4 files changed, 129 insertions, 15 deletions

diff --git a/lib/src/lib.rs b/lib/src/lib.rs
index ab4a14a..f0f26dd 100644
--- a/lib/src/lib.rs
+++ b/lib/src/lib.rs
@@ -4,7 +4,7 @@ mod make;
 pub use lints::LINTS;
 
 use rnix::{SyntaxElement, SyntaxKind, TextRange};
-use std::{default::Default, convert::Into};
+use std::{convert::Into, default::Default};
 
 /// Report generated by a lint
 #[derive(Debug, Default)]
@@ -32,11 +32,16 @@ impl Report {
         self
     }
     /// Add a diagnostic with a fix to this report
-    pub fn suggest<S: AsRef<str>>(mut self, at: TextRange, message: S, suggestion: Suggestion) -> Self {
-        self.diagnostics.push(Diagnostic::suggest(at, message, suggestion));
+    pub fn suggest<S: AsRef<str>>(
+        mut self,
+        at: TextRange,
+        message: S,
+        suggestion: Suggestion,
+    ) -> Self {
+        self.diagnostics
+            .push(Diagnostic::suggest(at, message, suggestion));
         self
     }
-
 }
 
 /// Mapping from a bytespan to an error message.
@@ -51,11 +56,19 @@ pub struct Diagnostic {
 impl Diagnostic {
     /// Construct a diagnostic.
     pub fn new(at: TextRange, message: String) -> Self {
-        Self { at, message, suggestion: None }
+        Self {
+            at,
+            message,
+            suggestion: None,
+        }
     }
     /// Construct a diagnostic with a fix.
     pub fn suggest<S: AsRef<str>>(at: TextRange, message: S, suggestion: Suggestion) -> Self {
-        Self { at, message: message.as_ref().into(), suggestion: Some(suggestion) }
+        Self {
+            at,
+            message: message.as_ref().into(),
+            suggestion: Some(suggestion),
+        }
     }
 }
 
@@ -72,7 +85,7 @@ impl Suggestion {
     pub fn new<E: Into<SyntaxElement>>(at: TextRange, fix: E) -> Self {
         Self {
             at,
-            fix: fix.into()
+            fix: fix.into(),
         }
     }
 }
@@ -86,10 +99,18 @@ pub trait Rule {
 /// Contains information about the lint itself. Do not implement manually,
 /// look at the `lint` attribute macro instead for implementing rules
 pub trait Metadata {
-    fn name() -> &'static str where Self: Sized;
-    fn note() -> &'static str where Self: Sized;
-    fn code() -> u32 where Self: Sized;
-    fn report() -> Report where Self: Sized;
+    fn name() -> &'static str
+    where
+        Self: Sized;
+    fn note() -> &'static str
+    where
+        Self: Sized;
+    fn code() -> u32
+    where
+        Self: Sized;
+    fn report() -> Report
+    where
+        Self: Sized;
     fn match_with(&self, with: &SyntaxKind) -> bool;
     fn match_kind(&self) -> SyntaxKind;
 }
diff --git a/lib/src/lints.rs b/lib/src/lints.rs
index 30c1678..98aa404 100644
--- a/lib/src/lints.rs
+++ b/lib/src/lints.rs
@@ -5,4 +5,5 @@ lint_map! {
     empty_let_in,
     manual_inherit,
     manual_inherit_from,
+    legacy_let_syntax,
 }
diff --git a/lib/src/lints/legacy_let_syntax.rs b/lib/src/lints/legacy_let_syntax.rs
new file mode 100644
index 0000000..c5588e2
--- /dev/null
+++ b/lib/src/lints/legacy_let_syntax.rs
@@ -0,0 +1,55 @@
+use crate::{make, Lint, Metadata, Report, Rule, Suggestion};
+
+use if_chain::if_chain;
+use macros::lint;
+use rnix::{
+    types::{EntryHolder, Ident, Key, LegacyLet, TokenWrapper, TypedNode},
+    NodeOrToken, SyntaxElement, SyntaxKind,
+};
+
+#[lint(
+    name = "legacy let syntax",
+    note = "Using undocumented `let` syntax",
+    code = 5,
+    match_with = SyntaxKind::NODE_LEGACY_LET
+)]
+struct ManualInherit;
+
+impl Rule for ManualInherit {
+    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+        if_chain! {
+            if let NodeOrToken::Node(node) = node;
+            if let Some(legacy_let) = LegacyLet::cast(node.clone());
+
+            if legacy_let
+                .entries()
+                .find(|kv| matches!(kv.key(), Some(k) if key_is_ident(&k, "body")))
+                .is_some();
+
+            then {
+                let inherits = legacy_let.inherits();
+                let entries = legacy_let.entries();
+                let attrset = make::attrset(inherits, entries, true);
+                let parenthesized = make::parenthesize(&attrset.node());
+                let selected = make::select(parenthesized.node(), &make::ident("body").node());
+
+                let at = node.text_range();
+                let message = "Prefer `rec` over undocumented `let` syntax";
+                let replacement = selected.node().clone();
+
+                Some(Self::report().suggest(at, message, Suggestion::new(at, replacement)))
+            } else {
+                None
+            }
+        }
+    }
+}
+
+fn key_is_ident(key_path: &Key, ident: &str) -> bool {
+    if let Some(key_node) = key_path.path().next() {
+        if let Some(key) = Ident::cast(key_node) {
+            return key.as_str() == ident;
+        }
+    }
+    false
+}
diff --git a/lib/src/make.rs b/lib/src/make.rs
index cf371a2..2a6450c 100644
--- a/lib/src/make.rs
+++ b/lib/src/make.rs
@@ -1,13 +1,20 @@
-use std::iter::IntoIterator;
+use std::{fmt::Write, iter::IntoIterator};
 
