fix(natu): preserve NixOS cfg bindings

src/natu/natu.rs

@@ -111,7 +111,7 @@ pub fn future_sight(files: Vec<SourceFile>) -> status::Result<Report> {
         }
 
         let graph = ScopeGraph::from_file(&parsed);
-        diagnostics.extend(rules::run_rules(&parsed, &graph));
+        diagnostics.extend(rules::run_rules(&parsed, &graph, &file.path));
     }
 
     Ok(Report {

src/natu/natu_test.rs

@@ -65,6 +65,18 @@ fn natu_reports_out_of_order_let_bindings() -> googletest::Result<()> {
     Ok(())
 }
 
+#[gtest]
+fn natu_preserves_nixos_cfg_bindings() -> googletest::Result<()> {
+    let report = natu::future_sight(vec![SourceFile {
+        path: PathBuf::from("configs/nixos/test.nix"),
+        source: "{ config, ... }: let\n  cfg = config.example;\n  value = cfg;\nin value\n".into(),
+    }])
+    .or_fail()?;
+
+    expect_that!(report.is_clean(), is_true());
+    Ok(())
+}
+
 #[gtest]
 fn natu_reports_unquoted_uri() -> googletest::Result<()> {
     let report = natu::future_sight(vec![fixture_source("testdata/lint_findings.nix")?]).or_fail()?;

src/natu/rules.rs

@@ -1,3 +1,5 @@
+use std::path::Path;
+
 use crate::FileId;
 use crate::ast;
 use crate::rules::manual_inherit::ManualInherit;
@@ -59,7 +61,7 @@ pub trait TokenRule {
     fn check(token: &Self::Token) -> Option<&'static str>;
 }
 
-pub fn run_rules(file: &ast::ParsedFile, graph: &ScopeGraph) -> Vec<Diagnostic> {
+pub fn run_rules(file: &ast::ParsedFile, graph: &ScopeGraph, path: &Path) -> Vec<Diagnostic> {
     let node_diagnostics = file
         .nodes
         .iter()
@@ -76,13 +78,17 @@ pub fn run_rules(file: &ast::ParsedFile, graph: &ScopeGraph) -> Vec<Diagnostic>
         .flat_map(|token| [run_token_rule::<UnquotedUri>(token)])
         .flatten();
 
-    let let_order_diagnostics = let_order::check(graph).into_iter().map(|finding| Finding {
-        rule_id: "let_order",
-        range: finding.range,
-        message: "Let bindings must follow dependency order",
-        binding: None,
-        expected_order: Some(finding.expected_order),
-    });
+    let ignore_cfg =
+        path.starts_with("configs/nixos") || path.to_string_lossy().contains("/configs/nixos/");
+    let let_order_diagnostics = let_order::check(graph, ignore_cfg)
+        .into_iter()
+        .map(|finding| Finding {
+            rule_id: "let_order",
+            range: finding.range,
+            message: "Let bindings must follow dependency order",
+            binding: None,
+            expected_order: Some(finding.expected_order),
+        });
 
     node_diagnostics
         .chain(token_diagnostics)

src/natu/rules/let_order.rs

@@ -8,36 +8,42 @@ pub struct Finding {
     pub expected_order: Vec<String>,
 }
 
-pub fn check(graph: &ScopeGraph) -> Vec<Finding> {
+pub fn check(graph: &ScopeGraph, ignore_cfg: bool) -> Vec<Finding> {
     graph
         .let_scopes()
         .iter()
         .flat_map(|let_scope| {
-            let expected = expected_order(graph, let_scope);
-            let is_ordered = expected.iter().enumerate().all(|(position, declaration)| {
-                let_scope
-                    .bindings
-                    .get(position)
-                    .is_some_and(|binding| binding.declaration == *declaration)
-            });
+            let expected = expected_order(graph, let_scope)
+                .into_iter()
+                .filter(|declaration| !ignore_cfg || binding_name(let_scope, *declaration) != "cfg")
+                .collect::<Vec<_>>();
+            let actual = let_scope
+                .bindings
+                .iter()
+                .filter(|binding| !ignore_cfg || binding.name != "cfg")
+                .map(|binding| binding.declaration)
+                .collect::<Vec<_>>();
 
-            (!is_ordered).then(|| Finding {
+            (!actual.starts_with(&expected)).then(|| Finding {
                 range: let_scope.range,
                 expected_order: expected
                     .iter()
-                    .filter_map(|declaration| {
-                        let_scope
-                            .bindings
-                            .iter()
-                            .find(|binding| binding.declaration == *declaration)
-                            .map(|binding| binding.name.clone())
-                    })
+                    .map(|declaration| binding_name(let_scope, *declaration).to_owned())
                     .collect(),
             })
         })
         .collect()
 }
 
+fn binding_name(let_scope: &LetScope, declaration: NodeId) -> &str {
+    &let_scope
+        .bindings
+        .iter()
+        .find(|binding| binding.declaration == declaration)
+        .expect("let declaration")
+        .name
+}
+
 fn expected_order(graph: &ScopeGraph, let_scope: &LetScope) -> Vec<NodeId> {
     let mut order = Vec::new();
     visit_references(graph, &let_scope.entry_references, let_scope, &mut order);