new lint: empty-let-in

1 files changed, 42 insertions, 0 deletions

diff --git a/lib/src/lints/empty_let_in.rs b/lib/src/lints/empty_let_in.rs
new file mode 100644
index 0000000..4b074e7
--- /dev/null
+++ b/lib/src/lints/empty_let_in.rs
@@ -0,0 +1,42 @@
+use crate::{Lint, Metadata, Report, Rule, Suggestion};
+
+use if_chain::if_chain;
+use macros::lint;
+use rnix::{
+    types::{LetIn, TypedNode, 
+        EntryHolder},
+    NodeOrToken, SyntaxElement, SyntaxKind,
+};
+
+#[lint(
+    name = "empty let-in",
+    note = "Useless let-in expression",
+    code = 2,
+    match_with = SyntaxKind::NODE_LET_IN
+)]
+struct EmptyLetIn;
+
+impl Rule for EmptyLetIn {
+    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+        if_chain! {
+            if let NodeOrToken::Node(let_in_node) = node;
+            if let Some(let_in_expr) = LetIn::cast(let_in_node.clone());
+            let entries = let_in_expr.entries();
+            let inherits = let_in_expr.inherits();
+
+            if entries.count() == 0;
+            if inherits.count() == 0;
+
+            if let Some(body) = let_in_expr.body();
+            then {
+                let at = node.text_range();
+                let replacement = body;
+                let message = "This let-in expression has no entries";
+                Some(Self::report().suggest(at, message, Suggestion::new(at, replacement)))
+            } else {
+                None
+            }
+        }
+    }
+}
+