Reverse precedence of syntax mappings specified on CLI

src/bin/bat/app.rs

@@ -130,7 +130,9 @@ impl App {
         }
 
         if let Some(values) = self.matches.get_many::<String>("map-syntax") {
-            for from_to in values {
+            // later args take precedence over earlier ones, hence `.rev()`
+            // see: https://github.com/sharkdp/bat/pull/2755#discussion_r1456416875
+            for from_to in values.rev() {
                 let parts: Vec<_> = from_to.split(':').collect();
 
                 if parts.len() != 2 {

src/syntax_mapping.rs

@@ -41,6 +41,8 @@ pub enum MappingTarget<'a> {
 #[derive(Debug, Clone, Default)]
 pub struct SyntaxMapping<'a> {
     /// User-defined mappings at run time.
+    ///
+    /// Rules in front have precedence.
     custom_mappings: Vec<(GlobMatcher, MappingTarget<'a>)>,
     pub(crate) ignored_suffixes: IgnoredSuffixes<'a>,
 }