perf(render): pre-size generated view output

2026-07-13 09:53:26 +02:00
parent 7db05356ae
commit d32f3cb893
6 changed files with 103 additions and 2 deletions
@@ -6,6 +6,10 @@ edition.workspace = true
 [lib]
 path = "src/lib.rs"

+[[bench]]
+name = "render"
+harness = false
+
 [dependencies]
 hemplate = { path = "../../hemplate/hemplate" }
 hemx-core = { path = "../hemx-core" }
@@ -0,0 +1,58 @@
+//! Generated-view rendering baseline: `cargo bench -p hemx --bench render`.
+
+use hemplate::Hemplate;
+use std::hint::black_box;
+use std::time::Instant;
+
+const ITERATIONS: u32 = 100_000;
+const ROUNDS: usize = 7;
+
+#[derive(Hemplate)]
+struct BenchPage {
+    title: String,
+    body: String,
+    items: Vec<String>,
+}
+
+fn page() -> BenchPage {
+    BenchPage {
+        title: String::from("Production readiness"),
+        body: "Checked hypermedia without a parallel client application. ".repeat(4),
+        items: (0..20).map(|index| format!("item-{index}")).collect(),
+    }
+}
+
+fn median_ns(mut render: impl FnMut() -> usize) -> u128 {
+    for _ in 0..10_000 {
+        black_box(render());
+    }
+    let mut rounds = [0_u128; ROUNDS];
+    for round in &mut rounds {
+        let start = Instant::now();
+        for _ in 0..ITERATIONS {
+            black_box(render());
+        }
+        *round = start.elapsed().as_nanos() / u128::from(ITERATIONS);
+    }
+    rounds.sort_unstable();
+    rounds[ROUNDS / 2]
+}
+
+fn main() {
+    let view = page();
+    let unhinted = median_ns(|| {
+        let mut html = String::new();
+        view.render_into(&mut html).expect("generated view renders");
+        black_box(html.len())
+    });
+    let hinted = median_ns(|| {
+        let mut html = String::with_capacity(view.size_hint());
+        view.render_into(&mut html).expect("generated view renders");
+        black_box(html.len())
+    });
+    println!(
+        "unhinted_median_ns={unhinted} hinted_median_ns={hinted} size_hint={} html_len={}",
+        view.size_hint(),
+        view.render().expect("generated view renders").len(),
+    );
+}
@@ -80,7 +80,7 @@ pub mod __private {
 }

 fn render_template(view: &impl hemplate::Hemplate) -> Html {
-    let mut html = String::new();
+    let mut html = String::with_capacity(view.size_hint());
    view.render_into(&mut html)
        .expect("hemplate view renders into hemx effect payload");
    __private::html_trusted(html)
@@ -186,6 +186,8 @@ pub mod prelude {

 #[cfg(test)]
 mod tests {
+    use std::cell::Cell;
+
    struct InlineView;

    impl hemplate::Hemplate for InlineView {
@@ -195,6 +197,29 @@ mod tests {
        }
    }

+    struct HintTrackingView(Cell<bool>);
+
+    impl hemplate::Hemplate for HintTrackingView {
+        fn render_into(&self, out: &mut String) -> Result<(), hemplate::error::HemplateError> {
+            out.push_str("<strong>hinted</strong>");
+            Ok(())
+        }
+
+        fn size_hint(&self) -> usize {
+            self.0.set(true);
+            23
+        }
+    }
+
+    #[test]
+    fn trusted_render_path_uses_the_view_size_hint() {
+        // req: view/003 req: html_safety/002
+        let view = HintTrackingView(Cell::new(false));
+
+        assert_eq!(crate::page(&view).as_str(), "<strong>hinted</strong>");
+        assert!(view.0.get(), "trusted render path must consult size_hint");
+    }
+
    #[test]
    fn page_is_the_short_safe_html_helper() {
        // req: dx/006 req: html_safety/002
@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html>
+<head><title>{+ self.title +}</title></head>
+<body>
+  <h1>{+ self.title +}</h1>
+  <p>{+ self.body +}</p>
+  <ul>
+    <li h-for="item in &self.items">{+ item +}</li>
+  </ul>
+</body>
+</html>