Add derives for Severity and Diagnostics (#1323)

Add derives for `Diagnostic`, `Severity` and `Diagnostics`, also `Deref`
for `Diagnostics`. In current shape these are very hard to work with,
which is caused by lack of basic functionalities (like `Eq`), also
`Diagnostics` can't be merged or extended with ready `Diagnostic` (only
by matching on it's `Severity` and then choosing correct method to
reconstruct in again)

plugins/cairo-lang-macro/src/types/mod.rs

@@ -158,7 +158,7 @@ impl From<AuxData> for Vec<u8> {
 }
 
 /// Diagnostic returned by the procedural macro.
-#[derive(Debug)]
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct Diagnostic {
     /// A human addressed message associated with the [`Diagnostic`].
     ///
@@ -176,7 +176,7 @@ pub struct Diagnostic {
 /// This should be roughly equivalent to the severity of Cairo diagnostics.
 ///
 /// The appropriate action for each diagnostic kind will be taken by `Scarb`.
-#[derive(Debug)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub enum Severity {
     /// An error has occurred.
     ///
@@ -189,7 +189,7 @@ pub enum Severity {
 }
 
 /// A set of diagnostics that arose during the computation.
-#[derive(Debug)]
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct Diagnostics(Vec<Diagnostic>);
 
 impl Diagnostic {
@@ -252,6 +252,18 @@ impl IntoIterator for Diagnostics {
     }
 }
 
+impl FromIterator<Diagnostic> for Diagnostics {
+    fn from_iter<T: IntoIterator<Item = Diagnostic>>(iter: T) -> Self {
+        Self(iter.into_iter().collect())
+    }
+}
+
+impl Extend<Diagnostic> for Diagnostics {
+    fn extend<T: IntoIterator<Item = Diagnostic>>(&mut self, iter: T) {
+        self.0.extend(iter);
+    }
+}
+
 impl ProcMacroResult {
     /// Create new [`ProcMacroResult`], empty diagnostics set.
     pub fn new(token_stream: TokenStream) -> Self {