Use pyftsubset for font subsetting

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "crates/pyftsubset/fonttools"]
+	path = crates/pyftsubset/fonttools
+	url = https://git.shadowfacts.net/shadowfacts/fonttools.git

Cargo.lock

@@ -24,7 +24,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e89da841a80418a9b391ebaea17f5c112ffaaa96f621d2c285b5174da76b9011"
 dependencies = [
  "cfg-if",
- "getrandom",
+ "getrandom 0.2.15",
  "once_cell",
  "version_check",
  "zerocopy",
@@ -155,6 +155,12 @@ version = "0.22.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "72b3254f16251a8381aa12e40e3c4d2f0199f8c6508fbecb9d91f575e0fbb8c6"
 
+[[package]]
+name = "bit-vec"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5e764a1d40d510daf35e07be9eb06e75770908c27d411ee6c92109c9840eaaf7"
+
 [[package]]
 name = "bitflags"
 version = "1.3.2"
@@ -517,6 +523,22 @@ version = "1.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5443807d6dff69373d433ab9ef5378ad8df50ca6298caf15de6e52e24aaf54d5"
 
+[[package]]
+name = "errno"
+version = "0.3.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "33d852cb9b869c2a9b3df2f71a3074817f01e1844f839a144f5fcef059a4eb5d"
+dependencies = [
+ "libc",
+ "windows-sys 0.59.0",
+]
+
+[[package]]
+name = "fastrand"
+version = "2.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "37909eebbb50d72f9059c3b6d82c0463f2ff062c9e95845c43a6c9c0355411be"
+
 [[package]]
 name = "filetime"
 version = "0.2.25"
@@ -683,10 +705,22 @@ dependencies = [
  "cfg-if",
  "js-sys",
  "libc",
- "wasi",
+ "wasi 0.11.0+wasi-snapshot-preview1",
  "wasm-bindgen",
 ]
 
+[[package]]
+name = "getrandom"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "43a49c392881ce6d5c3b8cb70f98717b7c07aabbdff06687b9030dbfbe2725f8"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "wasi 0.13.3+wasi-0.2.2",
+ "windows-targets",
+]
+
 [[package]]
 name = "gimli"
 version = "0.31.1"
@@ -722,7 +756,7 @@ name = "grass"
 version = "0.13.4"
 source = "git+https://git.shadowfacts.net/shadowfacts/grass.git?branch=custom-global-variables#e64e648b6174d23b6d4a8ad674eb443dc6fcbdff"
 dependencies = [
- "getrandom",
+ "getrandom 0.2.15",
  "grass_compiler",
 ]
 
@@ -749,6 +783,12 @@ dependencies = [
  "allocator-api2",
 ]
 
+[[package]]
+name = "heck"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2304e00983f87ffb38b55b444b5e3b60a884b5d30c0fca7d82fe33449bbe55ea"
+
 [[package]]
 name = "html5ever"
 version = "0.27.0"
@@ -935,6 +975,12 @@ dependencies = [
  "hashbrown",
 ]
 
+[[package]]
+name = "indoc"
+version = "2.0.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b248f5224d1d606005e02c97f5aa4e88eeb230488bcc03bc9ca4d7991399f2b5"
+
 [[package]]
 name = "inotify"
 version = "0.10.2"
@@ -1044,6 +1090,12 @@ dependencies = [
  "redox_syscall",
 ]
 
+[[package]]
+name = "linux-raw-sys"
+version = "0.4.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d26c52dbd32dccf2d10cac7725f8eae5296885fb5703b261f7d0a0739ec807ab"
+
 [[package]]
 name = "lock_api"
 version = "0.4.12"
@@ -1056,9 +1108,9 @@ dependencies = [
 
 [[package]]
 name = "log"
-version = "0.4.22"
+version = "0.4.25"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a7a70ba024b9dc04c27ea2f0c0548feb474ec5c54bba33a7f72f873a39d07b24"
+checksum = "04cbf5b083de1c7e0222a7a51dbfdba1cbe1c6ab0b15e29fff3f6c077fd9cd9f"
 
