Move implementation into len_zero.rs

Author: Urcra

clippy_lints/src/comparison_to_empty.rs

@@ -68,7 +68,45 @@ declare_clippy_lint! {
     "traits or impls with a public `len` method but no corresponding `is_empty` method"
 }
 
-declare_lint_pass!(LenZero => [LEN_ZERO, LEN_WITHOUT_IS_EMPTY]);
+declare_clippy_lint! {
+    /// **What it does:** Checks for comparing to an empty slice such as "" or [],`
+    /// and suggests using `.is_empty()` where applicable.
+    ///
+    /// **Why is this bad?** Some structures can answer `.is_empty()` much faster
+    /// than checking for equality. So it is good to get into the habit of using
+    /// `.is_empty()`, and having it is cheap.
+    /// Besides, it makes the intent clearer than a manual comparison in some contexts.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    ///
+    /// ```ignore
+    /// if s == "" {
+    ///     ..
+    /// }
+
+    /// if arr == [] {
+    ///     ..
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```ignore
+    /// if s.is_empty() {
+    ///     ..
+    /// }
+
+    /// if arr.is_empty() {
+    ///     ..
+    /// }
+    /// ```
+    pub COMPARISON_TO_EMPTY,
+    style,
+    "default lint description"
+}
+
+
+declare_lint_pass!(LenZero => [LEN_ZERO, LEN_WITHOUT_IS_EMPTY, COMPARISON_TO_EMPTY]);
 
 impl<'tcx> LateLintPass<'tcx> for LenZero {
     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
@@ -221,6 +259,8 @@ fn check_cmp(cx: &LateContext<'_>, span: Span, method: &Expr<'_>, lit: &Expr<'_>
         }
 
         check_len(cx, span, method_path.ident.name, args, &lit.node, op, compare_to)
+    } else {
+        check_empty_expr(cx, span, method, lit, op)
     }
 }
 
@@ -258,6 +298,48 @@ fn check_len(
     }
 }
 
+fn check_empty_expr(
+    cx: &LateContext<'_>,
+    span: Span,
+    lit1: &Expr<'_>,
+    lit2: &Expr<'_>,
+    op: &str
+) {
+    if (is_empty_array(lit2) || is_empty_string(lit2)) && has_is_empty(cx, lit1) {
+        let mut applicability = Applicability::MachineApplicable;
+        span_lint_and_sugg(
+            cx,
+            COMPARISON_TO_EMPTY,
+            span,
+            &format!("comparison to empty slice"),
+            &format!("using `{}is_empty` is clearer and more explicit", op),
+            format!(
+                "{}{}.is_empty()",
+                op,
+                snippet_with_applicability(cx, lit1.span, "_", &mut applicability)
+            ),
+            applicability,
+        );
+    }
+}
+
+fn is_empty_string(expr: &Expr<'_>) -> bool {
+    if let ExprKind::Lit(ref lit) = expr.kind {
+        if let LitKind::Str(lit, _) = lit.node {
+            let lit = lit.as_str();
+            return lit == "";
+        }
+    }
+    false
+}
+
+fn is_empty_array(expr: &Expr<'_>) -> bool {
+    if let ExprKind::Array(ref arr) = expr.kind {
+        return arr.is_empty();
+    }
+    false
+}
+
 /// Checks if this type has an `is_empty` method.
 fn has_is_empty(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
     /// Gets an `AssocItem` and return true if it matches `is_empty(self)`.

clippy_lints/src/len_zero.rs

@@ -171,7 +171,6 @@ mod checked_conversions;
 mod cognitive_complexity;
 mod collapsible_if;
 mod comparison_chain;
-mod comparison_to_empty;
 mod copies;
 mod copy_iterator;
 mod create_dir;
@@ -524,7 +523,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         &cognitive_complexity::COGNITIVE_COMPLEXITY,
         &collapsible_if::COLLAPSIBLE_IF,
         &comparison_chain::COMPARISON_CHAIN,
-        &comparison_to_empty::COMPARISON_TO_EMPTY,
+        &len_zero::COMPARISON_TO_EMPTY,
         &copies::IFS_SAME_COND,
         &copies::IF_SAME_THEN_ELSE,
         &copies::MATCH_SAME_ARMS,
@@ -1141,7 +1140,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(move || box disallowed_method::DisallowedMethod::new(&disallowed_methods));
     store.register_early_pass(|| box asm_syntax::InlineAsmX86AttSyntax);
     store.register_early_pass(|| box asm_syntax::InlineAsmX86IntelSyntax);
-    store.register_late_pass(|| box comparison_to_empty::ComparisonToEmpty);
 
 
     store.register_group(true, "clippy::restriction", Some("clippy_restriction"), vec![
@@ -1302,7 +1300,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&bytecount::NAIVE_BYTECOUNT),
         LintId::of(&collapsible_if::COLLAPSIBLE_IF),
         LintId::of(&comparison_chain::COMPARISON_CHAIN),
-        LintId::of(&comparison_to_empty::COMPARISON_TO_EMPTY),
+        LintId::of(&len_zero::COMPARISON_TO_EMPTY),
         LintId::of(&copies::IFS_SAME_COND),
         LintId::of(&copies::IF_SAME_THEN_ELSE),
         LintId::of(&derive::DERIVE_HASH_XOR_EQ),
@@ -1559,7 +1557,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&blocks_in_if_conditions::BLOCKS_IN_IF_CONDITIONS),
         LintId::of(&collapsible_if::COLLAPSIBLE_IF),
         LintId::of(&comparison_chain::COMPARISON_CHAIN),
-        LintId::of(&comparison_to_empty::COMPARISON_TO_EMPTY),
+        LintId::of(&len_zero::COMPARISON_TO_EMPTY),
         LintId::of(&doc::MISSING_SAFETY_DOC),
         LintId::of(&doc::NEEDLESS_DOCTEST_MAIN),
         LintId::of(&enum_variants::ENUM_VARIANT_NAMES),