From 07b2da884cda8103af50beb327723dec8204fc61 Mon Sep 17 00:00:00 2001 From: Tim Nielens Date: Tue, 6 Oct 2020 11:49:08 +0200 Subject: [PATCH] add lint less_concise_than_option_unwrap_or --- CHANGELOG.md | 1 + clippy_lints/src/less_concise_than.rs | 107 ++++++++++++++++++++++++ clippy_lints/src/lib.rs | 4 + clippy_lints/src/option_if_let_else.rs | 53 +----------- clippy_lints/src/utils/eager_or_lazy.rs | 2 +- clippy_lints/src/utils/usage.rs | 50 ++++++++++- src/lintlist/mod.rs | 7 ++ tests/ui/less_concise_than.fixed | 43 ++++++++++ tests/ui/less_concise_than.rs | 55 ++++++++++++ tests/ui/less_concise_than.stderr | 52 ++++++++++++ tests/ui/shadow.rs | 1 + tests/ui/shadow.stderr | 94 ++++++++++----------- 12 files changed, 369 insertions(+), 100 deletions(-) create mode 100644 clippy_lints/src/less_concise_than.rs create mode 100644 tests/ui/less_concise_than.fixed create mode 100644 tests/ui/less_concise_than.rs create mode 100644 tests/ui/less_concise_than.stderr diff --git a/CHANGELOG.md b/CHANGELOG.md index f21768c44..93ce6bb85 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -1781,6 +1781,7 @@ Released 2018-09-13 [`large_stack_arrays`]: https://rust-lang.github.io/rust-clippy/master/index.html#large_stack_arrays [`len_without_is_empty`]: https://rust-lang.github.io/rust-clippy/master/index.html#len_without_is_empty [`len_zero`]: https://rust-lang.github.io/rust-clippy/master/index.html#len_zero +[`less_concise_than_option_unwrap_or`]: https://rust-lang.github.io/rust-clippy/master/index.html#less_concise_than_option_unwrap_or [`let_and_return`]: https://rust-lang.github.io/rust-clippy/master/index.html#let_and_return [`let_underscore_lock`]: https://rust-lang.github.io/rust-clippy/master/index.html#let_underscore_lock [`let_underscore_must_use`]: https://rust-lang.github.io/rust-clippy/master/index.html#let_underscore_must_use diff --git a/clippy_lints/src/less_concise_than.rs b/clippy_lints/src/less_concise_than.rs new file mode 100644 index 000000000..097aff4b1 --- /dev/null +++ b/clippy_lints/src/less_concise_than.rs @@ -0,0 +1,107 @@ +use crate::utils; +use if_chain::if_chain; +use rustc_errors::Applicability; +use rustc_hir::{def, Arm, Expr, ExprKind, PatKind, QPath}; +use rustc_lint::{LateContext, LateLintPass}; +use rustc_session::{declare_lint_pass, declare_tool_lint}; + +declare_clippy_lint! { + /// **What it does:** + /// Finds patterns that can be encoded more concisely with `Option::unwrap_or`. + /// + /// **Why is this bad?** + /// Concise code helps focusing on behavior instead of boilerplate. + /// + /// **Known problems:** None. + /// + /// **Example:** + /// ```rust + /// match int_optional { + /// Some(v) => v, + /// None => 1, + /// } + /// ``` + /// + /// Use instead: + /// ```rust + /// int_optional.unwrap_or(1) + /// ``` + pub LESS_CONCISE_THAN_OPTION_UNWRAP_OR, + pedantic, + "finds patterns that can be encoded more concisely with `Option::unwrap_or`" +} + +declare_lint_pass!