following circumstance:
   38 ** A file `foo.c` exists on the VPATH
   39 ** A rule for `foo.c` exists with a dependency on `tool` and no commands
   40 ** `tool` is remade for some other reason earlier in the file
   41   In this case, pymake resets the VPATH of `foo.c`, while GNU make does not. This shouldn't
   42   happen in the real world, since a target found on the VPATH without commands is silly. But
   43   mozilla/js/src happens to have a rule, which I'm patching.
   44 
   45 * pymake does not implement any of the builtin implicit rules or the related variables. Mozilla
   46   only cares because pymake doesn't implicitly define $(RM), which I'm also fixing in the Mozilla
   47   code.
   48 
   49 ISSUES
   50 
   51 * Speed is a problem.
   52 
   53 FUTURE WORK
   54 
   55 * implement a new type of command which is implemented in python. This would allow us
   56 to replace the current `nsinstall` binary (and execution costs for the shell and binary) with an
   57 in-process python solution.
   58 
   59 AUTHOR
   60 
   61 Initial code was written by Benjamin Smedberg <benjamin@smedbergs.us>. For future releases see
   62 http://benjamin.smedbergs.us/pymake/
   63 
   64 See the LICENSE file for license information (MIT license)