18 files changed, 207 insertions, 29 deletions

diff --git a/lib/src/lib.rs b/lib/src/lib.rs
index a25b814..cc4818a 100644
--- a/lib/src/lib.rs
+++ b/lib/src/lib.rs
@@ -1,9 +1,11 @@
 #![recursion_limit = "1024"]
 mod lints;
 mod make;
+pub mod session;
 mod utils;
 
 pub use lints::LINTS;
+use session::SessionInfo;
 
 use rnix::{parser::ParseError, SyntaxElement, SyntaxKind, TextRange};
 use std::{convert::Into, default::Default};
@@ -221,7 +223,7 @@ impl Serialize for Suggestion {
 /// Lint logic is defined via this trait. Do not implement manually,
 /// look at the `lint` attribute macro instead for implementing rules
 pub trait Rule {
-    fn validate(&self, node: &SyntaxElement) -> Option<Report>;
+    fn validate(&self, node: &SyntaxElement, sess: &SessionInfo) -> Option<Report>;
 }
 
 /// Contains information about the lint itself. Do not implement manually,
diff --git a/lib/src/lints.rs b/lib/src/lints.rs
index 5de6b65..0add458 100644
--- a/lib/src/lints.rs
+++ b/lib/src/lints.rs
@@ -15,4 +15,5 @@ lints! {
     unquoted_uri,
     deprecated_is_null,
     empty_inherit,
+    faster_groupby,
 }
diff --git a/lib/src/lints/bool_comparison.rs b/lib/src/lints/bool_comparison.rs
index ed1e8bb..ef7f5d2 100644
--- a/lib/src/lints/bool_comparison.rs
+++ b/lib/src/lints/bool_comparison.rs
@@ -1,4 +1,4 @@
-use crate::{make, Metadata, Report, Rule, Suggestion};
+use crate::{make, session::SessionInfo, Metadata, Report, Rule, Suggestion};
 
 use if_chain::if_chain;
 use macros::lint;
@@ -35,7 +35,7 @@ use rnix::{
 struct BoolComparison;
 
 impl Rule for BoolComparison {
-    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+    fn validate(&self, node: &SyntaxElement, _sess: &SessionInfo) -> Option<Report> {
         if_chain! {
             if let NodeOrToken::Node(node) = node;
             if let Some(bin_expr) = BinOp::cast(node.clone());
diff --git a/lib/src/lints/collapsible_let_in.rs b/lib/src/lints/collapsible_let_in.rs
index aa7e5a7..1c04d9c 100644
--- a/lib/src/lints/collapsible_let_in.rs
+++ b/lib/src/lints/collapsible_let_in.rs
@@ -1,4 +1,4 @@
-use crate::{make, Metadata, Report, Rule, Suggestion};
+use crate::{make, session::SessionInfo, Metadata, Report, Rule, Suggestion};
 
 use if_chain::if_chain;
 use macros::lint;
@@ -45,7 +45,7 @@ use rowan::Direction;
 struct CollapsibleLetIn;
 
 impl Rule for CollapsibleLetIn {
-    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+    fn validate(&self, node: &SyntaxElement, _sess: &SessionInfo) -> Option<Report> {
         if_chain! {
             if let NodeOrToken::Node(node) = node;
             if let Some(let_in_expr) = LetIn::cast(node.clone());
diff --git a/lib/src/lints/deprecated_is_null.rs b/lib/src/lints/deprecated_is_null.rs
index c814e87..9e7c293 100644
--- a/lib/src/lints/deprecated_is_null.rs
+++ b/lib/src/lints/deprecated_is_null.rs
@@ -1,4 +1,4 @@
-use crate::{make, Metadata, Report, Rule, Suggestion};
+use crate::{make, session::SessionInfo, Metadata, Report, Rule, Suggestion};
 
 use if_chain::if_chain;
 use macros::lint;
@@ -35,7 +35,7 @@ use rnix::{
 struct DeprecatedIsNull;
 
