1 files changed, 64 insertions, 0 deletions
diff --git a/python/pymake/README b/python/pymake/README
new file mode 100644
index 000000000..4f0fdfea4
--- /dev/null
+++ b/python/pymake/README
@@ -0,0 +1,64 @@
+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) 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)