Fix #78549

Before #78430, string literals worked because `specialize_constructor`
didn't actually care too much which constructor was passed to it unless
needed. Since then, string literals are special cased and a bit hacky. I
did not anticipate patterns for the `&str` type other than string
literals, hence this bug. This makes string literals less hacky.

src/test/ui/issues/issue-30240.rs

@@ -1,9 +1,9 @@
 fn main() {
-    match "world" { //~ ERROR non-exhaustive patterns: `_`
+    match "world" { //~ ERROR non-exhaustive patterns: `&_`
         "hello" => {}
     }
 
-    match "world" { //~ ERROR non-exhaustive patterns: `_`
+    match "world" { //~ ERROR non-exhaustive patterns: `&_`
         ref _x if false => {}
         "hello" => {}
     }

src/test/ui/issues/issue-30240.stderr

@@ -1,17 +1,17 @@
-error[E0004]: non-exhaustive patterns: `_` not covered
+error[E0004]: non-exhaustive patterns: `&_` not covered
   --> $DIR/issue-30240.rs:2:11
    |
 LL |     match "world" {
-   |           ^^^^^^^ pattern `_` not covered
+   |           ^^^^^^^ pattern `&_` not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
    = note: the matched value is of type `&str`
 
-error[E0004]: non-exhaustive patterns: `_` not covered
+error[E0004]: non-exhaustive patterns: `&_` not covered
   --> $DIR/issue-30240.rs:6:11
    |
 LL |     match "world" {
-   |           ^^^^^^^ pattern `_` not covered
+   |           ^^^^^^^ pattern `&_` not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
    = note: the matched value is of type `&str`

src/test/ui/pattern/usefulness/issue-78549-ref-pat-and-str.rs

@@ -0,0 +1,25 @@
+// check-pass
+// From https://github.com/rust-lang/rust/issues/78549
+
+fn main() {
+    match "foo" {
+        "foo" => {},
+        &_ => {},
+    }
+
+    match "foo" {
+        &_ => {},
+        "foo" => {},
+    }
+
+    match ("foo", 0, "bar") {
+        (&_, 0, &_) => {},
+        ("foo", _, "bar") => {},
+        (&_, _, &_) => {},
+    }
+
+    match (&"foo", "bar") {
+        (&"foo", &_) => {},
+        (&&_, &_) => {},
+    }
+}