From 90b83d6f5d426c3dc556af9ee59fdb413c647688 Mon Sep 17 00:00:00 2001
From: alexion <contact@alexion.dev>
Date: Sat, 26 Sep 2026 23:14:08 -0400
Subject: [PATCH] feat(natu): report expected let order

---
 src/natu/natu.rs            | 29 +++++++++++++++++++++++++++
 src/natu/natu_test.rs       | 13 +++++++++++-
 src/natu/rules.rs           |  6 +++++-
 src/natu/rules/let_order.rs | 40 ++++++++++++++++++-------------------
 4 files changed, 66 insertions(+), 22 deletions(-)

diff --git a/src/natu/natu.rs b/src/natu/natu.rs
index d942ea5..bc84de2 100644
--- a/src/natu/natu.rs
+++ b/src/natu/natu.rs
@@ -1,3 +1,5 @@
+use std::collections::HashSet;
+
 mod ast;
 mod file_store;
 mod parser;
@@ -23,7 +25,34 @@ impl Report {
 
 impl std::fmt::Display for Report {
     fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let mut reported_let_order_files = HashSet::new();
+
         for diagnostic in &self.diagnostics {
+            if diagnostic.finding.rule_id == "let_order" {
+                if !reported_let_order_files.insert(diagnostic.file_id) {
+                    continue;
+                }
+
+                let file = self.files.get(diagnostic.file_id);
+                writeln!(
+                    formatter,
+                    "{} [let_order] Let bindings must follow dependency order",
+                    file.path.display()
+                )?;
+
+                for finding in self.diagnostics.iter().filter(|candidate| {
+                    candidate.file_id == diagnostic.file_id
+                        && candidate.finding.rule_id == "let_order"
+                }) {
+                    let (start, _) = line_range(&file.source, finding.finding.range);
+                    let expected_order =
+                        finding.finding.expected_order.as_ref().expect("let order");
+                    writeln!(formatter, "  line {start}: {}", expected_order.join(", "))?;
+                }
+
+                continue;
+            }
+
             let file = self.files.get(diagnostic.file_id);
             let (start, end) = line_range(&file.source, diagnostic.finding.range);
             let location = if start == end {
diff --git a/src/natu/natu_test.rs b/src/natu/natu_test.rs
index 45087bd..87b3c3d 100644
--- a/src/natu/natu_test.rs
+++ b/src/natu/natu_test.rs
@@ -50,7 +50,18 @@ fn natu_reports_out_of_order_let_bindings() -> googletest::Result<()> {
         .iter()
         .filter(|diagnostic| diagnostic.finding.rule_id == "let_order")
         .count();
-    expect_that!(let_order_count, eq(4));
+    expect_that!(let_order_count, eq(2));
+    expect_that!(
+        report.to_string(),
+        eq(concat!(
+            "testdata/lint_findings.nix:11 [manual_inherit] Use `inherit` for this assignment\n",
+            "testdata/lint_findings.nix:12 [manual_inherit_from] Use `inherit` for this selected attribute\n",
+            "testdata/lint_findings.nix:13 [unquoted_uri] URI literals should be quoted\n",
+            "testdata/lint_findings.nix [let_order] Let bindings must follow dependency order\n",
+            "  line 5: nestedSecond, nestedFirst\n",
+            "  line 2: first, second, nested\n",
+        ))
+    );
     Ok(())
 }
 
diff --git a/src/natu/rules.rs b/src/natu/rules.rs
index 558e302..7d0e6b8 100644
--- a/src/natu/rules.rs
+++ b/src/natu/rules.rs
@@ -22,6 +22,7 @@ pub struct Finding {
     pub range: ast::SourceRange,
     pub message: &'static str,
     pub binding: Option<String>,
+    pub expected_order: Option<Vec<String>>,
 }
 
 impl std::fmt::Display for Diagnostic {
@@ -79,7 +80,8 @@ pub fn run_rules(file: &ast::ParsedFile, graph: &ScopeGraph) -> Vec<Diagnostic>
         rule_id: "let_order",
         range: finding.range,
         message: "Let bindings must follow dependency order",
-        binding: Some(finding.binding),
+        binding: None,
+        expected_order: Some(finding.expected_order),
     });
 
     node_diagnostics
@@ -104,6 +106,7 @@ where
         range: node.range,
         message,
         binding: None,
+        expected_order: None,
     })
 }
 
@@ -119,5 +122,6 @@ where
         range: token.range,
         message,
         binding: None,
+        expected_order: None,
     })
 }
diff --git a/src/natu/rules/let_order.rs b/src/natu/rules/let_order.rs
index 7d01ebf..658291a 100644
--- a/src/natu/rules/let_order.rs
+++ b/src/natu/rules/let_order.rs
@@ -5,7 +5,7 @@ use crate::{
 
 pub struct Finding {
     pub range: ast::SourceRange,
-    pub binding: String,
+    pub expected_order: Vec<String>,
 }
 
 pub fn check(graph: &ScopeGraph) -> Vec<Finding> {
@@ -14,26 +14,26 @@ pub fn check(graph: &ScopeGraph) -> Vec<Finding> {
         .iter()
         .flat_map(|let_scope| {
             let expected = expected_order(graph, let_scope);
-            let positions = expected
-                .iter()
-                .enumerate()
-                .map(|(position, declaration)| (*declaration, position))
-                .collect::<Vec<_>>();
+            let is_ordered = expected.iter().enumerate().all(|(position, declaration)| {
+                let_scope
+                    .bindings
+                    .get(position)
+                    .is_some_and(|binding| binding.declaration == *declaration)
+            });
 
-            let_scope
-                .bindings
-                .iter()
-                .enumerate()
-                .filter_map(move |(position, binding)| {
-                    positions
-                        .iter()
-                        .find(|(declaration, _)| *declaration == binding.declaration)
-                        .filter(|(_, expected_position)| position != *expected_position)
-                        .map(|_| Finding {
-                            range: binding.range,
-                            binding: binding.name.clone(),
-                        })
-                })
+            (!is_ordered).then(|| Finding {
+                range: let_scope.bindings[0].range,
+                expected_order: expected
+                    .iter()
+                    .filter_map(|declaration| {
+                        let_scope
+                            .bindings
+                            .iter()
+                            .find(|binding| binding.declaration == *declaration)
+                            .map(|binding| binding.name.clone())
+                    })
+                    .collect(),
+            })
         })
         .collect()
 }