Fix explicit_into_iter_loop

Only lint when `into_iter` is an implementation of `IntoIterator`
Minor cleanups

clippy_lints/src/loops/explicit_into_iter_loop.rs

@@ -1,24 +1,25 @@
 use super::EXPLICIT_INTO_ITER_LOOP;
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::{match_trait_method, paths};
 use rustc_errors::Applicability;
 use rustc_hir::Expr;
 use rustc_lint::LateContext;
 use rustc_middle::ty::TyS;
 
-pub(super) fn check(cx: &LateContext<'_>, args: &'hir [Expr<'hir>], arg: &Expr<'_>) {
-    let receiver_ty = cx.typeck_results().expr_ty(&args[0]);
-    let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]);
-    if !TyS::same_type(receiver_ty, receiver_ty_adjusted) {
+pub(super) fn check(cx: &LateContext<'_>, self_arg: &'hir Expr<'hir>, call_expr: &Expr<'_>) {
+    let self_ty = cx.typeck_results().expr_ty(self_arg);
+    let self_ty_adjusted = cx.typeck_results().expr_ty_adjusted(self_arg);
+    if !(TyS::same_type(self_ty, self_ty_adjusted) && match_trait_method(cx, call_expr, &paths::INTO_ITERATOR)) {
         return;
     }
 
     let mut applicability = Applicability::MachineApplicable;
-    let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
+    let object = snippet_with_applicability(cx, self_arg.span, "_", &mut applicability);
     span_lint_and_sugg(
         cx,
         EXPLICIT_INTO_ITER_LOOP,
-        arg.span,
+        call_expr.span,
         "it is more concise to loop over containers instead of using explicit \
             iteration methods",
         "to write this more concisely, try",

clippy_lints/src/loops/explicit_iter_loop.rs

@@ -9,12 +9,12 @@
 use rustc_middle::ty::{self, Ty, TyS};
 use rustc_span::sym;
 
-pub(super) fn check(cx: &LateContext<'_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) {
+pub(super) fn check(cx: &LateContext<'_>, self_arg: &Expr<'_>, arg: &Expr<'_>, method_name: &str) {
     let should_lint = match method_name {
-        "iter" | "iter_mut" => is_ref_iterable_type(cx, &args[0]),
+        "iter" | "iter_mut" => is_ref_iterable_type(cx, self_arg),
         "into_iter" if match_trait_method(cx, arg, &paths::INTO_ITERATOR) => {
-            let receiver_ty = cx.typeck_results().expr_ty(&args[0]);
-            let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]);
+            let receiver_ty = cx.typeck_results().expr_ty(self_arg);
+            let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(self_arg);
             let ref_receiver_ty = cx.tcx.mk_ref(
                 cx.tcx.lifetimes.re_erased,
                 ty::TypeAndMut {
@@ -32,7 +32,7 @@ pub(super) fn check(cx: &LateContext<'_>, args: &[Expr<'_>], arg: &Expr<'_>, met
     }
 
     let mut applicability = Applicability::MachineApplicable;
-    let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
+    let object = snippet_with_applicability(cx, self_arg.span, "_", &mut applicability);
     let muta = if method_name == "iter_mut" { "mut " } else { "" };
     span_lint_and_sugg(
         cx,

clippy_lints/src/loops/mod.rs

@@ -602,16 +602,14 @@ fn check_for_loop<'tcx>(
 fn check_for_loop_arg(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) {
     let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
 
-    if let ExprKind::MethodCall(method, _, args, _) = arg.kind {
-        // just the receiver, no arguments
-        if args.len() == 1 {
+    if let ExprKind::MethodCall(method, _, [self_arg], _) = arg.kind {
         let method_name = &*method.ident.as_str();
         // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
         match method_name {
-                "iter" | "iter_mut" => explicit_iter_loop::check(cx, args, arg, method_name),
+            "iter" | "iter_mut" => explicit_iter_loop::check(cx, self_arg, arg, method_name),
             "into_iter" => {
-                    explicit_iter_loop::check(cx, args, arg, method_name);
-                    explicit_into_iter_loop::check(cx, args, arg);
+                explicit_iter_loop::check(cx, self_arg, arg, method_name);
+                explicit_into_iter_loop::check(cx, self_arg, arg);
             },
             "next" => {
                 next_loop_linted = iter_next_loop::check(cx, arg, expr);
@@ -619,7 +617,6 @@ fn check_for_loop_arg(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>, expr:
             _ => {},
         }
     }
-    }
 
     if !next_loop_linted {
         for_loops_over_fallibles::check(cx, pat, arg);

tests/ui/for_loop_fixable.fixed

@@ -281,3 +281,29 @@ mod issue_4958 {
         for _ in rr.into_iter() {}
     }
 }
+
+// explicit_into_iter_loop
+#[warn(clippy::explicit_into_iter_loop)]
+mod issue_6900 {
+    struct S;
+    impl S {
+        #[allow(clippy::should_implement_trait)]
+        pub fn into_iter<T>(self) -> I<T> {
+            unimplemented!()
+        }
+    }
+
+    struct I<T>(T);
+    impl<T> Iterator for I<T> {
+        type Item = T;
+        fn next(&mut self) -> Option<Self::Item> {
+            unimplemented!()
+        }
+    }
+
+    fn f() {
+        for _ in S.into_iter::<u32>() {
+            unimplemented!()
+        }
+    }
+}

tests/ui/for_loop_fixable.rs

@@ -281,3 +281,29 @@ fn more_tests() {
         for _ in rr.into_iter() {}
     }
 }
+
+// explicit_into_iter_loop
+#[warn(clippy::explicit_into_iter_loop)]
+mod issue_6900 {
+    struct S;
+    impl S {
+        #[allow(clippy::should_implement_trait)]
+        pub fn into_iter<T>(self) -> I<T> {
+            unimplemented!()
+        }
+    }
+
+    struct I<T>(T);
+    impl<T> Iterator for I<T> {
+        type Item = T;
+        fn next(&mut self) -> Option<Self::Item> {
+            unimplemented!()
+        }
+    }
+
+    fn f() {
+        for _ in S.into_iter::<u32>() {
+            unimplemented!()
+        }
+    }
+}