Add benchmark test for the loader

I'm making some changes that affect the performance
of the parser and the loader, and would like to
benchmark them together.

Unfortunately this required making a bunch of things
public (#[cfg(test)] doesn't seem to apply for
benchmarks), which isn't great.

benches/parse.rs

@@ -1,5 +1,6 @@
 use criterion::{criterion_group, criterion_main, Criterion};
-use std::io::Write;
+use n2::parse::Loader;
+use std::{io::Write, path::PathBuf, str::FromStr};
 
 pub fn bench_canon(c: &mut Criterion) {
     // TODO switch to canon_path_fast
@@ -31,6 +32,7 @@ impl n2::parse::Loader for NoOpLoader {
 
 fn generate_build_ninja() -> Vec<u8> {
     let mut buf: Vec<u8> = Vec::new();
+    write!(buf, "rule cc\n    command = touch $out",).unwrap();
     for i in 0..1000 {
         write!(
             buf,
@@ -85,5 +87,18 @@ pub fn bench_parse(c: &mut Criterion) {
     };
 }
 
-criterion_group!(benches, bench_canon, bench_parse);
+fn bench_load_synthetic(c: &mut Criterion) {
+    let mut input = generate_build_ninja();
+    input.push(0);
+    c.bench_function("load synthetic build.ninja", |b| {
+        b.iter(|| {
+            let mut loader = n2::load::Loader::new();
+            loader
+                .parse(PathBuf::from_str("build.ninja").unwrap(), &input)
+                .unwrap();
+        })
+    });
+}
+
+criterion_group!(benches, bench_canon, bench_parse, bench_load_synthetic);
 criterion_main!(benches);

src/lib.rs

@@ -5,7 +5,7 @@ mod depfile;
 mod eval;
 mod graph;
 mod hash;
-mod load;
+pub mod load;
 pub mod parse;
 mod process;
 #[cfg(unix)]

src/load.rs

@@ -43,7 +43,7 @@ impl<'a> eval::Env for BuildImplicitVars<'a> {
 
 /// Internal state used while loading.
 #[derive(Default)]
-struct Loader {
+pub struct Loader {
     graph: graph::Graph,
     default: Vec<FileId>,
     /// rule name -> list of (key, val)
@@ -64,7 +64,7 @@ impl parse::Loader for Loader {
 }
 
 impl Loader {
-    fn new() -> Self {
+    pub fn new() -> Self {
         let mut loader = Loader::default();
 
         loader.rules.insert("phony".to_owned(), SmallMap::default());
@@ -167,7 +167,7 @@ impl Loader {
         self.parse(path, &bytes)
     }
 
-    fn parse(&mut self, path: PathBuf, bytes: &[u8]) -> anyhow::Result<()> {
+    pub fn parse(&mut self, path: PathBuf, bytes: &[u8]) -> anyhow::Result<()> {
         let filename = std::rc::Rc::new(path);
 
         let mut parser = parse::Parser::new(&bytes);