review-classifier: keep the stored value out of a failed read's text

swarm-review-classifier/src/run.rs

@@ -188,7 +188,7 @@ impl KeySource for Store {
 
 /// `e` and each of its sources, joined by `: `. The store client's errors
 /// carry only a generic message at the top; the URL and the failure kind sit
-/// below it. Neither holds a token or key value.
+/// below it. For login errors only: they hold URLs and error kinds, not values.
 fn chain(e: &dyn std::error::Error) -> String {
     let mut out = e.to_string();
     let mut next = e.source();
@@ -208,6 +208,13 @@ fn login_failure(what: &str, e: &dyn std::error::Error) -> String {
     )
 }
 
+/// The run failure for a store read that failed with `e`. Shows `e` alone:
+/// a parse error's sources quote the stored value, and the failure text ends
+/// up in a review comment.
+fn read_failure(path: &str, e: &dyn std::error::Error) -> String {
+    format!("reading secret/{path}: {e}")
+}
+
 /// The key `field` takes from the object at `path`, trimmed; `None` when
 /// nothing or a blank is stored.
 async fn read_key<T: serde::de::DeserializeOwned>(
@@ -221,7 +228,7 @@ async fn read_key<T: serde::de::DeserializeOwned>(
     let stored: Option<T> = store
         .read_optional(path)
         .await
-        .map_err(|e| format!("reading secret/{path}: {}", chain(&e)))?;
+        .map_err(|e| read_failure(path, &e))?;
     Ok(stored
         .map(field)
         .map(|key| key.trim().to_owned())
@@ -418,6 +425,30 @@ mod tests {
         }
     }
 
+    /// A parse failure whose source quotes the stored value.
+    #[derive(Debug)]
+    struct Unparsable(serde_json::Error);
+
+    impl std::fmt::Display for Unparsable {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            f.write_str("error parsing the response")
+        }
+    }
+
+    impl std::error::Error for Unparsable {
+        fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+            Some(&self.0)
+        }
+    }
+
+    #[test]
+    fn read_failure_leaves_out_the_stored_value() {
+        let cause = serde_json::from_str::<u32>("\"hunter2\"").unwrap_err();
+        assert!(cause.to_string().contains("hunter2"), "control");
+        let text = read_failure("p", &Unparsable(cause));
+        assert_eq!(text, "reading secret/p: error parsing the response");
+    }
+
     #[test]
     fn chain_renders_every_level() {
         let e = Level(