Defaults *.fs to F#

src/assets.rs

@@ -428,6 +428,7 @@ mod tests {
         assert_eq!(test.syntax_for_file("test.h"), "C++");
         assert_eq!(test.syntax_for_file("test.sass"), "Sass");
         assert_eq!(test.syntax_for_file("test.js"), "JavaScript (Babel)");
+        assert_eq!(test.syntax_for_file("test.fs"), "F#");
     }
 
     #[test]

src/syntax_mapping.rs

@@ -23,6 +23,7 @@ impl<'a> SyntaxMapping<'a> {
     pub fn builtin() -> SyntaxMapping<'a> {
         let mut mapping = Self::empty();
         mapping.insert("*.h", MappingTarget::MapTo("C++")).unwrap();
+        mapping.insert("*.fs", MappingTarget::MapTo("F#")).unwrap();
         mapping
             .insert("build", MappingTarget::MapToUnknown)
             .unwrap();

tests/no_duplicate_extensions.rs

@@ -14,6 +14,8 @@ fn no_duplicate_extensions() {
         // The "Ruby Haml" syntax also comes with a '.sass' extension. However, we make sure
         // that 'sass' is mapped to the 'Sass' syntax.
         "sass",
+        // The '.fs' extension appears in F# and GLSL. We default to F#.
+        "fs",
     ];
 
     let assets = HighlightingAssets::from_binary();