Auto merge of rust-lang#9368 - nahuakang:improve-equatable-if-let, r=…

…flip1995

Improvement for  `equatable_if_let`

fixes rust-lang#9221

This PR makes sure that enums or structs not implementing `PartialEq` trait but still using the `if let` patterns can be linted to be rewritten with `matches!`.

If you added a new lint, here's a checklist for things that will be
checked during review or continuous integration.

- \[ ] Followed [lint naming conventions][lint_naming]
- \[x] Added passing UI tests (including committed `.stderr` file)
- \[x] `cargo test` passes locally
- \[ ] Executed `cargo dev update_lints`
- \[ ] Added lint documentation
- \[x] Run `cargo dev fmt`

---

changelog: Improve [`equatable_if_let`] with additional `matches!` suggestions.

clippy_lints/src/equatable_if_let.rs

@@ -1,7 +1,6 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::source::snippet_with_context;
 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, LintContext};
@@ -67,16 +66,14 @@ fn is_structural_partial_eq<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, other: T
 
 impl<'tcx> LateLintPass<'tcx> for PatternEquality {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
-        if_chain! {
-            if !in_external_macro(cx.sess(), expr.span);
-            if let ExprKind::Let(let_expr) = expr.kind;
-            if unary_pattern(let_expr.pat);
+        if !in_external_macro(cx.sess(), expr.span)
+            && let ExprKind::Let(let_expr) = expr.kind
+            && unary_pattern(let_expr.pat) {
             let exp_ty = cx.typeck_results().expr_ty(let_expr.init);
             let pat_ty = cx.typeck_results().pat_ty(let_expr.pat);
-            if is_structural_partial_eq(cx, exp_ty, pat_ty);
-            then {
+            let mut applicability = Applicability::MachineApplicable;
 
-                let mut applicability = Applicability::MachineApplicable;
+            if is_structural_partial_eq(cx, exp_ty, pat_ty) {
                 let pat_str = match let_expr.pat.kind {
                     PatKind::Struct(..) => format!(
                         "({})",
@@ -96,6 +93,20 @@ impl<'tcx> LateLintPass<'tcx> for PatternEquality {
                     ),
                     applicability,
                 );
+            } else {
+                span_lint_and_sugg(
+                    cx,
+                    EQUATABLE_IF_LET,
+                    expr.span,
+                    "this pattern matching can be expressed using `matches!`",
+                    "try",
+                    format!(
+                        "matches!({}, {})",
+                        snippet_with_context(cx, let_expr.init.span, expr.span.ctxt(), "..", &mut applicability).0,
+                        snippet_with_context(cx, let_expr.pat.span, expr.span.ctxt(), "..", &mut applicability).0,
+                    ),
+                    applicability,
+                );
             }
         }
     }

tests/ui/equatable_if_let.fixed

@@ -23,6 +23,11 @@ struct Struct {
     b: bool,
 }
 
+struct NoPartialEqStruct {
+    a: i32,
+    b: bool,
+}
+
 enum NotPartialEq {
     A,
     B,
@@ -47,6 +52,7 @@ fn main() {
     let e = Enum::UnitVariant;
     let f = NotPartialEq::A;
     let g = NotStructuralEq::A;
+    let h = NoPartialEqStruct { a: 2, b: false };
 
     // true
 
@@ -66,10 +72,11 @@ fn main() {
     if let Some(3 | 4) = c {}
     if let Struct { a, b: false } = d {}
     if let Struct { a: 2, b: x } = d {}
-    if let NotPartialEq::A = f {}
+    if matches!(f, NotPartialEq::A) {}
     if g == NotStructuralEq::A {}
-    if let Some(NotPartialEq::A) = Some(f) {}
+    if matches!(Some(f), Some(NotPartialEq::A)) {}
     if Some(g) == Some(NotStructuralEq::A) {}
+    if matches!(h, NoPartialEqStruct { a: 2, b: false }) {}
 
     macro_rules! m1 {
         (x) => {

tests/ui/equatable_if_let.rs

@@ -23,6 +23,11 @@ struct Struct {
     b: bool,
 }
 
+struct NoPartialEqStruct {
+    a: i32,
+    b: bool,
+}
+
 enum NotPartialEq {
     A,
     B,
@@ -47,6 +52,7 @@ fn main() {
     let e = Enum::UnitVariant;
     let f = NotPartialEq::A;
     let g = NotStructuralEq::A;
+    let h = NoPartialEqStruct { a: 2, b: false };
 
