css: dedupe font-family names in linear time

src/css/properties/font.rs

@@ -998,22 +998,9 @@ impl FontHandler {
 
         if let Some(f) = family.as_mut() {
             if f.len() > 1 {
-                // Dedupe
+                // Dedupe, keeping the first occurrence of each family.
                 let mut seen: FontFamilyHashMap<()> = Default::default();
-
-                let mut i: usize = 0;
-                while i < f.len() {
-                    use bun_collections::array_hash_map::MapEntry;
-                    match seen.entry(f.at(i).clone()) {
-                        MapEntry::Occupied(_) => {
-                            let _ = f.ordered_remove(i);
-                        }
-                        MapEntry::Vacant(v) => {
-                            v.insert(());
-                            i += 1;
-                        }
-                    }
-                }
+                f.retain(|family| seen.insert(family.clone(), ()).is_none());
             }
         }
 

test/js/bun/css/font-family-dedupe-quadratic.test.ts

@@ -0,0 +1,57 @@
+import { cssInternals } from "bun:internal-for-testing";
+import { expect, test } from "bun:test";
+import { bunEnv, bunExe } from "harness";
+
+// The font handler removes repeated family names from a `font-family` /
+// `font` value when minifying. It used to do so with an ordered remove per
+// duplicate, shifting the rest of the list down each time, so a value made
+// of n copies of the same name took O(n^2) to minify: 40k copies (80 KB of
+// CSS) kept a release build busy for several seconds, and the time
+// quadrupled with every doubling of the input. Dedupe is now a single
+// compaction pass.
+//
+// The size below is chosen so the old quadratic dedupe cannot finish before
+// the spawn timeout kills the child (it needs minutes even in a release
+// build) while the linear version finishes in a few seconds in a debug
+// build.
+test("font-family with many duplicate names minifies in linear time", async () => {
+  const n = 1_000_000;
+  const script = `
+    const { minifyTest } = require("bun:internal-for-testing").cssInternals;
+    const css = "a{font-family:" + Buffer.alloc(${n} * 2, "f,").toString() + "serif}";
+    console.log(minifyTest(css, ""));
+  `;
+
+  await using proc = Bun.spawn({
+    cmd: [bunExe(), "-e", script],
+    env: bunEnv,
+    stdout: "pipe",
+    stderr: "pipe",
+    timeout: 60_000,
+    killSignal: "SIGKILL",
+  });
+
+  const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+  expect({
+    stdout,
+    stderr: /error|panic|assert|crash|abort/i.test(stderr) ? stderr : "",
+    exitCode,
+    signalCode: proc.signalCode,
+  }).toEqual({
+    stdout: "a{font-family:f,serif}\n",
+    stderr: "",
+    exitCode: 0,
+    signalCode: null,
+  });
+}, 90_000);
+
+test("font-family dedupe keeps the first occurrence of each family in order", () => {
+  expect(
+    [
+      `a{font-family:Foo,serif,Foo,"Bar",serif,Bar,"serif"}`,
+      `a{font-family:serif,f,serif,f,sans-serif,f,serif}`,
+      `a{font:12px Foo,Foo,serif}`,
+    ].map(css => cssInternals.minifyTest(css, "")),
+  ).toEqual([`a{font-family:Foo,serif,Bar,"serif"}`, `a{font-family:serif,f,sans-serif}`, `a{font:12px Foo,serif}`]);
+});