improve MATCH_LIKE_MATCHES_MACRO lint

- add tests
- refactor match_same_arms lint
- prioritize match_expr_like_matches_macro over match_same_arms

10 files changed, 439 insertions, 236 deletions

diff --git a/clippy_lints/src/copies.rs b/clippy_lints/src/copies.rs
index 6c969c3ead0..46ce92ea6d7 100644
--- a/clippy_lints/src/copies.rs
+++ b/clippy_lints/src/copies.rs
@@ -1,13 +1,8 @@
-use crate::utils::{eq_expr_value, in_macro, SpanlessEq, SpanlessHash};
-use crate::utils::{get_parent_expr, higher, if_sequence, snippet, span_lint_and_note, span_lint_and_then};
-use rustc_data_structures::fx::FxHashMap;
-use rustc_hir::{Arm, Block, Expr, ExprKind, MatchSource, Pat, PatKind};
+use crate::utils::{eq_expr_value, in_macro, search_same, SpanlessEq, SpanlessHash};
+use crate::utils::{get_parent_expr, higher, if_sequence, span_lint_and_note};
+use rustc_hir::{Block, Expr};
 use rustc_lint::{LateContext, LateLintPass};
-use rustc_middle::ty::{Ty, TyS};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
-use rustc_span::symbol::Symbol;
-use std::collections::hash_map::Entry;
-use std::hash::BuildHasherDefault;
 
 declare_clippy_lint! {
     /// **What it does:** Checks for consecutive `if`s with the same condition.
@@ -108,48 +103,7 @@ declare_clippy_lint! {
     "`if` with the same `then` and `else` blocks"
 }
 
-declare_clippy_lint! {
-    /// **What it does:** Checks for `match` with identical arm bodies.
-    ///
-    /// **Why is this bad?** This is probably a copy & paste error. If arm bodies
-    /// are the same on purpose, you can factor them
-    /// [using `|`](https://doc.rust-lang.org/book/patterns.html#multiple-patterns).
-    ///
-    /// **Known problems:** False positive possible with order dependent `match`
-    /// (see issue
-    /// [#860](https://github.com/rust-lang/rust-clippy/issues/860)).
-    ///
-    /// **Example:**
-    /// ```rust,ignore
-    /// match foo {
-    ///     Bar => bar(),
-    ///     Quz => quz(),
-    ///     Baz => bar(), // <= oops
-    /// }
-    /// ```
-    ///
-    /// This should probably be
-    /// ```rust,ignore
-    /// match foo {
-    ///     Bar => bar(),
-    ///     Quz => quz(),
-    ///     Baz => baz(), // <= fixed
-    /// }
-    /// ```
-    ///
-    /// or if the original code was not a typo:
-    /// ```rust,ignore
-    /// match foo {
-    ///     Bar | Baz => bar(), // <= shows the intent better
-    ///     Quz => quz(),
-    /// }
-    /// ```
-    pub MATCH_SAME_ARMS,
-    pedantic,
-    "`match` with identical arm bodies"
-}
-
-declare_lint_pass!(CopyAndPaste => [IFS_SAME_COND, SAME_FUNCTIONS_IN_IF_CONDITION, IF_SAME_THEN_ELSE, MATCH_SAME_ARMS]);
+declare_lint_pass!(CopyAndPaste => [IFS_SAME_COND, SAME_FUNCTIONS_IN_IF_CONDITION, IF_SAME_THEN_ELSE]);
 
 impl<'tcx> LateLintPass<'tcx> for CopyAndPaste {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
@@ -167,7 +121,6 @@ impl<'tcx> LateLintPass<'tcx> for CopyAndPaste {
             lint_same_then_else(cx, &blocks);
             lint_same_cond(cx, &conds);
             lint_same_fns_in_if_cond(cx, &conds);
-            lint_match_arms(cx, expr);
         }
     }
 }
@@ -243,122 +196,6 @@ fn lint_same_fns_in_if_cond(cx: &LateContext<'_>, conds: &[&Expr<'_>]) {
     }
 }
 
