Fix division by zero with empty static set

integration-tests/build.rs

@@ -20,5 +20,12 @@ fn main() {
             "❤💯❤💯",
         ])
         .write_to_file(&Path::new(&env::var("OUT_DIR").unwrap()).join("test_atom.rs"))
+        .unwrap();
+
+    // All statically-known atoms are short enough to be represented inline,
+    // so the static set is empty. Ensure phf doesn’t divide by zero.
+    string_cache_codegen::AtomType::new("TestAtom2", "test_atom2!")
+        .atoms(&["a"])
+        .write_to_file(&Path::new(&env::var("OUT_DIR").unwrap()).join("test_atom2.rs"))
         .unwrap()
 }

integration-tests/src/lib.rs

@@ -19,6 +19,7 @@ use std::thread;
 use string_cache::StaticAtomSet;
 
 include!(concat!(env!("OUT_DIR"), "/test_atom.rs"));
+include!(concat!(env!("OUT_DIR"), "/test_atom2.rs"));
 pub type Atom = TestAtom;
 
 #[test]
@@ -358,14 +359,18 @@ fn test_eq_ignore_ascii_case() {
     assert!(Atom::from("").eq_ignore_ascii_case(&Atom::from("")));
     assert!(Atom::from("aZ9").eq_ignore_ascii_case(&Atom::from("aZ9")));
     assert!(Atom::from("aZ9").eq_ignore_ascii_case(&Atom::from("Az9")));
-    assert!(Atom::from("The Quick Brown Fox!")
-        .eq_ignore_ascii_case(&Atom::from("THE quick BROWN fox!")));
+    assert!(
+        Atom::from("The Quick Brown Fox!")
+            .eq_ignore_ascii_case(&Atom::from("THE quick BROWN fox!"))
+    );
     assert!(Atom::from("Je vais à Paris").eq_ignore_ascii_case(&Atom::from("je VAIS à PARIS")));
     assert!(!Atom::from("").eq_ignore_ascii_case(&Atom::from("az9")));
     assert!(!Atom::from("aZ9").eq_ignore_ascii_case(&Atom::from("")));
     assert!(!Atom::from("aZ9").eq_ignore_ascii_case(&Atom::from("9Za")));
-    assert!(!Atom::from("The Quick Brown Fox!")
-        .eq_ignore_ascii_case(&Atom::from("THE quick BROWN fox!!")));
+    assert!(
+        !Atom::from("The Quick Brown Fox!")
+            .eq_ignore_ascii_case(&Atom::from("THE quick BROWN fox!!"))
+    );
     assert!(!Atom::from("Je vais à Paris").eq_ignore_ascii_case(&Atom::from("JE vais À paris")));
 }
 
@@ -382,6 +387,22 @@ fn test_try_static() {
     assert!(Atom::try_static("not in the static table").is_none());
 }
 
+#[test]
+fn test_with_empty_static_set() {
+    assert_eq!(TestAtom2::from("a").as_str(), "a");
+    assert_eq!(
+        TestAtom2::from("longer-than-inline").as_str(),
+        "longer-than-inline"
+    );
+
+    // the dummy string used in `string_cache_codegen::AtomType::to_tokens`
+    // to make the static set non-empty
+    let dummy = " ".repeat(8);
+    let atom = TestAtom2::from(dummy);
+    assert!(atom.is_static());
+    assert_eq!(atom, test_atom2!("        "));
+}
+
 #[cfg(test)]
 #[path = "common-usage.rs"]
 mod common_usage;

string-cache-codegen/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "string_cache_codegen"
-version = "0.11.0"  # Also update ../README.md when making a semver-breaking change
+version = "0.11.1"  # Also update ../README.md when making a semver-breaking change
 authors = [ "The Servo Project Developers" ]
 description = "A codegen library for string-cache, developed as part of the Servo project."
 license = "MIT OR Apache-2.0"

string-cache-codegen/lib.rs

@@ -199,16 +199,25 @@ impl AtomType {
 
     #[expect(clippy::wrong_self_convention)] // Doesn’t matter on a private method
     fn to_tokens(&mut self) -> proc_macro2::TokenStream {
-        // Make `atom!("")` always work, and ensure the set is non-empty
-        // to avoid divisions by zero in rust-phf.
+        // Make `atom!("")` always work
         self.atoms.insert(String::new());
 
+        const MAX_INLINE_LEN: usize = 7;
+
         // Strings over 7 bytes added to static set, otherwise stored inline.
-        let (static_strs, inline_strs): (Vec<_>, Vec<_>) = self
+        let (mut static_strs, inline_strs): (Vec<_>, Vec<_>) = self
             .atoms
             .iter()
             .map(String::as_str)
-            .partition(|s| s.len() > 7);
+            .partition(|s| s.len() > MAX_INLINE_LEN);
+
+        let dummy;
+        if static_strs.is_empty() {
+            // Some arbitrary string that `Atom::from(&str)` won’t represent inline
+            dummy = " ".repeat(MAX_INLINE_LEN + 1);
+            // Make the static set non-empty to avoid divisions by zero in rust-phf
+            static_strs.push(&dummy);
+        }
 
         // Static strings
         let hash_state = phf_generator::generate_hash(&static_strs);