1 files changed, 41 insertions, 0 deletions

diff --git a/lib/src/lints/deprecated_is_null.rs b/lib/src/lints/deprecated_is_null.rs
new file mode 100644
index 0000000..99fb3fb
--- /dev/null
+++ b/lib/src/lints/deprecated_is_null.rs
@@ -0,0 +1,41 @@
+use crate::{make, Metadata, Report, Rule, Suggestion};
+
+use if_chain::if_chain;
+use macros::lint;
+use rnix::{
+    types::{Apply, Ident, TokenWrapper, TypedNode},
+    NodeOrToken, SyntaxElement, SyntaxKind,
+};
+
+#[lint(
+    name = "deprecated isNull",
+    note = "Found usage of deprecated builtin isNull",
+    code = 13,
+    match_with = SyntaxKind::NODE_APPLY
+)]
+struct DeprecatedIsNull;
+
+impl Rule for DeprecatedIsNull {
+    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+        if_chain! {
+            if let NodeOrToken::Node(node) = node;
+            if let Some(apply) = Apply::cast(node.clone());
+            if let Some(ident) = Ident::cast(apply.lambda()?);
+            if ident.as_str() == "isNull";
+
+            if let Some(value) = apply.value();
+            then {
+                let null = make::ident("null");
+                let binop = make::binary(&value, "==", null.node());
+                let parenthesized = make::parenthesize(binop.node());
+
+                let at = node.text_range();
+                let replacement = parenthesized.node().clone();
+                let message = "`isNull` is deprecated, check equality with `null` instead";
+                Some(self.report().suggest(at, message, Suggestion::new(at, replacement)))
+            } else {
+                None
+            }
+        }
+    }
+}