New lint [tuple_array_conversions]

CHANGELOG.md

@@ -5262,6 +5262,7 @@ Released 2018-09-13
 [`trivial_regex`]: https://rust-lang.github.io/rust-clippy/master/index.html#trivial_regex
 [`trivially_copy_pass_by_ref`]: https://rust-lang.github.io/rust-clippy/master/index.html#trivially_copy_pass_by_ref
 [`try_err`]: https://rust-lang.github.io/rust-clippy/master/index.html#try_err
+[`tuple_array_conversions`]: https://rust-lang.github.io/rust-clippy/master/index.html#tuple_array_conversions
 [`type_complexity`]: https://rust-lang.github.io/rust-clippy/master/index.html#type_complexity
 [`type_repetition_in_bounds`]: https://rust-lang.github.io/rust-clippy/master/index.html#type_repetition_in_bounds
 [`unchecked_duration_subtraction`]: https://rust-lang.github.io/rust-clippy/master/index.html#unchecked_duration_subtraction

book/src/lint_configuration.md

@@ -149,6 +149,7 @@ The minimum rust version that the project supports
 * [`manual_rem_euclid`](https://rust-lang.github.io/rust-clippy/master/index.html#manual_rem_euclid)
 * [`manual_retain`](https://rust-lang.github.io/rust-clippy/master/index.html#manual_retain)
 * [`type_repetition_in_bounds`](https://rust-lang.github.io/rust-clippy/master/index.html#type_repetition_in_bounds)
+* [`tuple_array_conversions`](https://rust-lang.github.io/rust-clippy/master/index.html#tuple_array_conversions)
 
 
 ## `cognitive-complexity-threshold`

clippy_lints/src/declared_lints.rs

@@ -624,6 +624,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::transmute::UNSOUND_COLLECTION_TRANSMUTE_INFO,
     crate::transmute::USELESS_TRANSMUTE_INFO,
     crate::transmute::WRONG_TRANSMUTE_INFO,
+    crate::tuple_array_conversions::TUPLE_ARRAY_CONVERSIONS_INFO,
     crate::types::BORROWED_BOX_INFO,
     crate::types::BOX_COLLECTION_INFO,
     crate::types::LINKEDLIST_INFO,

clippy_lints/src/lib.rs

@@ -311,6 +311,7 @@ mod to_digit_is_some;
 mod trailing_empty_array;
 mod trait_bounds;
 mod transmute;
+mod tuple_array_conversions;
 mod types;
 mod undocumented_unsafe_blocks;
 mod unicode;
@@ -1072,6 +1073,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     });
     store.register_late_pass(|_| Box::new(manual_range_patterns::ManualRangePatterns));
     store.register_early_pass(|| Box::new(visibility::Visibility));
+    store.register_late_pass(move |_| Box::new(tuple_array_conversions::TupleArrayConversions { msrv: msrv() }));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }
 