 [[package]]
 name = "mac"
@@ -1098,6 +1150,15 @@ version = "2.7.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "78ca9ab1a0babb1e7d5695e3530886289c18cf2f87ec19a575a0abdce112e3a3"
 
+[[package]]
+name = "memoffset"
+version = "0.9.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "488016bfae457b036d996092f6cb448677611ce4449e970ceaf42695203f218a"
+dependencies = [
+ "autocfg",
+]
+
 [[package]]
 name = "mime"
 version = "0.3.17"
@@ -1131,7 +1192,7 @@ checksum = "2886843bf800fba2e3377cff24abf6379b4c4d5c6681eaf9ea5b0d15090450bd"
 dependencies = [
  "libc",
  "log",
- "wasi",
+ "wasi 0.11.0+wasi-snapshot-preview1",
  "windows-sys 0.52.0",
 ]
 
@@ -1195,9 +1256,9 @@ dependencies = [
 
 [[package]]
 name = "once_cell"
-version = "1.20.2"
+version = "1.20.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1261fe7e33c73b354eab43b1273a57c8f967d0391e80353e51f764ac02cf6775"
+checksum = "945462a4b81e43c4e3ba96bd7b49d834c6f61198356aa858733bc4acf3cbe62e"
 
 [[package]]
 name = "parking_lot"
@@ -1375,6 +1436,12 @@ version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8b870d8c151b6f2fb93e84a13146138f05d02ed11c7e7c54f8826aaaf7c9f184"
 
+[[package]]
+name = "portable-atomic"
+version = "1.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "280dc24453071f1b63954171985a0b0d30058d287960968b9b2aca264c8d4ee6"
+
 [[package]]
 name = "ppv-lite86"
 version = "0.2.20"
@@ -1418,6 +1485,78 @@ version = "0.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "007d8adb5ddab6f8e3f491ac63566a7d5002cc7ed73901f72057943fa71ae1ae"
 
+[[package]]
+name = "pyftsubset"
+version = "0.1.0"
+dependencies = [
+ "log",
+ "pyo3",
+ "tempfile",
+]
+
+[[package]]
+name = "pyo3"
+version = "0.23.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "57fe09249128b3173d092de9523eaa75136bf7ba85e0d69eca241c7939c933cc"
+dependencies = [
+ "cfg-if",
+ "indoc",
+ "libc",
+ "memoffset",
+ "once_cell",
+ "portable-atomic",
+ "pyo3-build-config",
+ "pyo3-ffi",
+ "pyo3-macros",
+ "unindent",
+]
+
+[[package]]
+name = "pyo3-build-config"
+version = "0.23.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1cd3927b5a78757a0d71aa9dff669f903b1eb64b54142a9bd9f757f8fde65fd7"
+dependencies = [
+ "once_cell",
+ "target-lexicon",
+]
+
+[[package]]
+name = "pyo3-ffi"
+version = "0.23.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dab6bb2102bd8f991e7749f130a70d05dd557613e39ed2deeee8e9ca0c4d548d"
+dependencies = [
+ "libc",
+ "pyo3-build-config",
+]
+
+[[package]]
+name = "pyo3-macros"
+version = "0.23.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "91871864b353fd5ffcb3f91f2f703a22a9797c91b9ab497b1acac7b07ae509c7"
+dependencies = [
+ "proc-macro2",
+ "pyo3-macros-backend",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "pyo3-macros-backend"
+version = "0.23.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "43abc3b80bc20f3facd86cd3c60beed58c3e2aa26213f3cda368de39c60a27e4"
+dependencies = [
+ "heck",
+ "proc-macro2",
+ "pyo3-build-config",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "quick-xml"
 version = "0.37.2"
@@ -1464,7 +1603,7 @@ version = "0.6.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ec0be4795e2f6a28069bec0b5ff3e2ac9bafc99e6a9a7dc3547996c5c816922c"
 dependencies = [
- "getrandom",
+ "getrandom 0.2.15",
 ]
 
