Add replace_let_attrset assist

crates/ide/src/ide/assists/mod.rs

@@ -17,6 +17,7 @@ mod convert_to_inherit;
 mod flatten_attrset;
 mod pack_bindings;
 mod remove_empty_inherit;
+mod replace_let_attrset;
 
 use crate::{DefDatabase, FileRange, TextEdit, WorkspaceEdit};
 use syntax::ast::{self, AstNode};
@@ -45,6 +46,7 @@ pub(crate) fn assists(db: &dyn DefDatabase, frange: FileRange) -> Vec<Assist> {
         flatten_attrset::flatten_attrset,
         pack_bindings::pack_bindings,
         remove_empty_inherit::remove_empty_inherit,
+        replace_let_attrset::replace_let_attrset,
     ];
 
     let mut ctx = AssistsCtx::new(db, frange);

crates/ide/src/ide/assists/replace_let_attrset.rs

@@ -0,0 +1,74 @@
+//! Replace `let {...}` with `let ... in ...`.
+//!
+//! ```nix
+//! let { foo = "bar"; body = foo; }
+//! ```
+//! =>
+//! ```nix
+//! let foo = "bar" in foo
+//! ```
+use super::{AssistKind, AssistsCtx};
+use crate::TextEdit;
+use syntax::ast::{self, AstNode};
+
+pub(super) fn replace_let_attrset(ctx: &mut AssistsCtx<'_>) -> Option<()> {
+    let node = ctx.covering_node::<ast::AttrSet>()?;
+
+    if node.let_token().is_none() {
+        return None;
+    }
+
+    let is_body_node = |child: &syntax::SyntaxNode| {
+        if let Some(tok) = child.first_token() {
+            tok.text() == "body"
+        } else {
+            false
+        }
+    };
+
+    let body_binding = node.syntax().children().find(is_body_node)?.last_child()?;
+
+    let bindings: String = node
+        .syntax()
+        .children()
+        .filter(|child| !is_body_node(child))
+        .map(|b| b.text().to_string())
+        .collect::<Vec<String>>()
+        .join(" ");
+
+    ctx.add(
+        "replace_let_attrset",
+        "Replace `let {...}` with `let ... in ...`",
+        AssistKind::QuickFix,
+        vec![TextEdit {
+            delete: node.syntax().text_range(),
+            insert: format!("let {bindings} in {body_binding}").into(),
+        }],
+    );
+
+    Some(())
+}
+
+#[cfg(test)]
+mod tests {
+    use expect_test::expect;
+
+    define_check_assist!(super::replace_let_attrset);
+
+    #[test]
+    fn simple() {
+        check(
+            r#"let { $0foo = "bar"; body = foo; }"#,
+            expect![r#"let foo = "bar"; in foo"#],
+        );
+        check_no(r#"{ $0foo = "bar"; }"#);
+    }
+
+    #[test]
+    fn multiple_bindings() {
+        check(
+            r#"let { $0foo = "foo"; bar = "bar"; body = foo + bar; }"#,
+            expect![r#"let foo = "foo"; bar = "bar"; in foo + bar"#],
+        )
+    }
+}