-use rnix::{SyntaxNode, types::{TypedNode, self, TokenWrapper}};
+use rnix::{
+    types::{self, TokenWrapper, TypedNode},
+    SyntaxNode,
+};
 
 fn ast_from_text<N: TypedNode>(text: &str) -> N {
     let parse = rnix::parse(text);
     let node = match parse.node().descendants().find_map(N::cast) {
         Some(it) => it,
         None => {
-            panic!("Failed to make ast node `{}` from text `{}`", std::any::type_name::<N>(), text)
+            panic!(
+                "Failed to make ast node `{}` from text `{}`",
+                std::any::type_name::<N>(),
+                text
+            )
         }
     };
     node
@@ -30,7 +37,10 @@ pub fn inherit_stmt<'a>(nodes: impl IntoIterator<Item = &'a types::Ident>) -> ty
     ast_from_text(&format!("{{ inherit {}; }}", inherited_idents))
 }
 
-pub fn inherit_from_stmt<'a>(from: SyntaxNode, nodes: impl IntoIterator<Item = &'a types::Ident>) -> types::Inherit {
+pub fn inherit_from_stmt<'a>(
+    from: SyntaxNode,
+    nodes: impl IntoIterator<Item = &'a types::Ident>,
+) -> types::Inherit {
     let inherited_idents = nodes
         .into_iter()
         .map(|i| i.as_str().to_owned())
@@ -38,3 +48,30 @@ pub fn inherit_from_stmt<'a>(from: SyntaxNode, nodes: impl IntoIterator<Item = &
         .join(" ");
     ast_from_text(&format!("{{ inherit ({}) {}; }}", from, inherited_idents))
 }
+
+pub fn attrset(
+    inherits: impl IntoIterator<Item = types::Inherit>,
+    entries: impl IntoIterator<Item = types::KeyValue>,
+    recursive: bool,
+) -> types::AttrSet {
+    let mut buffer = String::new();
+
+    writeln!(buffer, "{}{{", if recursive { "rec " } else { "" }).unwrap();
+    for inherit in inherits.into_iter() {
+        writeln!(buffer, "    {}", inherit.node().text()).unwrap();
+    }
+    for entry in entries.into_iter() {
+        writeln!(buffer, "    {}", entry.node().text()).unwrap();
+    }
+    write!(buffer, "}}").unwrap();
+
+    ast_from_text(&buffer)
+}
+
+pub fn select(set: &SyntaxNode, index: &SyntaxNode) -> types::Select {
+    ast_from_text(&format!("{}.{}", set, index))
+}
+
+pub fn ident(text: &str) -> types::Ident {
+    ast_from_text(text)
+}