Rollup merge of #33584 - GuillaumeGomez:error_code_improvements, r=steveklabnik

Add more details and examples in error codes

r? @steveklabnik

src/librustc_const_eval/diagnostics.rs

@@ -62,8 +62,6 @@ fn foo(x: Empty) {
 However, this won't:
 
 ```compile_fail
-enum Empty {}
-
 fn foo(x: Option<String>) {
     match x {
         // empty
@@ -191,7 +189,7 @@ enum Terminator {
 let x = Some("s".to_string());
 
 match x {
-    op_string @ Some(s) => {},
+    op_string @ Some(s) => {}, // error: cannot bind by-move with sub-bindings
     None => {},
 }
 ```
@@ -288,7 +286,8 @@ struct X { x: (), }
 
 let x = Some((X { x: () }, X { x: () }));
 match x {
-    Some((y, ref z)) => {},
+    Some((y, ref z)) => {}, // error: cannot bind by-move and by-ref in the
+                            //        same pattern
     None => panic!()
 }
 ```
@@ -574,6 +573,12 @@ enum Method { GET, POST }
     let x = [0i32; len]; // error: expected constant integer for repeat count,
                          //        found variable
 ```
+
+Working example:
+
+```
+let x = [0i32; 10];
+```
 "##,
 
 }

src/librustc_typeck/diagnostics.rs

@@ -45,8 +45,8 @@ enum Fruit {
 
 ```compile_fail
 enum Fruit {
-    Apple(String, String),
-    Pear(u32),
+    Fruit::Apple(String, String),
+    Fruit::Pear(u32),
 }
 
 let x = Fruit::Apple(String::new(), String::new());
@@ -77,8 +77,8 @@ enum Number {
 
 // Assuming x is a Number we can pattern match on its contents.
 match x {
-    Zero(inside) => {},
-    One(inside) => {},
+    Number::Zero(inside) => {},
+    Number::One(inside) => {},
 }
 ```