Simplify code for picking previous date

Author: jonhoo

src/dist/dist.rs

@@ -646,29 +646,18 @@ fn update_from_dist_<'a>(
                 // try is _older_ than the current nightly, since we know that the user's current
                 // nightlys supports the components they have installed, and thus would always
                 // terminate the search.
-                if let Some(ref mut date) = toolchain.date {
-                    // recurse
-                    toolchain.date = Some(
-                        Utc.from_utc_date(
-                            &NaiveDate::parse_from_str(date, "%Y-%m-%d")
-                                .expect("we constructed this date string below"),
+                toolchain.date = Some(
+                    Utc.from_utc_date(
+                        &NaiveDate::parse_from_str(
+                            toolchain.date.as_ref().unwrap_or(&fetched),
+                            "%Y-%m-%d",
                         )
-                        .pred()
-                        .format("%Y-%m-%d")
-                        .to_string(),
-                    );
-                } else {
-                    // Pick a nightly that is one day older than the latest.
-                    toolchain.date = Some(
-                        Utc.from_utc_date(
-                            &NaiveDate::parse_from_str(&fetched, "%Y-%m-%d")
-                                .expect("manifest carries invalid date"),
-                        )
-                        .pred()
-                        .format("%Y-%m-%d")
-                        .to_string(),
-                    );
-                }
+                        .expect("Malformed manifest date"),
+                    )
+                    .pred()
+                    .format("%Y-%m-%d")
+                    .to_string(),
+                );
             }
         }
     }