Don't lint iter_with_drain on references

clippy_lints/src/methods/iter_with_drain.rs

@@ -1,72 +1,47 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::higher::Range;
 use clippy_utils::is_integer_const;
-use clippy_utils::ty::is_type_diagnostic_item;
-use clippy_utils::{
-    higher::{self, Range},
-    SpanlessEq,
-};
 use rustc_ast::ast::RangeLimits;
 use rustc_errors::Applicability;
 use rustc_hir::{Expr, ExprKind, QPath};
 use rustc_lint::LateContext;
-use rustc_span::symbol::{sym, Symbol};
+use rustc_span::symbol::sym;
 use rustc_span::Span;
 
 use super::ITER_WITH_DRAIN;
 
-const DRAIN_TYPES: &[Symbol] = &[sym::Vec, sym::VecDeque];
-
 pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, recv: &Expr<'_>, span: Span, arg: &Expr<'_>) {
-    let ty = cx.typeck_results().expr_ty(recv).peel_refs();
-    if let Some(drained_type) = DRAIN_TYPES.iter().find(|&&sym| is_type_diagnostic_item(cx, ty, sym)) {
-        // Refuse to emit `into_iter` suggestion on draining struct fields due
-        // to the strong possibility of processing unmovable field.
-        if let ExprKind::Field(..) = recv.kind {
-            return;
-        }
-
-        if let Some(range) = higher::Range::hir(arg) {
-            let left_full = match range {
-                Range { start: Some(start), .. } if is_integer_const(cx, start, 0) => true,
-                Range { start: None, .. } => true,
-                _ => false,
-            };
-            let full = left_full
-                && match range {
-                    Range {
-                        end: Some(end),
-                        limits: RangeLimits::HalfOpen,
-                        ..
-                    } => {
-                        // `x.drain(..x.len())` call
-                        if_chain! {
-                            if let ExprKind::MethodCall(len_path, len_args, _) = end.kind;
-                            if len_path.ident.name == sym::len && len_args.len() == 1;
-                            if let ExprKind::Path(QPath::Resolved(_, drain_path)) = recv.kind;
-                            if let ExprKind::Path(QPath::Resolved(_, len_path)) = len_args[0].kind;
-                            if SpanlessEq::new(cx).eq_path(drain_path, len_path);
-                            then { true }
-                            else { false }
-                        }
-                    },
-                    Range {
-                        end: None,
-                        limits: RangeLimits::HalfOpen,
-                        ..
-                    } => true,
-                    _ => false,
-                };
-            if full {
-                span_lint_and_sugg(
-                    cx,
-                    ITER_WITH_DRAIN,
-                    span.with_hi(expr.span.hi()),
-                    &format!("`drain(..)` used on a `{}`", drained_type),
-                    "try this",
-                    "into_iter()".to_string(),
-                    Applicability::MaybeIncorrect,
-                );
-            }
-        }
-    }
+    if !matches!(recv.kind, ExprKind::Field(..))
+        && let Some(adt) = cx.typeck_results().expr_ty(recv).ty_adt_def()
+        && let Some(ty_name) = cx.tcx.get_diagnostic_name(adt.did())
+        && matches!(ty_name, sym::Vec | sym::VecDeque)
+        && let Some(range) = Range::hir(arg)
+        && is_full_range(cx, recv, range)
+    {
+        span_lint_and_sugg(
+            cx,
+            ITER_WITH_DRAIN,
+            span.with_hi(expr.span.hi()),
+            &format!("`drain(..)` used on a `{}`", ty_name),
+            "try this",
+            "into_iter()".to_string(),
+            Applicability::MaybeIncorrect,
+        );
+    };
+}
+
+fn is_full_range(cx: &LateContext<'_>, container: &Expr<'_>, range: Range<'_>) -> bool {
+    range.start.map_or(true, |e| is_integer_const(cx, e, 0))
+        && range.end.map_or(true, |e| {
+            if range.limits == RangeLimits::HalfOpen
+                && let ExprKind::Path(QPath::Resolved(None, container_path)) = container.kind
+                && let ExprKind::MethodCall(name, [self_arg], _) = e.kind
+                && name.ident.name == sym::len
+                && let ExprKind::Path(QPath::Resolved(None, path)) = self_arg.kind
+            {
+                container_path.res == path.res
+            } else {
+                false
+            }
+        })
 }

tests/ui/iter_with_drain.fixed

@@ -39,6 +39,15 @@ fn should_not_help() {
     let _: Vec<_> = b.drain(0..a.len()).collect();
 }
 
+fn _closed_range(mut x: Vec<String>) {
+    let _: Vec<String> = x.drain(0..=x.len()).collect();
+}
+
+fn _with_mut(x: &mut Vec<String>, y: &mut VecDeque<String>) {
+    let _: Vec<String> = x.drain(..).collect();
+    let _: Vec<String> = y.drain(..).collect();
+}
+
 #[derive(Default)]
 struct Bomb {
     fire: Vec<u8>,

tests/ui/iter_with_drain.rs

@@ -39,6 +39,15 @@ fn should_not_help() {
     let _: Vec<_> = b.drain(0..a.len()).collect();
 }
 
+fn _closed_range(mut x: Vec<String>) {
+    let _: Vec<String> = x.drain(0..=x.len()).collect();
+}
+
+fn _with_mut(x: &mut Vec<String>, y: &mut VecDeque<String>) {
+    let _: Vec<String> = x.drain(..).collect();
+    let _: Vec<String> = y.drain(..).collect();
+}
+
 #[derive(Default)]
 struct Bomb {
     fire: Vec<u8>,