Add long error explanation for E0533

src/librustc_typeck/error_codes.rs

@@ -3610,6 +3610,43 @@ match r {
 ```
 "##,
 
+E0533: r##"
+An item which isn't a unit struct, a variant, nor a constant has been used as a
+match pattern.
+
+Erroneous code example:
+
+```compile_fail,E0533
+struct Tortoise;
+
+impl Tortoise {
+    fn turtle(&self) -> u32 { 0 }
+}
+
+match 0u32 {
+    Tortoise::turtle => {} // Error!
+    _ => {}
+}
+if let Tortoise::turtle = 0u32 {} // Same error!
+```
+
+If you want to match against a value returned by a method, you need to bind the
+value first:
+
+```
+struct Tortoise;
+
+impl Tortoise {
+    fn turtle(&self) -> u32 { 0 }
+}
+
+match 0u32 {
+    x if x == Tortoise.turtle() => {} // Bound into `x` then we compare it!
+    _ => {}
+}
+```
+"##,
+
 E0534: r##"
 The `inline` attribute was malformed.
 
@@ -4935,7 +4972,6 @@ and the pin is required to keep it in the same place in memory.
     E0377, // the trait `CoerceUnsized` may only be implemented for a coercion
            // between structures with the same definition
 //  E0558, // replaced with a generic attribute input check
-    E0533, // `{}` does not name a unit variant, unit struct or a constant
 //  E0563, // cannot determine a type for this `impl Trait` removed in 6383de15
     E0564, // only named lifetimes are allowed in `impl Trait`,
            // but `{}` was found in the type `{}`

src/test/ui/methods/method-path-in-pattern.rs

@@ -23,4 +23,10 @@ fn main() {
         <Foo>::trait_bar => {}
         //~^ ERROR expected unit struct/variant or constant, found method `<Foo>::trait_bar`
     }
+    if let Foo::bar = 0u32 {}
+    //~^ ERROR expected unit struct/variant or constant, found method `<Foo>::bar`
+    if let <Foo>::bar = 0u32 {}
+    //~^ ERROR expected unit struct/variant or constant, found method `<Foo>::bar`
+    if let Foo::trait_bar = 0u32 {}
+    //~^ ERROR expected unit struct/variant or constant, found method `<Foo>::trait_bar`
 }

src/test/ui/methods/method-path-in-pattern.stderr

@@ -16,5 +16,24 @@ error[E0533]: expected unit struct/variant or constant, found method `<Foo>::tra
 LL |         <Foo>::trait_bar => {}
    |         ^^^^^^^^^^^^^^^^
 
-error: aborting due to 3 previous errors
+error[E0533]: expected unit struct/variant or constant, found method `<Foo>::bar`
+  --> $DIR/method-path-in-pattern.rs:26:12
+   |
+LL |     if let Foo::bar = 0u32 {}
+   |            ^^^^^^^^
+
+error[E0533]: expected unit struct/variant or constant, found method `<Foo>::bar`
+  --> $DIR/method-path-in-pattern.rs:28:12
+   |
+LL |     if let <Foo>::bar = 0u32 {}
+   |            ^^^^^^^^^^
+
+error[E0533]: expected unit struct/variant or constant, found method `<Foo>::trait_bar`
+  --> $DIR/method-path-in-pattern.rs:30:12
+   |
+LL |     if let Foo::trait_bar = 0u32 {}
+   |            ^^^^^^^^^^^^^^
+
+error: aborting due to 6 previous errors
 
+For more information about this error, try `rustc --explain E0533`.

src/test/ui/qualified/qualified-path-params.stderr

@@ -15,4 +15,5 @@ LL |         0 ..= <S as Tr>::A::f::<u8> => {}
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0029`.
+Some errors have detailed explanations: E0029, E0533.
+For more information about an error, try `rustc --explain E0029`.

src/test/ui/type-alias-enum-variants/incorrect-variant-form-through-Self-issue-58006.stderr

@@ -6,3 +6,4 @@ LL |             Self::A => (),
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0533`.

src/test/ui/type-alias-enum-variants/incorrect-variant-form-through-alias-caught.stderr

@@ -39,5 +39,5 @@ LL |     let Alias::Unit() = panic!();
 
 error: aborting due to 5 previous errors
 
-Some errors have detailed explanations: E0164, E0618.
+Some errors have detailed explanations: E0164, E0533, E0618.
 For more information about an error, try `rustc --explain E0164`.