1 files changed, 284 insertions, 0 deletions
diff --git a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/reorder_impl_items.rs b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/reorder_impl_items.rs
new file mode 100644
index 000000000..208c3e109
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/reorder_impl_items.rs
@@ -0,0 +1,284 @@
+use hir::{PathResolution, Semantics};
+use ide_db::{FxHashMap, RootDatabase};
+use itertools::Itertools;
+use syntax::{
+    ast::{self, HasName},
+    ted, AstNode,
+};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: reorder_impl_items
+//
+// Reorder the items of an `impl Trait`. The items will be ordered
+// in the same order as in the trait definition.
+//
+// ```
+// trait Foo {
+//     type A;
+//     const B: u8;
+//     fn c();
+// }
+//
+// struct Bar;
+// $0impl Foo for Bar {
+//     const B: u8 = 17;
+//     fn c() {}
+//     type A = String;
+// }
+// ```
+// ->
+// ```
+// trait Foo {
+//     type A;
+//     const B: u8;
+//     fn c();
+// }
+//
+// struct Bar;
+// impl Foo for Bar {
+//     type A = String;
+//     const B: u8 = 17;
+//     fn c() {}
+// }
+// ```
+pub(crate) fn reorder_impl_items(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
+    let impl_ast = ctx.find_node_at_offset::<ast::Impl>()?;
+    let items = impl_ast.assoc_item_list()?;
+    let assoc_items = items.assoc_items().collect::<Vec<_>>();
+
+    let path = impl_ast
+        .trait_()
+        .and_then(|t| match t {
+            ast::Type::PathType(path) => Some(path),
+            _ => None,
+        })?
+        .path()?;
+
+    let ranks = compute_item_ranks(&path, ctx)?;
+    let sorted: Vec<_> = assoc_items
+        .iter()
+        .cloned()
+        .sorted_by_key(|i| {
+            let name = match i {
+                ast::AssocItem::Const(c) => c.name(),
+                ast::AssocItem::Fn(f) => f.name(),
+                ast::AssocItem::TypeAlias(t) => t.name(),
+                ast::AssocItem::MacroCall(_) => None,
+            };
+
+            name.and_then(|n| ranks.get(&n.to_string()).copied()).unwrap_or(usize::max_value())
+        })
+        .collect();
+
+    // Don't edit already sorted methods:
+    if assoc_items == sorted {
+        cov_mark::hit!(not_applicable_if_sorted);
+        return None;
+    }
+
+    let target = items.syntax().text_range();
+    acc.add(
+        AssistId("reorder_impl_items", AssistKind::RefactorRewrite),
+        "Sort items by trait definition",
+        target,
+        |builder| {
+            let assoc_items =
+                assoc_items.into_iter().map(|item| builder.make_mut(item)).collect::<Vec<_>>();
+            assoc_items
+                .into_iter()
+                .zip(sorted)
+                .for_each(|(old, new)| ted::replace(old.syntax(), new.clone_for_update().syntax()));
+        },
+    )
+}
+
+fn compute_item_ranks(
+    path: &ast::Path,
+    ctx: &AssistContext<'_>,
+) -> Option<FxHashMap<String, usize>> {
+    let td = trait_definition(path, &ctx.sema)?;
+
+    Some(
+        td.items(ctx.db())
+            .iter()
+            .flat_map(|i| i.name(ctx.db()))
+            .enumerate()
+            .map(|(idx, name)| (name.to_string(), idx))
+            .collect(),
+    )
+}
+
+fn trait_definition(path: &ast::Path, sema: &Semantics<'_, RootDatabase>) -> Option<hir::Trait> {
+    match sema.resolve_path(path)? {
+        PathResolution::Def(hir::ModuleDef::Trait(trait_)) => Some(trait_),
+        _ => None,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn not_applicable_if_sorted() {
+        cov_mark::check!(not_applicable_if_sorted);
+        check_assist_not_applicable(
+            reorder_impl_items,
+            r#"
+trait Bar {
+    type T;
+    const C: ();
+    fn a() {}
+    fn z() {}
+    fn b() {}
+}
+struct Foo;
+$0impl Bar for Foo {
+    type T = ();
+    const C: () = ();
+    fn a() {}
+    fn z() {}
+    fn b() {}
+}
+        "#,
+        )
+    }
+
+    #[test]
+    fn reorder_impl_trait_functions() {
+        check_assist(
+            reorder_impl_items,
+            r#"
+trait Bar {
+    fn a() {}
+    fn c() {}
+    fn b() {}
+    fn d() {}
+}
+
+struct Foo;
+$0impl Bar for Foo {
+    fn d() {}
+    fn b() {}
+    fn c() {}
+    fn a() {}
+}
+"#,
+            r#"
+trait Bar {
+    fn a() {}
+    fn c() {}
+    fn b() {}
+    fn d() {}
+}
+
+struct Foo;
+impl Bar for Foo {
+    fn a() {}
+    fn c() {}
+    fn b() {}
+    fn d() {}
+}
+"#,
+        )
+    }
+
+    #[test]
+    fn not_applicable_if_empty() {
+        check_assist_not_applicable(
+            reorder_impl_items,
+            r#"
+trait Bar {};
+struct Foo;
+$0impl Bar for Foo {}
+        "#,
+        )
+    }
+
+    #[test]
+    fn reorder_impl_trait_items() {
+        check_assist(
+            reorder_impl_items,
+            r#"
+trait Bar {
+    fn a() {}
+    type T0;
+    fn c() {}
+    const C1: ();
+    fn b() {}
+    type T1;
+    fn d() {}
+    const C0: ();
+}
+
+struct Foo;
+$0impl Bar for Foo {
+    type T1 = ();
+    fn d() {}
+    fn b() {}
+    fn c() {}
+    const C1: () = ();
+    fn a() {}
+    type T0 = ();
+    const C0: () = ();
+}
+        "#,
+            r#"
+trait Bar {
+    fn a() {}
+    type T0;
+    fn c() {}
+    const C1: ();
+    fn b() {}
+    type T1;
+    fn d() {}
+    const C0: ();
+}
+
+struct Foo;
+impl Bar for Foo {
+    fn a() {}
+    type T0 = ();
+    fn c() {}
+    const C1: () = ();
+    fn b() {}
+    type T1 = ();
+    fn d() {}
+    const C0: () = ();
+}
+        "#,
+        )
+    }
+
+    #[test]
+    fn reorder_impl_trait_items_uneven_ident_lengths() {
+        check_assist(
+            reorder_impl_items,
+            r#"
+trait Bar {
+    type Foo;
+    type Fooo;
+}
+
+struct Foo;
+impl Bar for Foo {
+    type Fooo = ();
+    type Foo = ();$0
+}"#,
+            r#"
+trait Bar {
+    type Foo;
+    type Fooo;
+}
+
+struct Foo;
+impl Bar for Foo {
+    type Foo = ();
+    type Fooo = ();
+}"#,
+        )
+    }
+}