1 files changed, 119 insertions, 0 deletions

diff --git a/crates/ra_assists/src/assists/flip_trait_bound.rs b/crates/ra_assists/src/assists/flip_trait_bound.rs
new file mode 100644
index 000000000..1625b241f
--- /dev/null
+++ b/crates/ra_assists/src/assists/flip_trait_bound.rs
@@ -0,0 +1,119 @@
+use hir::db::HirDatabase;
+use ra_syntax::{
+    algo::non_trivia_sibling,
+    ast::{self, AstNode},
+    Direction, T,
+};
+
+use crate::{Assist, AssistCtx, AssistId};
+
+// Assist: flip_trait_bound
+//
+// Flips two trait bounds.
+//
+// ```
+// fn foo<T: Clone +<|> Copy>() { }
+// ```
+// ->
+// ```
+// fn foo<T: Copy + Clone>() { }
+// ```
+pub(crate) fn flip_trait_bound(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    // We want to replicate the behavior of `flip_binexpr` by only suggesting
+    // the assist when the cursor is on a `+`
+    let plus = ctx.find_token_at_offset(T![+])?;
+
+    // Make sure we're in a `TypeBoundList`
+    if ast::TypeBoundList::cast(plus.parent()).is_none() {
+        return None;
+    }
+
+    let (before, after) = (
+        non_trivia_sibling(plus.clone().into(), Direction::Prev)?,
+        non_trivia_sibling(plus.clone().into(), Direction::Next)?,
+    );
+
+    ctx.add_action(AssistId("flip_trait_bound"), "flip trait bound", |edit| {
+        edit.target(plus.text_range());
+        edit.replace(before.text_range(), after.to_string());
+        edit.replace(after.text_range(), before.to_string());
+    });
+
+    ctx.build()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_target};
+
+    #[test]
+    fn flip_trait_bound_assist_available() {
+        check_assist_target(flip_trait_bound, "struct S<T> where T: A <|>+ B + C { }", "+")
+    }
+
+    #[test]
+    fn flip_trait_bound_not_applicable_for_single_trait_bound() {
+        check_assist_not_applicable(flip_trait_bound, "struct S<T> where T: <|>A { }")
+    }
+
+    #[test]
+    fn flip_trait_bound_works_for_struct() {
+        check_assist(
+            flip_trait_bound,
+            "struct S<T> where T: A <|>+ B { }",
+            "struct S<T> where T: B <|>+ A { }",
+        )
+    }
+
+    #[test]
+    fn flip_trait_bound_works_for_trait_impl() {
+        check_assist(
+            flip_trait_bound,
+            "impl X for S<T> where T: A +<|> B { }",
+            "impl X for S<T> where T: B +<|> A { }",
+        )
+    }
+
+    #[test]
+    fn flip_trait_bound_works_for_fn() {
+        check_assist(flip_trait_bound, "fn f<T: A <|>+ B>(t: T) { }", "fn f<T: B <|>+ A>(t: T) { }")
+    }
+
+    #[test]
+    fn flip_trait_bound_works_for_fn_where_clause() {
+        check_assist(
+            flip_trait_bound,
+            "fn f<T>(t: T) where T: A +<|> B { }",
+            "fn f<T>(t: T) where T: B +<|> A { }",
+        )
+    }
+
+    #[test]
+    fn flip_trait_bound_works_for_lifetime() {
+        check_assist(
+            flip_trait_bound,
+            "fn f<T>(t: T) where T: A <|>+ 'static { }",
+            "fn f<T>(t: T) where T: 'static <|>+ A { }",
+        )
+    }
+
+    #[test]
+    fn flip_trait_bound_works_for_complex_bounds() {
+        check_assist(
+            flip_trait_bound,
+            "struct S<T> where T: A<T> <|>+ b_mod::B<T> + C<T> { }",
+            "struct S<T> where T: b_mod::B<T> <|>+ A<T> + C<T> { }",
+        )
+    }
+
+    #[test]
+    fn flip_trait_bound_works_for_long_bounds() {
+        check_assist(
+            flip_trait_bound,
+            "struct S<T> where T: A + B + C + D + E + F +<|> G + H + I + J { }",
+            "struct S<T> where T: A + B + C + D + E + G +<|> F + H + I + J { }",
+        )
+    }
+}