Keep track of patterns that could have introduced a binding, but didn't

When we recover from a pattern parse error, or a pattern uses `..`, we keep track of that and affect resolution error for missing bindings that could have been provided by that pattern. We differentiate between `..` and parse recovery. We silence resolution errors likely caused by the pattern parse error.

```
error[E0425]: cannot find value `title` in this scope
  --> $DIR/struct-pattern-with-missing-fields-resolve-error.rs:19:30
   |
LL |         println!("[{}]({})", title, url);
   |                              ^^^^^ not found in this scope
   |
note: `Website` has a field `title` which could have been included in this pattern, but it wasn't
  --> $DIR/struct-pattern-with-missing-fields-resolve-error.rs:17:12
   |
LL | / struct Website {
LL | |     url: String,
LL | |     title: Option<String> ,
   | |     ----- defined here
LL | | }
   | |_-
...
LL |       if let Website { url, .. } = website {
   |              ^^^^^^^^^^^^^^^^^^^ this pattern doesn't include `title`, which is available in `Website`
```

Fix #74863.

1 files changed, 4 insertions, 1 deletions

diff --git a/compiler/rustc_ast_pretty/src/pprust/state.rs b/compiler/rustc_ast_pretty/src/pprust/state.rs
index 49e4a559e73..c6f106c3388 100644
--- a/compiler/rustc_ast_pretty/src/pprust/state.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state.rs
@@ -1653,11 +1653,14 @@ impl<'a> State<'a> {
                     },
                     |f| f.pat.span,
                 );
-                if *etc == ast::PatFieldsRest::Rest {
+                if let ast::PatFieldsRest::Rest | ast::PatFieldsRest::Recovered(_) = etc {
                     if !fields.is_empty() {
                         self.word_space(",");
                     }
                     self.word("..");
+                    if let ast::PatFieldsRest::Recovered(_) = etc {
+                        self.word("/* recovered parse error */");
+                    }
                 }
                 if !empty {
                     self.space();