Handle to_vec on for loop expression #8069

Author: smoelius

clippy_lints/src/methods/mod.rs

@@ -56,6 +56,7 @@ mod suspicious_splitn;
 mod uninit_assumed_init;
 mod unnecessary_filter_map;
 mod unnecessary_fold;
+mod unnecessary_iter_cloned;
 mod unnecessary_lazy_eval;
 mod unnecessary_to_owned;
 mod unwrap_or_else_default;

clippy_lints/src/methods/unnecessary_iter_cloned.rs

@@ -0,0 +1,177 @@
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::higher::ForLoop;
+use clippy_utils::source::snippet_opt;
+use clippy_utils::ty::{get_associated_type, get_iterator_item_ty, implements_trait};
+use clippy_utils::{fn_def_id, get_parent_expr, path_to_local_id, usage};
+use rustc_errors::Applicability;
+use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
+use rustc_hir::{def_id::DefId, BorrowKind, Expr, ExprKind, HirId, LangItem, Mutability, Pat};
+use rustc_lint::LateContext;
+use rustc_middle::{hir::map::Map, ty};
+use rustc_span::{sym, Symbol};
+
+use super::UNNECESSARY_TO_OWNED;
+
+pub fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, method_name: Symbol, receiver: &'tcx Expr<'tcx>) -> bool {
+    if_chain! {
+        if let Some(parent) = get_parent_expr(cx, expr);
+        if let Some(callee_def_id) = fn_def_id(cx, parent);
+        if is_into_iter(cx, callee_def_id);
+        then {
+            check_for_loop_iter(cx, parent, method_name, receiver)
+        } else {
+            false
+        }
+    }
+}
+
+/// Checks whether `expr` is an iterator in a `for` loop and, if so, determines whether the
+/// iterated-over items could be iterated over by reference. The reason why `check` above does not
+/// include this code directly is so that it can be called from
+/// `unnecessary_into_owned::check_into_iter_call_arg`.
+pub fn check_for_loop_iter(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx Expr<'tcx>,
+    method_name: Symbol,
+    receiver: &'tcx Expr<'tcx>,
+) -> bool {
+    if_chain! {
+        if let Some(grandparent) = get_parent_expr(cx, expr).and_then(|parent| get_parent_expr(cx, parent));
+        if let Some(ForLoop { pat, body, .. }) = ForLoop::hir(grandparent);
+        let (clone_or_copy_needed, addr_of_exprs) = clone_or_copy_needed(cx, pat, body);
+        if !clone_or_copy_needed;
+        if let Some(receiver_snippet) = snippet_opt(cx, receiver.span);
+        then {
+            let snippet = if_chain! {
+                if let ExprKind::MethodCall(maybe_iter_method_name, _, [collection], _) = receiver.kind;
+                if maybe_iter_method_name.ident.name == sym::iter;
+
+                if let Some(iterator_trait_id) = cx.tcx.get_diagnostic_item(sym::Iterator);
+                let receiver_ty = cx.typeck_results().expr_ty(receiver);
+                if implements_trait(cx, receiver_ty, iterator_trait_id, &[]);
+                if let Some(iter_item_ty) = get_iterator_item_ty(cx, receiver_ty);
+
+                if let Some(into_iterator_trait_id) = cx.tcx.get_diagnostic_item(sym::IntoIterator);
+                let collection_ty = cx.typeck_results().expr_ty(collection);
+                if implements_trait(cx, collection_ty, into_iterator_trait_id, &[]);
+                if let Some(into_iter_item_ty) = get_associated_type(cx, collection_ty, into_iterator_trait_id, "Item");
+
+                if iter_item_ty == into_iter_item_ty;
+                if let Some(collection_snippet) = snippet_opt(cx, collection.span);
+                then {
+                    collection_snippet
+                } else {
+                    receiver_snippet
+                }
+            };
+            span_lint_and_then(
+                cx,
+                UNNECESSARY_TO_OWNED,
+                expr.span,
+                &format!("unnecessary use of `{}`", method_name),
+                |diag| {
+                    diag.span_suggestion(expr.span, "use", snippet, Applicability::MachineApplicable);
+                    for addr_of_expr in addr_of_exprs {
