Add lint manual_inspect

CHANGELOG.md

@@ -5462,6 +5462,7 @@ Released 2018-09-13
 [`manual_find_map`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_find_map
 [`manual_flatten`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_flatten
 [`manual_hash_one`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_hash_one
+[`manual_inspect`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_inspect
 [`manual_instant_elapsed`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_instant_elapsed
 [`manual_is_ascii_check`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_is_ascii_check
 [`manual_is_finite`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_is_finite

clippy_config/src/msrvs.rs

@@ -18,7 +18,7 @@ macro_rules! msrv_aliases {
 // names may refer to stabilized feature flags or library items
 msrv_aliases! {
     1,77,0 { C_STR_LITERALS }
-    1,76,0 { PTR_FROM_REF }
+    1,76,0 { PTR_FROM_REF, OPTION_RESULT_INSPECT }
     1,71,0 { TUPLE_ARRAY_CONVERSIONS, BUILD_HASHER_HASH_ONE }
     1,70,0 { OPTION_RESULT_IS_VARIANT_AND, BINARY_HEAP_RETAIN }
     1,68,0 { PATH_MAIN_SEPARATOR_STR }

clippy_lints/src/declared_lints.rs

@@ -402,6 +402,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::methods::MANUAL_C_STR_LITERALS_INFO,
     crate::methods::MANUAL_FILTER_MAP_INFO,
     crate::methods::MANUAL_FIND_MAP_INFO,
+    crate::methods::MANUAL_INSPECT_INFO,
     crate::methods::MANUAL_IS_VARIANT_AND_INFO,
     crate::methods::MANUAL_NEXT_BACK_INFO,
     crate::methods::MANUAL_OK_OR_INFO,

