Review feedback

Exhaustively match against `FieldType` to determine if it's copyable.

oximeter/impl/src/schema/codegen.rs

@@ -78,7 +78,9 @@ fn emit_target(schema: &TimeseriesSchema) -> TokenStream {
 fn fields_are_copyable<'a>(
     mut fields: impl Iterator<Item = &'a FieldSchema>,
 ) -> bool {
-    !fields.any(|field| field.field_type == FieldType::String)
+    // Do a positive match, to ensure new variants don't actually derive copy
+    // inappropriately. Better we clone, in that case.
+    fields.all(FieldSchema::is_copyable)
 }
 
 fn compute_extra_derives(

oximeter/impl/src/schema/mod.rs

@@ -54,6 +54,13 @@ pub struct FieldSchema {
     pub description: String,
 }
 
+impl FieldSchema {
+    /// Return `true` if this field is copyable.
+    pub const fn is_copyable(&self) -> bool {
+        self.field_type.is_copyable()
+    }
+}
+
 /// The source from which a field is derived, the target or metric.
 #[derive(
     Clone,

oximeter/impl/src/types.rs

@@ -63,6 +63,29 @@ pub enum FieldType {
     Bool,
 }
 
+impl FieldType {
+    /// Return `true` if a field of this type is copyable.
+    ///
+    /// NOTE: This doesn't mean `self` is copyable, instead refering to a field
+    /// with this type.
+    pub const fn is_copyable(&self) -> bool {
+        match self {
+            FieldType::String => false,
+            FieldType::I8
+            | FieldType::U8
+            | FieldType::I16
+            | FieldType::U16
+            | FieldType::I32
+            | FieldType::U32
+            | FieldType::I64
+            | FieldType::U64
+            | FieldType::IpAddr
+            | FieldType::Uuid
+            | FieldType::Bool => true,
+        }
+    }
+}
+
 impl std::fmt::Display for FieldType {
     fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
         write!(f, "{:?}", self)