+                        match addr_of_expr.kind {
+                            ExprKind::AddrOf(_, _, referent) => {
+                                let span = addr_of_expr.span.with_hi(referent.span.lo());
+                                diag.span_suggestion(span, "remove this `&`", String::new(), Applicability::MachineApplicable);
+                            }
+                            _ => unreachable!(),
+                        }
+                    }
+                }
+            );
+            return true;
+        }
+    }
+    false
+}
+
+/// The core logic of `check_for_loop_iter` above, this function wraps a use of
+/// `CloneOrCopyVisitor`.
+fn clone_or_copy_needed(
+    cx: &LateContext<'tcx>,
+    pat: &Pat<'tcx>,
+    body: &'tcx Expr<'tcx>,
+) -> (bool, Vec<&'tcx Expr<'tcx>>) {
+    let mut visitor = CloneOrCopyVisitor {
+        cx,
+        binding_hir_ids: pat_bindings(pat),
+        clone_or_copy_needed: false,
+        addr_of_exprs: Vec::new(),
+    };
+    visitor.visit_expr(body);
+    (visitor.clone_or_copy_needed, visitor.addr_of_exprs)
+}
+
+/// Returns a vector of all `HirId`s bound by the pattern.
+fn pat_bindings(pat: &Pat<'_>) -> Vec<HirId> {
+    let mut collector = usage::ParamBindingIdCollector {
+        binding_hir_ids: Vec::new(),
+    };
+    collector.visit_pat(pat);
+    collector.binding_hir_ids
+}
+
+/// `clone_or_copy_needed` will be false when `CloneOrCopyVisitor` is done visiting if the only
+/// operations performed on `binding_hir_ids` are:
+/// * to take non-mutable references to them
+/// * to use them as non-mutable `&self` in method calls
+/// If any of `binding_hir_ids` is used in any other way, then `clone_or_copy_needed` will be true
+/// when `CloneOrCopyVisitor` is done visiting.
+struct CloneOrCopyVisitor<'cx, 'tcx> {
+    cx: &'cx LateContext<'tcx>,
+    binding_hir_ids: Vec<HirId>,
+    clone_or_copy_needed: bool,
+    addr_of_exprs: Vec<&'tcx Expr<'tcx>>,
+}
+
+impl<'cx, 'tcx> Visitor<'tcx> for CloneOrCopyVisitor<'cx, 'tcx> {
+    type Map = Map<'tcx>;
+
+    fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
+        NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
+    }
+
+    fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
+        walk_expr(self, expr);
+        if self.is_binding(expr) {
+            if let Some(parent) = get_parent_expr(self.cx, expr) {
+                match parent.kind {
+                    ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, _) => {
+                        self.addr_of_exprs.push(parent);
+                        return;
+                    },
+                    ExprKind::MethodCall(_, _, args, _) => {
+                        if_chain! {
+                            if args.iter().skip(1).all(|arg| !self.is_binding(arg));
+                            if let Some(method_def_id) = self.cx.typeck_results().type_dependent_def_id(parent.hir_id);
+                            let method_ty = self.cx.tcx.type_of(method_def_id);
+                            let self_ty = method_ty.fn_sig(self.cx.tcx).input(0).skip_binder();
+                            if matches!(self_ty.kind(), ty::Ref(_, _, Mutability::Not));
+                            then {
+                                return;
+                            }
+                        }
+                    },
+                    _ => {},
+                }
+            }
+            self.clone_or_copy_needed = true;
+        }
+    }
+}
+
+impl<'cx, 'tcx> CloneOrCopyVisitor<'cx, 'tcx> {
+    fn is_binding(&self, expr: &Expr<'tcx>) -> bool {
+        self.binding_hir_ids
+            .iter()
+            .any(|hir_id| path_to_local_id(expr, *hir_id))
+    }
+}
+
+/// Returns true if the named method is `IntoIterator::into_iter`.
+pub fn is_into_iter(cx: &LateContext<'_>, callee_def_id: DefId) -> bool {
+    cx.tcx.lang_items().require(LangItem::IntoIterIntoIter) == Ok(callee_def_id)
+}