 [[package]]
@@ -1523,6 +1662,19 @@ version = "0.1.24"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "719b953e2095829ee67db738b3bfa9fa368c94900df327b3f07fe6e794d2fe1f"
 
+[[package]]
+name = "rustix"
+version = "0.38.44"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fdb5bc1ae2baa591800df16c9ca78619bf65c0488b41b96ccec5d11220d8c154"
+dependencies = [
+ "bitflags 2.7.0",
+ "errno",
+ "libc",
+ "linux-raw-sys",
+ "windows-sys 0.59.0",
+]
+
 [[package]]
 name = "ryu"
 version = "1.0.18"
@@ -1727,6 +1879,26 @@ version = "1.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0bf256ce5efdfa370213c1dabab5935a12e49f2c58d15e9eac2870d3b4f27263"
 
+[[package]]
+name = "target-lexicon"
+version = "0.12.16"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "61c41af27dd6d1e27b1b16b489db798443478cef1f06a660c96db617ba5de3b1"
+
+[[package]]
+name = "tempfile"
+version = "3.16.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "38c246215d7d24f48ae091a2902398798e05d978b24315d6efbc00ede9a8bb91"
+dependencies = [
+ "cfg-if",
+ "fastrand",
+ "getrandom 0.3.1",
+ "once_cell",
+ "rustix",
+ "windows-sys 0.59.0",
+]
+
 [[package]]
 name = "tendril"
 version = "0.4.3"
@@ -2220,6 +2392,12 @@ version = "0.1.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7dd6e30e90baa6f72411720665d41d89b9a3d039dc45b8faea1ddd07f617f6af"
 
+[[package]]
+name = "unindent"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c7de7d73e1754487cb58364ee906a499937a0dfabd86bcb980fa99ec8c8fa2ce"
+
 [[package]]
 name = "utf-8"
 version = "0.7.6"
@@ -2239,6 +2417,7 @@ dependencies = [
  "ahash",
  "anyhow",
  "base64",
+ "bit-vec",
  "bitflags 2.7.0",
  "chrono",
  "clap",
@@ -2261,6 +2440,7 @@ dependencies = [
  "once_cell",
  "pulldown-cmark",
  "pulldown-cmark-escape",
+ "pyftsubset",
  "regex",
  "rss",
  "serde",
@@ -2308,6 +2488,15 @@ version = "0.11.0+wasi-snapshot-preview1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9c8d87e72b64a3b4db28d11ce29237c246188f4f51057d65a7eab63b7987e423"
 
+[[package]]
+name = "wasi"
+version = "0.13.3+wasi-0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "26816d2e1a4a36a2940b96c5296ce403917633dff8f3440e9b236ed6f6bacad2"
+dependencies = [
+ "wit-bindgen-rt",
+]
+
 [[package]]
 name = "wasm-bindgen"
 version = "0.2.99"
@@ -2471,6 +2660,15 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "wit-bindgen-rt"
+version = "0.33.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3268f3d866458b787f390cf61f4bbb563b922d091359f9608842999eaee3943c"
+dependencies = [
+ "bitflags 2.7.0",
+]
+
 [[package]]
 name = "xml5ever"
 version = "0.18.1"

Cargo.toml

@@ -2,6 +2,7 @@ workspace = { members = [
     "crates/compute_graph",
     "crates/compute_graph_macros",
     "crates/derive_test",
+    "crates/pyftsubset",
 ] }
 
