Merge #4857

4857: Fix invalid shorthand initialization diagnostic for tuple structs r=jonas-schievink a=OptimalStrategy

Initializing tuple structs explicitly, like in the example below, produces a "Shorthand struct initialization" diagnostic that leads to a compilation error when applied:
```rust
struct S(usize);

fn main() { 
    let s = S { 0: 0 };  // OK, but triggers the diagnostic
    // let s = S { 0 };  // Compilation error
}
```

This PR adds a check that the field name is not a literal.

Co-authored-by: OptimalStrategy <[email protected]>
Co-authored-by: OptimalStrategy <[email protected]>

Author: bors[bot]

crates/ra_ide/src/diagnostics.rs

@@ -187,7 +187,8 @@ fn check_struct_shorthand_initialization(
         if let (Some(name_ref), Some(expr)) = (record_field.name_ref(), record_field.expr()) {
             let field_name = name_ref.syntax().text().to_string();
             let field_expr = expr.syntax().text().to_string();
-            if field_name == field_expr {
+            let field_name_is_tup_index = name_ref.as_tuple_field().is_some();
+            if field_name == field_expr && !field_name_is_tup_index {
                 let mut edit_builder = TextEditBuilder::default();
                 edit_builder.delete(record_field.syntax().text_range());
                 edit_builder.insert(record_field.syntax().text_range().start(), field_name);
@@ -719,6 +720,18 @@ mod tests {
         "#,
             check_struct_shorthand_initialization,
         );
+        check_not_applicable(
+            r#"
+            struct A(usize);
+
+            fn main() {
+                A {
+                    0: 0
+                }
+            }
+        "#,
+            check_struct_shorthand_initialization,
+        );
 
         check_apply(
             r#"