Added lint match_vec_item

clippy_lints/src/lib.rs

@@ -249,6 +249,7 @@ mod macro_use;
 mod main_recursion;
 mod map_clone;
 mod map_unit_fn;
+mod match_vec_item;
 mod matches;
 mod mem_discriminant;
 mod mem_forget;
@@ -629,6 +630,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         &map_clone::MAP_CLONE,
         &map_unit_fn::OPTION_MAP_UNIT_FN,
         &map_unit_fn::RESULT_MAP_UNIT_FN,
+        &match_vec_item::MATCH_VEC_ITEM,
         &matches::INFALLIBLE_DESTRUCTURING_MATCH,
         &matches::MATCH_AS_REF,
         &matches::MATCH_BOOL,
@@ -1060,6 +1062,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|| box future_not_send::FutureNotSend);
     store.register_late_pass(|| box utils::internal_lints::CollapsibleCalls);
     store.register_late_pass(|| box if_let_mutex::IfLetMutex);
+    store.register_late_pass(|| box match_vec_item::MatchVecItem);
 
     store.register_group(true, "clippy::restriction", Some("clippy_restriction"), vec![
         LintId::of(&arithmetic::FLOAT_ARITHMETIC),
@@ -1277,6 +1280,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&map_clone::MAP_CLONE),
         LintId::of(&map_unit_fn::OPTION_MAP_UNIT_FN),
         LintId::of(&map_unit_fn::RESULT_MAP_UNIT_FN),
+        LintId::of(&match_vec_item::MATCH_VEC_ITEM),
         LintId::of(&matches::INFALLIBLE_DESTRUCTURING_MATCH),
         LintId::of(&matches::MATCH_AS_REF),
         LintId::of(&matches::MATCH_BOOL),
@@ -1469,6 +1473,7 @@ 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(&map_clone::MAP_CLONE),
+        LintId::of(&match_vec_item::MATCH_VEC_ITEM),
         LintId::of(&matches::INFALLIBLE_DESTRUCTURING_MATCH),
         LintId::of(&matches::MATCH_BOOL),
         LintId::of(&matches::MATCH_OVERLAPPING_ARM),

clippy_lints/src/match_vec_item.rs

@@ -0,0 +1,111 @@
+use crate::utils::{is_wild, span_lint_and_help};
+use if_chain::if_chain;
+use rustc_hir::{Arm, Expr, ExprKind, MatchSource};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_middle::lint::in_external_macro;
+use rustc_middle::ty::{self, AdtDef};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+
+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.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust, no_run
+    /// let arr = vec![0, 1, 2, 3];
+    /// let idx = 1;
+    ///
+    /// // Bad
+    /// match arr[idx] {
+    ///     0 => println!("{}", 0),
+    ///     1 => println!("{}", 3),
+    ///     _ => {},
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```rust, no_run
+    /// let arr = vec![0, 1, 2, 3];
+    /// let idx = 1;
+    ///
+    /// // Good
+    /// match arr.get(idx) {
+    ///     Some(0) => println!("{}", 0),
+    ///     Some(1) => println!("{}", 3),
+    ///     _ => {},
+    /// }
+    /// ```
+    pub MATCH_VEC_ITEM,
+    style,
+    "match vector by indexing can panic"
+}
+
+declare_lint_pass!(MatchVecItem => [MATCH_VEC_ITEM]);
+
+impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MatchVecItem {
+    fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'tcx>) {
+        if_chain! {
+            if !in_external_macro(cx.sess(), expr.span);
+            if let ExprKind::Match(ref ex, ref arms, MatchSource::Normal) = expr.kind;
+            if contains_wild_arm(arms);
+            if is_vec_indexing(cx, ex);
+
+            then {
+                span_lint_and_help(
+                    cx,
+                    MATCH_VEC_ITEM,
+                    expr.span,
+                    "indexing vector may panic",
+                    None,
+                    "consider using `get(..)` instead.",
+                );
+            }
+        }
+    }
+}
+
+fn contains_wild_arm(arms: &[Arm<'_>]) -> bool {
+    arms.iter().any(|arm| is_wild(&arm.pat) && is_unit_expr(arm.body))
+}
+
+fn is_vec_indexing<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
+    if_chain! {
+        if let ExprKind::Index(ref array, _) = expr.kind;
+        let ty = cx.tables.expr_ty(array);
+        if let ty::Adt(def, _) = ty.kind;
+        if is_vec(cx, def);
+
+        then {
+            return true;
+        }
+    }
+
+    false
+}
+
+fn is_vec<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, def: &'a AdtDef) -> bool {
+    if_chain! {
+        let def_path = cx.tcx.def_path(def.did);
+        if def_path.data.len() == 2;
+        if let Some(module) = def_path.data.get(0);
+        if module.data.as_symbol() == sym!(vec);
+        if let Some(name) = def_path.data.get(1);
+        if name.data.as_symbol() == sym!(Vec);
+
+        then {
+            return true;
+        }
+    }
+
+    false
+}
+
+fn is_unit_expr(expr: &Expr<'_>) -> bool {
+    match expr.kind {
+        ExprKind::Tup(ref v) if v.is_empty() => true,
+        ExprKind::Block(ref b, _) if b.stmts.is_empty() && b.expr.is_none() => true,
+        _ => false,
+    }
+}