new lint: empty_inherit

bin/tests/data/empty_inherit.nix

@@ -0,0 +1,3 @@
+{
+  inherit;
+}

bin/tests/snapshots/main__empty_inherit.snap

@@ -0,0 +1,13 @@
+---
+source: bin/tests/main.rs
+expression: "&out"
+
+---
+[W14] Warning: Found empty inherit statement
+   ╭─[data/empty_inherit.nix:2:3]
+   │
+ 2 │   inherit;
+   ·   ────┬───  
+   ·       ╰───── Remove this empty inherit statement
+───╯
+

lib/src/lib.rs

@@ -1,6 +1,7 @@
 #![recursion_limit = "1024"]
 mod lints;
 mod make;
+mod utils;
 
 pub use lints::LINTS;
 

lib/src/lints.rs

@@ -14,4 +14,5 @@ lints! {
     redundant_pattern_bind,
     unquoted_uri,
     deprecated_is_null,
+    empty_inherit,
 }

lib/src/lints/empty_inherit.rs

@@ -0,0 +1,53 @@
+use crate::{make, utils, Metadata, Report, Rule, Suggestion};
+
+use if_chain::if_chain;
+use macros::lint;
+use rnix::{
+    types::{Inherit, TypedNode},
+    NodeOrToken, SyntaxElement, SyntaxKind,
+};
+
+/// ## What it does
+/// Checks for empty inherit statements.
+///
+/// ## Why is this bad?
+/// Useless code, probably the result of a refactor.
+///
+/// ## Example
+///
+/// ```nix
+/// inherit;
+/// ```
+///
+/// Remove it altogether.
+#[lint(
+    name = "empty_inherit",
+    note = "Found empty inherit statement",
+    code = 14,
+    match_with = SyntaxKind::NODE_INHERIT
+)]
+struct EmptyInherit;
+
+impl Rule for EmptyInherit {
+    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+        if_chain! {
+            if let NodeOrToken::Node(node) = node;
+            if let Some(inherit_stmt) = Inherit::cast(node.clone());
+            if inherit_stmt.from().is_none();
+            if inherit_stmt.idents().count() == 0;
+            then {
+                let at = node.text_range();
+                let replacement = make::empty().node().clone();
+                let replacement_at = utils::with_preceeding_whitespace(node);
+                let message = "Remove this empty `inherit` statement";
+                Some(
+                    self
+                    .report()
+                    .suggest(at, message, Suggestion::new(replacement_at, replacement))
+                )
+            } else {
+                None
+            }
+        }
+    }
+}

lib/src/utils.rs

@@ -0,0 +1,16 @@
+use rnix::{SyntaxKind, SyntaxNode, TextRange};
+
+pub fn with_preceeding_whitespace(node: &SyntaxNode) -> TextRange {
+    let start = node
+        .prev_sibling_or_token()
+        .map(|t| {
+            if t.kind() == SyntaxKind::TOKEN_WHITESPACE {
+                t.text_range().start()
+            } else {
+                t.text_range().end()
+            }
+        })
+        .unwrap_or(node.text_range().start());
+    let end = node.text_range().end();
+    TextRange::new(start, end)
+}