Move responsibility for extracting names from paths lower

src/snapshot_middleware/util.rs

@@ -1,5 +1,7 @@
 use std::path::Path;
 
+use anyhow::Context;
+
 /// If the given string ends up with the given suffix, returns the portion of
 /// the string before the suffix.
 pub fn match_trailing<'a>(input: &'a str, suffix: &str) -> Option<&'a str> {
@@ -11,10 +13,31 @@ pub fn match_trailing<'a>(input: &'a str, suffix: &str) -> Option<&'a str> {
     }
 }
 
-/// If the given path has a file name, and that file name ends with the given
-/// suffix, returns the portion of the file name before the given suffix.
-pub fn match_file_name<'a>(path: &'a Path, suffix: &str) -> Option<&'a str> {
-    let file_name = path.file_name()?.to_str()?;
-
-    match_trailing(&file_name, suffix)
+pub trait PathExt {
+    fn file_name_ends_with(&self, suffix: &str) -> bool;
+    fn file_name_trim_end<'a>(&'a self, suffix: &str) -> anyhow::Result<&'a str>;
+}
+
+impl<P> PathExt for P
+where
+    P: AsRef<Path>,
+{
+    fn file_name_ends_with(&self, suffix: &str) -> bool {
+        self.as_ref()
+            .file_name()
+            .and_then(|name| name.to_str())
+            .map(|name| name.ends_with(suffix))
+            .unwrap_or(false)
+    }
+
+    fn file_name_trim_end<'a>(&'a self, suffix: &str) -> anyhow::Result<&'a str> {
+        let path = self.as_ref();
+        let file_name = path
+            .file_name()
+            .and_then(|name| name.to_str())
+            .with_context(|| format!("Path did not have a file name: {}", path.display()))?;
+
+        match_trailing(&file_name, suffix)
+            .with_context(|| format!("Path did not end in {}: {}", suffix, path.display()))
+    }
 }