 [package]
@@ -19,6 +20,7 @@ serde_json = "1.0"
 ahash = "0.8.11"
 anyhow = "1.0.95"
 base64 = "0.22.1"
+bit-vec = "0.8.0"
 bitflags = "2.7.0"
 chrono = { version = "0.4.39", features = ["serde"] }
 clap = { version = "4.5.23", features = ["cargo"] }
@@ -43,6 +45,7 @@ notify = "7.0.0"
 once_cell = "1.20.2"
 pulldown-cmark = "0.12.2"
 pulldown-cmark-escape = "0.11.0"
+pyftsubset = { path = "crates/pyftsubset" }
 regex = "1.11.1"
 rss = { version = "2.0.11", features = ["atom"] }
 serde = { version = "1.0", features = ["derive"] }

crates/pyftsubset/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "pyftsubset"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+log = "0.4.25"
+pyo3 = "0.23.4"
+tempfile = "3.16.0"

crates/pyftsubset/fonttools

@@ -0,0 +1 @@
+Subproject commit d6f40c2e453f3c07807fef7926a31717f180b660

crates/pyftsubset/src/lib.rs

@@ -0,0 +1,65 @@
+use std::{
+    ffi::CString,
+    fs::read_to_string,
+    io::{Read, Write},
+    path::Path,
+};
+
+use log::debug;
+use pyo3::{
+    ffi::c_str,
+    prelude::*,
+    types::{PyList, PyTuple},
+};
+use tempfile::NamedTempFile;
+
+pub fn subset(data: &[u8], unicodes: &[u32]) -> Vec<u8> {
+    pyo3::prepare_freethreaded_python();
+
+    let mut input = NamedTempFile::new().expect("input file");
+    input.write_all(data).expect("writing input");
+    let mut output = NamedTempFile::new().expect("output file");
+
+    let path = Path::new(concat!(env!("CARGO_MANIFEST_DIR"), "/fonttools/Lib"));
+    let init_path = path.join("fontTools/subset/__init__.py");
+    let py_init = CString::new(read_to_string(init_path).unwrap()).unwrap();
+    let result = Python::with_gil(|py| -> PyResult<Py<PyAny>> {
+        let syspath = py
+            .import("sys")?
+            .getattr("path")?
+            .downcast_into::<PyList>()?;
+        syspath.insert(0, path)?;
+        let app: Py<PyAny> = PyModule::from_code(py, py_init.as_c_str(), c_str!(""), c_str!(""))?
+            .getattr("main")?
+            .into();
+        let args = PyList::new(py, vec![
+            input.path().to_str().unwrap(),
+            &format_unicodes(unicodes),
+            &format!("--output-file={}", output.path().to_str().unwrap()),
+        ])?;
+        debug!("Running pyftsubset with {:?}", args);
+        let args_tuple = PyTuple::new(py, &[args])?;
+        app.call1(py, args_tuple)
+    });
+    result.expect("subsetting");
+
+    let mut buf = vec![];
+    output.read_to_end(&mut buf).expect("reading output");
+    buf
+}
+
+fn format_unicodes(unicodes: &[u32]) -> String {
+    use std::fmt::Write;
+
+    let mut s = "--unicodes=".to_owned();
+    let mut first = true;
+    for u in unicodes {
+        if first {
+            write!(s, "{:x}", u).expect("append unicode");
+            first = false;
+        } else {
+            write!(s, ",{:x}", u).expect("append unicode");
+        }
+    }
+    s
+}

site_test/css/fonts.scss

@@ -41,9 +41,17 @@
     font-weight: normal;
     font-style: normal;
 }
+
 @font-face {
     font-family: "Berkeley Mono";
     src: url("data:font/woff2;base64," + $berkeley-mono-italic) format("woff2");
     font-weight: normal;
     font-style: italic;
 }
+
+@font-face {
+    font-family: "Berkeley Mono";
+    src: url("data:font/woff2;base64," + $berkeley-mono-bold) format("woff2");
+    font-weight: bold;
+    font-style: normal;
+}

src/generator/css.rs

@@ -46,7 +46,7 @@ pub fn make_graph(
     );
 
