Deprecate match_on_vec_items lint (rust-lang#14217)

This lint does more harm than good: in its description, it proposes to
rewrite `match` on `Vec<_>` indexes or slices by a version which cannot
panic but masks the failure by choosing the default variant.

The `clippy::indexing_slicing` restriction lint covers those cases more
safely, by suggesting to use a non-panicking version to retrieve the
value from the container, without suggesting to fallback to the default
success variant in case of failure.

This PR is an (opposite) alternative to rust-lang#14208 (which will add a
suggestion to the lint matching the lint description). Discussion on
both PRs can be found [on
Zulip](https://rust-lang.zulipchat.com/#narrow/channel/257328-clippy/topic/Suggestions.20that.20suppress.20panics).

changelog: [`match_on_vec_items`]: deprecate lint

Author: samueltardieu

clippy_lints/src/declared_lints.rs

@@ -351,7 +351,6 @@ pub static LINTS: &[&crate::LintInfo] = &[
     crate::matches::MATCH_AS_REF_INFO,
     crate::matches::MATCH_BOOL_INFO,
     crate::matches::MATCH_LIKE_MATCHES_MACRO_INFO,
-    crate::matches::MATCH_ON_VEC_ITEMS_INFO,
     crate::matches::MATCH_OVERLAPPING_ARM_INFO,
     crate::matches::MATCH_REF_PATS_INFO,
     crate::matches::MATCH_SAME_ARMS_INFO,

clippy_lints/src/deprecated_lints.rs

@@ -42,6 +42,8 @@ declare_with_version! { DEPRECATED(DEPRECATED_VERSION): &[(&str, &str)] = &[
     ("clippy::wrong_pub_self_convention", "`clippy::wrong_self_convention` now covers this case via the `avoid-breaking-exported-api` config"),
     #[clippy::version = "1.86.0"]
     ("clippy::option_map_or_err_ok", "`clippy::manual_ok_or` covers this case"),
+    #[clippy::version = "1.86.0"]
+    ("clippy::match_on_vec_items", "`clippy::indexing_slicing` covers indexing and slicing on `Vec<_>`"),
     // end deprecated lints. used by `cargo dev deprecate_lint`
 ]}
 

clippy_lints/src/matches/match_on_vec_items.rs

@@ -8,7 +8,6 @@ mod manual_utils;
 mod match_as_ref;
 mod match_bool;
 mod match_like_matches;
-mod match_on_vec_items;
 mod match_ref_pats;
 mod match_same_arms;
 mod match_single_binding;
@@ -759,42 +758,6 @@ declare_clippy_lint! {
     "check if a `match` or `if let` can be simplified with `unwrap_or_default`"
 }
 
-declare_clippy_lint! {
-    /// ### What it does
-    /// Checks for `match vec[idx]` or `match vec[n..m]`.
-    ///
-    /// ### Why is this bad?
-    /// This can panic at runtime.
-    ///
-    /// ### Example
-    /// ```rust, no_run
-    /// let arr = vec![0, 1, 2, 3];
-    /// let idx = 1;
-    ///
-    /// match arr[idx] {
-    ///     0 => println!("{}", 0),
-    ///     1 => println!("{}", 3),
-    ///     _ => {},
-    /// }
-    /// ```
-    ///
-    /// Use instead:
-    /// ```rust, no_run
-    /// let arr = vec![0, 1, 2, 3];
-    /// let idx = 1;
-    ///
-    /// match arr.get(idx) {
-    ///     Some(0) => println!("{}", 0),
-    ///     Some(1) => println!("{}", 3),
-    ///     _ => {},
-    /// }
-    /// ```
-    #[clippy::version = "1.45.0"]
-    pub MATCH_ON_VEC_ITEMS,
-    pedantic,
-    "matching on vector elements can panic"
-}
-
 declare_clippy_lint! {
     /// ### What it does
     /// Checks for `match` expressions modifying the case of a string with non-compliant arms
@@ -1078,7 +1041,6 @@ impl_lint_pass!(Matches => [
     COLLAPSIBLE_MATCH,
     MANUAL_UNWRAP_OR,
     MANUAL_UNWRAP_OR_DEFAULT,
-    MATCH_ON_VEC_ITEMS,
     MATCH_STR_CASE_MISMATCH,
     SIGNIFICANT_DROP_IN_SCRUTINEE,
     TRY_ERR,
@@ -1156,7 +1118,6 @@ impl<'tcx> LateLintPass<'tcx> for Matches {
                     match_wild_enum::check(cx, ex, arms);
                     match_as_ref::check(cx, ex, arms, expr);
                     needless_match::check_match(cx, ex, arms, expr);
-                    match_on_vec_items::check(cx, ex);
                     match_str_case_mismatch::check(cx, ex, arms);
                     redundant_guards::check(cx, arms, self.msrv);
 

clippy_lints/src/matches/mod.rs

@@ -16,5 +16,6 @@
 #![warn(clippy::pub_enum_variant_names)] //~ ERROR: lint `clippy::pub_enum_variant_names`
 #![warn(clippy::wrong_pub_self_convention)] //~ ERROR: lint `clippy::wrong_pub_self_convention`
 #![warn(clippy::option_map_or_err_ok)] //~ ERROR: lint `clippy::option_map_or_err_ok`
+#![warn(clippy::match_on_vec_items)] //~ ERROR: lint `clippy::match_on_vec_items`
 
 fn main() {}

tests/ui/deprecated.rs

@@ -85,5 +85,11 @@ error: lint `clippy::option_map_or_err_ok` has been removed: `clippy::manual_ok_
 LL | #![warn(clippy::option_map_or_err_ok)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 14 previous errors
+error: lint `clippy::match_on_vec_items` has been removed: `clippy::indexing_slicing` covers indexing and slicing on `Vec<_>`
+  --> tests/ui/deprecated.rs:19:9
+   |
+LL | #![warn(clippy::match_on_vec_items)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 15 previous errors