Commit c1af5161 authored by Simon Sapin's avatar Simon Sapin Committed by Emilio Cobos Álvarez
Browse files

Bug 1587368 - servo: WebIDL codegen: Replace cmake with a single Python script. r=emilio

When playing around with Cargo’s new timing visualization:

… I was surprised to see the `script` crate’s build script take 76 seconds.
I did not expect WebIDL bindings generation to be *that* computationally

It turns out almost all of this time is overhead. The build script uses CMake
to generate bindings for each WebIDL file in parallel, but that causes a lot
of work to be repeated 366 times:

* Starting up a Python VM
* Importing (parts of) the Python standard library
* Importing ~16k lines of our Python code
* Recompiling the latter to bytecode, since we used `python -B` to disable
  writing `.pyc` file
* Deserializing with `cPickle` and recreating in memory the results
  of parsing all WebIDL files


This commit remove the use of CMake and cPickle for the `script` crate.
Instead, all WebIDL bindings generation is done sequentially
in a single Python process. This takes 2 to 3 seconds.
parent c00df807
......@@ -27,52 +27,28 @@ mod build_gecko {
pub fn generate() {}
fn find_python() -> String {
if Command::new("python2.7.exe")
return "python2.7.exe".to_owned();
if Command::new("python27.exe")
return "python27.exe".to_owned();
if Command::new("python.exe").arg("--version").output().is_ok() {
return "python.exe".to_owned();
"Can't find python (tried python2.7.exe, python27.exe, and python.exe)! ",
"Try fixing PATH or setting the PYTHON env var"
fn find_python() -> String {
if Command::new("python2.7")
} else {
lazy_static! {
pub static ref PYTHON: String = env::var("PYTHON").ok().unwrap_or_else(find_python);
pub static ref PYTHON: String = env::var("PYTHON").ok().unwrap_or_else(|| {
let candidates = if cfg!(windows) {
["python2.7.exe", "python27.exe", "python.exe"]
} else {
["python2.7", "python2", "python"]
for &name in &candidates {
if Command::new(name)
.map_or(false, |out| out.status.success())
return name.to_owned();
"Can't find python (tried {})! Try fixing PATH or setting the PYTHON env var",
candidates.join(", ")
fn generate_properties(engine: &str) {
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