-/// Implementation of `MATCH_SAME_ARMS`.
-fn lint_match_arms<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>) {
-    fn same_bindings<'tcx>(lhs: &FxHashMap<Symbol, Ty<'tcx>>, rhs: &FxHashMap<Symbol, Ty<'tcx>>) -> bool {
-        lhs.len() == rhs.len()
-            && lhs
-                .iter()
-                .all(|(name, l_ty)| rhs.get(name).map_or(false, |r_ty| TyS::same_type(l_ty, r_ty)))
-    }
-
-    if let ExprKind::Match(_, ref arms, MatchSource::Normal) = expr.kind {
-        let hash = |&(_, arm): &(usize, &Arm<'_>)| -> u64 {
-            let mut h = SpanlessHash::new(cx);
-            h.hash_expr(&arm.body);
-            h.finish()
-        };
-
-        let eq = |&(lindex, lhs): &(usize, &Arm<'_>), &(rindex, rhs): &(usize, &Arm<'_>)| -> bool {
-            let min_index = usize::min(lindex, rindex);
-            let max_index = usize::max(lindex, rindex);
-
-            // Arms with a guard are ignored, those can’t always be merged together
-            // This is also the case for arms in-between each there is an arm with a guard
-            (min_index..=max_index).all(|index| arms[index].guard.is_none()) &&
-                SpanlessEq::new(cx).eq_expr(&lhs.body, &rhs.body) &&
-                // all patterns should have the same bindings
-                same_bindings(&bindings(cx, &lhs.pat), &bindings(cx, &rhs.pat))
-        };
-
-        let indexed_arms: Vec<(usize, &Arm<'_>)> = arms.iter().enumerate().collect();
-        for (&(_, i), &(_, j)) in search_same(&indexed_arms, hash, eq) {
-            span_lint_and_then(
-                cx,
-                MATCH_SAME_ARMS,
-                j.body.span,
-                "this `match` has identical arm bodies",
-                |diag| {
-                    diag.span_note(i.body.span, "same as this");
-
-                    // Note: this does not use `span_suggestion` on purpose:
-                    // there is no clean way
-                    // to remove the other arm. Building a span and suggest to replace it to ""
-                    // makes an even more confusing error message. Also in order not to make up a
-                    // span for the whole pattern, the suggestion is only shown when there is only
-                    // one pattern. The user should know about `|` if they are already using it…
-
-                    let lhs = snippet(cx, i.pat.span, "<pat1>");
-                    let rhs = snippet(cx, j.pat.span, "<pat2>");
-
-                    if let PatKind::Wild = j.pat.kind {
-                        // if the last arm is _, then i could be integrated into _
-                        // note that i.pat cannot be _, because that would mean that we're
-                        // hiding all the subsequent arms, and rust won't compile
-                        diag.span_note(
-                            i.body.span,
-                            &format!(
-                                "`{}` has the same arm body as the `_` wildcard, consider removing it",
-                                lhs
-                            ),
-                        );
-                    } else {
-                        diag.span_help(i.pat.span, &format!("consider refactoring into `{} | {}`", lhs, rhs));
-                    }
-                },
-            );
-        }
-    }
-}
-
-/// Returns the list of bindings in a pattern.
-fn bindings<'tcx>(cx: &LateContext<'tcx>, pat: &Pat<'_>) -> FxHashMap<Symbol, Ty<'tcx>> {
-    fn bindings_impl<'tcx>(cx: &LateContext<'tcx>, pat: &Pat<'_>, map: &mut FxHashMap<Symbol, Ty<'tcx>>) {
-        match pat.kind {
-            PatKind::Box(ref pat) | PatKind::Ref(ref pat, _) => bindings_impl(cx, pat, map),
-            PatKind::TupleStruct(_, pats, _) => {
-                for pat in pats {
-                    bindings_impl(cx, pat, map);
-                }
-            },
-            PatKind::Binding(.., ident, ref as_pat) => {
-                if let Entry::Vacant(v) = map.entry(ident.name) {
-                    v.insert(cx.typeck_results().pat_ty(pat));
-                }
-                if let Some(ref as_pat) = *as_pat {
-                    bindings_impl(cx, as_pat, map);
-                }
-            },
-            PatKind::Or(fields) | PatKind::Tuple(fields, _) => {
-                for pat in fields {
-                    bindings_impl(cx, pat, map);
-                }
-            },
-            PatKind::Struct(_, fields, _) => {
-                for pat in fields {
-                    bindings_impl(cx, &pat.pat, map);
-                }
-            },
-            PatKind::Slice(lhs, ref mid, rhs) => {
-                for pat in lhs {
-                    bindings_impl(cx, pat, map);