clippy_lints/src/tuple_array_conversions.rs

@@ -0,0 +1,235 @@
+use clippy_utils::{
+    diagnostics::span_lint_and_help,
+    is_from_proc_macro,
+    msrvs::{self, Msrv},
+    path_to_local,
+};
+use rustc_ast::LitKind;
+use rustc_hir::{Expr, ExprKind, HirId, Node, Pat};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_middle::{lint::in_external_macro, ty};
+use rustc_session::{declare_tool_lint, impl_lint_pass};
+use std::iter::once;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for tuple<=>array conversions that are not done with `.into()`.
+    ///
+    /// ### Why is this bad?
+    /// It's unnecessary complexity. `.into()` works for tuples<=>arrays at or below 12 elements and
+    /// conveys the intent a lot better, while also leaving less room for hard to spot bugs!
+    ///
+    /// ### Example
+    /// ```rust,ignore
+    /// let t1 = &[(1, 2), (3, 4)];
+    /// let v1: Vec<[u32; 2]> = t1.iter().map(|&(a, b)| [a, b]).collect();
+    /// ```
+    /// Use instead:
+    /// ```rust,ignore
+    /// let t1 = &[(1, 2), (3, 4)];
+    /// let v1: Vec<[u32; 2]> = t1.iter().map(|&t| t.into()).collect();
+    /// ```
+    #[clippy::version = "1.72.0"]
+    pub TUPLE_ARRAY_CONVERSIONS,
+    complexity,
+    "checks for tuple<=>array conversions that are not done with `.into()`"
+}
+impl_lint_pass!(TupleArrayConversions => [TUPLE_ARRAY_CONVERSIONS]);
+
+#[derive(Clone)]
+pub struct TupleArrayConversions {
+    pub msrv: Msrv,
+}
+
+impl LateLintPass<'_> for TupleArrayConversions {
+    fn check_expr<'tcx>(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
+        if !in_external_macro(cx.sess(), expr.span) && self.msrv.meets(msrvs::TUPLE_ARRAY_CONVERSIONS) {
+            match expr.kind {
+                ExprKind::Array(elements) if (1..=12).contains(&elements.len()) => check_array(cx, expr, elements),
+                ExprKind::Tup(elements) if (1..=12).contains(&elements.len()) => check_tuple(cx, expr, elements),
+                _ => {},
+            }
+        }
+    }
+
+    extract_msrv_attr!(LateContext);
+}
+
+#[expect(
+    clippy::blocks_in_if_conditions,
+    reason = "not a FP, but this is much easier to understand"
+)]
+fn check_array<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, elements: &'tcx [Expr<'tcx>]) {
+    if should_lint(
+        cx,
+        elements,
+        // This is cursed.
+        Some,
+        |(first_id, local)| {
+            if let Node::Pat(pat) = local
+                && let parent = parent_pat(cx, pat)
+                && parent.hir_id == first_id
+            {
+                return matches!(
+                    cx.typeck_results().pat_ty(parent).peel_refs().kind(),
+                    ty::Tuple(len) if len.len() == elements.len()
+                );
+            }
+
+            false
+        },
+    ) || should_lint(
+        cx,
+        elements,
+        |(i, expr)| {
+            if let ExprKind::Field(path, field) = expr.kind && field.as_str() == i.to_string() {
+                return Some((i, path));
+            };
+
+            None
+        },
+        |(first_id, local)| {
+            if let Node::Pat(pat) = local
+                && let parent = parent_pat(cx, pat)
+                && parent.hir_id == first_id
+            {
+                return matches!(
+                    cx.typeck_results().pat_ty(parent).peel_refs().kind(),
+                    ty::Tuple(len) if len.len() == elements.len()
+                );
+            }
+
+            false
+        },
+    ) {
+        emit_lint(cx, expr, ToType::Array);
+    }
+}
+
+#[expect(
+    clippy::blocks_in_if_conditions,
+    reason = "not a FP, but this is much easier to understand"
+)]
+#[expect(clippy::cast_possible_truncation)]
+fn check_tuple<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, elements: &'tcx [Expr<'tcx>]) {
+    if should_lint(cx, elements, Some, |(first_id, local)| {
+        if let Node::Pat(pat) = local
+                && let parent = parent_pat(cx, pat)
+                && parent.hir_id == first_id
+            {
+                return matches!(
+                    cx.typeck_results().pat_ty(parent).peel_refs().kind(),
+                    ty::Array(_, len) if len.eval_target_usize(cx.tcx, cx.param_env) as usize == elements.len()
+                );
+            }
+
+        false
+    }) || should_lint(
+        cx,
+        elements,
+        |(i, expr)| {
+            if let ExprKind::Index(path, index) = expr.kind
+                && let ExprKind::Lit(lit) = index.kind
+                && let LitKind::Int(val, _) = lit.node
+                && val as usize == i
+            {
+                return Some((i, path));
+            };
+
+            None
+        },
+        |(first_id, local)| {
+            if let Node::Pat(pat) = local
+                && let parent = parent_pat(cx, pat)
+                && parent.hir_id == first_id
+            {
+                return matches!(
+                    cx.typeck_results().pat_ty(parent).peel_refs().kind(),
+                    ty::Array(_, len) if len.eval_target_usize(cx.tcx, cx.param_env) as usize == elements.len()
+                );
+            }
+
+            false
+        },
+    ) {
+        emit_lint(cx, expr, ToType::Tuple);
+    }
+}
+
+/// Walks up the `Pat` until it's reached the final containing `Pat`.
+fn parent_pat<'tcx>(cx: &LateContext<'tcx>, start: &'tcx Pat<'tcx>) -> &'tcx Pat<'tcx> {
+    let mut end = start;
+    for (_, node) in cx.tcx.hir().parent_iter(start.hir_id) {
+        if let Node::Pat(pat) = node {
+            end = pat;
+        } else {
+            break;
+        }
+    }
+    end
+}
+
+#[derive(Clone, Copy)]
+enum ToType {
+    Array,
+    Tuple,
+}
+
+impl ToType {
+    fn msg(self) -> &'static str {
+        match self {
+            ToType::Array => "it looks like you're trying to convert a tuple to an array",
+            ToType::Tuple => "it looks like you're trying to convert an array to a tuple",
+        }
+    }
+
+    fn help(self) -> &'static str {
+        match self {
+            ToType::Array => "use `.into()` instead, or `<[T; N]>::from` if type annotations are needed",
+            ToType::Tuple => "use `.into()` instead, or `<(T0, T1, ..., Tn)>::from` if type annotations are needed",
+        }
+    }
+}
+
+fn emit_lint<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, to_type: ToType) -> bool {
+    if !is_from_proc_macro(cx, expr) {
+        span_lint_and_help(
+            cx,
+            TUPLE_ARRAY_CONVERSIONS,
+            expr.span,
+            to_type.msg(),
+            None,
+            to_type.help(),
+        );
+
+        return true;
+    }
+
+    false
+}
+
+fn should_lint<'tcx>(
+    cx: &LateContext<'tcx>,
+    elements: &'tcx [Expr<'tcx>],
+    map: impl FnMut((usize, &'tcx Expr<'tcx>)) -> Option<(usize, &Expr<'_>)>,
+    predicate: impl FnMut((HirId, &Node<'tcx>)) -> bool,
+) -> bool {
+    if let Some(elements) = elements
+            .iter()
+            .enumerate()
+            .map(map)
+            .collect::<Option<Vec<_>>>()
+        && let Some(locals) = elements
+            .iter()
+            .map(|(_, element)| path_to_local(element).and_then(|local| cx.tcx.hir().find(local)))
+            .collect::<Option<Vec<_>>>()
+        && let [first, rest @ ..] = &*locals
+        && let Node::Pat(first_pat) = first
+        && let parent = parent_pat(cx, first_pat).hir_id
+        && rest.iter().chain(once(first)).map(|i| (parent, i)).all(predicate)
+    {
+        return true;
+    }
+
+    false
+}

