Unify OldDiagnostic and Message (#18391)

Summary
--

This PR unifies the remaining differences between `OldDiagnostic` and
`Message` (`OldDiagnostic` was only missing an optional `noqa_offset`
field) and
replaces `Message` with `OldDiagnostic`.

The biggest functional difference is that the combined `OldDiagnostic`
kind no
longer implements `AsRule` for an infallible conversion to `Rule`. This
was
pretty easy to work around with `is_some_and` and `is_none_or` in the
few places
it was needed. In `LintContext::report_diagnostic_if_enabled` we can
just use
the new `Violation::rule` method, which takes care of most cases.

Most of the interesting changes are in [this
range](8156992540)
before I started renaming.

Test Plan
--

Existing tests

Future Work
--

I think it's time to start shifting some of these fields to the new
`Diagnostic`
kind. I believe we want `Fix` for sure, but I'm less sure about the
others. We
may want to keep a thin wrapper type here anyway to implement a `rule`
method,
so we could leave some of these fields on that too.

crates/ruff_macros/src/map_codes.rs

@@ -254,9 +254,11 @@ fn generate_rule_to_code(linter_to_rules: &BTreeMap<Ident, BTreeMap<String, Rule
     }
 
     let mut rule_noqa_code_match_arms = quote!();
+    let mut noqa_code_rule_match_arms = quote!();
     let mut rule_group_match_arms = quote!();
+    let mut noqa_code_consts = quote!();
 
-    for (rule, codes) in rule_to_codes {
+    for (i, (rule, codes)) in rule_to_codes.into_iter().enumerate() {
         let rule_name = rule.segments.last().unwrap();
         assert_eq!(
             codes.len(),
@@ -292,6 +294,14 @@ See also https://github.com/astral-sh/ruff/issues/2186.
             #(#attrs)* Rule::#rule_name => NoqaCode(crate::registry::Linter::#linter.common_prefix(), #code),
         });
 
+        let const_ident = quote::format_ident!("NOQA_PREFIX_{}", i);
+        noqa_code_consts.extend(quote! {
+            const #const_ident: &str = crate::registry::Linter::#linter.common_prefix();
+        });
+        noqa_code_rule_match_arms.extend(quote! {
+            #(#attrs)* NoqaCode(#const_ident, #code) => Some(Rule::#rule_name),
+        });
+
         rule_group_match_arms.extend(quote! {
             #(#attrs)* Rule::#rule_name => #group,
         });
@@ -340,6 +350,16 @@ See also https://github.com/astral-sh/ruff/issues/2186.
                 }
             }
         }
+
+        impl NoqaCode {
+            pub fn rule(&self) -> Option<Rule> {
+                #noqa_code_consts
+                match self {
+                    #noqa_code_rule_match_arms
+                    _ => None
+                }
+            }
+        }
     };
     rule_to_code
 }

crates/ruff_macros/src/rule_namespace.rs

@@ -118,10 +118,6 @@ pub(crate) fn derive_impl(input: DeriveInput) -> syn::Result<proc_macro2::TokenS
                 None
             }
 
-            fn common_prefix(&self) -> &'static str {
-                match self { #common_prefix_match_arms }
-            }
-
             fn name(&self) -> &'static str {
                 match self { #name_match_arms }
             }
@@ -130,6 +126,16 @@ pub(crate) fn derive_impl(input: DeriveInput) -> syn::Result<proc_macro2::TokenS
                 match self { #url_match_arms }
             }
         }
+
+        impl #ident {
+            /// Returns the prefix that every single code that ruff uses to identify
+            /// rules from this linter starts with.  In the case that multiple
+            /// `#[prefix]`es are configured for the variant in the `Linter` enum
+            /// definition this is the empty string.
+            pub const fn common_prefix(&self) -> &'static str {
+                match self { #common_prefix_match_arms }
+            }
+        }
     })
 }