-                }
-                if let Some(ref mid) = *mid {
-                    bindings_impl(cx, mid, map);
-                }
-                for pat in rhs {
-                    bindings_impl(cx, pat, map);
-                }
-            },
-            PatKind::Lit(..) | PatKind::Range(..) | PatKind::Wild | PatKind::Path(..) => (),
-        }
-    }
-
-    let mut result = FxHashMap::default();
-    bindings_impl(cx, pat, &mut result);
-    result
-}
-
 fn search_same_sequenced<T, Eq>(exprs: &[T], eq: Eq) -> Option<(&T, &T)>
 where
     Eq: Fn(&T, &T) -> bool,
@@ -370,47 +207,3 @@ where
     }
     None
 }
-
-fn search_common_cases<'a, T, Eq>(exprs: &'a [T], eq: &Eq) -> Option<(&'a T, &'a T)>
-where
-    Eq: Fn(&T, &T) -> bool,
-{
-    if exprs.len() == 2 && eq(&exprs[0], &exprs[1]) {
-        Some((&exprs[0], &exprs[1]))
-    } else {
-        None
-    }
-}
-
-fn search_same<T, Hash, Eq>(exprs: &[T], hash: Hash, eq: Eq) -> Vec<(&T, &T)>
-where
-    Hash: Fn(&T) -> u64,
-    Eq: Fn(&T, &T) -> bool,
-{
-    if let Some(expr) = search_common_cases(&exprs, &eq) {
-        return vec![expr];
-    }
-
-    let mut match_expr_list: Vec<(&T, &T)> = Vec::new();
-
-    let mut map: FxHashMap<_, Vec<&_>> =
-        FxHashMap::with_capacity_and_hasher(exprs.len(), BuildHasherDefault::default());
-
-    for expr in exprs {
-        match map.entry(hash(expr)) {
-            Entry::Occupied(mut o) => {
-                for o in o.get() {
-                    if eq(o, expr) {
-                        match_expr_list.push((o, expr));
-                    }
-                }
-                o.get_mut().push(expr);
-            },
-            Entry::Vacant(v) => {
-                v.insert(vec![expr]);
-            },
-        }
-    }
-
-    match_expr_list
-}
diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
index 7c8cb90fe1c..459fdd70443 100644
--- a/clippy_lints/src/lib.rs
+++ b/clippy_lints/src/lib.rs
@@ -528,7 +528,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         &comparison_chain::COMPARISON_CHAIN,
         &copies::IFS_SAME_COND,
         &copies::IF_SAME_THEN_ELSE,
-        &copies::MATCH_SAME_ARMS,
         &copies::SAME_FUNCTIONS_IN_IF_CONDITION,
         &copy_iterator::COPY_ITERATOR,
         &create_dir::CREATE_DIR,
@@ -659,6 +658,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         &matches::MATCH_LIKE_MATCHES_MACRO,
         &matches::MATCH_OVERLAPPING_ARM,
         &matches::MATCH_REF_PATS,
+        &matches::MATCH_SAME_ARMS,
         &matches::MATCH_SINGLE_BINDING,
         &matches::MATCH_WILDCARD_FOR_SINGLE_VARIANTS,
         &matches::MATCH_WILD_ERR_ARM,
@@ -1204,7 +1204,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&attrs::INLINE_ALWAYS),
         LintId::of(&bit_mask::VERBOSE_BIT_MASK),
         LintId::of(&checked_conversions::CHECKED_CONVERSIONS),
-        LintId::of(&copies::MATCH_SAME_ARMS),
         LintId::of(&copies::SAME_FUNCTIONS_IN_IF_CONDITION),
         LintId::of(&copy_iterator::COPY_ITERATOR),
         LintId::of(&default_trait_access::DEFAULT_TRAIT_ACCESS),
@@ -1234,6 +1233,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&map_err_ignore::MAP_ERR_IGNORE),
         LintId::of(&match_on_vec_items::MATCH_ON_VEC_ITEMS),
         LintId::of(&matches::MATCH_BOOL),
+        LintId::of(&matches::MATCH_SAME_ARMS),
         LintId::of(&matches::MATCH_WILDCARD_FOR_SINGLE_VARIANTS),
         LintId::of(&matches::MATCH_WILD_ERR_ARM),
         LintId::of(&matches::SINGLE_MATCH_ELSE),
diff --git a/clippy_lints/src/matches.rs b/clippy_lints/src/matches.rs
index d93433c607f..4bdfca1a292 100644
--- a/clippy_lints/src/matches.rs
+++ b/clippy_lints/src/matches.rs
@@ -1,5 +1,4 @@
 use crate::consts::{constant, miri_to_const, Constant};
-use crate::utils::paths;
 use crate::utils::sugg::Sugg;
 use crate::utils::usage::is_unused;
 use crate::utils::{
@@ -8,8 +7,10 @@ use crate::utils::{
     snippet_block, snippet_with_applicability, span_lint_and_help, span_lint_and_note, span_lint_and_sugg,
     span_lint_and_then,
 };
+use crate::utils::{paths, search_same, SpanlessEq, SpanlessHash};
 use if_chain::if_chain;
 use rustc_ast::ast::LitKind;
+use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::Applicability;
 use rustc_hir::def::CtorKind;
 use rustc_hir::{
@@ -18,10 +19,12 @@ use rustc_hir::{
 };
 use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::lint::in_external_macro;
-use rustc_middle::ty::{self, Ty};
+use rustc_middle::ty::{self, Ty, TyS};
 use rustc_session::{declare_tool_lint, impl_lint_pass};
 use rustc_span::source_map::{Span, Spanned};
+use rustc_span::Symbol;
 use std::cmp::Ordering;
+use std::collections::hash_map::Entry;
 use std::collections::Bound;
 