clippy_lints/src/upper_case_acronyms.rs

@@ -65,7 +65,7 @@ fn correct_ident(ident: &str) -> String {
 
     let mut ident = fragments.clone().next().unwrap();
     for (ref prev, ref curr) in fragments.tuple_windows() {
-        if [prev, curr]
+        if <[&String; 2]>::from((prev, curr))
             .iter()
             .all(|s| s.len() == 1 && s.chars().next().unwrap().is_ascii_uppercase())
         {

clippy_lints/src/utils/conf.rs

@@ -294,7 +294,7 @@ define_Conf! {
     ///
     /// Suppress lints whenever the suggested change would cause breakage for other crates.
     (avoid_breaking_exported_api: bool = true),
-    /// Lint: MANUAL_SPLIT_ONCE, MANUAL_STR_REPEAT, CLONED_INSTEAD_OF_COPIED, REDUNDANT_FIELD_NAMES, OPTION_MAP_UNWRAP_OR, REDUNDANT_STATIC_LIFETIMES, FILTER_MAP_NEXT, CHECKED_CONVERSIONS, MANUAL_RANGE_CONTAINS, USE_SELF, MEM_REPLACE_WITH_DEFAULT, MANUAL_NON_EXHAUSTIVE, OPTION_AS_REF_DEREF, MAP_UNWRAP_OR, MATCH_LIKE_MATCHES_MACRO, MANUAL_STRIP, MISSING_CONST_FOR_FN, UNNESTED_OR_PATTERNS, FROM_OVER_INTO, PTR_AS_PTR, IF_THEN_SOME_ELSE_NONE, APPROX_CONSTANT, DEPRECATED_CFG_ATTR, INDEX_REFUTABLE_SLICE, MAP_CLONE, BORROW_AS_PTR, MANUAL_BITS, ERR_EXPECT, CAST_ABS_TO_UNSIGNED, UNINLINED_FORMAT_ARGS, MANUAL_CLAMP, MANUAL_LET_ELSE, UNCHECKED_DURATION_SUBTRACTION, COLLAPSIBLE_STR_REPLACE, SEEK_FROM_CURRENT, SEEK_REWIND, UNNECESSARY_LAZY_EVALUATIONS, TRANSMUTE_PTR_TO_REF, ALMOST_COMPLETE_RANGE, NEEDLESS_BORROW, DERIVABLE_IMPLS, MANUAL_IS_ASCII_CHECK, MANUAL_REM_EUCLID, MANUAL_RETAIN, TYPE_REPETITION_IN_BOUNDS.
+    /// Lint: MANUAL_SPLIT_ONCE, MANUAL_STR_REPEAT, CLONED_INSTEAD_OF_COPIED, REDUNDANT_FIELD_NAMES, OPTION_MAP_UNWRAP_OR, REDUNDANT_STATIC_LIFETIMES, FILTER_MAP_NEXT, CHECKED_CONVERSIONS, MANUAL_RANGE_CONTAINS, USE_SELF, MEM_REPLACE_WITH_DEFAULT, MANUAL_NON_EXHAUSTIVE, OPTION_AS_REF_DEREF, MAP_UNWRAP_OR, MATCH_LIKE_MATCHES_MACRO, MANUAL_STRIP, MISSING_CONST_FOR_FN, UNNESTED_OR_PATTERNS, FROM_OVER_INTO, PTR_AS_PTR, IF_THEN_SOME_ELSE_NONE, APPROX_CONSTANT, DEPRECATED_CFG_ATTR, INDEX_REFUTABLE_SLICE, MAP_CLONE, BORROW_AS_PTR, MANUAL_BITS, ERR_EXPECT, CAST_ABS_TO_UNSIGNED, UNINLINED_FORMAT_ARGS, MANUAL_CLAMP, MANUAL_LET_ELSE, UNCHECKED_DURATION_SUBTRACTION, COLLAPSIBLE_STR_REPLACE, SEEK_FROM_CURRENT, SEEK_REWIND, UNNECESSARY_LAZY_EVALUATIONS, TRANSMUTE_PTR_TO_REF, ALMOST_COMPLETE_RANGE, NEEDLESS_BORROW, DERIVABLE_IMPLS, MANUAL_IS_ASCII_CHECK, MANUAL_REM_EUCLID, MANUAL_RETAIN, TYPE_REPETITION_IN_BOUNDS, TUPLE_ARRAY_CONVERSIONS.
     ///
     /// The minimum rust version that the project supports
     (msrv: Option<String> = None),