clippy_lints/src/methods/manual_inspect.rs

@@ -0,0 +1,233 @@
+use clippy_config::msrvs::{self, Msrv};
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::source::{get_source_text, with_leading_whitespace, SpanRange};
+use clippy_utils::ty::get_field_by_name;
+use clippy_utils::visitors::{for_each_expr, for_each_expr_with_closures};
+use clippy_utils::{expr_use_ctxt, is_diag_item_method, is_diag_trait_item, path_to_local_id, ExprUseNode};
+use core::ops::ControlFlow;
+use rustc_errors::Applicability;
+use rustc_hir::{BindingMode, BorrowKind, ByRef, ClosureKind, Expr, ExprKind, Mutability, Node, PatKind};
+use rustc_lint::LateContext;
+use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow, AutoBorrowMutability};
+use rustc_span::{sym, BytePos, Span, Symbol, DUMMY_SP};
+
+use super::MANUAL_INSPECT;
+
+#[expect(clippy::too_many_lines)]
+pub(crate) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, arg: &Expr<'_>, name: &str, name_span: Span, msrv: &Msrv) {
+    if let ExprKind::Closure(c) = arg.kind
+        && matches!(c.kind, ClosureKind::Closure)
+        && let typeck = cx.typeck_results()
+        && let Some(fn_id) = typeck.type_dependent_def_id(expr.hir_id)
+        && (is_diag_trait_item(cx, fn_id, sym::Iterator)
+            || (msrv.meets(msrvs::OPTION_RESULT_INSPECT)
+                && (is_diag_item_method(cx, fn_id, sym::Option) || is_diag_item_method(cx, fn_id, sym::Result))))
+        && let body = cx.tcx.hir().body(c.body)
+        && let [param] = body.params
+        && let PatKind::Binding(BindingMode(ByRef::No, Mutability::Not), arg_id, _, None) = param.pat.kind
+        && let arg_ty = typeck.node_type(arg_id)
+        && let ExprKind::Block(block, _) = body.value.kind
+        && let Some(final_expr) = block.expr
+        && !block.stmts.is_empty()
+        && path_to_local_id(final_expr, arg_id)
+        && typeck.expr_adjustments(final_expr).is_empty()
+    {
+        let mut requires_copy = false;
+        let mut requires_deref = false;
+
+        // The number of unprocessed return expressions.
+        let mut ret_count = 0u32;
+
+        // The uses for which processing is delayed until after the visitor.
+        let mut delayed = vec![];
+
+        let ctxt = arg.span.ctxt();
+        let can_lint = for_each_expr(block.stmts, |e| {
+            if let ExprKind::Closure(c) = e.kind {
+                // Nested closures don't need to treat returns specially.
+                let _: Option<!> = for_each_expr_with_closures(cx, cx.tcx.hir().body(c.body).value, |e| {
+                    if path_to_local_id(e, arg_id) {
+                        let (kind, same_ctxt) = check_use(cx, e);
+                        match (kind, same_ctxt && e.span.ctxt() == ctxt) {
+                            (_, false) | (UseKind::Deref | UseKind::Return(..), true) => {
+                                requires_copy = true;
+                                requires_deref = true;
+                            },
+                            (UseKind::AutoBorrowed, true) => {},
+                            (UseKind::WillAutoDeref, true) => {
+                                requires_copy = true;
+                            },
+                            (kind, true) => delayed.push(kind),
+                        }
+                    }
+                    ControlFlow::Continue(())
+                });
+            } else if matches!(e.kind, ExprKind::Ret(_)) {
+                ret_count += 1;
+            } else if path_to_local_id(e, arg_id) {
+                let (kind, same_ctxt) = check_use(cx, e);
+                match (kind, same_ctxt && e.span.ctxt() == ctxt) {
+                    (UseKind::Return(..), false) => {
+                        return ControlFlow::Break(());
+                    },
+                    (_, false) | (UseKind::Deref, true) => {
+                        requires_copy = true;
+                        requires_deref = true;
+                    },
+                    (UseKind::AutoBorrowed, true) => {},
+                    (UseKind::WillAutoDeref, true) => {
+                        requires_copy = true;
+                    },
+                    (kind @ UseKind::Return(_), true) => {
+                        ret_count -= 1;
+                        delayed.push(kind);
+                    },
+                    (kind, true) => delayed.push(kind),
+                }
+            }
+            ControlFlow::Continue(())
+        })
+        .is_none();
+
+        if ret_count != 0 {
+            // A return expression that didn't return the original value was found.
+            return;
+        }
+
+        let mut edits = Vec::with_capacity(delayed.len() + 3);
+        let mut addr_of_edits = Vec::with_capacity(delayed.len());
+        for x in delayed {
+            match x {
+                UseKind::Return(s) => edits.push((with_leading_whitespace(cx, s).set_span_pos(s), String::new())),
+                UseKind::Borrowed(s) => {
+                    if let Some(src) = get_source_text(cx, s)
+                        && let Some(src) = src.as_str()
+                        && let trim_src = src.trim_start_matches(|x| matches!(x, ' ' | '\t' | '\n' | '\r' | '('))
+                        && trim_src.starts_with('&')
+                    {