 declare_clippy_lint! {
@@ -475,6 +478,47 @@ declare_clippy_lint! {
     "a match that could be written with the matches! macro"
 }
 
+declare_clippy_lint! {
+    /// **What it does:** Checks for `match` with identical arm bodies.
+    ///
+    /// **Why is this bad?** This is probably a copy & paste error. If arm bodies
+    /// are the same on purpose, you can factor them
+    /// [using `|`](https://doc.rust-lang.org/book/patterns.html#multiple-patterns).
+    ///
+    /// **Known problems:** False positive possible with order dependent `match`
+    /// (see issue
+    /// [#860](https://github.com/rust-lang/rust-clippy/issues/860)).
+    ///
+    /// **Example:**
+    /// ```rust,ignore
+    /// match foo {
+    ///     Bar => bar(),
+    ///     Quz => quz(),
+    ///     Baz => bar(), // <= oops
+    /// }
+    /// ```
+    ///
+    /// This should probably be
+    /// ```rust,ignore
+    /// match foo {
+    ///     Bar => bar(),
+    ///     Quz => quz(),
+    ///     Baz => baz(), // <= fixed
+    /// }
+    /// ```
+    ///
+    /// or if the original code was not a typo:
+    /// ```rust,ignore
+    /// match foo {
+    ///     Bar | Baz => bar(), // <= shows the intent better
+    ///     Quz => quz(),
+    /// }
+    /// ```
+    pub MATCH_SAME_ARMS,
+    pedantic,
+    "`match` with identical arm bodies"
+}
+
 #[derive(Default)]
 pub struct Matches {
     infallible_destructuring_match_linted: bool,
@@ -495,7 +539,8 @@ impl_lint_pass!(Matches => [
     INFALLIBLE_DESTRUCTURING_MATCH,
     REST_PAT_IN_FULLY_BOUND_STRUCTS,
     REDUNDANT_PATTERN_MATCHING,
-    MATCH_LIKE_MATCHES_MACRO
+    MATCH_LIKE_MATCHES_MACRO,
+    MATCH_SAME_ARMS,
 ]);
 
 impl<'tcx> LateLintPass<'tcx> for Matches {
@@ -505,7 +550,9 @@ impl<'tcx> LateLintPass<'tcx> for Matches {
         }
 
         redundant_pattern_match::check(cx, expr);
-        check_match_like_matches(cx, expr);
+        if !check_match_like_matches(cx, expr) {
+            lint_match_arms(cx, expr);
+        }
 
         if let ExprKind::Match(ref ex, ref arms, MatchSource::Normal) = expr.kind {
             check_single_match(cx, ex, arms, expr);
@@ -1063,32 +1110,47 @@ fn check_wild_in_or_pats(cx: &LateContext<'_>, arms: &[Arm<'_>]) {
 }
 
 /// Lint a `match` or `if let .. { .. } else { .. }` expr that could be replaced by `matches!`
-fn check_match_like_matches<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+fn check_match_like_matches<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
     if let ExprKind::Match(ex, arms, ref match_source) = &expr.kind {
         match match_source {
             MatchSource::Normal => find_matches_sugg(cx, ex, arms, expr, false),
             MatchSource::IfLetDesugar { .. } => find_matches_sugg(cx, ex, arms, expr, true),
-            _ => return,
+            _ => false,
         }
+    } else {
+        false
     }
 }
 
