diff --git a/CHANGELOG.md b/CHANGELOG.md index 2ec8b3d98f8..edc5cea1dd6 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -2161,6 +2161,7 @@ Released 2018-09-13 [`manual_filter_map`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_filter_map [`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_map`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_map [`manual_memcpy`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_memcpy [`manual_non_exhaustive`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_non_exhaustive [`manual_ok_or`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_ok_or diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs index 2e0bc4de801..b151c178afa 100644 --- a/clippy_lints/src/lib.rs +++ b/clippy_lints/src/lib.rs @@ -241,6 +241,7 @@ mod loops; mod macro_use; mod main_recursion; mod manual_async_fn; +mod manual_map; mod manual_non_exhaustive; mod manual_ok_or; mod manual_strip; @@ -706,6 +707,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: ¯o_use::MACRO_USE_IMPORTS, &main_recursion::MAIN_RECURSION, &manual_async_fn::MANUAL_ASYNC_FN, + &manual_map::MANUAL_MAP, &manual_non_exhaustive::MANUAL_NON_EXHAUSTIVE, &manual_ok_or::MANUAL_OK_OR, &manual_strip::MANUAL_STRIP, @@ -1262,6 +1264,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: store.register_late_pass(|| box case_sensitive_file_extension_comparisons::CaseSensitiveFileExtensionComparisons); store.register_late_pass(|| box redundant_slicing::RedundantSlicing); store.register_late_pass(|| box from_str_radix_10::FromStrRadix10); + store.register_late_pass(|| box manual_map::ManualMap); store.register_group(true, "clippy::restriction", Some("clippy_restriction"), vec![ LintId::of(&arithmetic::FLOAT_ARITHMETIC), @@ -1521,6 +1524,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: LintId::of(&loops::WHILE_LET_ON_ITERATOR), LintId::of(&main_recursion::MAIN_RECURSION), LintId::of(&manual_async_fn::MANUAL_ASYNC_FN), + LintId::of(&manual_map::MANUAL_MAP), LintId::of(&manual_non_exhaustive::MANUAL_NON_EXHAUSTIVE), LintId::of(&manual_strip::MANUAL_STRIP), LintId::of(&manual_unwrap_or::MANUAL_UNWRAP_OR), @@ -1750,6 +1754,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: LintId::of(&loops::WHILE_LET_ON_ITERATOR), LintId::of(&main_recursion::MAIN_RECURSION), LintId::of(&manual_async_fn::MANUAL_ASYNC_FN), + LintId::of(&manual_map::MANUAL_MAP), LintId::of(&manual_non_exhaustive::MANUAL_NON_EXHAUSTIVE), LintId::of(&map_clone::MAP_CLONE), LintId::of(&matches::INFALLIBLE_DESTRUCTURING_MATCH), diff --git a/clippy_lints/src/manual_map.rs b/clippy_lints/src/manual_map.rs new file mode 100644 index 00000000000..e399c8fda55 --- /dev/null +++ b/clippy_lints/src/manual_map.rs @@ -0,0 +1,262 @@ +use crate::utils::{ + is_type_diagnostic_item, match_def_path, paths, peel_hir_expr_refs, peel_mid_ty_refs_is_mutable, + snippet_with_applicability, span_lint_and_sugg, +}; +use rustc_ast::util::parser::PREC_POSTFIX; +use rustc_errors::Applicability; +use rustc_hir::{Arm, BindingAnnotation, Block, Expr, ExprKind, Mutability, Pat, PatKind, Path, QPath}; +use rustc_lint::{LateContext, LateLintPass, LintContext}; +use rustc_middle::lint::in_external_macro; +use rustc_session::{declare_lint_pass, declare_tool_lint}; +use rustc_span::symbol::{sym, Ident}; + +declare_clippy_lint! { + /// **What it does:** Checks for usages of `match` which could be implemented using `map` + /// + /// **Why is this bad?