Implement equatable if let lint

Author: HKalbasi

CHANGELOG.md

@@ -2695,6 +2695,7 @@ Released 2018-09-13
 [`enum_glob_use`]: https://rust-lang.github.io/rust-clippy/master/index.html#enum_glob_use
 [`enum_variant_names`]: https://rust-lang.github.io/rust-clippy/master/index.html#enum_variant_names
 [`eq_op`]: https://rust-lang.github.io/rust-clippy/master/index.html#eq_op
+[`equatable_if_let`]: https://rust-lang.github.io/rust-clippy/master/index.html#equatable_if_let
 [`erasing_op`]: https://rust-lang.github.io/rust-clippy/master/index.html#erasing_op
 [`eval_order_dependence`]: https://rust-lang.github.io/rust-clippy/master/index.html#eval_order_dependence
 [`excessive_precision`]: https://rust-lang.github.io/rust-clippy/master/index.html#excessive_precision

clippy_lints/src/attrs.rs

@@ -563,7 +563,7 @@ fn check_deprecated_cfg_attr(cx: &EarlyContext<'_>, attr: &Attribute) {
             skip_item.path.segments.last().expect("empty path in attribute").ident.name == sym::skip;
         // Only lint outer attributes, because custom inner attributes are unstable
         // Tracking issue: https://github.com/rust-lang/rust/issues/54726
-        if let AttrStyle::Outer = attr.style;
+        if attr.style == AttrStyle::Outer;
         then {
             span_lint_and_sugg(
                 cx,

clippy_lints/src/casts/cast_precision_loss.rs

@@ -12,7 +12,7 @@ pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, ca
     }
 
     let from_nbits = utils::int_ty_to_nbits(cast_from, cx.tcx);
-    let to_nbits = if let ty::Float(FloatTy::F32) = cast_to.kind() {
+    let to_nbits = if cast_to.kind() == &ty::Float(FloatTy::F32) {
         32
     } else {
         64

clippy_lints/src/derive.rs

@@ -393,7 +393,7 @@ impl<'tcx> Visitor<'tcx> for UnsafeVisitor<'_, 'tcx> {
 
         if_chain! {
             if let Some(header) = kind.header();
-            if let Unsafety::Unsafe = header.unsafety;
+            if header.unsafety == Unsafety::Unsafe;
             then {
                 self.has_unsafe = true;
             }
@@ -408,7 +408,7 @@ impl<'tcx> Visitor<'tcx> for UnsafeVisitor<'_, 'tcx> {
         }
 
         if let ExprKind::Block(block, _) = expr.kind {
-            if let BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided) = block.rules {
+            if block.rules == BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided) {
                 self.has_unsafe = true;
             }
         }

clippy_lints/src/equatable_if_let.rs

@@ -0,0 +1,100 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::ty::implements_trait;
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind, Pat, PatKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::ty::Ty;
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for pattern matchings that can be expressed using equality.
+    ///
+    /// ### Why is this bad?
+    ///
+    /// * It reads better and has less cognitive load because equality won't cause binding.
+    /// * It is a [Yoda condition](https://en.wikipedia.org/wiki/Yoda_conditions). Yoda conditions are widely
+    /// criticized for increasing the cognitive load of reading the code.
+    /// * Equality is a simple bool expression and can be merged with `&&` and `||` and
+    /// reuse if blocks
+    ///
+    /// ### Example
+    /// ```rust,ignore
+    /// if let Some(2) = x {
+    ///     do_thing();
+    /// }
+    /// ```
+    /// Should be written
+    /// ```rust,ignore
+    /// if x == Some(2) {
+    ///     do_thing();
+    /// }
+    /// ```
+    pub EQUATABLE_IF_LET,
+    nursery,
+    "using pattern matching instead of equality"
+}
+
+declare_lint_pass!(PatternEquality => [EQUATABLE_IF_LET]);
+
+/// detects if pattern matches just one thing
+fn unary_pattern(pat: &Pat<'_>) -> bool {
+    fn array_rec(pats: &[Pat<'_>]) -> bool {
+        pats.iter().all(unary_pattern)
+    }
+    match &pat.kind {
+        PatKind::Slice(_, _, _) | PatKind::Range(_, _, _) | PatKind::Binding(..) | PatKind::Wild | PatKind::Or(_) => {
+            false
+        },
+        PatKind::Struct(_, a, etc) => !etc && a.iter().all(|x| unary_pattern(x.pat)),
+        PatKind::Tuple(a, etc) | PatKind::TupleStruct(_, a, etc) => !etc.is_some() && array_rec(a),
+        PatKind::Ref(x, _) | PatKind::Box(x) => unary_pattern(x),
+        PatKind::Path(_) | PatKind::Lit(_) => true,
+    }
+}
+
+fn is_structural_partial_eq(cx: &LateContext<'tcx>, ty: Ty<'tcx>, other: Ty<'tcx>) -> bool {
+    if let Some(def_id) = cx.tcx.lang_items().eq_trait() {
+        implements_trait(cx, ty, def_id, &[other.into()])
+    } else {
+        false
+    }
+}
+
+impl<'tcx> LateLintPass<'tcx> for PatternEquality {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
+        if_chain! {
+            if let ExprKind::Let(pat, exp, _) = expr.kind;
+            if unary_pattern(pat);
+            let exp_ty = cx.typeck_results().expr_ty(exp);
+            let pat_ty = cx.typeck_results().pat_ty(pat);
+            if is_structural_partial_eq(cx, exp_ty, pat_ty);
+            then {
+
+                let mut applicability = Applicability::MachineApplicable;
+                let pat_str = match pat.kind {
+                    PatKind::Struct(..) => format!(
+                        "({})",
+                        snippet_with_applicability(cx, pat.span, "..", &mut applicability),
+                    ),
+                    _ => snippet_with_applicability(cx, pat.span, "..", &mut applicability).to_string(),
+                };
+                span_lint_and_sugg(
+                    cx,
+                    EQUATABLE_IF_LET,
+                    expr.span,
+                    "this pattern matching can be expressed using equality",
+                    "try",
+                    format!(
+                        "{} == {}",
+                        snippet_with_applicability(cx, exp.span, "..", &mut applicability),
+                        pat_str,
+                    ),
+                    applicability,
+                );
+            }
+        }
+    }
+}