     // true
 
@@ -70,6 +76,7 @@ fn main() {
     if let NotStructuralEq::A = g {}
     if let Some(NotPartialEq::A) = Some(f) {}
     if let Some(NotStructuralEq::A) = Some(g) {}
+    if let NoPartialEqStruct { a: 2, b: false } = h {}
 
     macro_rules! m1 {
         (x) => {

tests/ui/equatable_if_let.stderr

@@ -1,70 +1,88 @@
 error: this pattern matching can be expressed using equality
-  --> $DIR/equatable_if_let.rs:53:8
+  --> $DIR/equatable_if_let.rs:59:8
    |
 LL |     if let 2 = a {}
    |        ^^^^^^^^^ help: try: `a == 2`
    |
    = note: `-D clippy::equatable-if-let` implied by `-D warnings`
 
 error: this pattern matching can be expressed using equality
-  --> $DIR/equatable_if_let.rs:54:8
+  --> $DIR/equatable_if_let.rs:60:8
    |
 LL |     if let Ordering::Greater = a.cmp(&b) {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `a.cmp(&b) == Ordering::Greater`
 
 error: this pattern matching can be expressed using equality
-  --> $DIR/equatable_if_let.rs:55:8
+  --> $DIR/equatable_if_let.rs:61:8
    |
 LL |     if let Some(2) = c {}
    |        ^^^^^^^^^^^^^^^ help: try: `c == Some(2)`
 
 error: this pattern matching can be expressed using equality
-  --> $DIR/equatable_if_let.rs:56:8
+  --> $DIR/equatable_if_let.rs:62:8
    |
 LL |     if let Struct { a: 2, b: false } = d {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `d == (Struct { a: 2, b: false })`
 
 error: this pattern matching can be expressed using equality
-  --> $DIR/equatable_if_let.rs:57:8
+  --> $DIR/equatable_if_let.rs:63:8
    |
 LL |     if let Enum::TupleVariant(32, 64) = e {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `e == Enum::TupleVariant(32, 64)`
 
 error: this pattern matching can be expressed using equality
-  --> $DIR/equatable_if_let.rs:58:8
+  --> $DIR/equatable_if_let.rs:64:8
    |
 LL |     if let Enum::RecordVariant { a: 64, b: 32 } = e {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `e == (Enum::RecordVariant { a: 64, b: 32 })`
 
 error: this pattern matching can be expressed using equality
-  --> $DIR/equatable_if_let.rs:59:8
+  --> $DIR/equatable_if_let.rs:65:8
    |
 LL |     if let Enum::UnitVariant = e {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `e == Enum::UnitVariant`
 
 error: this pattern matching can be expressed using equality
-  --> $DIR/equatable_if_let.rs:60:8
+  --> $DIR/equatable_if_let.rs:66:8
    |
 LL |     if let (Enum::UnitVariant, &Struct { a: 2, b: false }) = (e, &d) {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `(e, &d) == (Enum::UnitVariant, &Struct { a: 2, b: false })`
 
+error: this pattern matching can be expressed using `matches!`
+  --> $DIR/equatable_if_let.rs:75:8
+   |
+LL |     if let NotPartialEq::A = f {}
+   |        ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `matches!(f, NotPartialEq::A)`
+
 error: this pattern matching can be expressed using equality
-  --> $DIR/equatable_if_let.rs:70:8
+  --> $DIR/equatable_if_let.rs:76:8
    |
 LL |     if let NotStructuralEq::A = g {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `g == NotStructuralEq::A`
 
+error: this pattern matching can be expressed using `matches!`
+  --> $DIR/equatable_if_let.rs:77:8
+   |
+LL |     if let Some(NotPartialEq::A) = Some(f) {}
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `matches!(Some(f), Some(NotPartialEq::A))`
+
 error: this pattern matching can be expressed using equality
-  --> $DIR/equatable_if_let.rs:72:8
+  --> $DIR/equatable_if_let.rs:78:8
    |
 LL |     if let Some(NotStructuralEq::A) = Some(g) {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Some(g) == Some(NotStructuralEq::A)`
 
-error: this pattern matching can be expressed using equality
+error: this pattern matching can be expressed using `matches!`
   --> $DIR/equatable_if_let.rs:79:8
    |
+LL |     if let NoPartialEqStruct { a: 2, b: false } = h {}
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `matches!(h, NoPartialEqStruct { a: 2, b: false })`
+
+error: this pattern matching can be expressed using equality
+  --> $DIR/equatable_if_let.rs:86:8
+   |
 LL |     if let m1!(x) = "abc" {
    |        ^^^^^^^^^^^^^^^^^^ help: try: `"abc" == m1!(x)`
 
-error: aborting due to 11 previous errors
+error: aborting due to 14 previous errors