1 files changed, 213 insertions, 0 deletions

diff --git a/crates/assists/src/handlers/unmerge_use.rs b/crates/assists/src/handlers/unmerge_use.rs
new file mode 100644
index 000000000..d7dfe70d9
--- /dev/null
+++ b/crates/assists/src/handlers/unmerge_use.rs
@@ -0,0 +1,213 @@
+use syntax::{
+    algo::SyntaxRewriter,
+    ast::{self, edit::AstNodeEdit, VisibilityOwner},
+    AstNode, SyntaxKind,
+};
+
+use crate::{
+    assist_context::{AssistContext, Assists},
+    AssistId, AssistKind,
+};
+
+// Assist: unmerge_use
+//
+// Extracts single use item from use list.
+//
+// ```
+// use std::fmt::{Debug, Display$0};
+// ```
+// ->
+// ```
+// use std::fmt::{Debug};
+// use std::fmt::Display;
+// ```
+pub(crate) fn unmerge_use(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let tree: ast::UseTree = ctx.find_node_at_offset()?;
+
+    let tree_list = tree.syntax().parent().and_then(ast::UseTreeList::cast)?;
+    if tree_list.use_trees().count() < 2 {
+        return None;
+    }
+
+    let use_: ast::Use = tree_list.syntax().ancestors().find_map(ast::Use::cast)?;
+    let path = resolve_full_path(&tree)?;
+
+    let new_use = ast::make::use_(
+        use_.visibility(),
+        ast::make::use_tree(path, None, tree.rename(), tree.star_token().is_some()),
+    );
+
+    let mut rewriter = SyntaxRewriter::default();
+    rewriter += tree.remove();
+    rewriter.insert_after(use_.syntax(), &ast::make::tokens::single_newline());
+    if let ident_level @ 1..=usize::MAX = use_.indent_level().0 as usize {
+        rewriter.insert_after(
+            use_.syntax(),
+            &ast::make::tokens::whitespace(&" ".repeat(4 * ident_level)),
+        );
+    }
+    rewriter.insert_after(use_.syntax(), new_use.syntax());
+
+    let target = tree.syntax().text_range();
+    acc.add(
+        AssistId("unmerge_use", AssistKind::RefactorRewrite),
+        "Unmerge use",
+        target,
+        |builder| {
+            builder.rewrite(rewriter);
+        },
+    )
+}
+
+fn resolve_full_path(tree: &ast::UseTree) -> Option<ast::Path> {
+    let mut paths = tree
+        .syntax()
+        .ancestors()
+        .take_while(|n| n.kind() != SyntaxKind::USE_KW)
+        .filter_map(ast::UseTree::cast)
+        .filter_map(|t| t.path());
+
+    let mut final_path = paths.next()?;
+    for path in paths {
+        final_path = ast::make::path_concat(path, final_path)
+    }
+    Some(final_path)
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn skip_single_use_item() {
+        check_assist_not_applicable(
+            unmerge_use,
+            r"
+use std::fmt::Debug$0;
+",
+        );
+        check_assist_not_applicable(
+            unmerge_use,
+            r"
+use std::fmt::{Debug$0};
+",
+        );
+        check_assist_not_applicable(
+            unmerge_use,
+            r"
+use std::fmt::Debug as Dbg$0;
+",
+        );
+    }
+
+    #[test]
+    fn skip_single_glob_import() {
+        check_assist_not_applicable(
+            unmerge_use,
+            r"
+use std::fmt::*$0;
+",
+        );
+    }
+
+    #[test]
+    fn unmerge_use_item() {
+        check_assist(
+            unmerge_use,
+            r"
+use std::fmt::{Debug, Display$0};
+",
+            r"
+use std::fmt::{Debug};
+use std::fmt::Display;
+",
+        );
+
+        check_assist(
+            unmerge_use,
+            r"
+use std::fmt::{Debug, format$0, Display};
+",
+            r"
+use std::fmt::{Debug, Display};
+use std::fmt::format;
+",
+        );
+    }
+
+    #[test]
+    fn unmerge_glob_import() {
+        check_assist(
+            unmerge_use,
+            r"
+use std::fmt::{*$0, Display};
+",
+            r"
+use std::fmt::{Display};
+use std::fmt::*;
+",
+        );
+    }
+
+    #[test]
+    fn unmerge_renamed_use_item() {
+        check_assist(
+            unmerge_use,
+            r"
+use std::fmt::{Debug, Display as Disp$0};
+",
+            r"
+use std::fmt::{Debug};
+use std::fmt::Display as Disp;
+",
+        );
+    }
+
+    #[test]
+    fn unmerge_indented_use_item() {
+        check_assist(
+            unmerge_use,
+            r"
+mod format {
+    use std::fmt::{Debug, Display$0 as Disp, format};
+}
+",
+            r"
+mod format {
+    use std::fmt::{Debug, format};
+    use std::fmt::Display as Disp;
+}
+",
+        );
+    }
+
+    #[test]
+    fn unmerge_nested_use_item() {
+        check_assist(
+            unmerge_use,
+            r"
+use foo::bar::{baz::{qux$0, foobar}, barbaz};
+",
+            r"
+use foo::bar::{baz::{foobar}, barbaz};
+use foo::bar::baz::qux;
+",
+        );
+    }
+
+    #[test]
+    fn unmerge_use_item_with_visibility() {
+        check_assist(
+            unmerge_use,
+            r"
+pub use std::fmt::{Debug, Display$0};
+",
+            r"
+pub use std::fmt::{Debug};
+pub use std::fmt::Display;
+",
+        );
+    }
+}