1 files changed, 152 insertions, 0 deletions

diff --git a/crates/assists/src/handlers/move_bounds.rs b/crates/assists/src/handlers/move_bounds.rs
new file mode 100644
index 000000000..e2e461520
--- /dev/null
+++ b/crates/assists/src/handlers/move_bounds.rs
@@ -0,0 +1,152 @@
+use syntax::{
+    ast::{self, edit::AstNodeEdit, make, AstNode, NameOwner, TypeBoundsOwner},
+    match_ast,
+    SyntaxKind::*,
+    T,
+};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: move_bounds_to_where_clause
+//
+// Moves inline type bounds to a where clause.
+//
+// ```
+// fn apply<T, U, <|>F: FnOnce(T) -> U>(f: F, x: T) -> U {
+//     f(x)
+// }
+// ```
+// ->
+// ```
+// fn apply<T, U, F>(f: F, x: T) -> U where F: FnOnce(T) -> U {
+//     f(x)
+// }
+// ```
+pub(crate) fn move_bounds_to_where_clause(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let type_param_list = ctx.find_node_at_offset::<ast::GenericParamList>()?;
+
+    let mut type_params = type_param_list.type_params();
+    if type_params.all(|p| p.type_bound_list().is_none()) {
+        return None;
+    }
+
+    let parent = type_param_list.syntax().parent()?;
+    if parent.children_with_tokens().any(|it| it.kind() == WHERE_CLAUSE) {
+        return None;
+    }
+
+    let anchor = match_ast! {
+        match parent {
+            ast::Fn(it) => it.body()?.syntax().clone().into(),
+            ast::Trait(it) => it.assoc_item_list()?.syntax().clone().into(),
+            ast::Impl(it) => it.assoc_item_list()?.syntax().clone().into(),
+            ast::Enum(it) => it.variant_list()?.syntax().clone().into(),
+            ast::Struct(it) => {
+                it.syntax().children_with_tokens()
+                    .find(|it| it.kind() == RECORD_FIELD_LIST || it.kind() == T![;])?
+            },
+            _ => return None
+        }
+    };
+
+    let target = type_param_list.syntax().text_range();
+    acc.add(
+        AssistId("move_bounds_to_where_clause", AssistKind::RefactorRewrite),
+        "Move to where clause",
+        target,
+        |edit| {
+            let new_params = type_param_list
+                .type_params()
+                .filter(|it| it.type_bound_list().is_some())
+                .map(|type_param| {
+                    let without_bounds = type_param.remove_bounds();
+                    (type_param, without_bounds)
+                });
+
+            let new_type_param_list = type_param_list.replace_descendants(new_params);
+            edit.replace_ast(type_param_list.clone(), new_type_param_list);
+
+            let where_clause = {
+                let predicates = type_param_list.type_params().filter_map(build_predicate);
+                make::where_clause(predicates)
+            };
+
+            let to_insert = match anchor.prev_sibling_or_token() {
+                Some(ref elem) if elem.kind() == WHITESPACE => {
+                    format!("{} ", where_clause.syntax())
+                }
+                _ => format!(" {}", where_clause.syntax()),
+            };
+            edit.insert(anchor.text_range().start(), to_insert);
+        },
+    )
+}
+
+fn build_predicate(param: ast::TypeParam) -> Option<ast::WherePred> {
+    let path = {
+        let name_ref = make::name_ref(&param.name()?.syntax().to_string());
+        let segment = make::path_segment(name_ref);
+        make::path_unqualified(segment)
+    };
+    let predicate = make::where_pred(path, param.type_bound_list()?.bounds());
+    Some(predicate)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::tests::check_assist;
+
+    #[test]
+    fn move_bounds_to_where_clause_fn() {
+        check_assist(
+            move_bounds_to_where_clause,
+            r#"
+            fn foo<T: u32, <|>F: FnOnce(T) -> T>() {}
+            "#,
+            r#"
+            fn foo<T, F>() where T: u32, F: FnOnce(T) -> T {}
+            "#,
+        );
+    }
+
+    #[test]
+    fn move_bounds_to_where_clause_impl() {
+        check_assist(
+            move_bounds_to_where_clause,
+            r#"
+            impl<U: u32, <|>T> A<U, T> {}
+            "#,
+            r#"
+            impl<U, T> A<U, T> where U: u32 {}
+            "#,
+        );
+    }
+
+    #[test]
+    fn move_bounds_to_where_clause_struct() {
+        check_assist(
+            move_bounds_to_where_clause,
+            r#"
+            struct A<<|>T: Iterator<Item = u32>> {}
+            "#,
+            r#"
+            struct A<T> where T: Iterator<Item = u32> {}
+            "#,
+        );
+    }
+
+    #[test]
+    fn move_bounds_to_where_clause_tuple_struct() {
+        check_assist(
+            move_bounds_to_where_clause,
+            r#"
+            struct Pair<<|>T: u32>(T, T);
+            "#,
+            r#"
+            struct Pair<T>(T, T) where T: u32;
+            "#,
+        );
+    }
+}