Permit deserialization of data structures from streams

Previously we were insisting on being able to borrow data from the
source data, which isn't always possible. Implement visitors appropriately to
avoid that.

Author: Mark-Simulacrum

collector/src/lib.rs

@@ -75,8 +75,24 @@ impl<'de> Deserialize<'de> for Sha {
     where
         D: serde::de::Deserializer<'de>,
     {
-        let s: &'de str = <&'de str>::deserialize(deserializer)?;
-        Ok(s.into())
+        use serde::de::Visitor;
+        struct ShaVisitor;
+        impl<'de> Visitor<'de> for ShaVisitor {
+            type Value = Sha;
+
+            fn expecting(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                f.write_str("a string")
+            }
+
+            fn visit_str<E>(self, s: &str) -> Result<Sha, E> {
+                Ok(s.into())
+            }
+
+            fn visit_borrowed_str<E>(self, s: &'de str) -> Result<Sha, E> {
+                Ok(s.into())
+            }
+        }
+        deserializer.deserialize_str(ShaVisitor)
     }
 }