** Using the `map` method is clearer and more concise. + /// + /// **Known problems:** None. + /// + /// **Example:** + /// + /// ```rust + /// match Some(0) { + /// Some(x) => Some(x + 1), + /// None => None, + /// }; + /// ``` + /// Use instead: + /// ```rust + /// Some(0).map(|x| x + 1); + /// ``` + pub MANUAL_MAP, + style, + "reimplementation of `map`" +} + +declare_lint_pass!(ManualMap => [MANUAL_MAP]); + +impl LateLintPass<'_> for ManualMap { + fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { + if in_external_macro(cx.sess(), expr.span) { + return; + } + + if let ExprKind::Match(scrutinee, [arm1 @ Arm { guard: None, .. }, arm2 @ Arm { guard: None, .. }], _) = + expr.kind + { + let (scrutinee_ty, ty_ref_count, ty_mutability) = + peel_mid_ty_refs_is_mutable(cx.typeck_results().expr_ty(scrutinee)); + if !is_type_diagnostic_item(cx, scrutinee_ty, sym::option_type) + || !is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(expr), sym::option_type) + { + return; + } + + let (some_expr, some_pat, pat_ref_count, is_wild_none) = + match (try_parse_pattern(cx, arm1.pat), try_parse_pattern(cx, arm2.pat)) { + (Some(OptionPat::Wild), Some(OptionPat::Some { pattern, ref_count })) + if is_none_expr(cx, arm1.body) => + { + (arm2.body, pattern, ref_count, true) + }, + (Some(OptionPat::None), Some(OptionPat::Some { pattern, ref_count })) + if is_none_expr(cx, arm1.body) => + { + (arm2.body, pattern, ref_count, false) + }, + (Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::Wild)) + if is_none_expr(cx, arm2.body) => + { + (arm1.body, pattern, ref_count, true) + }, + (Some(OptionPat::Some { pattern, ref_count }), Some(OptionPat::None)) + if is_none_expr(cx, arm2.body) => + { + (arm1.body, pattern, ref_count, false) + }, + _ => return, + }; + + // Top level or patterns aren't allowed in closures. + if matches!(some_pat.kind, PatKind::Or(_)) { + return; + } + + let some_expr = match get_some_expr(cx, some_expr) { + Some(expr) => expr, + None => return, + }; + + // Determine which binding mode to use. + let explicit_ref = some_pat.contains_explicit_ref_binding(); + let binding_mutability = explicit_ref.or(if ty_ref_count != pat_ref_count { + Some(ty_mutability) + } else { + None + }); + let as_ref_str = match binding_mutability { + Some(Mutability::Mut) => ".as_mut()", + Some(Mutability::Not) => ".as_ref()", + None => "", + }; + + let mut app = Applicability::MachineApplicable; + + // Remove address-of expressions from the scrutinee. `as_ref` will be called, + // the type is copyable, or the option is being passed by value. + let scrutinee = peel_hir_expr_refs(scrutinee).0; + let scrutinee_str = snippet_with_applicability(cx, scrutinee.span, "_", &mut app); + let scrutinee_str = if expr.precedence().order() < PREC_POSTFIX { + // Parens are needed to chain method calls. + format!("({})", scrutinee_str) + } else { + scrutinee_str.into() + }; + + let body_str = if let PatKind::Binding(annotation, _, some_binding, None) = some_pat.kind { + if let Some(func) = can_pass_as_func(cx, some_binding, some_expr) { + snippet_with_applicability(cx, func.span, "..", &mut app).into_owned() + } else { + // `ref` and `ref mut` annotations were handled earlier. + let annotation = if matches!(annotation, BindingAnnotation::Mutable) { + "mut " + } else { + "" + }; + format!