From 4b7d3834ab54313e96fec207f4b5944156013d65 Mon Sep 17 00:00:00 2001
From: alexion <contact@alexion.dev>
Date: Sat, 19 Sep 2026 21:27:23 -0400
Subject: [PATCH] feat(xatu): add manual inherit lint

---
 src/xatu/BUILD                      |   1 +
 src/xatu/ast.rs                     |  31 ++-------
 src/xatu/parser.rs                  | 104 ++++++----------------------
 src/xatu/rules.rs                   |  10 ++-
 src/xatu/rules/manual_inherit.rs    |  23 ++++++
 src/xatu/testdata/clean.nix         |   5 ++
 src/xatu/testdata/lint_findings.nix |   1 +
 src/xatu/xatu_test.rs               |  13 ++++
 8 files changed, 77 insertions(+), 111 deletions(-)
 create mode 100644 src/xatu/rules/manual_inherit.rs

diff --git a/src/xatu/BUILD b/src/xatu/BUILD
index 4a72c08..ea83932 100644
--- a/src/xatu/BUILD
+++ b/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",
     ],
diff --git a/src/xatu/ast.rs b/src/xatu/ast.rs
index 1addbf4..4b3c25c 100644
--- a/src/xatu/ast.rs
+++ b/src/xatu/ast.rs
@@ -28,20 +28,13 @@ impl std::fmt::Display for SourceRange {
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum NodeData {
-    Apply(Apply),
-    LetIn(LetIn),
-    Inherit(Inherit),
+    Binding(Binding),
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
-pub struct Apply {
-    pub function: Expr,
-}
-
-#[derive(Debug, Clone, PartialEq, Eq)]
-pub enum Expr {
-    Ident(Ident),
-    Select(Box<Select>),
+pub struct Binding {
+    pub key: Ident,
+    pub value: Ident,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -49,22 +42,6 @@ pub struct Ident {
     pub name: String,
 }
 
-#[derive(Debug, Clone, PartialEq, Eq)]
-pub struct Select {
-    pub receiver: Expr,
-    pub attrs: Vec<Ident>,
-}
-
-#[derive(Debug, Clone, PartialEq, Eq)]
-pub struct LetIn {
-    pub binding_count: usize,
-}
-
-#[derive(Debug, Clone, PartialEq, Eq)]
-pub struct Inherit {
-    pub attr_count: usize,
-}
-
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Token {
     pub range: SourceRange,
diff --git a/src/xatu/parser.rs b/src/xatu/parser.rs
index e92f605..7bc6948 100644
--- a/src/xatu/parser.rs
+++ b/src/xatu/parser.rs
@@ -1,4 +1,4 @@
-use rnix::ast::HasEntry;
+use rnix::ast::Attr;
 use rowan::ast::AstNode;
 
 use crate::{FileId, ast};
@@ -37,43 +37,42 @@ 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_LET_IN => convert_let_in(node),
-        rnix::SyntaxKind::NODE_INHERIT => convert_inherit(node),
+        rnix::SyntaxKind::NODE_ATTRPATH_VALUE => convert_binding(node),
         _ => None,
     }
 }
 
-fn convert_apply(node: rnix::SyntaxNode) -> Option<ast::Node> {
-    let apply = rnix::ast::Apply::cast(node)?;
-    let range = apply.syntax().text_range().into();
-    let data = apply.try_into().ok()?;
+fn convert_binding(node: rnix::SyntaxNode) -> Option<ast::Node> {
+    let binding = rnix::ast::AttrpathValue::cast(node)?;
+    let range = binding.syntax().text_range().into();
+    let data = binding.try_into().ok()?;
 
     Some(ast::Node {
         range,
-        data: ast::NodeData::Apply(data),
+        data: ast::NodeData::Binding(data),
     })
 }
 
-impl TryFrom<rnix::ast::Apply> for ast::Apply {
+impl TryFrom<rnix::ast::AttrpathValue> for ast::Binding {
     type Error = ();
 
-    fn try_from(apply: rnix::ast::Apply) -> Result<Self, Self::Error> {
-        Ok(Self {
-            function: apply.lambda().ok_or(())?.try_into()?,
-        })
-    }
-}
+    fn try_from(binding: rnix::ast::AttrpathValue) -> Result<Self, Self::Error> {
+        let mut attrs = binding.attrpath().ok_or(())?.attrs();
+        let key = match attrs.next().ok_or(())? {
+            Attr::Ident(ident) => ident.into(),
+            _ => return Err(()),
+        };
 