clippy_lints/src/methods/unnecessary_to_owned.rs

@@ -1,8 +1,9 @@
 use super::implicit_clone::is_clone_like;
+use super::unnecessary_iter_cloned::{self, is_into_iter};
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::source::snippet_opt;
-use clippy_utils::ty::{implements_trait, is_copy, peel_mid_ty_refs};
-use clippy_utils::{get_parent_expr, is_diag_item_method, is_diag_trait_item};
+use clippy_utils::ty::{get_associated_type, get_iterator_item_ty, implements_trait, is_copy, peel_mid_ty_refs};
+use clippy_utils::{fn_def_id, get_parent_expr, is_diag_item_method, is_diag_trait_item};
 use rustc_errors::Applicability;
 use rustc_hir::{def_id::DefId, BorrowKind, Expr, ExprKind};
 use rustc_lint::LateContext;
@@ -18,17 +19,23 @@ use super::UNNECESSARY_TO_OWNED;
 pub fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, method_name: Symbol, args: &'tcx [Expr<'tcx>]) {
     if_chain! {
         if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
-        if is_to_owned_like(cx, method_name, method_def_id);
         if let [receiver] = args;
         then {
-            // At this point, we know the call is of a `to_owned`-like function. The functions
-            // `check_addr_of_expr` and `check_call_arg` determine whether the call is unnecessary
-            // based on its context, that is, whether it is a referent in an `AddrOf` expression or
-            // an argument in a function call.
-            if check_addr_of_expr(cx, expr, method_name, method_def_id, receiver) {
-                return;
+            if is_cloned_or_copied(cx, method_name, method_def_id) {
+                unnecessary_iter_cloned::check(cx, expr, method_name, receiver);
+            } else if is_to_owned_like(cx, method_name, method_def_id) {
+                // At this point, we know the call is of a `to_owned`-like function. The functions
+                // `check_addr_of_expr` and `check_call_arg` determine whether the call is unnecessary
+                // based on its context, that is, whether it is a referent in an `AddrOf` expression, an
+                // argument in a `into_iter` call, or an argument in the call of some other function.
+                if check_addr_of_expr(cx, expr, method_name, method_def_id, receiver) {
+                    return;
+                }
+                if check_into_iter_call_arg(cx, expr, method_name, receiver) {
+                    return;
+                }
+                check_other_call_arg(cx, expr, method_name, receiver);
             }
-            check_call_arg(cx, expr, method_name, receiver);
         }
     }
 }
@@ -116,29 +123,34 @@ fn check_addr_of_expr(
                     return true;
                 }
             }
-            if implements_deref_trait(cx, receiver_ty, target_ty) {
-                if n_receiver_refs > 0 {
-                    span_lint_and_sugg(
-                        cx,
-                        UNNECESSARY_TO_OWNED,
-                        parent.span,
-                        &format!("unnecessary use of `{}`", method_name),
-                        "use",
-                        receiver_snippet,
-                        Applicability::MachineApplicable,
-                    );
-                } else {
-                    span_lint_and_sugg(
-                        cx,
-                        UNNECESSARY_TO_OWNED,
-                        expr.span.with_lo(receiver.span.hi()),
-                        &format!("unnecessary use of `{}`", method_name),
-                        "remove this",
-                        String::new(),
-                        Applicability::MachineApplicable,
-                    );
+            if_chain! {
+                if let Some(deref_trait_id) = cx.tcx.get_diagnostic_item(sym::Deref);
+                if implements_trait(cx, receiver_ty, deref_trait_id, &[]);
+                if get_associated_type(cx, receiver_ty, deref_trait_id, "Target") == Some(target_ty);
+                then {
+                    if n_receiver_refs > 0 {
+                        span_lint_and_sugg(
+                            cx,
+                            UNNECESSARY_TO_OWNED,
+                            parent.span,
+                            &format!("unnecessary use of `{}`", method_name),
+                            "use",
+                            receiver_snippet,
+                            Applicability::MachineApplicable,
+                        );
+                    } else {
+                        span_lint_and_sugg(
+                            cx,
+                            UNNECESSARY_TO_OWNED,
+                            expr.span.with_lo(receiver.span.hi()),
+                            &format!("unnecessary use of `{}`", method_name),
+                            "remove this",
+                            String::new(),
+                            Applicability::MachineApplicable,
+                        );
+                    }
+                    return true;
                 }
-                return true;
             }
             if_chain! {
                 if let Some(as_ref_trait_id) = cx.tcx.get_diagnostic_item(sym::AsRef);
@@ -161,9 +173,55 @@ fn check_addr_of_expr(
     false
 }
 