     let character_sets = character_sets::make_graph(builder, render_inputs, render_dynamic_inputs);
-    let assertion = builder.add_rule(AssertNoBoldMonospace(character_sets.clone()));
+    let assertion = builder.add_rule(AssertNoBoldItalicMonospace(character_sets.clone()));
 
     let fonts = [
         (
@@ -79,6 +79,11 @@ pub fn make_graph(
             content_path("css/fonts/BerkeleyMono-Oblique.woff2"),
             FontKey::MONOSPACE.union(FontKey::ITALIC),
         ),
+        (
+            "berkeley-mono-bold",
+            content_path("css/fonts/BerkeleyMono-Bold.woff2"),
+            FontKey::MONOSPACE.union(FontKey::BOLD),
+        ),
     ];
     for (name, path, font_key) in fonts.into_iter() {
         let file = read_file(path, builder, &mut *watcher_);
@@ -223,12 +228,11 @@ impl Rule for ConvertToBase64 {
 }
 
 #[derive(InputVisitable)]
-struct AssertNoBoldMonospace(Input<CharacterSets>);
+struct AssertNoBoldItalicMonospace(Input<CharacterSets>);
-impl Rule for AssertNoBoldMonospace {
+impl Rule for AssertNoBoldItalicMonospace {
     type Output = ();
     fn evaluate(&mut self) -> Self::Output {
         let sets = self.input_0();
-        assert!(sets.bold_monospace().is_empty());
         assert!(sets.bold_italic_monospace().is_empty());
     }
 }

src/generator/css/character_sets.rs

@@ -1,3 +1,4 @@
+use bit_vec::BitVec;
 use bitflags::bitflags;
 use compute_graph::{
     NodeId,
@@ -9,7 +10,7 @@ use compute_graph::{
 use html5ever::{
     Attribute, local_name,
     tokenizer::{
-        BufferQueue, TagKind, Token, TokenSink, TokenSinkResult, Tokenizer, TokenizerOpts,
+        BufferQueue, Tag, TagKind, Token, TokenSink, TokenSinkResult, Tokenizer, TokenizerOpts,
         TokenizerResult,
     },
 };
@@ -105,7 +106,7 @@ impl Rule for UnionDynamicCharacterSets {
 }
 
 fn get_character_sets(html: &str) -> CharacterSets {
-    let accumulator = CharacterSetAccumulator::default();
+    let accumulator = CharacterSetAccumulator::new();
     let mut tokenizer = Tokenizer::new(accumulator, TokenizerOpts::default());
     let mut queue = BufferQueue::default();
     queue.push_back(html.into());
@@ -205,7 +206,7 @@ impl std::fmt::Debug for CharacterSets {
 }
 
 bitflags! {
-    #[derive(Clone, Copy)]
+    #[derive(Clone, Copy, PartialEq)]
     pub struct FontKey: u8 {
         const BOLD = 1;
         const ITALIC = 1 << 1;
@@ -215,41 +216,72 @@ bitflags! {
 
 const FONT_VARIATIONS: usize = FontKey::all().bits() as usize + 1;
 