-impl TryFrom<rnix::ast::Expr> for ast::Expr {
-    type Error = ();
-
-    fn try_from(expr: rnix::ast::Expr) -> Result<Self, Self::Error> {
-        match expr {
-            rnix::ast::Expr::Ident(ident) => Ok(Self::Ident(ident.into())),
-            rnix::ast::Expr::Select(select) => Ok(Self::Select(Box::new(select.try_into()?))),
-            _ => Err(()),
+        if attrs.next().is_some() {
+            return Err(());
         }
+
+        let value = match binding.value().ok_or(())? {
+            rnix::ast::Expr::Ident(ident) => ident.into(),
+            _ => return Err(()),
+        };
+
+        Ok(Self { key, value })
     }
 }
 
@@ -85,63 +84,6 @@ impl From<rnix::ast::Ident> for ast::Ident {
     }
 }
 
-impl TryFrom<rnix::ast::Select> for ast::Select {
-    type Error = ();
-
-    fn try_from(select: rnix::ast::Select) -> Result<Self, Self::Error> {
-        Ok(Self {
-            receiver: select.expr().ok_or(())?.try_into()?,
-            attrs: select
-                .attrpath()
-                .ok_or(())?
-                .attrs()
-                .map(|attr| match attr {
-                    rnix::ast::Attr::Ident(ident) => Ok(ident.into()),
-                    _ => Err(()),
-                })
-                .collect::<Result<Vec<_>, _>>()?,
-        })
-    }
-}
-
-fn convert_let_in(node: rnix::SyntaxNode) -> Option<ast::Node> {
-    let let_in = rnix::ast::LetIn::cast(node)?;
-
-    Some(ast::Node {
-        range: let_in.syntax().text_range().into(),
-        data: ast::NodeData::LetIn(let_in.into()),
-    })
-}
-
-impl From<rnix::ast::LetIn> for ast::LetIn {
-    fn from(let_in: rnix::ast::LetIn) -> Self {
-        Self {
-            binding_count: let_in.attrpath_values().count()
-                + let_in
-                    .inherits()
-                    .map(|inherit| inherit.attrs().count())
-                    .sum::<usize>(),
-        }
-    }
-}
-
-fn convert_inherit(node: rnix::SyntaxNode) -> Option<ast::Node> {
-    let inherit = rnix::ast::Inherit::cast(node)?;
-
-    Some(ast::Node {
-        range: inherit.syntax().text_range().into(),
-        data: ast::NodeData::Inherit(inherit.into()),
-    })
-}
-
-impl From<rnix::ast::Inherit> for ast::Inherit {
-    fn from(inherit: rnix::ast::Inherit) -> Self {
-        Self {
-            attr_count: inherit.attrs().count(),
-        }
-    }
-}
-
 fn convert_token(token: rnix::SyntaxToken) -> Option<ast::Token> {
     match token.kind() {
         rnix::SyntaxKind::TOKEN_URI => Some(ast::Token {
diff --git a/src/xatu/rules.rs b/src/xatu/rules.rs
index 45af16e..598e8d7 100644
--- a/src/xatu/rules.rs
+++ b/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,
diff --git a/src/xatu/rules/manual_inherit.rs b/src/xatu/rules/manual_inherit.rs
new file mode 100644
index 0000000..9a6a7a9
--- /dev/null
+++ b/src/xatu/rules/manual_inherit.rs
@@ -0,0 +1,23 @@
+use crate::{ast, rules::NodeRule};
+
+pub struct ManualInherit;
+
+impl NodeRule for ManualInherit {
+    type Node = ast::Binding;
+
+    const ID: &'static str = "manual_inherit";
+
+    fn select(data: &ast::NodeData) -> Option<&Self::Node> {
+        let ast::NodeData::Binding(binding) = data;
+
+        Some(binding)
+    }
+
+    fn check(node: &Self::Node) -> Option<&'static str> {
+        if node.key == node.value {
+            Some("Use `inherit` for this assignment")
+        } else {
+            None
+        }
+    }
+}
diff --git a/src/xatu/testdata/clean.nix b/src/xatu/testdata/clean.nix
index 0963365..01c2d4b 100644
--- a/src/xatu/testdata/clean.nix
+++ b/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;
 }
diff --git a/src/xatu/testdata/lint_findings.nix b/src/xatu/testdata/lint_findings.nix
index 1b922e8..e31135d 100644
--- a/src/xatu/testdata/lint_findings.nix
+++ b/src/xatu/testdata/lint_findings.nix
@@ -1,3 +1,4 @@
 {
+  package = package;
   url = https://example.com;
 }
diff --git a/src/xatu/xatu_test.rs b/src/xatu/xatu_test.rs
index 57ce7f4..3a4e8b9 100644
--- a/src/xatu/xatu_test.rs
+++ b/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(())
+}