+                        let range = s.into_range();
+                        #[expect(clippy::cast_possible_truncation)]
+                        let start = BytePos(range.start.0 + (src.len() - trim_src.len()) as u32);
+                        addr_of_edits.push(((start..BytePos(start.0 + 1)).set_span_pos(s), String::new()));
+                    } else {
+                        requires_copy = true;
+                        requires_deref = true;
+                    }
+                },
+                UseKind::FieldAccess(name, e) => {
+                    let Some(mut ty) = get_field_by_name(cx.tcx, arg_ty.peel_refs(), name) else {
+                        requires_copy = true;
+                        continue;
+                    };
+                    let mut prev_expr = e;
+
+                    for (_, parent) in cx.tcx.hir().parent_iter(e.hir_id) {
+                        if let Node::Expr(e) = parent {
+                            match e.kind {
+                                ExprKind::Field(_, name)
+                                    if let Some(fty) = get_field_by_name(cx.tcx, ty.peel_refs(), name.name) =>
+                                {
+                                    ty = fty;
+                                    prev_expr = e;
+                                    continue;
+                                },
+                                ExprKind::AddrOf(BorrowKind::Ref, ..) => break,
+                                _ if matches!(
+                                    typeck.expr_adjustments(prev_expr).first(),
+                                    Some(Adjustment {
+                                        kind: Adjust::Borrow(AutoBorrow::Ref(_, AutoBorrowMutability::Not))
+                                            | Adjust::Deref(_),
+                                        ..
+                                    })
+                                ) =>
+                                {
+                                    break;
+                                },
+                                _ => {},
+                            }
+                        }
+                        requires_copy |= !ty.is_copy_modulo_regions(cx.tcx, cx.param_env);
+                        break;
+                    }
+                },
+                // Already processed uses.
+                UseKind::AutoBorrowed | UseKind::WillAutoDeref | UseKind::Deref => {},
+            }
+        }
+
+        if can_lint
+            && (!requires_copy || arg_ty.is_copy_modulo_regions(cx.tcx, cx.param_env))
+            // This case could be handled, but a fair bit of care would need to be taken.
+            && (!requires_deref || arg_ty.is_freeze(cx.tcx, cx.param_env))
+        {
+            if requires_deref {
+                edits.push((param.span.shrink_to_lo(), "&".into()));
+            } else {
+                edits.extend(addr_of_edits);
+            }
+            edits.push((
+                name_span,
+                String::from(match name {
+                    "map" => "inspect",
+                    "map_err" => "inspect_err",
+                    _ => return,
+                }),
+            ));
+            edits.push((
+                with_leading_whitespace(cx, final_expr.span).set_span_pos(final_expr.span),
+                String::new(),
+            ));
+            let app = if edits.iter().any(|(s, _)| s.from_expansion()) {
+                Applicability::MaybeIncorrect
+            } else {
+                Applicability::MachineApplicable
+            };
+            span_lint_and_then(cx, MANUAL_INSPECT, name_span, "", |diag| {
+                diag.multipart_suggestion("try", edits, app);
+            });
+        }
+    }
+}
+
+enum UseKind<'tcx> {
+    AutoBorrowed,
+    WillAutoDeref,
+    Deref,
+    Return(Span),
+    Borrowed(Span),
+    FieldAccess(Symbol, &'tcx Expr<'tcx>),
+}
+
+/// Checks how the value is used, and whether it was used in the same `SyntaxContext`.
+fn check_use<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) -> (UseKind<'tcx>, bool) {
+    let use_cx = expr_use_ctxt(cx, e);
+    if use_cx
+        .adjustments
+        .first()
+        .is_some_and(|a| matches!(a.kind, Adjust::Deref(_)))
+    {
+        return (UseKind::AutoBorrowed, use_cx.same_ctxt);
+    }
+    let res = match use_cx.use_node(cx) {
+        ExprUseNode::Return(_) => {
+            if let ExprKind::Ret(Some(e)) = use_cx.node.expect_expr().kind {
+                UseKind::Return(e.span)
+            } else {
+                return (UseKind::Return(DUMMY_SP), false);
+            }
+        },
+        ExprUseNode::FieldAccess(name) => UseKind::FieldAccess(name.name, use_cx.node.expect_expr()),
+        ExprUseNode::Callee | ExprUseNode::MethodArg(_, _, 0)
+            if use_cx
+                .adjustments
+                .first()
+                .is_some_and(|a| matches!(a.kind, Adjust::Borrow(AutoBorrow::Ref(_, AutoBorrowMutability::Not)))) =>
+        {
+            UseKind::AutoBorrowed
+        },
+        ExprUseNode::Callee | ExprUseNode::MethodArg(_, _, 0) => UseKind::WillAutoDeref,
+        ExprUseNode::AddrOf(BorrowKind::Ref, _) => UseKind::Borrowed(use_cx.node.expect_expr().span),
+        _ => UseKind::Deref,
+    };
+    (res, use_cx.same_ctxt)
+}