 /// Lint a `match` or desugared `if let` for replacement by `matches!`
-fn find_matches_sugg(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>], expr: &Expr<'_>, desugared: bool) {
+fn find_matches_sugg(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>], expr: &Expr<'_>, desugared: bool) -> bool {
     if_chain! {
-        if arms.len() == 2;
+        if arms.len() >= 2;
         if cx.typeck_results().expr_ty(expr).is_bool();
-        if is_wild(&arms[1].pat);
-        if let Some(first) = find_bool_lit(&arms[0].body.kind, desugared);
-        if let Some(second) = find_bool_lit(&arms[1].body.kind, desugared);
-        if first != second;
+        if let Some((b1_arm, b0_arms)) = arms.split_last();
+        if let Some(b0) = find_bool_lit(&b0_arms[0].body.kind, desugared);
+        if let Some(b1) = find_bool_lit(&b1_arm.body.kind, desugared);
+        if is_wild(&b1_arm.pat);
+        if b0 != b1;
+        let if_guard = &b0_arms[0].guard;
+        if if_guard.is_none() || b0_arms.len() == 1;
+        if b0_arms[1..].iter()
+            .all(|arm| {
+                find_bool_lit(&arm.body.kind, desugared).map_or(false, |b| b == b0) &&
+                arm.guard.is_none()
+            });
         then {
             let mut applicability = Applicability::MachineApplicable;
-
-            let pat_and_guard = if let Some(Guard::If(g)) = arms[0].guard {
-                format!("{} if {}", snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability), snippet_with_applicability(cx, g.span, "..", &mut applicability))
+            let pat = {
+                use itertools::Itertools as _;
+                b0_arms.iter()
+                    .map(|arm| snippet_with_applicability(cx, arm.pat.span, "..", &mut applicability))
+                    .join(" | ")
+            };
+            let pat_and_guard = if let Some(Guard::If(g)) = if_guard {
+                format!("{} if {}", pat, snippet_with_applicability(cx, g.span, "..", &mut applicability))
             } else {
-                format!("{}", snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability))
+                pat
             };
             span_lint_and_sugg(
                 cx,
@@ -1098,12 +1160,15 @@ fn find_matches_sugg(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>], expr
                 "try this",
                 format!(
                     "{}matches!({}, {})",
-                    if first { "" } else { "!" },
+                    if b0 { "" } else { "!" },
                     snippet_with_applicability(cx, ex.span, "..", &mut applicability),
                     pat_and_guard,
                 ),
                 applicability,
-            )
+            );
+            true
+        } else {
+            false
         }
     }
 }
@@ -1657,3 +1722,119 @@ fn test_overlapping() {
         ],)
     );
 }
+
+/// Implementation of `MATCH_SAME_ARMS`.
+fn lint_match_arms<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>) {
+    fn same_bindings<'tcx>(lhs: &FxHashMap<Symbol, Ty<'tcx>>, rhs: &FxHashMap<Symbol, Ty<'tcx>>) -> bool {
+        lhs.len() == rhs.len()
+            && lhs
+                .iter()
+                .all(|(name, l_ty)| rhs.get(name).map_or(false, |r_ty| TyS::same_type(l_ty, r_ty)))
+    }
+
+    if let ExprKind::Match(_, ref arms, MatchSource::Normal) = expr.kind {
+        let hash = |&(_, arm): &(usize, &Arm<'_>)| -> u64 {
+            let mut h = SpanlessHash::new(cx);
+            h.hash_expr(&arm.body);
+            h.finish()
+        };
+
+        let eq = |&(lindex, lhs): &(usize, &Arm<'_>), &(rindex, rhs): &(usize, &Arm<'_>)| -> bool {
+            let min_index = usize::min(lindex, rindex);
+            let max_index = usize::max(lindex, rindex);
+
+            // Arms with a guard are ignored, those can’t always be merged together
+            // This is also the case for arms in-between each there is an arm with a guard
+            (min_index..=max_index).all(|index| arms[index].guard.is_none()) &&
+                SpanlessEq::new(cx).eq_expr(&lhs.body, &rhs.body) &&
+                // all patterns should have the same bindings
