Auto merge of rust-lang#16752 - Lindronics:destructure-struct-binding, r=Veykril

fix: Don't destructure struct with no public fields

Unfortunately I missed this case in rust-lang#16638.

If a struct only has private members, the assist should not be applicable. Though valid syntax exists (`Foo { .. }`), it isn't particularly useful. Since this case applies to a lot of common types (`Arc`, `Vec`, ...), it probably makes the most sense to hide the action.

As a side effect, this also disables the action for unit structs, where it also isn't particularly useful. I'd be open to changing it though if you think it makes more sense to keep it.

This also fixes the `make::record_pat_field_list` function to produce valid syntax if the field list is empty, as it is used in other places too.

## Current behaviour
```rust
// In crate `other_crate`
pub struct Foo { bar: i32 }

// In current crate
fn do_something(foo: other_crate::Foo) {}

// Becomes
fn do_something(other_crate::Foo { , .. }: other_crate::Foo) {}
```

## Fixed behaviour
Assist should not be applicable in this case anymore.

Author: bors

crates/ide-assists/src/handlers/destructure_struct_binding.rs

@@ -107,6 +107,10 @@ fn collect_data(ident_pat: ast::IdentPat, ctx: &AssistContext<'_>) -> Option<Str
     let visible_fields =
         fields.into_iter().filter(|field| field.is_visible_from(ctx.db(), module)).collect_vec();
 
+    if visible_fields.is_empty() {
+        return None;
+    }
+
     let has_private_members =
         (is_non_exhaustive && is_foreign_crate) || visible_fields.len() < n_fields;
 
@@ -413,7 +417,7 @@ mod tests {
 
     #[test]
     fn unit_struct() {
-        check_assist(
+        check_assist_not_applicable(
             destructure_struct_binding,
             r#"
             struct Foo;
@@ -422,13 +426,6 @@ mod tests {
                 let $0foo = Foo;
             }
             "#,
-            r#"
-            struct Foo;
-
-            fn main() {
-                let Foo = Foo;
-            }
-            "#,
         )
     }
 
@@ -739,4 +736,18 @@ mod tests {
             "#,
         )
     }
+
+    #[test]
+    fn record_struct_no_public_members() {
+        check_assist_not_applicable(
+            destructure_struct_binding,
+            r#"
+            //- /lib.rs crate:dep
+            pub struct Foo { bar: i32, baz: i32 };
+
+            //- /main.rs crate:main deps:dep
+            fn main($0foo: dep::Foo) {}
+            "#,
+        )
+    }
 }

crates/syntax/src/ast/make.rs

@@ -724,7 +724,10 @@ pub fn record_pat_field_list(
 ) -> ast::RecordPatFieldList {
     let mut fields = fields.into_iter().join(", ");
     if let Some(rest_pat) = rest_pat {
-        format_to!(fields, ", {rest_pat}");
+        if !fields.is_empty() {
+            fields.push_str(", ");
+        }
+        format_to!(fields, "{rest_pat}");
     }
     ast_from_text(&format!("fn f(S {{ {fields} }}: ()))"))
 }