add a bench for workspace initialization

Author: Muscraft

benches/benchsuite/Cargo.toml

@@ -10,6 +10,7 @@ description = "Benchmarking suite for Cargo."
 
 [dependencies]
 cargo = { path = "../.." }
+cargo-test-support = { path = "../../crates/cargo-test-support" }
 # Consider removing html_reports in 0.4 and switching to `cargo criterion`.
 criterion = { version = "0.3.5", features = ["html_reports"] }
 flate2 = { version = "1.0.3", default-features = false, features = ["zlib"] }
@@ -22,3 +23,7 @@ bench = false
 [[bench]]
 name = "resolve"
 harness = false
+
+[[bench]]
+name = "workspace_initialization"
+harness = false

benches/benchsuite/benches/workspace_initialization.rs

@@ -0,0 +1,27 @@
+use benchsuite::fixtures;
+use cargo::core::Workspace;
+use criterion::{criterion_group, criterion_main, Criterion};
+
+fn workspace_initialization(c: &mut Criterion) {
+    let fixtures = fixtures!();
+    let mut group = c.benchmark_group("workspace_initialization");
+    for (ws_name, ws_root) in fixtures.workspaces() {
+        let config = fixtures.make_config(&ws_root);
+        // The resolver info is initialized only once in a lazy fashion. This
+        // allows criterion to skip this workspace if the user passes a filter
+        // on the command-line (like `cargo bench -- workspace_initialization/tikv`).
+        group.bench_function(ws_name, |b| {
+            b.iter(|| Workspace::new(&ws_root.join("Cargo.toml"), &config).unwrap())
+        });
+    }
+    group.finish();
+}
+
+// Criterion complains about the measurement time being too small, but the
+// measurement time doesn't seem important to me, what is more important is
+// the number of iterations which defaults to 100, which seems like a
+// reasonable default. Otherwise, the measurement time would need to be
+// changed per workspace. We wouldn't want to spend 60s on every workspace,
+// that would take too long and isn't necessary for the smaller workspaces.
+criterion_group!(benches, workspace_initialization);
+criterion_main!(benches);