Add ast ident iterator

clippy_lints/src/utils/ast_utils.rs

@@ -10,6 +10,8 @@ use rustc_ast::{self as ast, *};
 use rustc_span::symbol::Ident;
 use std::mem;
 
+pub mod ident_iter;
+
 /// Checks if each element in the first slice is contained within the latter as per `eq_fn`.
 pub fn unordered_over<X>(left: &[X], right: &[X], mut eq_fn: impl FnMut(&X, &X) -> bool) -> bool {
     left.len() == right.len() && left.iter().all(|l| right.iter().any(|r| eq_fn(l, r)))

clippy_lints/src/utils/ast_utils/ident_iter.rs

@@ -0,0 +1,45 @@
+use core::iter::FusedIterator;
+use rustc_ast::visit::{walk_attribute, walk_expr, Visitor};
+use rustc_ast::{Attribute, Expr};
+use rustc_span::symbol::Ident;
+
+pub struct IdentIter(std::vec::IntoIter<Ident>);
+
+impl Iterator for IdentIter {
+    type Item = Ident;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.0.next()
+    }
+}
+
+impl FusedIterator for IdentIter {}
+
+impl From<&Expr> for IdentIter {
+    fn from(expr: &Expr) -> Self {
+        let mut visitor = IdentCollector::default();
+
+        walk_expr(&mut visitor, expr);
+
+        IdentIter(visitor.0.into_iter())
+    }
+}
+
+impl From<&Attribute> for IdentIter {
+    fn from(attr: &Attribute) -> Self {
+        let mut visitor = IdentCollector::default();
+
+        walk_attribute(&mut visitor, attr);
+
+        IdentIter(visitor.0.into_iter())
+    }
+}
+
+#[derive(Default)]
+struct IdentCollector(Vec<Ident>);
+
+impl Visitor<'_> for IdentCollector {
+    fn visit_ident(&mut self, ident: Ident) {
+        self.0.push(ident);
+    }
+}