+                same_bindings(&bindings(cx, &lhs.pat), &bindings(cx, &rhs.pat))
+        };
+
+        let indexed_arms: Vec<(usize, &Arm<'_>)> = arms.iter().enumerate().collect();
+        for (&(_, i), &(_, j)) in search_same(&indexed_arms, hash, eq) {
+            span_lint_and_then(
+                cx,
+                MATCH_SAME_ARMS,
+                j.body.span,
+                "this `match` has identical arm bodies",
+                |diag| {
+                    diag.span_note(i.body.span, "same as this");
+
+                    // Note: this does not use `span_suggestion` on purpose:
+                    // there is no clean way
+                    // to remove the other arm. Building a span and suggest to replace it to ""
+                    // makes an even more confusing error message. Also in order not to make up a
+                    // span for the whole pattern, the suggestion is only shown when there is only
+                    // one pattern. The user should know about `|` if they are already using it…
+
+                    let lhs = snippet(cx, i.pat.span, "<pat1>");
+                    let rhs = snippet(cx, j.pat.span, "<pat2>");
+
+                    if let PatKind::Wild = j.pat.kind {
+                        // if the last arm is _, then i could be integrated into _
+                        // note that i.pat cannot be _, because that would mean that we're
+                        // hiding all the subsequent arms, and rust won't compile
+                        diag.span_note(
+                            i.body.span,
+                            &format!(
+                                "`{}` has the same arm body as the `_` wildcard, consider removing it",
+                                lhs
+                            ),
+                        );
+                    } else {
+                        diag.span_help(i.pat.span, &format!("consider refactoring into `{} | {}`", lhs, rhs));
+                    }
+                },
+            );
+        }
+    }
+}
+
+/// Returns the list of bindings in a pattern.
+fn bindings<'tcx>(cx: &LateContext<'tcx>, pat: &Pat<'_>) -> FxHashMap<Symbol, Ty<'tcx>> {
+    fn bindings_impl<'tcx>(cx: &LateContext<'tcx>, pat: &Pat<'_>, map: &mut FxHashMap<Symbol, Ty<'tcx>>) {
+        match pat.kind {
+            PatKind::Box(ref pat) | PatKind::Ref(ref pat, _) => bindings_impl(cx, pat, map),
+            PatKind::TupleStruct(_, pats, _) => {
+                for pat in pats {
+                    bindings_impl(cx, pat, map);
+                }
+            },
+            PatKind::Binding(.., ident, ref as_pat) => {
+                if let Entry::Vacant(v) = map.entry(ident.name) {
+                    v.insert(cx.typeck_results().pat_ty(pat));
+                }
+                if let Some(ref as_pat) = *as_pat {
+                    bindings_impl(cx, as_pat, map);
+                }
+            },
+            PatKind::Or(fields) | PatKind::Tuple(fields, _) => {
+                for pat in fields {
+                    bindings_impl(cx, pat, map);
+                }
+            },
+            PatKind::Struct(_, fields, _) => {
+                for pat in fields {
+                    bindings_impl(cx, &pat.pat, map);
+                }
+            },
+            PatKind::Slice(lhs, ref mid, rhs) => {
+                for pat in lhs {
+                    bindings_impl(cx, pat, map);
+                }
+                if let Some(ref mid) = *mid {
+                    bindings_impl(cx, mid, map);
+                }
+                for pat in rhs {
+                    bindings_impl(cx, pat, map);
+                }
+            },
+            PatKind::Lit(..) | PatKind::Range(..) | PatKind::Wild | PatKind::Path(..) => (),
+        }
+    }
+
+    let mut result = FxHashMap::default();
+    bindings_impl(cx, pat, &mut result);
+    result
+}
diff --git a/clippy_lints/src/utils/mod.rs b/clippy_lints/src/utils/mod.rs
index a1ecca0961a..0a8a4a5f9ae 100644
--- a/clippy_lints/src/utils/mod.rs
+++ b/clippy_lints/src/utils/mod.rs
@@ -27,11 +27,14 @@ pub use self::diagnostics::*;
 pub use self::hir_utils::{both, eq_expr_value, over, SpanlessEq, SpanlessHash};
 