 impl Rule for DeprecatedIsNull {
-    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+    fn validate(&self, node: &SyntaxElement, _sess: &SessionInfo) -> Option<Report> {
         if_chain! {
             if let NodeOrToken::Node(node) = node;
             if let Some(apply) = Apply::cast(node.clone());
diff --git a/lib/src/lints/empty_inherit.rs b/lib/src/lints/empty_inherit.rs
index 9ae4cf2..871c218 100644
--- a/lib/src/lints/empty_inherit.rs
+++ b/lib/src/lints/empty_inherit.rs
@@ -1,4 +1,4 @@
-use crate::{make, utils, Metadata, Report, Rule, Suggestion};
+use crate::{make, session::SessionInfo, utils, Metadata, Report, Rule, Suggestion};
 
 use if_chain::if_chain;
 use macros::lint;
@@ -29,7 +29,7 @@ use rnix::{
 struct EmptyInherit;
 
 impl Rule for EmptyInherit {
-    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+    fn validate(&self, node: &SyntaxElement, _sess: &SessionInfo) -> Option<Report> {
         if_chain! {
             if let NodeOrToken::Node(node) = node;
             if let Some(inherit_stmt) = Inherit::cast(node.clone());
diff --git a/lib/src/lints/empty_let_in.rs b/lib/src/lints/empty_let_in.rs
index d33d0ae..e42f658 100644
--- a/lib/src/lints/empty_let_in.rs
+++ b/lib/src/lints/empty_let_in.rs
@@ -1,4 +1,4 @@
-use crate::{Metadata, Report, Rule, Suggestion};
+use crate::{session::SessionInfo, Metadata, Report, Rule, Suggestion};
 
 use if_chain::if_chain;
 use macros::lint;
@@ -34,7 +34,7 @@ use rnix::{
 struct EmptyLetIn;
 
 impl Rule for EmptyLetIn {
-    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+    fn validate(&self, node: &SyntaxElement, _sess: &SessionInfo) -> Option<Report> {
         if_chain! {
             if let NodeOrToken::Node(node) = node;
             if let Some(let_in_expr) = LetIn::cast(node.clone());
diff --git a/lib/src/lints/empty_pattern.rs b/lib/src/lints/empty_pattern.rs
index f66a3b1..e03708b 100644
--- a/lib/src/lints/empty_pattern.rs
+++ b/lib/src/lints/empty_pattern.rs
@@ -1,4 +1,4 @@
-use crate::{make, Metadata, Report, Rule, Suggestion};
+use crate::{make, session::SessionInfo, Metadata, Report, Rule, Suggestion};
 
 use if_chain::if_chain;
 use macros::lint;
@@ -43,7 +43,7 @@ use rnix::{
 struct EmptyPattern;
 
 impl Rule for EmptyPattern {
-    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+    fn validate(&self, node: &SyntaxElement, _sess: &SessionInfo) -> Option<Report> {
         if_chain! {
             if let NodeOrToken::Node(node) = node;
             if let Some(pattern) = Pattern::cast(node.clone());
diff --git a/lib/src/lints/eta_reduction.rs b/lib/src/lints/eta_reduction.rs
index 580f4a0..8e9d2a3 100644
--- a/lib/src/lints/eta_reduction.rs
+++ b/lib/src/lints/eta_reduction.rs
@@ -1,4 +1,4 @@
-use crate::{Metadata, Report, Rule, Suggestion};
+use crate::{session::SessionInfo, Metadata, Report, Rule, Suggestion};
 
 use if_chain::if_chain;
 use macros::lint;
@@ -42,7 +42,7 @@ use rnix::{
 struct EtaReduction;
 
