Fix unwrap ICE from struct field ident in AST pretty

compiler/rustc_ast_pretty/src/pprust/state/item.rs

@@ -524,7 +524,11 @@ impl<'a> State<'a> {
                         self.maybe_print_comment(field.span.lo());
                         self.print_outer_attributes(&field.attrs);
                         self.print_visibility(&field.vis);
-                        self.print_ident(field.ident.unwrap());
+                        if let Some(ident) = field.ident {
+                            self.print_ident(ident);
+                        } else {
+                            self.word("_");
+                        }
                         self.word_nbsp(":");
                         self.print_type(&field.ty);
                         self.word(",");

tests/ui/structs/struct-field-ident-issue-140333.rs

@@ -0,0 +1,12 @@
+fn a() -> impl b< //~ ERROR cannot find trait `b` in this scope
+    [c; { //~ ERROR cannot find type `c` in this scope
+    struct D {
+            #[a] //~ ERROR annot find attribute `a` in this scope
+            bar: e, //~ ERROR cannot find type `e` in this scope
+        }
+    }],
+> {
+    todo!("need to implement")
+}
+
+fn main() {}

tests/ui/structs/struct-field-ident-issue-140333.stderr

@@ -0,0 +1,40 @@
+error: cannot find attribute `a` in this scope
+  --> $DIR/struct-field-ident-issue-140333.rs:4:15
+   |
+LL |             #[a]
+   |               ^
+   |
+   = note: `a` is in scope, but it is a function, not an attribute
+
+error[E0405]: cannot find trait `b` in this scope
+  --> $DIR/struct-field-ident-issue-140333.rs:1:16
+   |
+LL | fn a() -> impl b<
+   |                ^ not found in this scope
+
+error[E0412]: cannot find type `c` in this scope
+  --> $DIR/struct-field-ident-issue-140333.rs:2:6
+   |
+LL |     [c; {
+   |      ^ not found in this scope
+   |
+help: you might be missing a type parameter
+   |
+LL | fn a<c>() -> impl b<
+   |     +++
+
+error[E0412]: cannot find type `e` in this scope
+  --> $DIR/struct-field-ident-issue-140333.rs:5:18
+   |
+LL |             bar: e,
+   |                  ^ not found in this scope
+   |
+help: you might be missing a type parameter
+   |
+LL |     struct D<e> {
+   |             +++
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0405, E0412.
+For more information about an error, try `rustc --explain E0405`.