(LessConciseThan => [LESS_CONCISE_THAN_OPTION_UNWRAP_OR]); + +impl LateLintPass<'_> for LessConciseThan { + fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) { + if utils::in_macro(expr.span) { + return; + } + if lint_option_unwrap_or_case(cx, expr) { + return; + } + } +} + +fn lint_option_unwrap_or_case<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool { + #[allow(clippy::needless_bool)] + fn applicable_none_arm<'a>(arms: &'a [Arm<'a>]) -> Option<&'a Arm<'a>> { + if_chain! { + if arms.len() == 2; + if arms.iter().all(|arm| arm.guard.is_none()); + if let Some((idx, none_arm)) = arms.iter().enumerate().find(|(_, arm)| + if_chain! { + if let PatKind::Path(ref qpath) = arm.pat.kind; + if utils::match_qpath(qpath, &utils::paths::OPTION_NONE); + then { true } + else { false } + } + ); + let some_arm = &arms[1 - idx]; + if let PatKind::TupleStruct(ref some_qpath, &[some_binding], _) = some_arm.pat.kind; + if utils::match_qpath(some_qpath, &utils::paths::OPTION_SOME); + if let PatKind::Binding(_, binding_hir_id, ..) = some_binding.kind; + if let ExprKind::Path(QPath::Resolved(_, body_path)) = some_arm.body.kind; + if let def::Res::Local(body_path_hir_id) = body_path.res; + if body_path_hir_id == binding_hir_id; + then { Some(none_arm) } + else { None } + } + } + if_chain! { + if !utils::usage::contains_return_break_continue_macro(expr); + if let ExprKind::Match (match_expr, match_arms, _) = expr.kind; + let ty = cx.typeck_results().expr_ty(match_expr); + if utils::is_type_diagnostic_item(cx, ty, sym!(option_type)); + if let Some(none_arm) = applicable_none_arm(match_arms); + if let Some(match_expr_snippet) = utils::snippet_opt(cx, match_expr.span); + if let Some(none_body_snippet) = utils::snippet_opt(cx, none_arm.body.span); + if let Some(indent) = utils::indent_of(cx, expr.span); + then { + let reindented_none_body = + utils::reindent_multiline(none_body_snippet.into(), true, Some(indent)); + let eager_eval = utils::eager_or_lazy::is_eagerness_candidate(cx, none_arm.body); + let method = if eager_eval { + "unwrap_or" + } else { + "unwrap_or_else" + }; + utils::span_lint_and_sugg( + cx, + LESS_CONCISE_THAN_OPTION_UNWRAP_OR, expr.span, + "this pattern can be more concisely encoded with `Option::unwrap_or`", + "replace with", + format!( + "{}.{}({}{})", + match_expr_snippet, + method, + if eager_eval { ""} else { "|| " }, + reindented_none_body + ), + Applicability::MachineApplicable, + ); + true + } else { false} + } +} diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs index 26a727687..2e9900815 100644 --- a/clippy_lints/src/lib.rs +++ b/clippy_lints/src/lib.rs @@ -224,6 +224,7 @@ mod large_const_arrays; mod large_enum_variant; mod large_stack_arrays; mod len_zero; +mod less_concise_than; mod let_if_seq; mod let_underscore; mod lifetimes; @@ -609,6 +610,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: &large_stack_arrays::LARGE_STACK_ARRAYS, &len_zero::LEN_WITHOUT_IS_EMPTY, &len_zero::LEN_ZERO, + &less_concise_than::LESS_CONCISE_THAN_OPTION_UNWRAP_OR, &let_if_seq::USELESS_LET_IF_SEQ, &let_underscore::LET_UNDERSCORE_LOCK, &let_underscore::LET_UNDERSCORE_MUST_USE, @@ -1126,6 +1128,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: store.register_late_pass(|| box repeat_once::RepeatOnce); store.register_late_pass(|| box unwrap_in_result::UnwrapInResult); store.register_late_pass(|| box self_assignment::SelfAssignment); + store.register_late_pass(|| box less_concise_than::LessConciseThan); store.register_late_pass(|| box float_equality_without_abs::FloatEqualityWithoutAbs); store.register_late_pass(|| box async_yields_async::AsyncYieldsAsync); store.register_late_pass(|| box manual_strip::ManualStrip); @@ -1210,6 +1213,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: LintId::of(&infinite_iter::MAYBE_INFINITE_ITER), LintId::of(&items_after_statements::ITEMS_AFTER_STATEMENTS), LintId::of(&large_stack_arrays::LARGE_STACK_ARRAYS), + LintId::of(&less_concise_than::LESS_CONCISE_THAN_OPTION_UNWRAP_OR), LintId::of(&literal_representation::LARGE_DIGIT_GROUPS), LintId::of(&literal_representation::UNREADABLE_LITERAL), LintId::of(&loops::EXPLICIT_INTO_ITER_LOOP), diff --git a/clippy_lints/src/option_if_let_else.rs b/clippy_lints/src/option_if_let_else.rs index 383a62da8..eb7624b25 100644 --- a/clippy_lints/src/option_if_let_else.rs +++ b/clippy_lints/src/option_if_let_else.rs @@ -5,10 +5,8 @@ use crate::utils::{is_type_diagnostic_item, paths, span_lint_and_sugg}; use if_chain::if_chain; use rustc_errors::Applicability; -use rustc_hir::intravisit::{NestedVisitorMap, Visitor}; use rustc_hir::{Arm, BindingAnnotation, Block, Expr, ExprKind, MatchSource, Mutability, PatKind, UnOp}; use rustc_lint::{LateContext, LateLintPass}; -use rustc_middle::hir::map::Map; use rustc_session::{declare_lint_pass, declare_tool_lint}; declare_clippy_lint! { @@ -84,53 +82,6 @@ struct OptionIfLetElseOccurence { wrap_braces: bool, } -struct ReturnBreakContinueMacroVisitor { - seen_return_break_continue: bool, -} - -impl ReturnBreakContinueMacroVisitor { - fn new() -> ReturnBreakContinueMacroVisitor { - ReturnBreakContinueMacroVisitor { - seen_return_break_continue: false, - } - } -} - -impl<'tcx> Visitor<'tcx> for ReturnBreakContinueMacroVisitor { - type Map = Map<'tcx>; - fn nested_visit_map(&mut self) -> NestedVisitorMap { - NestedVisitorMap::None - } - - fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) { - if self.seen_return_break_continue { - // No need to look farther if we've already seen one of them - return; - } - match &ex.kind { - ExprKind::Ret(..) | ExprKind::Break(..) | ExprKind::Continue(..) => { - self.seen_return_break_continue = true; - }, - // Something special could be done here to handle while or for loop - // desugaring, as this will detect a break if there's a while loop - // or a for loop inside the expression. - _ => { - if utils::in_macro(ex.span) { - self.seen_return_break_continue = true; - } else { - rustc_hir::intravisit::walk_expr(self, ex); - } - }, - } - } -} - -fn contains_return_break_continue_macro(expression: &Expr<'_>) -> bool { - let mut recursive_visitor = ReturnBreakContinueMacroVisitor::new(); - recursive_visitor.visit_expr(expression); - recursive_visitor.seen_return_break_continue -} - /// Extracts the body of a given arm. If the arm contains only an expression, /// then it returns the expression. Otherwise, it returns the entire block fn extract_body_from_arm<'a>(arm: &'a Arm<'a>) -> Option<&'a Expr<'a>> { @@ -208,8 +159,8 @@ fn detect_option_if_let_else<'tcx>( if let PatKind::TupleStruct(struct_qpath, &[inner_pat], _) = &arms[0].pat.kind; if utils::match_qpath(struct_qpath, &paths::OPTION_SOME); if let PatKind::Binding(bind_annotation, _, id, _) = &inner_pat.kind; - if !contains_return_break_continue_macro(arms[0].body); - if !contains_return_break_continue_macro(arms[1].body); + if !utils::usage::contains_return_break_continue_macro(arms[0].body); + if !utils::usage::contains_return_break_continue_macro(arms[1].body); then { let capture_mut = if bind_annotation == &BindingAnnotation::Mutable { "mut " } else { "" }; let some_body = extract_body_from_arm(&arms[0])?; diff --git a/clippy_lints/src/utils/eager_or_lazy.rs b/clippy_lints/src/utils/eager_or_lazy.rs index 6938d9971..30e812c28 100644 --- a/clippy_lints/src/utils/eager_or_lazy.rs +++ b/clippy_lints/src/utils/eager_or_lazy.rs @@ -82,7 +82,7 @@ fn identify_some_pure_patterns(expr: &Expr<'_>) -> bool { /// Identify some potentially computationally expensive patterns. /// This function is named so to stress that its implementation is non-exhaustive. /// It returns FNs and FPs. -fn identify_some_potentially_expensive_patterns<'a, 'tcx>(cx: &'a LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool { +fn identify_some_potentially_expensive_patterns<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool { // Searches an expression for method calls or function calls that aren't ctors struct FunCallFinder<'a, 'tcx> { cx: &'a LateContext<'tcx>, diff --git a/clippy_lints/src/utils/usage.rs b/clippy_lints/src/utils/usage.rs index ea1dc3be2..2fd6046eb 100644 --- a/clippy_lints/src/utils/usage.rs +++ b/clippy_lints/src/utils/usage.rs @@ -1,10 +1,11 @@ +use crate::utils; use crate::utils::match_var; use rustc_data_structures::fx::FxHashSet; use rustc_hir as hir; use rustc_hir::def::Res; use rustc_hir::intravisit; use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor}; -use rustc_hir::{Expr, HirId, Path}; +use rustc_hir::{Expr, ExprKind, HirId, Path}; use rustc_infer::infer::TyCtxtInferExt; use rustc_lint::LateContext; use rustc_middle::hir::map::Map; @@ -174,3 +175,50 @@ impl<'a, 'tcx> intravisit::Visitor<'tcx> for BindingUsageFinder<'a, 'tcx> { intravisit::NestedVisitorMap::OnlyBodies(self.cx.tcx.hir()) } } + +struct ReturnBreakContinueMacroVisitor { + seen_return_break_continue: bool, +} + +impl ReturnBreakContinueMacroVisitor { + fn new() -> ReturnBreakContinueMacroVisitor { + ReturnBreakContinueMacroVisitor { + seen_return_break_continue: false, + } + } +} + +impl<'tcx> Visitor<'tcx> for ReturnBreakContinueMacroVisitor { + type Map = Map<'tcx>; + fn nested_visit_map(&mut self) -> NestedVisitorMap { + NestedVisitorMap::None + } + + fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) { + if self.seen_return_break_continue { + // No need to look farther if we've already seen one of them + return; + } + match &ex.kind { + ExprKind::Ret(..) | ExprKind::Break(..) | ExprKind::Continue(..) => { + self.seen_return_break_continue = true; + }, + // Something special could be done here to handle while or for loop + // desugaring, as this will detect a break if there's a while loop + // or a for loop inside the expression. + _ => { + if utils::in_macro(ex.span) { + self.seen_return_break_continue = true; + } else { + rustc_hir::intravisit::walk_expr(self, ex); + } + }, + } + } +} + +pub fn contains_return_break_continue_macro(expression: &Expr<'_>) -> bool { + let mut recursive_visitor = ReturnBreakContinueMacroVisitor::new(); + recursive_visitor.visit_expr(expression); + recursive_visitor.seen_return_break_continue +} diff --git a/src/lintlist/mod.rs b/src/lintlist/mod.rs index 624223ff7..6dc95fcfd 100644 --- a/src/lintlist/mod.rs +++ b/src/lintlist/mod.rs @@ -1075,6 +1075,13 @@ vec![ deprecation: None, module: "len_zero", }, + Lint { + name: "less_concise_than_option_unwrap_or", + group: "pedantic", + desc: "finds patterns that can be encoded more concisely with `Option::unwrap_or`", + deprecation: None, + module: "less_concise_than", + }, Lint { name: "let_and_return", group: "style", diff --git a/tests/ui/less_concise_than.fixed b/tests/ui/less_concise_than.fixed new file mode 100644 index 000000000..52b69ebba --- /dev/null +++ b/tests/ui/less_concise_than.fixed @@ -0,0 +1,43 @@ +// run-rustfix +#![warn(clippy::less_concise_than_option_unwrap_or)] +#![allow(dead_code)] + +fn