find expansions more efficiently

clippy_lints/src/useless_conversion.rs

@@ -40,6 +40,7 @@ declare_clippy_lint! {
 #[derive(Default)]
 pub struct UselessConversion {
     try_desugar_arm: Vec<HirId>,
+    expn_depth: u32,
 }
 
 impl_lint_pass!(UselessConversion => [USELESS_CONVERSION]);
@@ -102,21 +103,11 @@ fn into_iter_deep_call<'hir>(cx: &LateContext<'_>, mut expr: &'hir Expr<'hir>) -
     (expr, depth)
 }
 
-/// Checks if the given `expr` is an argument of a macro invocation.
-/// This is a slow-ish operation, so consider calling this late
-/// to avoid slowing down the lint in the happy path when not emitting a warning
-fn is_macro_argument(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
-    if let Some(parent) = get_parent_expr(cx, expr) {
-        parent.span.from_expansion() || is_macro_argument(cx, parent)
-    } else {
-        false
-    }
-}
-
 #[expect(clippy::too_many_lines)]
 impl<'tcx> LateLintPass<'tcx> for UselessConversion {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
         if e.span.from_expansion() {
+            self.expn_depth += 1;
             return;
         }
 
@@ -185,7 +176,7 @@ impl<'tcx> LateLintPass<'tcx> for UselessConversion {
                             && let Some(&into_iter_param) = sig.inputs().get(kind.param_pos(arg_pos))
                             && let ty::Param(param) = into_iter_param.kind()
                             && let Some(span) = into_iter_bound(cx, parent_fn_did, into_iter_did, param.index)
-                            && !is_macro_argument(cx, e)
+                            && self.expn_depth == 0
                         {
                             // Get the "innermost" `.into_iter()` call, e.g. given this expression:
                             // `foo.into_iter().into_iter()`
@@ -321,5 +312,8 @@ impl<'tcx> LateLintPass<'tcx> for UselessConversion {
         if Some(&e.hir_id) == self.try_desugar_arm.last() {
             self.try_desugar_arm.pop();
         }
+        if e.span.from_expansion() {
+            self.expn_depth -= 1;
+        }
     }
 }

tests/ui/useless_conversion.fixed

@@ -153,6 +153,20 @@ fn main() {
     let _ = vec![s4, s4, s4].into_iter();
 }
 
+#[allow(dead_code)]
+fn issue11065_fp() {
+    use std::option::IntoIter;
+    fn takes_into_iter(_: impl IntoIterator<Item = i32>) {}
+
+    macro_rules! x {
+        ($e:expr) => {
+            takes_into_iter($e);
+            let _: IntoIter<i32> = $e; // removing `.into_iter()` leads to a type error here
+        };
+    }
+    x!(Some(5).into_iter());
+}
+
 #[allow(dead_code)]
 fn explicit_into_iter_fn_arg() {
     fn a<T>(_: T) {}

tests/ui/useless_conversion.rs

@@ -153,6 +153,20 @@ fn main() {
     let _ = vec![s4, s4, s4].into_iter().into_iter();
 }
 
+#[allow(dead_code)]
+fn issue11065_fp() {
+    use std::option::IntoIter;
+    fn takes_into_iter(_: impl IntoIterator<Item = i32>) {}
+
+    macro_rules! x {
+        ($e:expr) => {
+            takes_into_iter($e);
+            let _: IntoIter<i32> = $e; // removing `.into_iter()` leads to a type error here
+        };
+    }
+    x!(Some(5).into_iter());
+}
+
 #[allow(dead_code)]
 fn explicit_into_iter_fn_arg() {
     fn a<T>(_: T) {}

tests/ui/useless_conversion.stderr

@@ -119,61 +119,61 @@ LL |     let _ = vec![s4, s4, s4].into_iter().into_iter();
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider removing `.into_iter()`: `vec![s4, s4, s4].into_iter()`
 
 error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
-  --> $DIR/useless_conversion.rs:169:7
+  --> $DIR/useless_conversion.rs:183:7
    |
 LL |     b(vec![1, 2].into_iter());
    |       ^^^^^^^^^^^^^^^^^^^^^^ help: consider removing the `.into_iter()`: `vec![1, 2]`
    |
 note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
-  --> $DIR/useless_conversion.rs:159:13
+  --> $DIR/useless_conversion.rs:173:13
    |
 LL |     fn b<T: IntoIterator<Item = i32>>(_: T) {}
    |             ^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
-  --> $DIR/useless_conversion.rs:170:7
+  --> $DIR/useless_conversion.rs:184:7
    |
 LL |     c(vec![1, 2].into_iter());
    |       ^^^^^^^^^^^^^^^^^^^^^^ help: consider removing the `.into_iter()`: `vec![1, 2]`
    |
 note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
-  --> $DIR/useless_conversion.rs:160:18
+  --> $DIR/useless_conversion.rs:174:18
    |
 LL |     fn c(_: impl IntoIterator<Item = i32>) {}
    |                  ^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
-  --> $DIR/useless_conversion.rs:171:7
+  --> $DIR/useless_conversion.rs:185:7
    |
 LL |     d(vec![1, 2].into_iter());
    |       ^^^^^^^^^^^^^^^^^^^^^^ help: consider removing the `.into_iter()`: `vec![1, 2]`
    |
 note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
-  --> $DIR/useless_conversion.rs:163:12
+  --> $DIR/useless_conversion.rs:177:12
    |
 LL |         T: IntoIterator<Item = i32>,
    |            ^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
-  --> $DIR/useless_conversion.rs:174:7
+  --> $DIR/useless_conversion.rs:188:7
    |
 LL |     b(vec![1, 2].into_iter().into_iter());
    |       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider removing the `.into_iter()`s: `vec![1, 2]`
    |
 note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
-  --> $DIR/useless_conversion.rs:159:13
+  --> $DIR/useless_conversion.rs:173:13
    |
 LL |     fn b<T: IntoIterator<Item = i32>>(_: T) {}
    |             ^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
-  --> $DIR/useless_conversion.rs:175:7
+  --> $DIR/useless_conversion.rs:189:7
    |
 LL |     b(vec![1, 2].into_iter().into_iter().into_iter());
    |       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider removing the `.into_iter()`s: `vec![1, 2]`
    |
 note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
-  --> $DIR/useless_conversion.rs:159:13
+  --> $DIR/useless_conversion.rs:173:13
    |
 LL |     fn b<T: IntoIterator<Item = i32>>(_: T) {}
    |             ^^^^^^^^^^^^^^^^^^^^^^^^