fix(xatu): count bindings in empty let expressions

AGENTS.md

@@ -96,6 +96,8 @@
 - `rules_rust` `rust_test` targets cannot set both `crate` and `srcs`.
   Use one input style per test target.
 - Rust tests in this monorepo live in separate `*_test.rs` files, not inline `#[cfg(test)]` modules.
+- `rnix::ast::HasEntry::entries()` includes assignments and `inherit` statements.
+  Use `attrpath_values()` when code needs only assignment entries.
 - Ariadne Rust tests are declared in Bazel `BUILD` files; do not add `[[test]]` entries to
   `src/ariadne/Cargo.toml` unless explicitly requested.
 - In this monorepo, "dotfiles" refers to the dotfiles/NixOS configuration under `src/dotfiles/` and `configs/nixos/`.

src/xatu/ast.rs

@@ -57,8 +57,7 @@ pub struct Select {
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct LetIn {
-    pub entry_count: usize,
-    pub inherit_count: usize,
+    pub binding_count: usize,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]

src/xatu/parser.rs

@@ -117,8 +117,11 @@ impl From<rnix::ast::LetIn> for ast::LetIn {
         use rnix::ast::HasEntry;
 
         Self {
-            entry_count: let_in.entries().count(),
-            inherit_count: let_in.inherits().count(),
+            binding_count: let_in.attrpath_values().count()
+                + let_in
+                    .inherits()
+                    .map(|inherit| inherit.attrs().count())
+                    .sum::<usize>(),
         }
     }
 }

src/xatu/rules/empty_let_in.rs

@@ -15,7 +15,7 @@ impl NodeRule for EmptyLetIn {
     }
 
     fn check(node: &Self::Node) -> Option<&'static str> {
-        if node.entry_count == 0 && node.inherit_count == 0 {
+        if node.binding_count == 0 {
             Some("let expression has no bindings")
         } else {
             None

src/xatu/xatu_test.rs

@@ -145,7 +145,7 @@ fn xatu_reports_commented_empty_let_in() -> googletest::Result<()> {
 }
 
 #[gtest]
-fn empty_inherit_prevents_empty_let_in_finding() -> googletest::Result<()> {
+fn xatu_reports_empty_let_with_empty_inherit() -> googletest::Result<()> {
     let report =
         xatu::future_sight(vec![fixture_source("testdata/lint_interactions.nix")?]).or_fail()?;
 
@@ -154,7 +154,7 @@ fn empty_inherit_prevents_empty_let_in_finding() -> googletest::Result<()> {
         .iter()
         .map(|diagnostic| diagnostic.finding.rule_id)
         .collect::<Vec<_>>();
-    expect_that!(findings, eq(&vec!["empty_inherit"]));
+    expect_that!(findings, eq(&vec!["empty_let_in", "empty_inherit"]));
     Ok(())
 }