document the new behavior and add test for float in struct

Author: y21

clippy_lints/src/matches/redundant_guards.rs

@@ -161,6 +161,11 @@ fn emit_redundant_guards<'tcx>(
 }
 
 /// Checks if the given `Expr` can also be represented as a `Pat`.
+///
+/// All literals generally also work as patterns, however float literals are special.
+/// They are currently (as of 2023/08/08) still allowed in patterns, but that will become
+/// an error in the future, and rustc already actively warns against this (see rust#41620),
+/// so we don't consider those as usable within patterns for linting purposes.
 fn expr_can_be_pat(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
     for_each_expr(expr, |expr| {
         if match expr.kind {

tests/ui/redundant_guards.fixed

@@ -15,11 +15,17 @@ struct B {
 
 struct C(u32, u32);
 
+#[derive(PartialEq)]
+struct FloatWrapper(f32);
 fn issue11304() {
     match 0.1 {
         x if x == 0.0 => todo!(),
         _ => todo!(),
     }
+    match FloatWrapper(0.1) {
+        x if x == FloatWrapper(0.0) => todo!(),
+        _ => todo!(),
+    }
 }
 
 fn main() {

tests/ui/redundant_guards.rs

@@ -15,11 +15,17 @@ struct B {
 
 struct C(u32, u32);
 
+#[derive(PartialEq)]
+struct FloatWrapper(f32);
 fn issue11304() {
     match 0.1 {
         x if x == 0.0 => todo!(),
         _ => todo!(),
     }
+    match FloatWrapper(0.1) {
+        x if x == FloatWrapper(0.0) => todo!(),
+        _ => todo!(),
+    }
 }
 
 fn main() {

tests/ui/redundant_guards.stderr

@@ -1,5 +1,5 @@
 error: redundant guard
-  --> $DIR/redundant_guards.rs:28:20
+  --> $DIR/redundant_guards.rs:34:20
    |
 LL |         C(x, y) if let 1 = y => ..,
    |                    ^^^^^^^^^
@@ -12,7 +12,7 @@ LL +         C(x, 1) => ..,
    |
 
 error: redundant guard
-  --> $DIR/redundant_guards.rs:34:20
+  --> $DIR/redundant_guards.rs:40:20
    |
 LL |         Some(x) if matches!(x, Some(1) if true) => ..,
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -23,7 +23,7 @@ LL |         Some(Some(1)) if true => ..,
    |              ~~~~~~~  ~~~~~~~
 
 error: redundant guard
-  --> $DIR/redundant_guards.rs:35:20
+  --> $DIR/redundant_guards.rs:41:20
    |
 LL |         Some(x) if matches!(x, Some(1)) => {
    |                    ^^^^^^^^^^^^^^^^^^^^
@@ -35,7 +35,7 @@ LL +         Some(Some(1)) => {
    |
 
 error: redundant guard
-  --> $DIR/redundant_guards.rs:39:20
+  --> $DIR/redundant_guards.rs:45:20
    |
 LL |         Some(x) if let Some(1) = x => ..,
    |                    ^^^^^^^^^^^^^^^
@@ -47,7 +47,7 @@ LL +         Some(Some(1)) => ..,
    |
 
 error: redundant guard
-  --> $DIR/redundant_guards.rs:40:20
+  --> $DIR/redundant_guards.rs:46:20
    |
 LL |         Some(x) if x == Some(2) => ..,
    |                    ^^^^^^^^^^^^
@@ -59,7 +59,7 @@ LL +         Some(Some(2)) => ..,
    |
 
 error: redundant guard
-  --> $DIR/redundant_guards.rs:63:20
+  --> $DIR/redundant_guards.rs:69:20
    |
 LL |         B { e } if matches!(e, Some(A(2))) => ..,
    |                    ^^^^^^^^^^^^^^^^^^^^^^^
@@ -71,7 +71,7 @@ LL +         B { e: Some(A(2)) } => ..,
    |
 
 error: redundant guard
-  --> $DIR/redundant_guards.rs:100:20
+  --> $DIR/redundant_guards.rs:106:20
    |
 LL |         E::A(y) if y == "not from an or pattern" => {},
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -83,7 +83,7 @@ LL +         E::A("not from an or pattern") => {},
    |
 
 error: redundant guard
-  --> $DIR/redundant_guards.rs:107:14
+  --> $DIR/redundant_guards.rs:113:14
    |
 LL |         x if matches!(x, Some(0)) => ..,
    |              ^^^^^^^^^^^^^^^^^^^^