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# vs. CMake | ||
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GYP was originally created to generate native IDE project files (Visual Studio, Xcode) for building [Chromium](http://www.chromim.org). | ||
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The functionality of GYP is very similar to the [CMake](http://www.cmake.org) | ||
build tool. Bradley Nelson wrote up the following description of why the team | ||
created GYP instead of using CMake. The text below is copied from | ||
http://www.mail-archive.com/[email protected]/msg11029.html | ||
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``` | ||
Re: [webkit-dev] CMake as a build system? | ||
Bradley Nelson | ||
Mon, 19 Apr 2010 22:38:30 -0700 | ||
Here's the innards of an email with a laundry list of stuff I came up with a | ||
while back on the gyp-developers list in response to Mike Craddick regarding | ||
what motivated gyp's development, since we were aware of cmake at the time | ||
(we'd even started a speculative port): | ||
I did an exploratory port of portions of Chromium to cmake (I think I got as | ||
far as net, base, sandbox, and part of webkit). | ||
There were a number of motivations, not all of which would apply to other | ||
projects. Also, some of the design of gyp was informed by experience at | ||
Google with large projects built wholly from source, leading to features | ||
absent from cmake, but not strictly required for Chromium. | ||
1. Ability to incrementally transition on Windows. It took us about 6 months | ||
to switch fully to gyp. Previous attempts to move to scons had taken a long | ||
time and failed, due to the requirement to transition while in flight. For a | ||
substantial period of time, we had a hybrid of checked in vcproj and gyp generated | ||
vcproj. To this day we still have a good number of GUIDs pinned in the gyp files, | ||
because different parts of our release pipeline have leftover assumptions | ||
regarding manipulating the raw sln/vcprojs. This transition occurred from | ||
the bottom up, largely because modules like base were easier to convert, and | ||
had a lower churn rate. During early stages of the transition, the majority | ||
of the team wasn't even aware they were using gyp, as it integrated into | ||
their existing workflow, and only affected modules that had been converted. | ||
2. Generation of a more 'normal' vcproj file. Gyp attempts, particularly on | ||
Windows, to generate vcprojs which resemble hand generated projects. It | ||
doesn't generate any Makefile type projects, but instead produces msvs | ||
Custom Build Steps and Custom Build Rules. This makes the resulting projects | ||
easier to understand from the IDE and avoids parts of the IDE that simply | ||
don't function correctly if you use Makefile projects. Our early hope with | ||
gyp was to support the least common denominator of features present in each | ||
of the platform specific project file formats, rather than falling back on | ||
generated Makefiles/shell scripts to emulate some common abstraction. CMake by | ||
comparison makes a good faith attempt to use native project features, but | ||
falls back on generated scripts in order to preserve the same semantics on | ||
each platforms. | ||
3. Abstraction on the level of project settings, rather than command line | ||
flags. In gyp's syntax you can add nearly any option present in a hand | ||
generated xcode/vcproj file. This allows you to use abstractions built into | ||
the IDEs rather than reverse engineering them possibly incorrectly for | ||
things like: manifest generation, precompiled headers, bundle generation. | ||
When somebody wants to use a particular menu option from msvs, I'm able to | ||
do a web search on the name of the setting from the IDE and provide them | ||
with a gyp stanza that does the equivalent. In many cases, not all project | ||
file constructs correspond to command line flags. | ||
4. Strong notion of module public/private interface. Gyp allows targets to | ||
publish a set of direct_dependent_settings, specifying things like | ||
include_dirs, defines, platforms specific settings, etc. This means that | ||
when module A depends on module B, it automatically acquires the right build | ||
settings without module A being filled with assumptions/knowledge of exactly | ||
how module B is built. Additionally, all of the transitive dependencies of | ||
module B are pulled in. This avoids their being a single top level view of | ||
the project, rather each gyp file expresses knowledge about its immediate | ||
neighbors. This keep local knowledge local. CMake effectively has a large | ||
shared global namespace. | ||
5. Cross platform generation. CMake is not able to generate all project | ||
files on all platforms. For example xcode projects cannot be generated from | ||
windows (cmake uses mac specific libraries to do project generation). This | ||
means that for instance generating a tarball containing pregenerated | ||
projects for all platforms is hard with Cmake (requires distribution to | ||
several machine types). | ||
6. Gyp has rudimentary cross compile support. Currently we've added enough | ||
functionality to gyp to support x86 -> arm cross compiles. Last I checked | ||
this functionality wasn't present in cmake. (This occurred later). | ||
That being said there are a number of drawbacks currently to gyp: | ||
1. Because platform specific settings are expressed at the project file | ||
level (rather than the command line level). Settings which might otherwise | ||
be shared in common between platforms (flags to gcc on mac/linux), end up | ||
being repeated twice. Though in fairness there is actually less sharing here | ||
than you'd think. include_dirs and defines actually represent 90% of what | ||
can be typically shared. | ||
2. CMake may be more mature, having been applied to a broader range of | ||
projects. There a number of 'tool modules' for cmake, which are shared in a | ||
common community. | ||
3. gyp currently makes some nasty assumptions about the availability of | ||
chromium's hermetic copy of cygwin on windows. This causes you to either | ||
have to special case a number of rules, or swallow this copy of cygwin as a | ||
build time dependency. | ||
4. CMake includes a fairly readable imperative language. Currently Gyp has a | ||
somewhat poorly specified declarative language (variable expansion happens | ||
in sometimes weird and counter-intuitive ways). In fairness though, gyp assumes | ||
that external python scripts can be used as an escape hatch. Also gyp avoids | ||
a lot of the things you'd need imperative code for, by having a nice target | ||
settings publication mechanism. | ||
5. (Feature/drawback depending on personal preference). Gyp's syntax is | ||
DEEPLY nested. It suffers from all of Lisp's advantages and drawbacks. | ||
-BradN | ||
``` |
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# Hacking | ||
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## Getting the sources | ||
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Git is required to hack on anything, you can set up a git clone of GYP | ||
as follows: | ||
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``` | ||
mkdir foo | ||
cd foo | ||
git clone [email protected]:nodejs/gyp-next.git | ||
cd gyp | ||
``` | ||
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(this will clone gyp underneath it into `foo/gyp`. | ||
`foo` can be any directory name you want. Once you've done that, | ||
you can use the repo like anything other Git repo. | ||
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## Testing your change | ||
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GYP has a suite of tests which you can run with the provided test driver | ||
to make sure your changes aren't breaking anything important. | ||
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You run the test driver with e.g. | ||
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``` sh | ||
$ python -m pip install --upgrade pip setuptools | ||
$ pip install --editable ".[dev]" | ||
$ python -m pytest | ||
``` | ||
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See [Testing](Testing.md) for more details on the test framework. | ||
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Note that it can be handy to look at the project files output by the tests | ||
to diagnose problems. The easiest way to do that is by kindly asking the | ||
test driver to leave the temporary directories it creates in-place. | ||
This is done by setting the enviroment variable "PRESERVE", e.g. | ||
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``` | ||
set PRESERVE=all # On Windows | ||
export PRESERVE=all # On saner platforms. | ||
``` | ||
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## Reviewing your change | ||
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All changes to GYP must be code reviewed before submission. |
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