unwrap_or() { + // int case + Some(1).unwrap_or(42); + + // richer none expr + Some(1).unwrap_or_else(|| 1 + 42); + + // multiline case + Some(1).unwrap_or_else(|| { + let a = 1 + 42; + let b = a + 42; + b + 42 + }); + + // string case + Some("Bob").unwrap_or("Alice"); + + // don't lint + match Some(1) { + Some(i) => i + 2, + None => 42, + }; + match Some(1) { + Some(i) => i, + None => return, + }; + for j in 0..4 { + match Some(j) { + Some(i) => i, + None => continue, + }; + match Some(j) { + Some(i) => i, + None => break, + }; + } +} + +fn main() {} diff --git a/tests/ui/less_concise_than.rs b/tests/ui/less_concise_than.rs new file mode 100644 index 000000000..bb2a8f205 --- /dev/null +++ b/tests/ui/less_concise_than.rs @@ -0,0 +1,55 @@ +// run-rustfix +#![warn(clippy::less_concise_than_option_unwrap_or)] +#![allow(dead_code)] + +fn unwrap_or() { + // int case + match Some(1) { + Some(i) => i, + None => 42, + }; + + // richer none expr + match Some(1) { + Some(i) => i, + None => 1 + 42, + }; + + // multiline case + match Some(1) { + Some(i) => i, + None => { + let a = 1 + 42; + let b = a + 42; + b + 42 + }, + }; + + // string case + match Some("Bob") { + Some(i) => i, + None => "Alice", + }; + + // don't lint + match Some(1) { + Some(i) => i + 2, + None => 42, + }; + match Some(1) { + Some(i) => i, + None => return, + }; + for j in 0..4 { + match Some(j) { + Some(i) => i, + None => continue, + }; + match Some(j) { + Some(i) => i, + None => break, + }; + } +} + +fn main() {} diff --git a/tests/ui/less_concise_than.stderr b/tests/ui/less_concise_than.stderr new file mode 100644 index 000000000..e3e8a406d --- /dev/null +++ b/tests/ui/less_concise_than.stderr @@ -0,0 +1,52 @@ +error: this pattern can be more concisely encoded with `Option::unwrap_or` + --> $DIR/less_concise_than.rs:7:5 + | +LL | / match Some(1) { +LL | | Some(i) => i, +LL | | None => 42, +LL | | }; + | |_____^ help: replace with: `Some(1).unwrap_or(42)` + | + = note: `-D clippy::less-concise-than-option-unwrap-or` implied by `-D warnings` + +error: this pattern can be more concisely encoded with `Option::unwrap_or` + --> $DIR/less_concise_than.rs:13:5 + | +LL | / match Some(1) { +LL | | Some(i) => i, +LL | | None => 1 + 42, +LL | | }; + | |_____^ help: replace with: `Some(1).unwrap_or_else(|| 1 + 42)` + +error: this pattern can be more concisely encoded with `Option::unwrap_or` + --> $DIR/less_concise_than.rs:19:5 + | +LL | / match Some(1) { +LL | | Some(i) => i, +LL | | None => { +LL | | let a = 1 + 42; +... | +LL | | }, +LL | | }; + | |_____^ + | +help: replace with + | +LL | Some(1).unwrap_or_else(|| { +LL | let a = 1 + 42; +LL | let b = a + 42; +LL | b + 42 +LL | }); + | + +error: this pattern can be more concisely encoded with `Option::unwrap_or` + --> $DIR/less_concise_than.rs:29:5 + | +LL | / match Some("Bob") { +LL | | Some(i) => i, +LL | | None => "Alice", +LL | | }; + | |_____^ help: replace with: `Some("Bob").unwrap_or("Alice")` + +error: aborting due to 4 previous errors + diff --git a/tests/ui/shadow.rs b/tests/ui/shadow.rs index bd91ae4e9..e7441293d 100644 --- a/tests/ui/shadow.rs +++ b/tests/ui/shadow.rs @@ -8,6 +8,7 @@ #![allow( unused_parens, unused_variables, + clippy::less_concise_than_option_unwrap_or, clippy::missing_docs_in_private_items, clippy::single_match )] diff --git a/tests/ui/shadow.stderr b/tests/ui/shadow.stderr index 8a831375b..7c1ad2949 100644 --- a/tests/ui/shadow.stderr +++ b/tests/ui/shadow.stderr @@ -1,135 +1,135 @@ error: `x` is shadowed by itself in `&mut x` - --> $DIR/shadow.rs:26:5 + --> $DIR/shadow.rs:27:5 | LL | let x = &mut x; | ^^^^^^^^^^^^^^^ | = note: `-D clippy::shadow-same` implied by `-D warnings` note: previous binding is here - --> $DIR/shadow.rs:25:13 + --> $DIR/shadow.rs:26:13 | LL | let mut x = 1; | ^ error: `x` is shadowed by itself in `{ x }` - --> $DIR/shadow.rs:27:5 - | -LL | let x = { x }; - | ^^^^^^^^^^^^^^ - | -note: previous binding is here - --> $DIR/shadow.rs:26:9 - | -LL | let x = &mut x; - | ^ - -error: `x` is shadowed by itself in `(&*x)` --> $DIR/shadow.rs:28:5 | -LL | let x = (&*x); +LL | let x = { x }; | ^^^^^^^^^^^^^^ | note: previous binding is here --> $DIR/shadow.rs:27:9 | +LL | let x = &mut x; + | ^ + +error: `x` is shadowed by itself in `(&*x)` + --> $DIR/shadow.rs:29:5 + | +LL | let x = (&*x); + | ^^^^^^^^^^^^^^ + | +note: previous binding is here + --> $DIR/shadow.rs:28:9 + | LL | let x = { x }; | ^ error: `x` is shadowed by `{ *x + 1 }` which reuses the original value - --> $DIR/shadow.rs:29:9 + --> $DIR/shadow.rs:30:9 | LL | let x = { *x + 1 }; | ^ | = note: `-D clippy::shadow-reuse` implied by `-D warnings` note: initialization happens here - --> $DIR/shadow.rs:29:13 + --> $DIR/shadow.rs:30:13 | LL | let x = { *x + 1 }; | ^^^^^^^^^^ note: previous binding is here - --> $DIR/shadow.rs:28:9 + --> $DIR/shadow.rs:29:9 | LL | let x = (&*x); | ^ error: `x` is shadowed by `id(x)` which reuses the original value - --> $DIR/shadow.rs:30:9 - | -LL | let x = id(x); - | ^ - | -note: initialization happens here - --> $DIR/shadow.rs:30:13 - | -LL | let x = id(x); - | ^^^^^ -note: previous binding is here - --> $DIR/shadow.rs:29:9 - | -LL | let x = { *x + 1 }; - | ^ - -error: `x` is shadowed by `(1, x)` which reuses the original value --> $DIR/shadow.rs:31:9 | -LL | let x = (1, x); +LL | let x = id(x); | ^ | note: initialization happens here --> $DIR/shadow.rs:31:13 | -LL | let x = (1, x); - | ^^^^^^ +LL | let x = id(x); + | ^^^^^ note: previous binding is here --> $DIR/shadow.rs:30:9 | -LL | let x = id(x); +LL | let x = { *x + 1 }; | ^ -error: `x` is shadowed by `first(x)` which reuses the original value +error: `x` is shadowed by `(1, x)` which reuses the original value --> $DIR/shadow.rs:32:9 | -LL | let x = first(x); +LL | let x = (1, x); | ^ | note: initialization happens here --> $DIR/shadow.rs:32:13 | +LL | let x = (1, x); + | ^^^^^^ +note: previous binding is here + --> $DIR/shadow.rs:31:9 + | +LL | let x = id(x); + | ^ + +error: `x` is shadowed by `first(x)` which reuses the original value + --> $DIR/shadow.rs:33:9 + | +LL | let x = first(x); + | ^ + | +note: initialization happens here + --> $DIR/shadow.rs:33:13 + | LL | let x = first(x); | ^^^^^^^^ note: previous binding is here - --> $DIR/shadow.rs:31:9 + --> $DIR/shadow.rs:32:9 | LL | let x = (1, x); | ^ error: `x` is being shadowed - --> $DIR/shadow.rs:34:9 + --> $DIR/shadow.rs:35:9 | LL | let x = y; | ^ | = note: `-D clippy::shadow-unrelated` implied by `-D warnings` note: initialization happens here - --> $DIR/shadow.rs:34:13 + --> $DIR/shadow.rs:35:13 | LL | let x = y; | ^ note: previous binding is here - --> $DIR/shadow.rs:32:9 + --> $DIR/shadow.rs:33:9 | LL | let x = first(x); | ^ error: `x` shadows a previous declaration - --> $DIR/shadow.rs:36:5 + --> $DIR/shadow.rs:37:5 | LL | let x; | ^^^^^^ | note: previous binding is here - --> $DIR/shadow.rs:34:9 + --> $DIR/shadow.rs:35:9 | LL | let x = y; | ^