Ensure Copy is derived for all query sources where possible

Since we have a lot of methods like `filter` which need to be able to
consume `self`, we want to make sure that we return types which are
`Copy` whenever possible for ergonomics. Ultimately this ends up being
completely meaningless for many cases, since the concrete types often
end up with a size of 0.

src/macros.rs

@@ -62,7 +62,7 @@ macro_rules! table {
                 use $crate::types::*;
 
                 #[allow(non_camel_case_types, dead_code)]
-                #[derive(Debug)]
+                #[derive(Debug, Clone, Copy)]
                 pub struct star;
 
                 impl Column for star {
@@ -79,7 +79,7 @@ macro_rules! table {
                 }
 
                 $(#[allow(non_camel_case_types, dead_code)]
-                #[derive(Debug)]
+                #[derive(Debug, Clone, Copy)]
                 pub struct $column_name;
 
                 impl Column for $column_name {

src/query_source/filter.rs

@@ -2,6 +2,7 @@ use expression::SelectableExpression;
 use types;
 use {QuerySource};
 
+#[derive(Clone, Copy)]
 pub struct FilteredQuerySource<T, P> {
     source: T,
     predicate: P,

src/query_source/select.rs

@@ -3,6 +3,7 @@ use types::NativeSqlType;
 use std::marker::PhantomData;
 use expression::SelectableExpression;
 
+#[derive(Copy, Clone)]
 pub struct SelectSqlQuerySource<A, S, E> {
     columns: E,
     source: S,

src/types/mod.rs

@@ -7,26 +7,26 @@ use row::Row;
 use std::error::Error;
 use std::io::Write;
 
-pub struct Bool;
+#[derive(Clone, Copy)] pub struct Bool;
 
-pub struct SmallSerial;
-pub struct Serial;
-pub struct BigSerial;
+#[derive(Clone, Copy)] pub struct SmallSerial;
+#[derive(Clone, Copy)] pub struct Serial;
+#[derive(Clone, Copy)] pub struct BigSerial;
 
-pub struct SmallInt;
-pub struct Integer;
-pub struct BigInt;
+#[derive(Clone, Copy)] pub struct SmallInt;
+#[derive(Clone, Copy)] pub struct Integer;
+#[derive(Clone, Copy)] pub struct BigInt;
 
-pub struct Float;
-pub struct Double;
+#[derive(Clone, Copy)] pub struct Float;
+#[derive(Clone, Copy)] pub struct Double;
 
-pub struct VarChar;
-pub struct Text;
+#[derive(Clone, Copy)] pub struct VarChar;
+#[derive(Clone, Copy)] pub struct Text;
 
-pub struct Binary;
+#[derive(Clone, Copy)] pub struct Binary;
 
-pub struct Nullable<T: NativeSqlType>(T);
-pub struct Array<T: NativeSqlType>(T);
+#[derive(Clone, Copy)] pub struct Nullable<T: NativeSqlType>(T);
+#[derive(Clone, Copy)] pub struct Array<T: NativeSqlType>(T);
 
 pub trait NativeSqlType {}