feat(xatu): add manual inherit lint

src/xatu/BUILD

@@ -8,6 +8,7 @@ rust_library(
         "file_store.rs",
         "parser.rs",
         "rules.rs",
+        "rules/manual_inherit.rs",
         "rules/unquoted_uri.rs",
         "xatu.rs",
     ],

src/xatu/ast.rs

@@ -29,6 +29,7 @@ impl std::fmt::Display for SourceRange {
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum NodeData {
     Apply(Apply),
+    AttrpathValue(AttrpathValue),
     LetIn(LetIn),
     Inherit(Inherit),
 }
@@ -38,6 +39,12 @@ pub struct Apply {
     pub function: Expr,
 }
 
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct AttrpathValue {
+    pub key: Ident,
+    pub value: Ident,
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum Expr {
     Ident(Ident),

src/xatu/parser.rs

@@ -1,4 +1,4 @@
-use rnix::ast::HasEntry;
+use rnix::ast::{Attr, HasEntry};
 use rowan::ast::AstNode;
 
 use crate::{FileId, ast};
@@ -38,6 +38,7 @@ fn convert_syntax(syntax: rnix::SyntaxNode) -> (Vec<ast::Node>, Vec<ast::Token>)
 fn convert_node(node: rnix::SyntaxNode) -> Option<ast::Node> {
     match node.kind() {
         rnix::SyntaxKind::NODE_APPLY => convert_apply(node),
+        rnix::SyntaxKind::NODE_ATTRPATH_VALUE => convert_attrpath_value(node),
         rnix::SyntaxKind::NODE_LET_IN => convert_let_in(node),
         rnix::SyntaxKind::NODE_INHERIT => convert_inherit(node),
         _ => None,
@@ -65,6 +66,40 @@ impl TryFrom<rnix::ast::Apply> for ast::Apply {
     }
 }
 
+fn convert_attrpath_value(node: rnix::SyntaxNode) -> Option<ast::Node> {
+    let attrpath_value = rnix::ast::AttrpathValue::cast(node)?;
+    let range = attrpath_value.syntax().text_range().into();
+    let data = attrpath_value.try_into().ok()?;
+
+    Some(ast::Node {
+        range,
+        data: ast::NodeData::AttrpathValue(data),
+    })
+}
+
+impl TryFrom<rnix::ast::AttrpathValue> for ast::AttrpathValue {
+    type Error = ();
+
+    fn try_from(attrpath_value: rnix::ast::AttrpathValue) -> Result<Self, Self::Error> {
+        let mut attrs = attrpath_value.attrpath().ok_or(())?.attrs();
+        let key = match attrs.next().ok_or(())? {
+            Attr::Ident(ident) => ident.into(),
+            _ => return Err(()),
+        };
+
+        if attrs.next().is_some() {
+            return Err(());
+        }
+
+        let value = match attrpath_value.value().ok_or(())? {
+            rnix::ast::Expr::Ident(ident) => ident.into(),
+            _ => return Err(()),
+        };
+
+        Ok(Self { key, value })
+    }
+}
+
 impl TryFrom<rnix::ast::Expr> for ast::Expr {
     type Error = ();
 

src/xatu/rules.rs

@@ -1,7 +1,9 @@
 use crate::FileId;
 use crate::ast;
+use crate::rules::manual_inherit::ManualInherit;
 use crate::rules::unquoted_uri::UnquotedUri;
 
+pub mod manual_inherit;
 pub mod unquoted_uri;
 
 #[derive(Debug)]
@@ -27,7 +29,6 @@ impl std::fmt::Display for Diagnostic {
     }
 }
 
-#[expect(dead_code, reason = "retained for planned node rules")]
 pub trait NodeRule {
     type Node;
 
@@ -47,7 +48,11 @@ pub trait TokenRule {
 }
 
 pub fn run_rules(file: &ast::ParsedFile) -> Vec<Diagnostic> {
-    let node_diagnostics = file.nodes.iter().flat_map(|_| std::iter::empty());
+    let node_diagnostics = file
+        .nodes
+        .iter()
+        .flat_map(|node| [run_node_rule::<ManualInherit>(node)])
+        .flatten();
     let token_diagnostics = file
         .tokens
         .iter()
@@ -63,7 +68,6 @@ pub fn run_rules(file: &ast::ParsedFile) -> Vec<Diagnostic> {
         .collect()
 }
 
-#[expect(dead_code, reason = "retained for planned node rules")]
 fn run_node_rule<R>(node: &ast::Node) -> Option<Finding>
 where
     R: NodeRule,

src/xatu/rules/manual_inherit.rs

@@ -0,0 +1,24 @@
+use crate::{ast, rules::NodeRule};
+
+pub struct ManualInherit;
+
+impl NodeRule for ManualInherit {
+    type Node = ast::AttrpathValue;
+
+    const ID: &'static str = "manual_inherit";
+
+    fn select(data: &ast::NodeData) -> Option<&Self::Node> {
+        match data {
+            ast::NodeData::AttrpathValue(attrpath_value) => Some(attrpath_value),
+            _ => None,
+        }
+    }
+
+    fn check(node: &Self::Node) -> Option<&'static str> {
+        if node.key == node.value {
+            Some("This assignment is better written with `inherit`")
+        } else {
+            None
+        }
+    }
+}

src/xatu/testdata/clean.nix

@@ -4,4 +4,9 @@
   path = ./. + "/foo";
   url = "https://example.com";
   inherit pkgs;
+  different = other;
+  nested.package = nested.package;
+  "quoted" = quoted;
+  ${dynamic} = dynamic;
+  from = pkgs.from;
 }

src/xatu/testdata/lint_findings.nix

@@ -1,3 +1,4 @@
 {
+  package = package;
   url = https://example.com;
 }

src/xatu/xatu_test.rs

@@ -64,3 +64,16 @@ fn xatu_reports_unquoted_uri() -> googletest::Result<()> {
     );
     Ok(())
 }
+
+#[gtest]
+fn xatu_reports_manual_inherit() -> googletest::Result<()> {
+    let report = xatu::future_sight(vec![fixture_source("testdata/lint_findings.nix")?]).or_fail()?;
+
+    let manual_inherit_count = report
+        .diagnostics
+        .iter()
+        .filter(|diagnostic| diagnostic.finding.rule_id == "manual_inherit")
+        .count();
+    expect_that!(manual_inherit_count, eq(1));
+    Ok(())
+}