 use std::borrow::Cow;
+use std::collections::hash_map::Entry;
+use std::hash::BuildHasherDefault;
 use std::mem;
 
 use if_chain::if_chain;
 use rustc_ast::ast::{self, Attribute, LitKind};
 use rustc_attr as attr;
+use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
@@ -1465,6 +1468,41 @@ pub fn is_slice_of_primitives(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<S
     None
 }
 
+/// returns list of all pairs (a, b) from `exprs` such that `eq(a, b)`
+/// `hash` must be comformed with `eq`
+pub fn search_same<T, Hash, Eq>(exprs: &[T], hash: Hash, eq: Eq) -> Vec<(&T, &T)>
+where
+    Hash: Fn(&T) -> u64,
+    Eq: Fn(&T, &T) -> bool,
+{
+    if exprs.len() == 2 && eq(&exprs[0], &exprs[1]) {
+        return vec![(&exprs[0], &exprs[1])];
+    }
+
+    let mut match_expr_list: Vec<(&T, &T)> = Vec::new();
+
+    let mut map: FxHashMap<_, Vec<&_>> =
+        FxHashMap::with_capacity_and_hasher(exprs.len(), BuildHasherDefault::default());
+
+    for expr in exprs {
+        match map.entry(hash(expr)) {
+            Entry::Occupied(mut o) => {
+                for o in o.get() {
+                    if eq(o, expr) {
+                        match_expr_list.push((o, expr));
+                    }
+                }
+                o.get_mut().push(expr);
+            },
+            Entry::Vacant(v) => {
+                v.insert(vec![expr]);
+            },
+        }
+    }
+
+    match_expr_list
+}
+
 #[macro_export]
 macro_rules! unwrap_cargo_metadata {
     ($cx: ident, $lint: ident, $deps: expr) => {{
diff --git a/src/lintlist/mod.rs b/src/lintlist/mod.rs
index 6272ce45efb..aba436e5c02 100644
--- a/src/lintlist/mod.rs
+++ b/src/lintlist/mod.rs
@@ -1304,7 +1304,7 @@ vec![
         group: "pedantic",
         desc: "`match` with identical arm bodies",
         deprecation: None,
-        module: "copies",
+        module: "matches",
     },
     Lint {
         name: "match_single_binding",
diff --git a/tests/ui/match_expr_like_matches_macro.fixed b/tests/ui/match_expr_like_matches_macro.fixed
index f3e19092480..7f4ebf56673 100644
--- a/tests/ui/match_expr_like_matches_macro.fixed
+++ b/tests/ui/match_expr_like_matches_macro.fixed
@@ -1,7 +1,7 @@
 // run-rustfix
 
 #![warn(clippy::match_like_matches_macro)]
-#![allow(unreachable_patterns)]
+#![allow(unreachable_patterns, dead_code)]
 
 fn main() {
     let x = Some(5);
@@ -33,4 +33,70 @@ fn main() {
         _ => true,
         None => false,
     };
+
+    enum E {
+        A(u32),
+        B(i32),
+        C,
+        D,
+    };
+    let x = E::A(2);
+    {
+        // lint
+        let _ans = matches!(x, E::A(_) | E::B(_));
+    }
+    {
+        // lint
+        let _ans = !matches!(x, E::B(_) | E::C);
+    }
+    {
+        // no lint
+        let _ans = match x {
+            E::A(_) => false,
+            E::B(_) => false,
+            E::C => true,
+            _ => true,
+        };
+    }
+    {
+        // no lint
+        let _ans = match x {
+            E::A(_) => true,
+            E::B(_) => false,
+            E::C => false,
+            _ => true,
+        };
+    }
+    {
+        // no lint
+        let _ans = match x {
+            E::A(a) if a < 10 => false,
+            E::B(a) if a < 10 => false,
+            _ => true,
+        };
+    }
+    {
+        // no lint
+        let _ans = match x {
+            E::A(_) => false,
+            E::B(a) if a < 10 => false,
+            _ => true,
+        };
+    }
+    {
+        // no lint
+        let _ans = match x {
+            E::A(a) => a == 10,
+            E::B(_) => false,
+            _ => true,
+        };
+    }
+    {
+        // no lint
+        let _ans = match x {
+            E::A(_) => false,
+            E::B(_) => true,
+            _ => false,
+        };
+    }
 }
diff --git a/tests/ui/match_expr_like_matches_macro.rs b/tests/ui/match_expr_like_matches_macro.rs
index fbae7c18b92..aee56dd4a5e 100644
--- a/tests/ui/match_expr_like_matches_macro.rs
+++ b/tests/ui/match_expr_like_matches_macro.rs
@@ -1,7 +1,7 @@
 // run-rustfix
 