 impl Rule for EtaReduction {
-    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+    fn validate(&self, node: &SyntaxElement, _sess: &SessionInfo) -> Option<Report> {
         if_chain! {
             if let NodeOrToken::Node(node) = node;
             if let Some(lambda_expr) = Lambda::cast(node.clone());
diff --git a/lib/src/lints/faster_groupby.rs b/lib/src/lints/faster_groupby.rs
new file mode 100644
index 0000000..c496125
--- /dev/null
+++ b/lib/src/lints/faster_groupby.rs
@@ -0,0 +1,72 @@
+use crate::{
+    make,
+    session::{SessionInfo, Version},
+    Metadata, Report, Rule, Suggestion,
+};
+
+use if_chain::if_chain;
+use macros::lint;
+use rnix::{
+    types::{Select, TypedNode},
+    NodeOrToken, SyntaxElement, SyntaxKind,
+};
+
+/// ## What it does
+/// Checks for `lib.groupBy`.
+///
+/// ## Why is this bad?
+/// Nix 2.5 introduces `builtins.groupBy` which is faster and does
+/// not require a lib import.
+///
+/// ## Example
+///
+/// ```nix
+/// lib.groupBy (x: if x > 2 then "big" else "small") [ 1 2 3 4 5 6 ];
+/// # { big = [ 3 4 5 6 ]; small = [ 1 2 ]; }
+/// ```
+///
+/// Replace `lib.groupBy` with `builtins.groupBy`:
+///
+/// ```
+/// builtins.groupBy (x: if x > 2 then "big" else "small") [ 1 2 3 4 5 6 ];
+/// ```
+#[lint(
+    name = "faster_groupby",
+    note = "Found lib.groupBy",
+    code = 15,
+    match_with = SyntaxKind::NODE_SELECT
+)]
+struct FasterGroupBy;
+
+impl Rule for FasterGroupBy {
+    fn validate(&self, node: &SyntaxElement, sess: &SessionInfo) -> Option<Report> {
+        let lint_version = "nix (Nix) 2.5".parse::<Version>().unwrap();
+        if_chain! {
+            if sess.version() >=  &lint_version;
+            if let NodeOrToken::Node(node) = node;
+            if let Some(select_expr) = Select::cast(node.clone());
+            if let Some(select_from) = select_expr.set();
+            if let Some(group_by_attr) = select_expr.index();
+
+            // a heuristic to lint on nixpkgs.lib.groupBy
+            // and lib.groupBy and its variants
+            if select_from.text().to_string() != "builtins";
+            if group_by_attr.text().to_string() == "groupBy";
+
+            then {
+                let at = node.text_range();
+                let replacement = {
+                    let builtins = make::ident("builtins");
+                    make::select(builtins.node(), &group_by_attr).node().clone()
+                };
+                let message = format!("Prefer `builtins.groupBy` over `{}.groupBy`", select_from);
+                Some(
+                    self.report()
+                        .suggest(at, message, Suggestion::new(at, replacement)),
+                )
+            } else {
+                None
+            }
+        }
+    }
+}
diff --git a/lib/src/lints/legacy_let_syntax.rs b/lib/src/lints/legacy_let_syntax.rs
index 5d0028b..e0b8980 100644
--- a/lib/src/lints/legacy_let_syntax.rs
+++ b/lib/src/lints/legacy_let_syntax.rs
@@ -1,4 +1,4 @@
-use crate::{make, Metadata, Report, Rule, Suggestion};
+use crate::{make, session::SessionInfo, Metadata, Report, Rule, Suggestion};
 
 use if_chain::if_chain;
 use macros::lint;
@@ -44,7 +44,7 @@ use rnix::{
 struct ManualInherit;
 
 impl Rule for ManualInherit {
-    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+    fn validate(&self, node: &SyntaxElement, _sess: &SessionInfo) -> Option<Report> {
         if_chain! {
             if let NodeOrToken::Node(node) = node;
             if let Some(legacy_let) = LegacyLet::cast(node.clone());
diff --git a/lib/src/lints/manual_inherit.rs b/lib/src/lints/manual_inherit.rs
index 7717dc9..4fddce5 100644
--- a/lib/src/lints/manual_inherit.rs
+++ b/lib/src/lints/manual_inherit.rs
@@ -1,4 +1,4 @@
-use crate::{make, Metadata, Report, Rule, Suggestion};
+use crate::{make, session::SessionInfo, Metadata, Report, Rule, Suggestion};
 
