use quote to generate font-awesome code

crates/font-awesome-as-a-crate/Cargo.toml

@@ -6,3 +6,8 @@ license = "CC-BY-4.0 AND MIT"
 description = "Font Awesome Free, packaged as a crate"
 repository = "https://github.com/rust-lang/docs.rs"
 
+[build-dependencies]
+quote = "1.0.37"
+proc-macro2 = "1.0.86"
+syn = "2.0.77"
+prettyplease = "0.2.22"

crates/font-awesome-as-a-crate/build.rs

@@ -1,11 +1,6 @@
-use std::{
-    collections::HashMap,
-    env,
-    fmt::Write as FmtWrite,
-    fs::{read_dir, File},
-    io::{Read, Write},
-    path::Path,
-};
+use proc_macro2::Literal;
+use quote::{format_ident, quote};
+use std::{collections::HashMap, env, fs, path::Path};
 
 fn main() {
     println!("cargo::rustc-check-cfg=cfg(font_awesome_out_dir)");
@@ -22,70 +17,91 @@ fn capitalize_first_letter(s: &str) -> String {
 }
 
 fn write_fontawesome_sprite() {
+    let mut match_arms = vec![];
     let mut types = HashMap::new();
-    let dest_path = Path::new(&env::var("OUT_DIR").unwrap()).join("fontawesome.rs");
-    let mut dest_file = File::create(dest_path).unwrap();
-    dest_file
-        .write_all(b"const fn fontawesome_svg(dir:&str,file:&str)->&'static str{match(dir.as_bytes(),file.as_bytes()){")
-        .expect("fontawesome fn write");
+
     for (dirname, trait_name) in &[
         ("brands", "Brands"),
         ("regular", "Regular"),
         ("solid", "Solid"),
     ] {
-        let dir = read_dir(Path::new("fontawesome-free-6.2.0-desktop/svgs").join(dirname)).unwrap();
-        let mut data = String::new();
+        let dir =
+            fs::read_dir(Path::new("fontawesome-free-6.2.0-desktop/svgs").join(dirname)).unwrap();
+
         for file in dir {
             let file = file.expect("fontawesome directory access");
+            let data = fs::read_to_string(file.path()).expect("fontawesome file read");
+
             let filename = file
                 .file_name()
                 .into_string()
-                .expect("fontawesome filenames are unicode");
-            let mut file = File::open(file.path()).expect("fontawesome file access");
-            data.clear();
-            file.read_to_string(&mut data)
-                .expect("fontawesome file read");
-            // if this assert goes off, add more hashes here and in the format! below
-            assert!(!data.contains("###"), "file {filename} breaks raw string");
-            let filename = filename.replace(".svg", "");
-            dest_file
-                .write_all(
-                    format!(r####"(b"{dirname}",b"{filename}")=>r#"{data}"#,"####).as_bytes(),
-                )
-                .expect("write fontawesome file");
+                .expect("fontawesome filenames are unicode")
+                .replace(".svg", "");
+
+            let dirname_literal = Literal::byte_string(dirname.as_bytes());
+            let filename_literal = Literal::byte_string(filename.as_bytes());
+            match_arms.push(quote! {
+                (#dirname_literal, #filename_literal) => #data,
+            });
+
             types
                 .entry(filename)
                 .or_insert_with(|| (data.clone(), Vec::with_capacity(3)))
                 .1
                 .push(trait_name);
         }
     }
-    dest_file
-        .write_all(b"_=>\"\"}} pub mod icons { use super::{IconStr, Regular, Brands, Solid};")
-        .expect("fontawesome fn write");
+
+    let mut types_output = vec![];
 
     for (icon, (data, kinds)) in types {
         let mut type_name = "Icon".to_string();
         type_name.extend(icon.split('-').map(capitalize_first_letter));
-        let kinds = kinds.iter().fold(String::new(), |mut acc, k| {
-            let _ = writeln!(acc, "impl {k} for {type_name} {{}}");
-            acc
+        let type_name = format_ident!("{}", type_name);
+
+        let kind_impls: Vec<_> = kinds
+            .iter()
+            .map(|k| {
+                let k = format_ident!("{}", k);
+                quote! {
+                    impl #k for #type_name {}
+                }
+            })
+            .collect();
+
+        types_output.push(quote! {
+            #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+            pub struct #type_name;
+
+            impl IconStr for #type_name {
+                fn icon_name(&self) -> &'static str { #icon }
+                fn icon_str(&self) -> &'static str { #data }
+            }
+
+            #(#kind_impls)*
         });
-        dest_file
-            .write_all(
-                format!(
-                    "\n#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub struct {type_name};
-impl IconStr for {type_name} {{
-    fn icon_name(&self) -> &'static str {{ r#\"{icon}\"# }}
-    fn icon_str(&self) -> &'static str {{ r#\"{data}\"# }}
-}}
-{kinds}"
-                )
-                .as_bytes(),
-            )
-            .expect("write fontawesome file types");
     }
 
-    dest_file.write_all(b"}").expect("fontawesome fn write");
+    let token_stream = quote! {
+        const fn fontawesome_svg(dir: &str, file: &str) -> &'static str {
+            // we are using byte literals to match because they can be evaluated in a
+            // `const` context, and `str` cannot.
+            match(dir.as_bytes(), file.as_bytes()) {
+                #(#match_arms)*
+                _=> ""
+            }
+        }
+
+        pub mod icons {
+            use super::{IconStr, Regular, Brands, Solid};
+
+            #(#types_output)*
+        }
+    };
+
+    let dest_path = Path::new(&env::var("OUT_DIR").unwrap()).join("fontawesome.rs");
+
+    let output = prettyplease::unparse(&syn::parse2(token_stream).unwrap());
+
+    fs::write(&dest_path, output.as_bytes()).expect("fontawesome output write");
 }