diff --git a/rust/Cargo.lock b/rust/Cargo.lock
index d5c457f5..3b11604a 100644
--- a/rust/Cargo.lock
+++ b/rust/Cargo.lock
@@ -13,7 +13,6 @@ dependencies = [
  "getset",
  "indexmap 2.9.0",
  "itertools 0.14.0",
- "lazy_static",
  "parameterized",
  "pyo3",
  "rayon",
@@ -274,12 +273,6 @@ version = "1.0.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4a5f13b858c8d314ee3e8f639011f7ccefe71f97f96e50151fb991f267928e2c"
 
-[[package]]
-name = "lazy_static"
-version = "1.5.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "bbd2bcb4c963f2ddae06a2efc7e9f3591312473c50c6685e1f298068316e66fe"
-
 [[package]]
 name = "libc"
 version = "0.2.172"
diff --git a/rust/Cargo.toml b/rust/Cargo.toml
index 1b346c8a..c9ca82aa 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -13,7 +13,6 @@ bimap = "0.6.3"
 slotmap = "1.0.7"
 getset = "0.1.3"
 derive-new = "0.7.0"
-lazy_static = "1.5.0"
 string-interner = "0.18.0"
 thiserror = "2.0.11"
 itertools = "0.14.0"
diff --git a/rust/src/filesystem.rs b/rust/src/filesystem.rs
index 844c6ad3..1ae4b987 100644
--- a/rust/src/filesystem.rs
+++ b/rust/src/filesystem.rs
@@ -1,3 +1,4 @@
+use itertools::Itertools;
 use pyo3::exceptions::{PyFileNotFoundError, PyUnicodeDecodeError};
 use pyo3::prelude::*;
 use regex::Regex;
@@ -5,16 +6,16 @@ use std::collections::HashMap;
 use std::ffi::OsStr;
 use std::fs;
 use std::path::{Path, PathBuf};
+use std::sync::LazyLock;
 use unindent::unindent;
-use lazy_static::lazy_static;
 
 
-lazy_static! {
-    static ref ENCODING_RE: Regex = Regex::new(r"^[ \t\f]*#.*?coding[:=][ \t]*([-_.a-zA-Z0-9]+)").unwrap();
-}
+static ENCODING_RE: LazyLock<Regex> = LazyLock::new(|| {
+    Regex::new(r"^[ \t\f]*#.*?coding[:=][ \t]*([-_.a-zA-Z0-9]+)").unwrap()
+});
 
 pub trait FileSystem: Send + Sync {
-    fn sep(&self) -> String;
+    fn sep(&self) -> &str;
 
     fn join(&self, components: Vec<String>) -> String;
 
@@ -37,8 +38,8 @@ pub struct PyRealBasicFileSystem {
 }
 
 impl FileSystem for RealBasicFileSystem {
-    fn sep(&self) -> String {
-        std::path::MAIN_SEPARATOR.to_string()
+    fn sep(&self) -> &str {
+        std::path::MAIN_SEPARATOR_STR
     }
 
     fn join(&self, components: Vec<String>) -> String {
@@ -46,7 +47,7 @@ impl FileSystem for RealBasicFileSystem {
         for component in components {
             path.push(component);
         }
-        path.to_str().unwrap().to_string()
+        path.to_str().expect("Path components should be valid unicode").to_string()
     }
 
     fn split(&self, file_name: &str) -> (String, String) {
@@ -65,8 +66,8 @@ impl FileSystem for RealBasicFileSystem {
         };
 
         (
-            head.to_str().unwrap().to_string(),
-            tail.to_str().unwrap().to_string(),
+            head.to_str().expect("Path components should be valid unicode").to_string(),
+            tail.to_str().expect("Path components should be valid unicode").to_string(),
         )
     }
 
@@ -136,7 +137,7 @@ impl PyRealBasicFileSystem {
     }
 
     #[getter]
-    fn sep(&self) -> String {
+    fn sep(&self) -> &str {
         self.inner.sep()
     }
 
@@ -191,17 +192,16 @@ impl FakeBasicFileSystem {
 }
 
 impl FileSystem for FakeBasicFileSystem {
-    fn sep(&self) -> String {
-        "/".to_string()
+    fn sep(&self) -> &str {
+        "/"
     }
 
     fn join(&self, components: Vec<String>) -> String {
         let sep = self.sep();
         components
             .into_iter()
-            .map(|c| c.trim_end_matches(&sep).to_string())
-            .collect::<Vec<String>>()
-            .join(&sep)
+            .map(|c| c.trim_end_matches(sep).to_string())
+            .join(sep)
     }
 
     fn split(&self, file_name: &str) -> (String, String) {
@@ -217,8 +217,8 @@ impl FileSystem for FakeBasicFileSystem {
             tail = path.file_name().unwrap_or(OsStr::new(""));
         }
         (
-            head.to_str().unwrap().to_string(),
-            tail.to_str().unwrap().to_string(),
+            head.to_str().expect("Path components should be valid unicode").to_string(),
+            tail.to_str().expect("Path components should be valid unicode").to_string(),
         )
     }
 
@@ -230,7 +230,7 @@ impl FileSystem for FakeBasicFileSystem {
     fn read(&self, file_name: &str) -> PyResult<String> {
         match self.contents.get(file_name) {
             Some(file_name) => Ok(file_name.clone()),
-            None => Err(PyFileNotFoundError::new_err("")),
+            None => Err(PyFileNotFoundError::new_err(format!("No such file: {file_name}"))),
         }
     }
 }
@@ -246,7 +246,7 @@ impl PyFakeBasicFileSystem {
     }
 
