Use a derive macro for Violations (#14557)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

crates/ruff_diagnostics/src/lib.rs

@@ -2,7 +2,7 @@ pub use diagnostic::{Diagnostic, DiagnosticKind};
 pub use edit::Edit;
 pub use fix::{Applicability, Fix, IsolationLevel};
 pub use source_map::{SourceMap, SourceMarker};
-pub use violation::{AlwaysFixableViolation, FixAvailability, Violation};
+pub use violation::{AlwaysFixableViolation, FixAvailability, Violation, ViolationMetadata};
 
 mod diagnostic;
 mod edit;

crates/ruff_diagnostics/src/violation.rs

@@ -1,3 +1,4 @@
+use crate::DiagnosticKind;
 use std::fmt::{Debug, Display};
 
 #[derive(Debug, Copy, Clone)]
@@ -17,7 +18,16 @@ impl Display for FixAvailability {
     }
 }
 
-pub trait Violation: Debug + PartialEq + Eq {
+pub trait ViolationMetadata {
+    /// Returns the rule name of this violation
+    fn rule_name() -> &'static str;
+
+    /// Returns an explanation of what this violation catches,
+    /// why it's bad, and what users should do instead.
+    fn explain() -> Option<&'static str>;
+}
+
+pub trait Violation: ViolationMetadata {
     /// `None` in the case a fix is never available or otherwise Some
     /// [`FixAvailability`] describing the available fix.
     const FIX_AVAILABILITY: FixAvailability = FixAvailability::None;
@@ -41,7 +51,7 @@ pub trait Violation: Debug + PartialEq + Eq {
 
 /// This trait exists just to make implementing the [`Violation`] trait more
 /// convenient for violations that can always be fixed.
-pub trait AlwaysFixableViolation: Debug + PartialEq + Eq {
+pub trait AlwaysFixableViolation: ViolationMetadata {
     /// The message used to describe the violation.
     fn message(&self) -> String;
 
@@ -69,3 +79,16 @@ impl<V: AlwaysFixableViolation> Violation for V {
         <Self as AlwaysFixableViolation>::message_formats()
     }
 }
+
+impl<T> From<T> for DiagnosticKind
+where
+    T: Violation,
+{
+    fn from(value: T) -> Self {
+        Self {
+            body: Violation::message(&value),
+            suggestion: Violation::fix_title(&value),
+            name: T::rule_name().to_string(),
+        }
+    }
+}