clippy_lints/src/erasing_op.rs

@@ -47,7 +47,7 @@ impl<'tcx> LateLintPass<'tcx> for ErasingOp {
 }
 
 fn check(cx: &LateContext<'_>, e: &Expr<'_>, span: Span) {
-    if let Some(Constant::Int(0)) = constant_simple(cx, cx.typeck_results(), e) {
+    if constant_simple(cx, cx.typeck_results(), e) == Some(Constant::Int(0)) {
         span_lint(
             cx,
             ERASING_OP,

clippy_lints/src/escape.rs

@@ -90,7 +90,7 @@ impl<'tcx> LateLintPass<'tcx> for BoxedLocal {
                 for trait_item in items {
                     if trait_item.id.hir_id() == hir_id {
                         // be sure we have `self` parameter in this function
-                        if let AssocItemKind::Fn { has_self: true } = trait_item.kind {
+                        if trait_item.kind == (AssocItemKind::Fn { has_self: true }) {
                             trait_self_ty = Some(
                                 TraitRef::identity(cx.tcx, trait_item.id.def_id.to_def_id())
                                     .self_ty()

clippy_lints/src/eta_reduction.rs

@@ -116,7 +116,7 @@ impl<'tcx> LateLintPass<'tcx> for EtaReduction {
                     if let Some(mut snippet) = snippet_opt(cx, callee.span) {
                         if_chain! {
                             if let ty::Closure(_, substs) = callee_ty.peel_refs().kind();
-                            if let ClosureKind::FnMut = substs.as_closure().kind();
+                            if substs.as_closure().kind() == ClosureKind::FnMut;
                             if get_enclosing_loop_or_closure(cx.tcx, expr).is_some()
                                 || UsedAfterExprVisitor::is_found(cx, callee);
 

clippy_lints/src/eval_order_dependence.rs

@@ -141,7 +141,7 @@ impl<'a, 'tcx> Visitor<'tcx> for DivergenceVisitor<'a, 'tcx> {
                 match typ.kind() {
                     ty::FnDef(..) | ty::FnPtr(_) => {
                         let sig = typ.fn_sig(self.cx.tcx);
-                        if let ty::Never = self.cx.tcx.erase_late_bound_regions(sig).output().kind() {
+                        if self.cx.tcx.erase_late_bound_regions(sig).output().kind() == &ty::Never {
                             self.report_diverging_sub_expr(e);
                         }
                     },

clippy_lints/src/identity_op.rs

@@ -1,5 +1,4 @@
 use clippy_utils::source::snippet;
-use if_chain::if_chain;
 use rustc_hir::{BinOp, BinOpKind, Expr, ExprKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty;
@@ -62,16 +61,9 @@ impl<'tcx> LateLintPass<'tcx> for IdentityOp {
 
 fn is_allowed(cx: &LateContext<'_>, cmp: BinOp, left: &Expr<'_>, right: &Expr<'_>) -> bool {
     // `1 << 0` is a common pattern in bit manipulation code
-    if_chain! {
-        if let BinOpKind::Shl = cmp.node;
-        if let Some(Constant::Int(0)) = constant_simple(cx, cx.typeck_results(), right);
-        if let Some(Constant::Int(1)) = constant_simple(cx, cx.typeck_results(), left);
-        then {
-            return true;
-        }
-    }
-
-    false
+    cmp.node == BinOpKind::Shl
+        && constant_simple(cx, cx.typeck_results(), right) == Some(Constant::Int(0))
+        && constant_simple(cx, cx.typeck_results(), left) == Some(Constant::Int(1))
 }
 
 #[allow(clippy::cast_possible_wrap)]