     #[getter]
-    fn sep(&self) -> String {
+    fn sep(&self) -> &str {
         self.inner.sep()
     }
 
@@ -288,7 +288,8 @@ pub fn parse_indented_file_system_string(file_system_string: &str) -> HashMap<St
     let buffer = file_system_string.replace("\r\n", "\n");
     let lines: Vec<&str> = buffer.split('\n').collect();
 
-    for line_raw in lines.clone() {
+    let first_line_starts_with_slash = lines[0].trim().starts_with('/');
+    for line_raw in lines {
         let line = line_raw.trim_end(); // Remove trailing whitespace
         if line.is_empty() {
             continue; // Skip empty lines
@@ -331,7 +332,7 @@ pub fn parse_indented_file_system_string(file_system_string: &str) -> HashMap<St
             let mut joined = path_stack.join("/");
             // If the original root started with a slash, ensure the final path does too.
             // But be careful not to double-slash if a component is e.g. "/root"
-            if lines[0].trim().starts_with('/') && !joined.starts_with('/') {
+            if first_line_starts_with_slash && !joined.starts_with('/') {
                 joined = format!("/{joined}");
             }
             joined
@@ -353,7 +354,7 @@ pub fn parse_indented_file_system_string(file_system_string: &str) -> HashMap<St
     // Edge case: If the very first line was a file and it ended up on the stack, it needs to be processed.
     // This handles single-file inputs like "myfile.txt"
     if !path_stack.is_empty()
-        && !path_stack.last().unwrap().ends_with('/')
+        && !path_stack.last().expect("path_stack should be non-empty").ends_with('/')
         && !file_paths_map.contains_key(&path_stack.join("/"))
     {
         file_paths_map.insert(path_stack.join("/"), String::new());
diff --git a/rust/src/graph/mod.rs b/rust/src/graph/mod.rs
index 88ffe891..54674648 100644
--- a/rust/src/graph/mod.rs
+++ b/rust/src/graph/mod.rs
@@ -1,10 +1,9 @@
 use bimap::BiMap;
 use derive_new::new;
 use getset::{CopyGetters, Getters};
-use lazy_static::lazy_static;
 use rustc_hash::{FxHashMap, FxHashSet};
 use slotmap::{SecondaryMap, SlotMap, new_key_type};
-use std::sync::RwLock;
+use std::sync::{LazyLock, RwLock};
 use string_interner::backend::StringBackend;
 use string_interner::{DefaultSymbol, StringInterner};
 
@@ -16,15 +15,18 @@ pub mod import_chain_queries;
 
 pub(crate) mod pathfinding;
 
-lazy_static! {
-    static ref MODULE_NAMES: RwLock<StringInterner<StringBackend>> =
-        RwLock::new(StringInterner::default());
-    static ref IMPORT_LINE_CONTENTS: RwLock<StringInterner<StringBackend>> =
-        RwLock::new(StringInterner::default());
-    static ref EMPTY_MODULE_TOKENS: FxHashSet<ModuleToken> = FxHashSet::default();
-    static ref EMPTY_IMPORT_DETAILS: FxHashSet<ImportDetails> = FxHashSet::default();
-    static ref EMPTY_IMPORTS: FxHashSet<(ModuleToken, ModuleToken)> = FxHashSet::default();
-}
+static MODULE_NAMES: LazyLock<RwLock<StringInterner<StringBackend>>> = LazyLock::new(|| {
+    RwLock::new(StringInterner::default())
+});
+static IMPORT_LINE_CONTENTS: LazyLock<RwLock<StringInterner<StringBackend>>> = LazyLock::new(|| {
+    RwLock::new(StringInterner::default())
+});
+static EMPTY_MODULE_TOKENS: LazyLock<FxHashSet<ModuleToken>> = LazyLock::new(|| {
+    FxHashSet::default()
+});
+static EMPTY_IMPORT_DETAILS: LazyLock<FxHashSet<ImportDetails>> = LazyLock::new(|| {
+    FxHashSet::default()
+});
 
 new_key_type! { pub struct ModuleToken; }
 
diff --git a/rust/src/module_expressions.rs b/rust/src/module_expressions.rs
index df1b02b0..6e2a1687 100644
--- a/rust/src/module_expressions.rs
+++ b/rust/src/module_expressions.rs
@@ -1,15 +1,14 @@
 use crate::errors::{GrimpError, GrimpResult};
 use const_format::formatcp;
 use itertools::Itertools;
-use lazy_static::lazy_static;
 use regex::Regex;
 use std::fmt::Display;
 use std::str::FromStr;
+use std::sync::LazyLock;
 
-lazy_static! {
-    static ref MODULE_EXPRESSION_PATTERN: Regex =
-        Regex::new(r"^(\w+|\*{1,2})(\.(\w+|\*{1,2}))*$").unwrap();
-}
+static MODULE_EXPRESSION_PATTERN: LazyLock<Regex> = LazyLock::new(|| {
+        Regex::new(r"^(\w+|\*{1,2})(\.(\w+|\*{1,2}))*$").unwrap()
+});
 
 /// A module expression is used to refer to sets of modules.
 ///