Fix css module hashing with implicit CSS grid line names (parcel-bundler#129)

Author: devongovett

src/bundler.rs

@@ -736,11 +736,11 @@ mod tests {
       "#
     }, "/a.css");
     assert_eq!(res, indoc! { r#"
-      .a_6lixEq_1 {
+      ._6lixEq_a {
         color: green;
       }
 
-      .a_6lixEq {
+      ._6lixEq_a {
         color: red;
       }
     "#});

src/css_modules.rs

@@ -49,10 +49,9 @@ pub(crate) struct CssModule<'a> {
 
 impl<'a> CssModule<'a> {
   pub fn add_local(&mut self, exported: &str, local: &str) {
-    let hash = &self.hash;
     self.exports.entry(exported.into())
       .or_insert_with(|| CssModuleExport {
-        name: format!("{}_{}", local, hash),
+        name: get_hashed_name(self.hash, local),
         composes: vec![],
         is_referenced: false
       });
@@ -65,7 +64,7 @@ impl<'a> CssModule<'a> {
       }
       std::collections::hash_map::Entry::Vacant(entry) => {
         entry.insert(CssModuleExport {
-          name: format!("{}_{}", name, self.hash),
+          name: get_hashed_name(self.hash, name),
           composes: vec![],
           is_referenced: true
         });
@@ -80,7 +79,7 @@ impl<'a> CssModule<'a> {
           parcel_selectors::parser::Component::Class(ref id) => {
             for name in &composes.names {
               let reference = match &composes.from {
-                None => CssModuleReference::Local { name: format!("{}_{}", name.0, self.hash) },
+                None => CssModuleReference::Local { name: get_hashed_name(self.hash, name.0.as_ref()) },
                 Some(ComposesFrom::Global) => CssModuleReference::Global { name: name.0.as_ref().into() },
                 Some(ComposesFrom::File(file)) => CssModuleReference::Dependency {
                   name: name.0.to_string(),
@@ -107,10 +106,21 @@ impl<'a> CssModule<'a> {
   }
 }
 
+fn get_hashed_name(hash: &str, name: &str) -> String {
+  // Hash must come first so that CSS grid identifiers work.
+  // This is because grid lines may have an implicit -start or -end appended.
+  format!("{}_{}", hash, name)
+}
+
 pub(crate) fn hash(s: &str) -> String {
   let mut hasher = DefaultHasher::new();
   s.hash(&mut hasher);
   let hash = hasher.finish() as u32;
 
-  ENCODER.encode(&hash.to_le_bytes())
+  let hash = ENCODER.encode(&hash.to_le_bytes());
+  if matches!(hash.as_bytes()[0], b'0'..=b'9') {
+    format!("_{}", hash)
+  } else {
+    hash
+  }
 }