 use if_chain::if_chain;
 use macros::lint;
@@ -40,7 +40,7 @@ use rnix::{
 struct ManualInherit;
 
 impl Rule for ManualInherit {
-    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+    fn validate(&self, node: &SyntaxElement, _sess: &SessionInfo) -> Option<Report> {
         if_chain! {
             if let NodeOrToken::Node(node) = node;
             if let Some(key_value_stmt) = KeyValue::cast(node.clone());
diff --git a/lib/src/lints/manual_inherit_from.rs b/lib/src/lints/manual_inherit_from.rs
index 05d6bc8..a62a6c7 100644
--- a/lib/src/lints/manual_inherit_from.rs
+++ b/lib/src/lints/manual_inherit_from.rs
@@ -1,4 +1,4 @@
-use crate::{make, Metadata, Report, Rule, Suggestion};
+use crate::{make, session::SessionInfo, Metadata, Report, Rule, Suggestion};
 
 use if_chain::if_chain;
 use macros::lint;
@@ -40,7 +40,7 @@ use rnix::{
 struct ManualInherit;
 
 impl Rule for ManualInherit {
-    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+    fn validate(&self, node: &SyntaxElement, _sess: &SessionInfo) -> Option<Report> {
         if_chain! {
             if let NodeOrToken::Node(node) = node;
             if let Some(key_value_stmt) = KeyValue::cast(node.clone());
diff --git a/lib/src/lints/redundant_pattern_bind.rs b/lib/src/lints/redundant_pattern_bind.rs
index 88ce4b0..56957ce 100644
--- a/lib/src/lints/redundant_pattern_bind.rs
+++ b/lib/src/lints/redundant_pattern_bind.rs
@@ -1,4 +1,4 @@
-use crate::{Metadata, Report, Rule, Suggestion};
+use crate::{session::SessionInfo, Metadata, Report, Rule, Suggestion};
 
 use if_chain::if_chain;
 use macros::lint;
@@ -35,7 +35,7 @@ use rnix::{
 struct RedundantPatternBind;
 
 impl Rule for RedundantPatternBind {
-    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+    fn validate(&self, node: &SyntaxElement, _sess: &SessionInfo) -> Option<Report> {
         if_chain! {
             if let NodeOrToken::Node(node) = node;
             if let Some(pattern) = Pattern::cast(node.clone());
diff --git a/lib/src/lints/unquoted_splice.rs b/lib/src/lints/unquoted_splice.rs
index 7649fbc..ba1641a 100644
--- a/lib/src/lints/unquoted_splice.rs
+++ b/lib/src/lints/unquoted_splice.rs
@@ -1,4 +1,4 @@
-use crate::{make, Metadata, Report, Rule, Suggestion};
+use crate::{make, session::SessionInfo, Metadata, Report, Rule, Suggestion};
 
 use if_chain::if_chain;
 use macros::lint;
@@ -40,7 +40,7 @@ use rnix::{
 struct UnquotedSplice;
 
 impl Rule for UnquotedSplice {
-    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+    fn validate(&self, node: &SyntaxElement, _sess: &SessionInfo) -> Option<Report> {
         if_chain! {
             if let NodeOrToken::Node(node) = node;
             if Dynamic::cast(node.clone()).is_some();
diff --git a/lib/src/lints/unquoted_uri.rs b/lib/src/lints/unquoted_uri.rs
index 8835338..440b278 100644
--- a/lib/src/lints/unquoted_uri.rs
+++ b/lib/src/lints/unquoted_uri.rs
@@ -1,4 +1,4 @@
-use crate::{make, Metadata, Report, Rule, Suggestion};
+use crate::{make, session::SessionInfo, Metadata, Report, Rule, Suggestion};
 
 use if_chain::if_chain;
 use macros::lint;
@@ -46,7 +46,7 @@ use rnix::{types::TypedNode, NodeOrToken, SyntaxElement, SyntaxKind};
 struct UnquotedUri;
 
