Add ide-assist: move_for_binder

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

@@ -0,0 +1,82 @@
+use ide_db::assists::AssistId;
+use syntax::{
+    SyntaxKind,
+    ast::{self, AstNode, make::tokens},
+    syntax_editor::Position,
+};
+
+use crate::assist_context::{AssistContext, Assists};
+
+// Assist: move_for_binder
+//
+// Move for-binder to where predicate.
+//
+// ```
+// fn foo<F>()
+// where
+//     F: $0for<'a> Fn(&'a str)
+// {}
+// ```
+// ->
+// ```
+// fn foo<F>()
+// where
+//     for<'a> F: Fn(&'a str)
+// {}
+// ```
+pub(crate) fn move_for_binder(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
+    let for_binder = ctx.find_node_at_offset::<ast::ForBinder>()?;
+    let where_pred = ctx.find_node_at_offset::<ast::WherePred>()?;
+
+    if where_pred.for_binder().is_some() || !ctx.has_empty_selection() {
+        return None;
+    }
+
+    let label = "Move for-binder to where predicate";
+    let target = for_binder.syntax().text_range();
+    acc.add(AssistId::refactor_rewrite("move_for_binder"), label, target, |builder| {
+        let mut edit = builder.make_editor(for_binder.syntax());
+
+        if let Some(next) = for_binder.syntax().next_sibling_or_token()
+            && next.kind() == SyntaxKind::WHITESPACE
+        {
+            edit.delete(next);
+        }
+
+        edit.delete(for_binder.syntax());
+        edit.insert(Position::before(where_pred.syntax()), tokens::single_space());
+        edit.insert(Position::before(where_pred.syntax()), for_binder.syntax().clone_for_update());
+
+        builder.add_file_edits(ctx.vfs_file_id(), edit);
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_assist_not_applicable;
+
+    use super::*;
+
+    #[test]
+    fn not_applicable_on_exists() {
+        check_assist_not_applicable(
+            move_for_binder,
+            r#"
+            fn foo<F>()
+            where
+                for<'b> F: $0for<'a> Fn(&'a str)
+            {}
+            "#,
+        );
+
+        check_assist_not_applicable(
+            move_for_binder,
+            r#"
+            fn foo<F>()
+            where
+                $0for<'a> F: Fn(&'a str)
+            {}
+            "#,
+        );
+    }
+}

crates/ide-assists/src/lib.rs

@@ -189,6 +189,7 @@ mod handlers {
     mod merge_nested_if;
     mod move_bounds;
     mod move_const_to_impl;
+    mod move_for_binder;
     mod move_from_mod_rs;
     mod move_guard;
     mod move_module_to_file;
@@ -326,6 +327,7 @@ mod handlers {
             merge_nested_if::merge_nested_if,
             move_bounds::move_bounds_to_where_clause,
             move_const_to_impl::move_const_to_impl,
+            move_for_binder::move_for_binder,
             move_from_mod_rs::move_from_mod_rs,
             move_guard::move_arm_cond_to_match_guard,
             move_guard::move_guard_to_arm_body,

crates/ide-assists/src/tests/generated.rs

@@ -2640,6 +2640,25 @@ impl S {
     )
 }
 
+#[test]
+fn doctest_move_for_binder() {
+    check_doc_test(
+        "move_for_binder",
+        r#####"
+fn foo<F>()
+where
+    F: $0for<'a> Fn(&'a str)
+{}
+"#####,
+        r#####"
+fn foo<F>()
+where
+    for<'a> F: Fn(&'a str)
+{}
+"#####,
+    )
+}
+
 #[test]
 fn doctest_move_from_mod_rs() {
     check_doc_test(