treewide: enforce strict clippy check

fix-lang/Cargo.toml

@@ -8,3 +8,6 @@ ere = { workspace = true }
 gc-arena = { workspace = true }
 num_enum = { workspace = true }
 string-interner = { workspace = true }
+
+[lints]
+workspace = true

fix-lang/src/lib.rs

@@ -8,7 +8,7 @@ use num_enum::TryFromPrimitive;
 
 macro_rules! define_builtins {
     ($(($name:literal, $variant:ident, $arity:expr)),* $(,)?) => {
-        pub const BUILTINS: &[(&str, u8)] = &[
+        const BUILTINS: &[(&str, u8)] = &[
             $(($name, $arity),)*
         ];
 
@@ -18,6 +18,10 @@ macro_rules! define_builtins {
         pub enum BuiltinId {
             $($variant,)*
         }
+
+        impl BuiltinId {
+            pub const ALL: [Self; BUILTINS.len()] = [$(Self::$variant,)*];
+        }
     };
 }
 
@@ -127,6 +131,36 @@ define_builtins! {
     ("__zipAttrsWith",             ZipAttrsWith,             2),
 }
 
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+pub struct BuiltinInfo {
+    pub name: &'static str,
+    pub global_name: &'static str,
+    pub global: bool,
+    pub arity: u8,
+}
+
+impl BuiltinId {
+    pub const TOTAL: usize = BUILTINS.len();
+
+    #[expect(
+        clippy::indexing_slicing,
+        reason = "a `BuiltinId` discriminant is always a valid index into the `BUILTINS` table"
+    )]
+    #[inline(always)]
+    pub fn info(self) -> BuiltinInfo {
+        let (global_name, arity) = BUILTINS[self as usize];
+        let (name, global) = global_name
+            .strip_prefix("__")
+            .map_or((global_name, true), |name| (name, false));
+        BuiltinInfo {
+            name,
+            global_name,
+            global,
+            arity,
+        }
+    }
+}
+
 #[repr(transparent)]
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Collect)]
 #[collect(require_static)]
@@ -427,6 +461,10 @@ fn fmt_nix_float(f: &mut Formatter<'_>, x: f64) -> FmtResult {
     let precision: i32 = 6;
     let exp = x.abs().log10().floor() as i32;
 
+    #[expect(
+        clippy::cast_sign_loss,
+        reason = "this branch runs only when exp < precision, so precision-1-exp and precision-1 are non-negative"
+    )]
     let formatted = if exp >= -4 && exp < precision {
         let decimal_places = (precision - 1 - exp) as usize;
         format!("{x:.decimal_places$}")
@@ -451,11 +489,9 @@ fn fmt_nix_float(f: &mut Formatter<'_>, x: f64) -> FmtResult {
     };
 
     if formatted.contains('.') {
-        if let Some(e_pos) = formatted.find('e') {
-            let trimmed = formatted[..e_pos]
-                .trim_end_matches('0')
-                .trim_end_matches('.');
-            write!(f, "{}{}", trimmed, &formatted[e_pos..])
+        if let Some((head, tail)) = formatted.split_once('e') {
+            let trimmed = head.trim_end_matches('0').trim_end_matches('.');
+            write!(f, "{trimmed}e{tail}")
         } else {
             let trimmed = formatted.trim_end_matches('0').trim_end_matches('.');
             write!(f, "{trimmed}")