+/// Checks whether `expr` is an argument in an `into_iter` call and, if so, determines whether its
+/// call of a `to_owned`-like function is unnecessary.
+fn check_into_iter_call_arg(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx Expr<'tcx>,
+    method_name: Symbol,
+    receiver: &'tcx Expr<'tcx>,
+) -> bool {
+    if_chain! {
+        if let Some(parent) = get_parent_expr(cx, expr);
+        if let Some(callee_def_id) = fn_def_id(cx, parent);
+        if is_into_iter(cx, callee_def_id);
+        if let Some(iterator_trait_id) = cx.tcx.get_diagnostic_item(sym::Iterator);
+        let parent_ty = cx.typeck_results().expr_ty(parent);
+        if implements_trait(cx, parent_ty, iterator_trait_id, &[]);
+        if let Some(item_ty) = get_iterator_item_ty(cx, parent_ty);
+        if let Some(receiver_snippet) = snippet_opt(cx, receiver.span);
+        then {
+            if unnecessary_iter_cloned::check_for_loop_iter(cx, parent, method_name, receiver) {
+                return true;
+            }
+            let cloned_or_copied = if is_copy(cx, item_ty) {
+                "copied"
+            } else {
+                "cloned"
+            };
+            span_lint_and_sugg(
+                cx,
+                UNNECESSARY_TO_OWNED,
+                parent.span,
+                &format!("unnecessary use of `{}`", method_name),
+                "use",
+                format!("{}.iter().{}()", receiver_snippet, cloned_or_copied),
+                Applicability::MachineApplicable,
+            );
+            return true;
+        }
+    }
+    false
+}
+
 /// Checks whether `expr` is an argument in a function call and, if so, determines whether its call
 /// of a `to_owned`-like function is unnecessary.
-fn check_call_arg(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, method_name: Symbol, receiver: &'tcx Expr<'tcx>) {
+fn check_other_call_arg(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx Expr<'tcx>,
+    method_name: Symbol,
+    receiver: &'tcx Expr<'tcx>,
+) -> bool {
     if_chain! {
         if let Some((maybe_call, maybe_arg)) = skip_addr_of_ancestors(cx, expr);
         if let Some((callee_def_id, call_substs, call_args)) = get_callee_substs_and_args(cx, maybe_call);
@@ -186,7 +244,8 @@ fn check_call_arg(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, method_name: S
             if let [projection_predicate] = projection_predicates[..] {
                 let normalized_ty =
                     cx.tcx.subst_and_normalize_erasing_regions(call_substs, cx.param_env, projection_predicate.ty);
-                implements_deref_trait(cx, receiver_ty, normalized_ty)
+                implements_trait(cx, receiver_ty, deref_trait_id, &[])
+                    && get_associated_type(cx, receiver_ty, deref_trait_id, "Target") == Some(normalized_ty)
             } else {
                 false
             }
@@ -215,8 +274,10 @@ fn check_call_arg(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, method_name: S
                 format!("{:&>width$}{}", "", receiver_snippet, width = n_refs),
                 Applicability::MachineApplicable,
             );
+            return true;
         }
     }
+    false
 }
 
 /// Walks an expression's ancestors until it finds a non-`AddrOf` expression. Returns the first such
@@ -315,22 +376,10 @@ fn compose_substs(cx: &LateContext<'tcx>, left: &[GenericArg<'tcx>], right: Subs
         .collect()
 }
 
-/// Helper function to check whether a type implements the `Deref` trait.
-fn implements_deref_trait(cx: &LateContext<'tcx>, ty: Ty<'tcx>, deref_target_ty: Ty<'tcx>) -> bool {
-    if_chain! {
-        if let Some(deref_trait_id) = cx.tcx.get_diagnostic_item(sym::Deref);
-        if implements_trait(cx, ty, deref_trait_id, &[]);
-        if let Some(deref_target_id) = cx.tcx.lang_items().deref_target();
-        let substs = cx.tcx.mk_substs_trait(ty, &[]);
-        let projection_ty = cx.tcx.mk_projection(deref_target_id, substs);
-        let normalized_ty = cx.tcx.normalize_erasing_regions(cx.param_env, projection_ty);
-        if normalized_ty == deref_target_ty;
-        then {
-            true
-        } else {
-            false
-        }
-    }
+/// Returns true if the named method is `Iterator::cloned` or `Iterator::copied`.
+fn is_cloned_or_copied(cx: &LateContext<'_>, method_name: Symbol, method_def_id: DefId) -> bool {
+    (method_name.as_str() == "cloned" || method_name.as_str() == "copied")
+        && is_diag_trait_item(cx, method_def_id, sym::Iterator)
 }
 
 /// Returns true if the named method can be used to convert the receiver to its "owned"