clippy_lints/src/methods/mod.rs

@@ -53,6 +53,7 @@ mod iter_with_drain;
 mod iterator_step_by_zero;
 mod join_absolute_paths;
 mod manual_c_str_literals;
+mod manual_inspect;
 mod manual_is_variant_and;
 mod manual_next_back;
 mod manual_ok_or;
@@ -4112,6 +4113,27 @@ declare_clippy_lint! {
     "is_ascii() called on a char iterator"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for uses of `map` which return the original item.
+    ///
+    /// ### Why is this bad?
+    /// `inspect` is both clearer in intent and shorter.
+    ///
+    /// ### Example
+    /// ```no_run
+    /// let x = Some(0).map(|x| { println!("{x}"); x });
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// let x = Some(0).inspect(|x| println!("{x}"));
+    /// ```
+    #[clippy::version = "1.78.0"]
+    pub MANUAL_INSPECT,
+    complexity,
+    "use of `map` returning the original item"
+}
+
 pub struct Methods {
     avoid_breaking_exported_api: bool,
     msrv: Msrv,
@@ -4278,6 +4300,7 @@ impl_lint_pass!(Methods => [
     MANUAL_C_STR_LITERALS,
     UNNECESSARY_GET_THEN_CHECK,
     NEEDLESS_CHARACTER_ITERATION,
+    MANUAL_INSPECT,
 ]);
 
 /// Extracts a method call name, args, and `Span` of the method name.
@@ -4782,6 +4805,7 @@ impl Methods {
                         }
                     }
                     map_identity::check(cx, expr, recv, m_arg, name, span);
+                    manual_inspect::check(cx, expr, m_arg, name, span, &self.msrv);
                 },
                 ("map_or", [def, map]) => {
                     option_map_or_none::check(cx, expr, recv, def, map);

clippy_utils/src/source.rs

@@ -13,8 +13,17 @@ use std::borrow::Cow;
 use std::ops::Range;
 
 /// A type which can be converted to the range portion of a `Span`.
-pub trait SpanRange {
+pub trait SpanRange: Sized {
     fn into_range(self) -> Range<BytePos>;
+    fn set_span_pos(self, sp: Span) -> Span {
+        let range = self.into_range();
+        SpanData {
+            lo: range.start,
+            hi: range.end,
+            ..sp.data()
+        }
+        .span()
+    }
 }
 impl SpanRange for Span {
     fn into_range(self) -> Range<BytePos> {
@@ -60,6 +69,22 @@ pub fn get_source_text(cx: &impl LintContext, sp: impl SpanRange) -> Option<Sour
     f(cx.sess().source_map(), sp.into_range())
 }
 
+pub fn with_leading_whitespace(cx: &impl LintContext, sp: impl SpanRange) -> Range<BytePos> {
+    #[expect(clippy::needless_pass_by_value, clippy::cast_possible_truncation)]
+    fn f(src: SourceFileRange, sp: Range<BytePos>) -> Range<BytePos> {
+        let Some(text) = &src.sf.src else {
+            return sp;
+        };
+        let len = src.range.start - text[..src.range.start].trim_end().len();
+        BytePos(sp.start.0 - len as u32)..sp.end
+    }
+    let sp = sp.into_range();
+    match get_source_text(cx, sp.clone()) {
+        Some(src) => f(src, sp),
+        None => sp,
+    }
+}
+
 /// Like `snippet_block`, but add braces if the expr is not an `ExprKind::Block`.
 pub fn expr_block<T: LintContext>(
     cx: &T,

clippy_utils/src/ty.rs

@@ -1364,3 +1364,17 @@ pub fn get_adt_inherent_method<'a>(cx: &'a LateContext<'_>, ty: Ty<'_>, method_n
         None
     }
 }
+
+/// Get's the type of a field by name.
+pub fn get_field_by_name<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, name: Symbol) -> Option<Ty<'tcx>> {
+    match *ty.kind() {
+        ty::Adt(def, args) if def.is_union() || def.is_struct() => def
+            .non_enum_variant()
+            .fields
+            .iter()
+            .find(|f| f.name == name)
+            .map(|f| f.ty(tcx, args)),
+        ty::Tuple(args) => name.as_str().parse::<usize>().ok().and_then(|i| args.get(i).copied()),
+        _ => None,
+    }
+}

tests/ui/copy_iterator.rs

@@ -1,4 +1,5 @@
 #![warn(clippy::copy_iterator)]
+#![allow(clippy::manual_inspect)]
 
 #[derive(Copy, Clone)]
 struct Countdown(u8);

tests/ui/copy_iterator.stderr

@@ -1,5 +1,5 @@
 error: you are implementing `Iterator` on a `Copy` type
-  --> tests/ui/copy_iterator.rs:6:1
+  --> tests/ui/copy_iterator.rs:7:1
    |
 LL | / impl Iterator for Countdown {
 LL | |