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

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(|_| Box::new(tuple_array_conversions::TupleArrayConversions));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }
 

clippy_lints/src/tuple_array_conversions.rs

@@ -0,0 +1,187 @@
+use clippy_utils::{diagnostics::span_lint_and_help, is_from_proc_macro, path_to_local};
+use rustc_hir::*;
+use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_middle::{lint::in_external_macro, ty};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+
+declare_clippy_lint! {
+    /// ### What it does
+    ///
+    /// ### Why is this bad?
+    ///
+    /// ### 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,
+    "default lint description"
+}
+declare_lint_pass!(TupleArrayConversions => [TUPLE_ARRAY_CONVERSIONS]);
+
+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) {
+            _ = check_array(cx, expr) || check_tuple(cx, expr);
+        }
+    }
+}
+
+fn check_array<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
+    let ExprKind::Array(elements) = expr.kind else {
+        return false;
+    };
+    if !(1..=12).contains(&elements.len()) {
+        return false;
+    }
+
+    if let Some(locals) = path_to_locals(cx, elements)
+        && locals.iter().all(|local| {
+            matches!(
+                local,
+                Node::Pat(pat) if matches!(
+                    cx.typeck_results().pat_ty(backtrack_pat(cx, pat)).peel_refs().kind(),
+                    ty::Tuple(_),
+                ),
+            )
+        })
+    {
+        return emit_lint(cx, expr, ToType::Array);
+    }
+
+    if let Some(elements) = elements
+            .iter()
+            .map(|expr| {
+                if let ExprKind::Field(path, _) = expr.kind {
+                    return Some(path);
+                };
+
+                None
+            })
+            .collect::<Option<Vec<&Expr<'_>>>>()
+        && let Some(locals) = path_to_locals(cx, elements)
+        && locals.iter().all(|local| {
+            matches!(
+                local,
+                Node::Pat(pat) if matches!(
+                    cx.typeck_results().pat_ty(backtrack_pat(cx, pat)).peel_refs().kind(),
+                    ty::Tuple(_),
+                ),
+            )
+        })
+    {
+        return emit_lint(cx, expr, ToType::Array);
+    }
+
+    false
+}
+
+fn check_tuple<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
+    let ExprKind::Tup(elements) = expr.kind else {
+        return false;
+    };
+    if !(1..=12).contains(&elements.len()) {
+        return false;
+    };
+    if let Some(locals) = path_to_locals(cx, elements)
+        && locals.iter().all(|local| {
+            matches!(
+                local,
+                Node::Pat(pat) if matches!(
+                    cx.typeck_results().pat_ty(backtrack_pat(cx, pat)).peel_refs().kind(),
+                    ty::Array(_, _),
+                ),
+            )
+        })
+    {
+        return emit_lint(cx, expr, ToType::Tuple);
+    }
+
+    if let Some(elements) = elements
+            .iter()
+            .map(|expr| {
+                if let ExprKind::Index(path, _) = expr.kind {
+                    return Some(path);
+                };
+
+                None
+            })
+            .collect::<Option<Vec<&Expr<'_>>>>()
+        && let Some(locals) = path_to_locals(cx, elements.clone())
+        && locals.iter().all(|local| {
+            matches!(
+                local,
+                Node::Pat(pat) if cx.typeck_results()
+                    .pat_ty(backtrack_pat(cx, pat))
+                    .peel_refs()
+                    .is_array()
+            )
+        })
+    {
+        return emit_lint(cx, expr, ToType::Tuple);
+    }
+
+    false
+}
+
+/// Walks up the `Pat` until it's reached the final containing `Pat`.
+fn backtrack_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
+}
+
+fn path_to_locals<'tcx>(
+    cx: &LateContext<'tcx>,
+    exprs: impl IntoIterator<Item = &'tcx Expr<'tcx>>,
+) -> Option<Vec<Node<'tcx>>> {
+    exprs
+        .into_iter()
+        .map(|element| path_to_local(element).and_then(|local| cx.tcx.hir().find(local)))
+        .collect()
+}
+
+#[derive(Clone, Copy)]
+enum ToType {
+    Array,
+    Tuple,
+}
+
+impl ToType {
+    fn help(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 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.help(),
+            None,
+            "use `.into()` instead",
+        );
+
+        return true;
+    }
+
+    false
+}

tests/ui/tuple_array_conversions.rs

@@ -0,0 +1,43 @@
+//@aux-build:proc_macros.rs:proc-macro
+#![allow(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]);
+    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();
+    }
+}

tests/ui/tuple_array_conversions.stderr

@@ -0,0 +1,59 @@
+error: it looks like you're trying to convert an array to a tuple
+  --> $DIR/tuple_array_conversions.rs:10:13
+   |
+LL |     let x = (x[0], x[1]);
+   |             ^^^^^^^^^^^^
+   |
+   = help: use `.into()` instead
+   = note: `-D clippy::tuple-array-conversions` implied by `-D warnings`
+
+error: it looks like you're trying to convert a tuple to an array
+  --> $DIR/tuple_array_conversions.rs:11:13
+   |
+LL |     let x = [x.0, x.1];
+   |             ^^^^^^^^^^
+   |
+   = help: use `.into()` instead
+
+error: it looks like you're trying to convert an array to a tuple
+  --> $DIR/tuple_array_conversions.rs:13:13
+   |
+LL |     let x = (x[0], x[1]);
+   |             ^^^^^^^^^^^^
+   |
+   = help: use `.into()` instead
+
+error: it looks like you're trying to convert a tuple to an array
+  --> $DIR/tuple_array_conversions.rs:16:53
+   |
+LL |     let v1: Vec<[u32; 2]> = t1.iter().map(|&(a, b)| [a, b]).collect();
+   |                                                     ^^^^^^
+   |
+   = help: use `.into()` instead
+
+error: it looks like you're trying to convert a tuple to an array
+  --> $DIR/tuple_array_conversions.rs:17:38
+   |
+LL |     t1.iter().for_each(|&(a, b)| _ = [a, b]);
+   |                                      ^^^^^^
+   |
+   = help: use `.into()` instead
+
+error: it looks like you're trying to convert an array to a tuple
+  --> $DIR/tuple_array_conversions.rs:18:55
+   |
+LL |     let t2: Vec<(u32, u32)> = v1.iter().map(|&[a, b]| (a, b)).collect();
+   |                                                       ^^^^^^
+   |
+   = help: use `.into()` instead
+
+error: it looks like you're trying to convert a tuple to an array
+  --> $DIR/tuple_array_conversions.rs:19:38
+   |
+LL |     t1.iter().for_each(|&(a, b)| _ = [a, b]);
+   |                                      ^^^^^^
+   |
+   = help: use `.into()` instead
+
+error: aborting due to 7 previous errors
+