( + "|{}{}| {}", + annotation, + some_binding, + snippet_with_applicability(cx, some_expr.span, "..", &mut app) + ) + } + } else if !is_wild_none && explicit_ref.is_none() { + // TODO: handle explicit reference annotations. + format!( + "|{}| {}", + snippet_with_applicability(cx, some_pat.span, "..", &mut app), + snippet_with_applicability(cx, some_expr.span, "..", &mut app) + ) + } else { + // Refutable bindings and mixed reference annotations can't be handled by `map`. + return; + }; + + span_lint_and_sugg( + cx, + MANUAL_MAP, + expr.span, + "manual implementation of `Option::map`", + "try this", + format!("{}{}.map({})", scrutinee_str, as_ref_str, body_str), + app, + ); + } + } +} + +// Checks whether the expression could be passed as a function, or whether a closure is needed. +// Returns the function to be passed to `map` if it exists. +fn can_pass_as_func(cx: &LateContext<'tcx>, binding: Ident, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> { + match expr.kind { + ExprKind::Call(func, [arg]) + if matches!(arg.kind, + ExprKind::Path(QPath::Resolved(None, Path { segments: [path], ..})) + if path.ident == binding + ) && cx.typeck_results().expr_adjustments(arg).is_empty() => + { + Some(func) + }, + _ => None, + } +} + +enum OptionPat<'a> { + Wild, + None, + Some { + // The pattern contained in the `Some` tuple. + pattern: &'a Pat<'a>, + // The number of references before the `Some` tuple. + // e.g. `&&Some(_)` has a ref count of 2. + ref_count: usize, + }, +} + +// Try to parse into a recognized `Option` pattern. +// i.e. `_`, `None`, `Some(..)`, or a reference to any of those. +fn try_parse_pattern(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>) -> Option> { + fn f(cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>, ref_count: usize) -> Option> { + match pat.kind { + PatKind::Wild => Some(OptionPat::Wild), + PatKind::Ref(pat, _) => f(cx, pat, ref_count + 1), + PatKind::Path(QPath::Resolved(None, path)) + if path + .res + .opt_def_id() + .map_or(false, |id| match_def_path(cx, id, &paths::OPTION_NONE)) => + { + Some(OptionPat::None) + }, + PatKind::TupleStruct(QPath::Resolved(None, path), [pattern], _) + if path + .res + .opt_def_id() + .map_or(false, |id| match_def_path(cx, id, &paths::OPTION_SOME)) => + { + Some(OptionPat::Some { pattern, ref_count }) + }, + _ => None, + } + } + f(cx, pat, 0) +} + +// Checks for an expression wrapped by the `Some` constructor. Returns the contained expression. +fn get_some_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> { + // TODO: Allow more complex expressions. + match expr.kind { + ExprKind::Call( + Expr { + kind: ExprKind::Path(QPath::Resolved(None, path)), + .. + }, + [arg], + ) => { + if match_def_path(cx, path.res.opt_def_id()?, &paths::OPTION_SOME) { + Some(arg) + } else { + None + } + }, + ExprKind::Block( + Block { + stmts: [], + expr: Some(expr), + .. + }, + _, + ) => get_some_expr(cx, expr), + _ => None, + } +} + +// Checks for the `None` value. +fn is_none_expr(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool { + match expr.kind { + ExprKind::Path(QPath::Resolved(None, path)) => path + .res + .opt_def_id() + .map_or(false, |id| match_def_path(cx, id, &paths::OPTION_NONE)), + ExprKind::Block( + Block { + stmts: [], + expr: Some(expr), + .. + }, + _, + ) => is_none_expr(cx, expr), + _ => false, + } +} diff --git a/clippy_lints/src/utils/mod.rs b/clippy_lints/src/utils/mod.rs