Update proc macro to preserve attributes that are common across all child codes

Author: zanieb

crates/ruff_macros/src/map_codes.rs

@@ -8,7 +8,7 @@ use syn::{
     Ident, ItemFn, LitStr, Pat, Path, Stmt, Token,
 };
 
-use crate::rule_code_prefix::{get_prefix_ident, if_all_same};
+use crate::rule_code_prefix::{get_prefix_ident, intersection_all};
 
 /// A rule entry in the big match statement such a
 /// `(Pycodestyle, "E112") => (RuleGroup::Nursery, rules::pycodestyle::rules::logical_lines::NoIndentedBlock),`
@@ -142,12 +142,13 @@ pub(crate) fn map_codes(func: &ItemFn) -> syn::Result<TokenStream> {
 
         for (prefix, rules) in &rules_by_prefix {
             let prefix_ident = get_prefix_ident(prefix);
-            let attr = match if_all_same(rules.iter().map(|(.., attrs)| attrs)) {
-                Some(attr) => quote!(#(#attr)*),
-                None => quote!(),
+            let attrs = intersection_all(rules.iter().map(|(.., attrs)| attrs.as_slice()));
+            let attrs = match attrs.as_slice() {
+                [] => quote!(),
+                [..] => quote!(#(#attrs)*),
             };
             all_codes.push(quote! {
-                #attr Self::#linter(#linter::#prefix_ident)
+                #attrs Self::#linter(#linter::#prefix_ident)
             });
         }
 
@@ -159,12 +160,13 @@ pub(crate) fn map_codes(func: &ItemFn) -> syn::Result<TokenStream> {
                 quote!(#(#attrs)* Rule::#rule_name)
             });
             let prefix_ident = get_prefix_ident(&prefix);
-            let attr = match if_all_same(rules.iter().map(|(.., attrs)| attrs)) {
-                Some(attr) => quote!(#(#attr)*),
-                None => quote!(),
+            let attrs = intersection_all(rules.iter().map(|(.., attrs)| attrs.as_slice()));
+            let attrs = match attrs.as_slice() {
+                [] => quote!(),
+                [..] => quote!(#(#attrs)*),
             };
             prefix_into_iter_match_arms.extend(quote! {
-                #attr #linter::#prefix_ident => vec![#(#rule_paths,)*].into_iter(),
+                #attrs #linter::#prefix_ident => vec![#(#rule_paths,)*].into_iter(),
             });
         }
 

crates/ruff_macros/src/rule_code_prefix.rs

@@ -89,21 +89,39 @@ fn attributes_for_prefix(
     codes: &BTreeSet<String>,
     attributes: &BTreeMap<String, &[Attribute]>,
 ) -> proc_macro2::TokenStream {
-    match if_all_same(codes.iter().map(|code| attributes[code])) {
-        Some(attr) => quote!(#(#attr)*),
-        None => quote!(),
+    let attrs = intersection_all(codes.iter().map(|code| attributes[code]));
+    match attrs.as_slice() {
+        [] => quote!(),
+        [..] => quote!(#(#attrs)*),
     }
 }
 
-/// If all values in an iterator are the same, return that value. Otherwise,
-/// return `None`.
-pub(crate) fn if_all_same<T: PartialEq>(iter: impl Iterator<Item = T>) -> Option<T> {
-    let mut iter = iter.peekable();
-    let first = iter.next()?;
-    if iter.all(|x| x == first) {
-        Some(first)
+/// Collect all the items from an iterable of slices that are present in all slices.
+pub(crate) fn intersection_all<'a, T: PartialEq>(
+    mut slices: impl Iterator<Item = &'a [T]>,
+) -> Vec<&'a T> {
+    if let Some(slice) = slices.next() {
+        // Collect all the items in the first slice
+        let mut intersection = Vec::with_capacity(slice.len());
+        for item in slice {
+            intersection.push(item);
+        }
+        // Then remove all of the items that are not present in each of the
+        // remaining slices
+        while let Some(slice) = slices.next() {
+            let mut mismatches = Vec::with_capacity(slice.len());
+            for (idx, item) in intersection.iter().enumerate() {
+                if !slice.contains(item) {
+                    mismatches.push(idx)
+                }
+            }
+            for idx in mismatches {
+                intersection.remove(idx);
+            }
+        }
+        intersection
     } else {
-        None
+        Vec::new()
     }
 }