 impl Rule for UnquotedUri {
-    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+    fn validate(&self, node: &SyntaxElement, _sess: &SessionInfo) -> Option<Report> {
         if_chain! {
             if let NodeOrToken::Token(token) = node;
             then {
diff --git a/lib/src/lints/useless_parens.rs b/lib/src/lints/useless_parens.rs
index 09d6f04..9cba4b3 100644
--- a/lib/src/lints/useless_parens.rs
+++ b/lib/src/lints/useless_parens.rs
@@ -1,4 +1,4 @@
-use crate::{Diagnostic, Metadata, Report, Rule, Suggestion};
+use crate::{session::SessionInfo, Diagnostic, Metadata, Report, Rule, Suggestion};
 
 use if_chain::if_chain;
 use macros::lint;
@@ -45,7 +45,7 @@ use rnix::{
 struct UselessParens;
 
 impl Rule for UselessParens {
-    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+    fn validate(&self, node: &SyntaxElement, _sess: &SessionInfo) -> Option<Report> {
         if_chain! {
             if let NodeOrToken::Node(node) = node;
             if let Some(parsed_type_node) = ParsedType::cast(node.clone());
diff --git a/lib/src/session.rs b/lib/src/session.rs
new file mode 100644
index 0000000..8d142ec
--- /dev/null
+++ b/lib/src/session.rs
@@ -0,0 +1,103 @@
+use std::{cmp::Ordering, str::FromStr};
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub struct Version {
+    major: u16,
+    minor: u16,
+    patch: Option<u16>,
+}
+
+impl Ord for Version {
+    fn cmp(&self, other: &Self) -> Ordering {
+        let score = |v: &Version| v.major * 100 + v.minor * 10 + v.patch.unwrap_or(0);
+        score(self).cmp(&score(other))
+    }
+}
+
+impl PartialOrd for Version {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+fn parse_number(s: &str) -> Option<u16> {
+    s.chars()
+        .take_while(|c| c.is_digit(10))
+        .collect::<String>()
+        .parse::<u16>()
+        .ok()
+}
+
+fn parse_version(s: &str) -> Option<Version> {
+    match s.split(' ').collect::<Vec<_>>().as_slice() {
+        [_, _, version] => {
+            let mut parts = version.split('.');
+            let major = parse_number(parts.next()?)?;
+            let minor = parse_number(parts.next()?)?;
+            let patch = parts.next().map(|p| parse_number(p)).flatten();
+            Some(Version {
+                major,
+                minor,
+                patch,
+            })
+        }
+        _ => None,
+    }
+}
+
+impl FromStr for Version {
+    type Err = ();
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        parse_version(s).ok_or(())
+    }
+}
+
+#[non_exhaustive]
+pub struct SessionInfo {
+    nix_version: Version,
+}
+
+impl SessionInfo {
+    pub fn from_version(nix_version: Version) -> Self {
+        Self { nix_version }
+    }
+
+    pub fn version(&self) -> &Version {
+        &self.nix_version
+    }
+}
+
+pub fn get_nix_version() -> Option<Version> {
+    "nix (Nix) 2.4pre20211006_53e4794".parse::<Version>().ok()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn parse_trivial() {
+        let v = "nix (Nix) 1.6.1".parse::<Version>().ok();
+        assert!(v.is_some())
+    }
+
+    #[test]
+    fn parse() {
+        let v = "nix (Nix) 2.4pre20211006_53e4794".parse::<Version>().ok();
+        assert!(v.is_some())
+    }
+
+    #[test]
+    fn compare_trivial() {
+        let v1 = "nix (Nix) 1.6.1".parse::<Version>().ok();
+        let v2 = "nix (Nix) 1.7.2".parse::<Version>().ok();
+        assert!(v2 > v1);
+    }
+
+    #[test]
+    fn compare() {
+        let v1 = "nix (Nix) 1.7".parse::<Version>().ok();
+        let v2 = "nix (Nix) 2.4pre20211006_53e4794".parse::<Version>().ok();
+        assert!(v2 >= v1);
+    }
+}