index fafa1400156..40771449264 100644 --- a/clippy_lints/src/utils/mod.rs +++ b/clippy_lints/src/utils/mod.rs @@ -32,7 +32,7 @@ use std::collections::hash_map::Entry; use std::hash::BuildHasherDefault; use if_chain::if_chain; -use rustc_ast::ast::{self, Attribute, LitKind}; +use rustc_ast::ast::{self, Attribute, BorrowKind, LitKind, Mutability}; use rustc_data_structures::fx::FxHashMap; use rustc_errors::Applicability; use rustc_hir as hir; @@ -1672,6 +1672,18 @@ pub fn peel_n_hir_expr_refs(expr: &'a Expr<'a>, count: usize) -> (&'a Expr<'a>, f(expr, 0, count) } +/// Peels off all references on the expression. Returns the underlying expression and the number of +/// references removed. +pub fn peel_hir_expr_refs(expr: &'a Expr<'a>) -> (&'a Expr<'a>, usize) { + fn f(expr: &'a Expr<'a>, count: usize) -> (&'a Expr<'a>, usize) { + match expr.kind { + ExprKind::AddrOf(BorrowKind::Ref, _, expr) => f(expr, count + 1), + _ => (expr, count), + } + } + f(expr, 0) +} + /// Peels off all references on the type. Returns the underlying type and the number of references /// removed. pub fn peel_mid_ty_refs(ty: Ty<'_>) -> (Ty<'_>, usize) { @@ -1685,6 +1697,19 @@ pub fn peel_mid_ty_refs(ty: Ty<'_>) -> (Ty<'_>, usize) { peel(ty, 0) } +/// Peels off all references on the type.Returns the underlying type, the number of references +/// removed, and whether the pointer is ultimately mutable or not. +pub fn peel_mid_ty_refs_is_mutable(ty: Ty<'_>) -> (Ty<'_>, usize, Mutability) { + fn f(ty: Ty<'_>, count: usize, mutability: Mutability) -> (Ty<'_>, usize, Mutability) { + match ty.kind() { + ty::Ref(_, ty, Mutability::Mut) => f(ty, count + 1, mutability), + ty::Ref(_, ty, Mutability::Not) => f(ty, count + 1, Mutability::Not), + _ => (ty, count, mutability), + } + } + f(ty, 0, Mutability::Mut) +} + #[macro_export] macro_rules! unwrap_cargo_metadata { ($cx: ident, $lint: ident, $deps: expr) => {{ diff --git a/tests/ui/manual_map_option.fixed b/tests/ui/manual_map_option.fixed new file mode 100644 index 00000000000..6cb9a37b230 --- /dev/null +++ b/tests/ui/manual_map_option.fixed @@ -0,0 +1,61 @@ +// run-rustfix + +#![warn(clippy::manual_map)] +#![allow(clippy::no_effect, clippy::map_identity, clippy::unit_arg, clippy::match_ref_pats)] + +fn main() { + Some(0).map(|_| 2); + + Some(0).map(|x| x + 1); + + Some("").map(|x| x.is_empty()); + + Some(0).map(|x| !x); + + #[rustfmt::skip] + Some(0).map(std::convert::identity); + + Some(&String::new()).map(|x| str::len(x)); + + match Some(0) { + Some(x) if false => Some(x + 1), + _ => None, + }; + + Some([0, 1]).as_ref().map(|x| x[0]); + + Some(0).map(|x| x * 2); + + Some(String::new()).as_ref().map(|x| x.is_empty()); + + Some(String::new()).as_ref().map(|x| x.len()); + + Some(0).map(|x| x + x); + + Some(String::new()).as_mut().map(|x| x.push_str("")); + + Some(String::new()).as_ref().map(|x| &**x); + + Some(String::new()).as_ref().map(|x| x.is_empty()); + + Some((0, 1, 2)).map(|(x, y, z)| x + y + z); + + Some([1, 2, 3]).map(|[first, ..]