2 files changed, 60 insertions, 0 deletions

diff --git a/lib/src/lints.rs b/lib/src/lints.rs
index d31a754..439fd8f 100644
--- a/lib/src/lints.rs
+++ b/lib/src/lints.rs
@@ -17,4 +17,5 @@ lints! {
     empty_inherit,
     faster_groupby,
     faster_zipattrswith,
+    deprecated_to_path,
 }
diff --git a/lib/src/lints/deprecated_to_path.rs b/lib/src/lints/deprecated_to_path.rs
new file mode 100644
index 0000000..36cbe35
--- /dev/null
+++ b/lib/src/lints/deprecated_to_path.rs
@@ -0,0 +1,59 @@
+use crate::{session::SessionInfo, Metadata, Report, Rule};
+
+use if_chain::if_chain;
+use macros::lint;
+use rnix::{
+    types::{Apply, TypedNode},
+    NodeOrToken, SyntaxElement, SyntaxKind,
+};
+
+/// ## What it does
+/// Checks for usage of the `toPath` function.
+///
+/// ## Why is this bad?
+/// `toPath` is deprecated.
+///
+/// ## Example
+///
+/// ```nix
+/// builtins.toPath "/path"
+/// ```
+///
+/// Try these instead:
+///
+/// ```nix
+/// # to convert the string to an absolute path:
+/// /. + "/path"
+/// # => /abc
+///
+/// # to convert the string to a path relative to the current directory:
+/// ./. + "/bin"
+/// # => /home/np/statix/bin
+/// ```
+#[lint(
+    name = "deprecated_to_path",
+    note = "Found usage of deprecated builtin toPath",
+    code = 17,
+    match_with = SyntaxKind::NODE_APPLY
+)]
+struct DeprecatedIsNull;
+
+static ALLOWED_PATHS: &[&str; 2] = &["builtins.toPath", "toPath"];
+
+impl Rule for DeprecatedIsNull {
+    fn validate(&self, node: &SyntaxElement, _sess: &SessionInfo) -> Option<Report> {
+        if_chain! {
+            if let NodeOrToken::Node(node) = node;
+            if let Some(apply) = Apply::cast(node.clone());
+            let lambda_path = apply.lambda()?.to_string();
+            if ALLOWED_PATHS.iter().any(|&p| p == lambda_path.as_str());
+            then {
+                let at = node.text_range();
+                let message = format!("`{}` is deprecated, see `:doc builtins.toPath` within the REPL for more", lambda_path);
+                Some(self.report().diagnostic(at, message))
+            } else {
+                None
+            }
+        }
+    }
+}