+#[derive(Default)]
+struct FontKeyStack {
+    bold: BitVec,
+    italic: BitVec,
+    monospace: BitVec,
+}
+
+impl FontKeyStack {
+    fn push(&mut self, key: FontKey) {
+        self.bold.push(key.contains(FontKey::BOLD));
+        self.italic.push(key.contains(FontKey::ITALIC));
+        self.monospace.push(key.contains(FontKey::MONOSPACE));
+    }
+
+    fn pop(&mut self) {
+        self.bold.pop();
+        self.italic.pop();
+        self.monospace.pop();
+    }
+
+    fn all_ored(&self) -> FontKey {
+        let mut all = FontKey::empty();
+        if self.bold.any() {
+            all.insert(FontKey::BOLD);
+        }
+        if self.italic.any() {
+            all.insert(FontKey::ITALIC);
+        }
+        if self.monospace.any() {
+            all.insert(FontKey::MONOSPACE);
+        }
+        all
+    }
+}
+
 // N.B.: html5ever 0.28.0 changed TokenSink::process_token to take &self.
 // At which point we upgrade, the state on this type will need to use something
 // else to provide interior mutability.
-#[derive(Default)]
 struct CharacterSetAccumulator {
     characters: CharacterSets,
-    depths: [usize; 3],
+    keys: FontKeyStack,
 }
 impl CharacterSetAccumulator {
+    fn new() -> Self {
+        assert_eq!(FontKey::BOLD.bits().trailing_zeros(), 0);
+        assert_eq!(FontKey::ITALIC.bits().trailing_zeros(), 1);
+        assert_eq!(FontKey::MONOSPACE.bits().trailing_zeros(), 2);
+
+        Self {
+            characters: CharacterSets::default(),
+            keys: FontKeyStack::default(),
+        }
+    }
+
     fn handle_token(&mut self, token: Token) {
         match token {
             Token::TagToken(tag) => {
-                let depth = if tag.name == local_name!("strong") || tag.name == local_name!("b") {
-                    &mut self.depths[0]
-                } else if tag.name == local_name!("em")
-                    || tag.name == local_name!("i")
-                    || tag.attrs.iter().any(Self::is_hl_cmt)
-                {
-                    &mut self.depths[1]
-                } else if tag.name == local_name!("code") {
-                    &mut self.depths[2]
-                } else {
-                    return;
-                };
                 if tag.kind == TagKind::StartTag {
-                    *depth += 1;
+                    let key = Self::font_key_for(&tag);
+                    self.keys.push(key);
                 } else {
-                    *depth -= 1;
+                    self.keys.pop();
                 }
             }
             Token::CharacterTokens(s) => {
-                let mut key = FontKey::empty();
+                let key = self.keys.all_ored();
-                key.set(FontKey::BOLD, self.depths[0] > 0);
-                key.set(FontKey::ITALIC, self.depths[1] > 0);
-                key.set(FontKey::MONOSPACE, self.depths[2] > 0);
                 let set = self.characters.get_mut(key);
                 set.extend(s.chars());
             }
@@ -257,6 +289,32 @@ impl CharacterSetAccumulator {
         }
     }
 
+    fn font_key_for(tag: &Tag) -> FontKey {
+        if tag.name == local_name!("strong") || tag.name == local_name!("b") || Self::is_header(tag)
+        {
+            FontKey::BOLD
+        } else if tag.name == local_name!("em")
+            || tag.name == local_name!("i")
+            || tag.name == local_name!("header")
+            || tag.attrs.iter().any(Self::is_hl_cmt)
+        {
+            FontKey::ITALIC
+        } else if tag.name == local_name!("code") {
+            FontKey::MONOSPACE
+        } else {
+            FontKey::empty()
+        }
+    }
+
+    fn is_header(tag: &Tag) -> bool {
+        tag.name == local_name!("h1")
+            || tag.name == local_name!("h2")
+            || tag.name == local_name!("h3")
+            || tag.name == local_name!("h4")
+            || tag.name == local_name!("h5")
+            || tag.name == local_name!("h6")
+    }
+
     fn is_hl_cmt(attr: &Attribute) -> bool {
         attr.name.prefix == None
             && attr.name.local == local_name!("class")

src/generator/css/font_subset.rs

@@ -4,6 +4,7 @@ use compute_graph::{
     rule::Rule,
     synchronicity::Asynchronous,
 };
+use pyftsubset::subset;
 
 use super::character_sets::{CharacterSets, FontKey};
 
@@ -41,6 +42,11 @@ struct SubsetFont {
 impl Rule for SubsetFont {
     type Output = Vec<u8>;
     fn evaluate(&mut self) -> Self::Output {
-        self.font().clone()
+        let unicodes = self
+            .characters()
+            .iter()
+            .map(|&c| c as u32)
+            .collect::<Vec<_>>();
+        subset(self.font().as_ref(), &unicodes)
     }
 }