| first); + + Some((String::new(), "test")).as_ref().map(|(x, y)| (y, x)); + + match Some((String::new(), 0)) { + Some((ref x, y)) => Some((y, x)), + None => None, + }; + + match Some(Some(0)) { + Some(Some(_)) | Some(None) => Some(0), + None => None, + }; + + match Some(Some((0, 1))) { + Some(Some((x, 1))) => Some(x), + _ => None, + }; +} diff --git a/tests/ui/manual_map_option.rs b/tests/ui/manual_map_option.rs new file mode 100644 index 00000000000..b9753060b99 --- /dev/null +++ b/tests/ui/manual_map_option.rs @@ -0,0 +1,113 @@ +// run-rustfix + +#![warn(clippy::manual_map)] +#![allow(clippy::no_effect, clippy::map_identity, clippy::unit_arg, clippy::match_ref_pats)] + +fn main() { + match Some(0) { + Some(_) => Some(2), + None:: => None, + }; + + match Some(0) { + Some(x) => Some(x + 1), + _ => None, + }; + + match Some("") { + Some(x) => Some(x.is_empty()), + None => None, + }; + + if let Some(x) = Some(0) { + Some(!x) + } else { + None + }; + + #[rustfmt::skip] + match Some(0) { + Some(x) => { Some(std::convert::identity(x)) } + None => { None } + }; + + match Some(&String::new()) { + Some(x) => Some(str::len(x)), + None => None, + }; + + match Some(0) { + Some(x) if false => Some(x + 1), + _ => None, + }; + + match &Some([0, 1]) { + Some(x) => Some(x[0]), + &None => None, + }; + + match &Some(0) { + &Some(x) => Some(x * 2), + None => None, + }; + + match Some(String::new()) { + Some(ref x) => Some(x.is_empty()), + _ => None, + }; + + match &&Some(String::new()) { + Some(x) => Some(x.len()), + _ => None, + }; + + match &&Some(0) { + &&Some(x) => Some(x + x), + &&_ => None, + }; + + match &mut Some(String::new()) { + Some(x) => Some(x.push_str("")), + None => None, + }; + + match &mut Some(String::new()) { + Some(ref x) => Some(&**x), + None => None, + }; + + match &mut &Some(String::new()) { + Some(x) => Some(x.is_empty()), + &mut _ => None, + }; + + match Some((0, 1, 2)) { + Some((x, y, z)) => Some(x + y + z), + None => None, + }; + + match Some([1, 2, 3]) { + Some([first, ..]) => Some(first), + None => None, + }; + + match &Some((String::new(), "test")) { + Some((x, y)) => Some((y, x)), + None => None, + }; + + match Some((String::new(), 0)) { + Some((ref x, y)) => Some((y, x)), + None => None, + }; + + match Some(Some(0)) { + Some(Some(_)) | Some(None) => Some(0), + None => None, + }; + + match Some(Some((0, 1))) { + Some(Some((x, 1))) => Some(x), + _ => None, + }; +} diff --git a/tests/ui/manual_map_option.stderr b/tests/ui/manual_map_option.stderr new file mode 100644 index 00000000000..f8e1bda83b2 --- /dev/null +++ b/tests/ui/manual_map_option.stderr @@ -0,0 +1,158 @@ +error: manual implementation of `Option::map` + --> $DIR/manual_map_option.rs:7:5 + | +LL | / match Some(0) { +LL | | Some(_) => Some(2), +LL | | None:: => None, +LL | | }; + | |_____^ help: try this: `Some(0).map(|_| 2)` + | + = note: `-D clippy::manual-map` implied by `-D warnings` + +error: manual implementation of `Option::map` + --> $DIR/manual_map_option.rs:12:5 + | +LL | / match Some(0) { +LL | | Some(x) => Some(x + 1), +LL | | _ => None, +LL | | }; + | |_____^ help: try this: `Some(0).map(|x| x + 1)` + +error: manual implementation of `Option::map` + --> $DIR/manual_map_option.rs:17:5 + | +LL | / match Some("") { +LL | | Some(x) => Some(x.is_empty()), +LL | | None => None, +LL | | }; + | |_____^ help: try this: `Some("").map(|x| x.is_empty())` + +error: manual implementation of `Option::map` + --> $DIR/manual_map_option.rs:22:5 + | +LL | / if let Some(x) = Some(0) { +LL | | Some(!x) +LL | | } else { +LL | | None +LL | | }; + | |_____^ help: try this: `Some(0).map(|x| !x)` + +error: manual implementation of `Option::map` + --> $DIR/manual_map_option.rs:29:5 + | +LL | / match Some(0) { +LL | | Some(x) => { Some(std::convert::identity(x)) } +LL | | None => { None } +LL | | }; + | |_____^ help: try this: `Some(0).map(std::convert::identity)` + +error: manual implementation of `Option::map` + --> $DIR/manual_map_option.rs:34:5 + | +LL | / match Some(&String::new()) { +LL | | Some(x) => Some(str::len(x)), +LL | | None => None, +LL | | }; + | |_____^ help: try this: `Some(&String::new()).map(|x| str::len(x))` + +error: manual implementation of `Option::map` + --> $DIR/manual_map_option.rs:44:5 + | +LL | / match &Some([0, 1]) { +LL | | Some(x) => Some(x[0]), +LL | | &None => None, +LL | | }; + | |_____^ help: try this: `Some([0, 1]).as_ref().map(|x| x[0])` + +error: manual implementation of `Option::map` + --> $DIR/manual_map_option.rs:49:5 + | +LL | / match &Some(0) { +LL | | &Some(x) => Some(x * 2), +LL | | None => None, +LL | | }; + | |_____^ help: try this: `Some(0).map(|x| x * 2)` + +error: manual implementation of `Option::map` + --> $DIR/manual_map_option.rs:54:5 + | +LL | / match Some(String::new()) { +LL | | Some(ref x) => Some(x.is_empty()), +LL | | _ => None, +LL | | }; + | |_____^ help: try this: `Some(String::new()).as_ref().map(|x| x.is_empty())` + +error: manual implementation of `Option::map` + --> $DIR/manual_map_option.rs:59:5 + | +LL | / match &&Some(String::new()) { +LL | | Some(x) => Some(x.len()), +LL | | _ => None, +LL | | }; + | |_____^ help: try this: `Some(String::new()).as_ref().map(|x| x.len())` + +error: manual implementation of `Option::map` + --> $DIR/manual_map_option.rs:64:5 + | +LL | / match &&Some(0) { +LL | | &&Some(x) => Some(x + x), +LL | | &&_ => None, +LL | | }; + | |_____^ help: try this: `Some(0).map(|x| x + x)` + +error: manual implementation of `Option::map` + --> $DIR/manual_map_option.rs:69:5 + | +LL | / match &mut Some(String::new()) { +LL | | Some(x) => Some(x.push_str("")), +LL | | None => None, +LL | | }; + | |_____^ help: try this: `Some(String::new()).as_mut().map(|x| x.push_str(""))` + +error: manual implementation of `Option::map` + --> $DIR/manual_map_option.rs:74:5 + | +LL | / match &mut Some(String::new()) { +LL | | Some(ref x) => Some(&**x), +LL | | None => None, +LL | | }; + | |_____^ help: try this: `Some(String::new()).as_ref().map(|x| &**x)` + +error: manual implementation of `Option::map` + --> $DIR/manual_map_option.rs:79:5 + | +LL | / match &mut &Some(String::new()) { +LL | | Some(x) => Some(x.is_empty()), +LL | | &mut _ => None, +LL | | }; + | |_____^ help: try this: `Some(String::new()).as_ref().map(|x| x.is_empty())` + +error: manual implementation of `Option::map` + --> $DIR/manual_map_option.rs:84:5 + | +LL | / match Some((0, 1, 2)) { +LL | | Some((x, y, z)) => Some(x + y + z), +LL | | None => None, +LL | | }; + | |_____^ help: try this: `Some((0, 1, 2)).map(|(x, y, z)| x + y + z)` + +error: manual implementation of `Option::map` + --> $DIR/manual_map_option.rs:89:5 + | +LL | / match Some([1, 2, 3]) { +LL | | Some([first, ..]) => Some(first), +LL | | None => None, +LL | | }; + | |_____^ help: try this: `Some([1, 2, 3]).map(|[first, ..]| first)` + +error: manual implementation of `Option::map` + --> $DIR/manual_map_option.rs:94:5 + | +LL | / match &Some((String::new(), "test")) { +LL | | Some((x, y)) => Some((y, x)), +LL | | None => None, +LL | | }; + | |_____^ help: try this: `Some((String::new(), "test")).as_ref().map(|(x, y)| (y, x))` + +error: aborting due to 17 previous errors +