 #![warn(clippy::match_like_matches_macro)]
-#![allow(unreachable_patterns)]
+#![allow(unreachable_patterns, dead_code)]
 
 fn main() {
     let x = Some(5);
@@ -45,4 +45,78 @@ fn main() {
         _ => true,
         None => false,
     };
+
+    enum E {
+        A(u32),
+        B(i32),
+        C,
+        D,
+    };
+    let x = E::A(2);
+    {
+        // lint
+        let _ans = match x {
+            E::A(_) => true,
+            E::B(_) => true,
+            _ => false,
+        };
+    }
+    {
+        // lint
+        let _ans = match x {
+            E::B(_) => false,
+            E::C => false,
+            _ => true,
+        };
+    }
+    {
+        // no lint
+        let _ans = match x {
+            E::A(_) => false,
+            E::B(_) => false,
+            E::C => true,
+            _ => true,
+        };
+    }
+    {
+        // no lint
+        let _ans = match x {
+            E::A(_) => true,
+            E::B(_) => false,
+            E::C => false,
+            _ => true,
+        };
+    }
+    {
+        // no lint
+        let _ans = match x {
+            E::A(a) if a < 10 => false,
+            E::B(a) if a < 10 => false,
+            _ => true,
+        };
+    }
+    {
+        // no lint
+        let _ans = match x {
+            E::A(_) => false,
+            E::B(a) if a < 10 => false,
+            _ => true,
+        };
+    }
+    {
+        // no lint
+        let _ans = match x {
+            E::A(a) => a == 10,
+            E::B(_) => false,
+            _ => true,
+        };
+    }
+    {
+        // no lint
+        let _ans = match x {
+            E::A(_) => false,
+            E::B(_) => true,
+            _ => false,
+        };
+    }
 }
diff --git a/tests/ui/match_expr_like_matches_macro.stderr b/tests/ui/match_expr_like_matches_macro.stderr
index 4668f8565a6..c52e41c7889 100644
--- a/tests/ui/match_expr_like_matches_macro.stderr
+++ b/tests/ui/match_expr_like_matches_macro.stderr
@@ -48,5 +48,27 @@ error: if let .. else expression looks like `matches!` macro
 LL |     let _zzz = if let Some(5) = x { true } else { false };
    |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `matches!(x, Some(5))`
 
-error: aborting due to 5 previous errors
+error: match expression looks like `matches!` macro
+  --> $DIR/match_expr_like_matches_macro.rs:58:20
+   |
+LL |           let _ans = match x {
+   |  ____________________^
+LL | |             E::A(_) => true,
+LL | |             E::B(_) => true,
+LL | |             _ => false,
+LL | |         };
+   | |_________^ help: try this: `matches!(x, E::A(_) | E::B(_))`
+
+error: match expression looks like `matches!` macro
+  --> $DIR/match_expr_like_matches_macro.rs:66:20
+   |
+LL |           let _ans = match x {
+   |  ____________________^
+LL | |             E::B(_) => false,
+LL | |             E::C => false,
+LL | |             _ => true,
+LL | |         };
+   | |_________^ help: try this: `!matches!(x, E::B(_) | E::C)`
+
+error: aborting due to 7 previous errors
 
diff --git a/tests/ui/match_same_arms2.rs b/tests/ui/match_same_arms2.rs
index e1401d2796a..06d91497242 100644
--- a/tests/ui/match_same_arms2.rs
+++ b/tests/ui/match_same_arms2.rs
@@ -119,6 +119,22 @@ fn match_same_arms() {
             unreachable!();
         },
     }
+
+    match_expr_like_matches_macro_priority();
+}
+
+fn match_expr_like_matches_macro_priority() {
+    enum E {
+        A,
+        B,
+        C,
+    }
+    let x = E::A;
+    let _ans = match x {
+        E::A => false,
+        E::B => false,
+        _ => true,
+    };
 }
 
 fn main() {}
diff --git a/tests/ui/match_same_arms2.stderr b/tests/ui/match_same_arms2.stderr
index 26c65f32ad7..fccaf805616 100644
--- a/tests/ui/match_same_arms2.stderr
+++ b/tests/ui/match_same_arms2.stderr
@@ -141,5 +141,18 @@ LL |         Ok(3) => println!("ok"),
    |         ^^^^^
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 7 previous errors
+error: match expression looks like `matches!` macro
+  --> $DIR/match_same_arms2.rs:133:16
+   |
+LL |       let _ans = match x {
+   |  ________________^
+LL | |         E::A => false,
+LL | |         E::B => false,
+LL | |         _ => true,
+LL | |     };
+   | |_____^ help: try this: `!matches!(x, E::A | E::B)`
+   |
+   = note: `-D clippy::match-like-matches-macro` implied by `-D warnings`
+
+error: aborting due to 8 previous errors