clippy_utils/src/msrvs.rs

@@ -19,6 +19,7 @@ macro_rules! msrv_aliases {
 
 // names may refer to stabilized feature flags or library items
 msrv_aliases! {
+    1,71,0 { TUPLE_ARRAY_CONVERSIONS }
     1,70,0 { OPTION_IS_SOME_AND }
     1,68,0 { PATH_MAIN_SEPARATOR_STR }
     1,65,0 { LET_ELSE, POINTER_CAST_CONSTNESS }

tests/ui/tuple_array_conversions.rs

@@ -0,0 +1,73 @@
+//@aux-build:proc_macros.rs:proc-macro
+#![allow(clippy::no_effect, clippy::useless_vec, unused)]
+#![warn(clippy::tuple_array_conversions)]
+
+#[macro_use]
+extern crate proc_macros;
+
+fn main() {
+    let x = [1, 2];
+    let x = (x[0], x[1]);
+    let x = [x.0, x.1];
+    let x = &[1, 2];
+    let x = (x[0], x[1]);
+
+    let t1: &[(u32, u32)] = &[(1, 2), (3, 4)];
+    let v1: Vec<[u32; 2]> = t1.iter().map(|&(a, b)| [a, b]).collect();
+    t1.iter().for_each(|&(a, b)| _ = [a, b]);
+    let t2: Vec<(u32, u32)> = v1.iter().map(|&[a, b]| (a, b)).collect();
+    t1.iter().for_each(|&(a, b)| _ = [a, b]);
+    // Do not lint
+    let v2: Vec<[u32; 2]> = t1.iter().map(|&t| t.into()).collect();
+    let t3: Vec<(u32, u32)> = v2.iter().map(|&v| v.into()).collect();
+    let x = [1; 13];
+    let x = (
+        x[0], x[1], x[2], x[3], x[4], x[5], x[6], x[7], x[8], x[9], x[10], x[11], x[12],
+    );
+    let x = [x.0, x.1, x.2, x.3, x.4, x.5, x.6, x.7, x.8, x.9, x.10, x.11, x.12];
+    let x = (1, 2);
+    let x = (x.0, x.1);
+    let x = [1, 2];
+    let x = [x[0], x[1]];
+    let x = vec![1, 2];
+    let x = (x[0], x[1]);
+    let x = [1; 3];
+    let x = (x[0],);
+    let x = (1, 2, 3);
+    let x = [x.0];
+    let x = (1, 2);
+    let y = (1, 2);
+    [x.0, y.0];
+    [x.0, y.1];
+    let x = [x.0, x.0];
+    let x = (x[0], x[0]);
+    external! {
+        let t1: &[(u32, u32)] = &[(1, 2), (3, 4)];
+        let v1: Vec<[u32; 2]> = t1.iter().map(|&(a, b)| [a, b]).collect();
+        let t2: Vec<(u32, u32)> = v1.iter().map(|&[a, b]| (a, b)).collect();
+    }
+    with_span! {
+        span
+        let t1: &[(u32, u32)] = &[(1, 2), (3, 4)];
+        let v1: Vec<[u32; 2]> = t1.iter().map(|&(a, b)| [a, b]).collect();
+        let t2: Vec<(u32, u32)> = v1.iter().map(|&[a, b]| (a, b)).collect();
+    }
+}
+
+#[clippy::msrv = "1.70.0"]
+fn msrv_too_low() {
+    let x = [1, 2];
+    let x = (x[0], x[1]);
+    let x = [x.0, x.1];
+    let x = &[1, 2];
+    let x = (x[0], x[1]);
+}
+
+#[clippy::msrv = "1.71.0"]
+fn msrv_juust_right() {
+    let x = [1, 2];
+    let x = (x[0], x[1]);
+    let x = [x.0, x.1];
+    let x = &[1, 2];
+    let x = (x[0], x[1]);
+}