diff --git a/src/context.rs b/src/context.rs
index ce200206..7a35dd40 100644
--- a/src/context.rs
+++ b/src/context.rs
@@ -5,9 +5,8 @@ use crate::modules;
 use clap::ArgMatches;
 use git2::{Repository, RepositoryState};
 use once_cell::sync::OnceCell;
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 use std::env;
-use std::ffi::OsStr;
 use std::fs;
 use std::path::{Path, PathBuf};
 use std::string::String;
@@ -23,8 +22,8 @@ pub struct Context<'a> {
     /// The current working directory that starship is being called in.
     pub current_dir: PathBuf,
 
-    /// A vector containing the full paths of all the files in `current_dir`.
-    dir_files: OnceCell<Vec<PathBuf>>,
+    /// A struct containing directory contents in a lookup-optimised format.
+    dir_contents: OnceCell<DirContents>,
 
     /// Properties to provide to modules.
     pub properties: HashMap<&'a str, String>,
@@ -80,7 +79,7 @@ impl<'a> Context<'a> {
             config,
             properties,
             current_dir,
-            dir_files: OnceCell::new(),
+            dir_contents: OnceCell::new(),
             repo: OnceCell::new(),
             shell,
         }
@@ -117,7 +116,7 @@ impl<'a> Context<'a> {
     // see ScanDir for methods
     pub fn try_begin_scan(&'a self) -> Option<ScanDir<'a>> {
         Some(ScanDir {
-            dir_files: self.get_dir_files().ok()?,
+            dir_contents: self.dir_contents().ok()?,
             files: &[],
             folders: &[],
             extensions: &[],
@@ -145,26 +144,101 @@ impl<'a> Context<'a> {
             })
     }
 
-    pub fn get_dir_files(&self) -> Result<&Vec<PathBuf>, std::io::Error> {
-        let start_time = SystemTime::now();
-        let scan_timeout = Duration::from_millis(self.config.get_root_config().scan_timeout);
+    pub fn dir_contents(&self) -> Result<&DirContents, std::io::Error> {
+        self.dir_contents.get_or_try_init(|| {
+            let timeout = Duration::from_millis(self.config.get_root_config().scan_timeout);
+            DirContents::from_path_with_timeout(&self.current_dir, timeout)
+        })
+    }
+}
 
-        self.dir_files
-            .get_or_try_init(|| -> Result<Vec<PathBuf>, std::io::Error> {
-                let dir_files = fs::read_dir(&self.current_dir)?
-                    .take_while(|_item| {
-                        SystemTime::now().duration_since(start_time).unwrap() < scan_timeout
-                    })
-                    .filter_map(Result::ok)
-                    .map(|entry| entry.path())
-                    .collect::<Vec<PathBuf>>();
+#[derive(Debug)]
+pub struct DirContents {
+    // HashSet of all files, no folders, relative to the base directory given at construction.
+    files: HashSet<PathBuf>,
+    // HashSet of all file names, e.g. the last section without any folders, as strings.
+    file_names: HashSet<String>,
+    // HashSet of all folders, relative to the base directory given at construction.
+    folders: HashSet<PathBuf>,
+    // HashSet of all extensions found, without dots, e.g. "js" instead of ".js".
+    extensions: HashSet<String>,
+}
 
-                log::trace!(
-                    "Building a vector of directory files took {:?}",
-                    SystemTime::now().duration_since(start_time).unwrap()
-                );
-                Ok(dir_files)
-            })
+impl DirContents {
+    fn from_path(base: &PathBuf) -> Result<Self, std::io::Error> {
+        Self::from_path_with_timeout(base, Duration::from_secs(30))
+    }
+
+    fn from_path_with_timeout(base: &PathBuf, timeout: Duration) -> Result<Self, std::io::Error> {
+        let start = SystemTime::now();
+
+        let mut folders: HashSet<PathBuf> = HashSet::new();
+        let mut files: HashSet<PathBuf> = HashSet::new();
+        let mut file_names: HashSet<String> = HashSet::new();
+        let mut extensions: HashSet<String> = HashSet::new();
+
+        fs::read_dir(base)?
+            .take_while(|_| SystemTime::now().duration_since(start).unwrap() < timeout)
+            .filter_map(Result::ok)
+            .for_each(|entry| {
+                let path = PathBuf::from(entry.path().strip_prefix(base).unwrap());
+                if entry.path().is_dir() {
+                    folders.insert(path);
+                } else {
+                    if !path.to_string_lossy().starts_with('.') {
+                        path.extension()
+                            .map(|ext| extensions.insert(ext.to_string_lossy().to_string()));
+                    }
+                    if let Some(file_name) = path.file_name() {
+                        file_names.insert(file_name.to_string_lossy().to_string());
+                    }
+                    files.insert(path);
+                }
+            });
+
+        log::trace!(
+            "Building HashSets of directory files, folders and extensions took {:?}",
+            SystemTime::now().duration_since(start).unwrap()
+        );
+
+        Ok(DirContents {
+            folders,
+            files,
+            file_names,
+            extensions,
+        })
+    }
+
+    pub fn files(&self) -> impl Iterator<Item = &PathBuf> {
+        self.files.iter()
+    }
+
+    pub fn has_file(&self, path: &str) -> bool {
+        self.files.contains(Path::new(path))
+    }
+
+    pub fn has_file_name(&self, name: &str) -> bool {
+        self.file_names.contains(name)
+    }
+
+    pub fn has_any_file_name(&self, names: &[&str]) -> bool {
+        names.iter().any(|name| self.has_file_name(name))
+    }
+
+    pub fn has_folder(&self, path: &str) -> bool {
+        self.folders.contains(Path::new(path))
+    }
+
+    pub fn has_any_folder(&self, paths: &[&str]) -> bool {
+        paths.iter().any(|path| self.has_folder(path))
+    }
+
+    pub fn has_extension(&self, ext: &str) -> bool {
+        self.extensions.contains(ext)
+    }
+
+    pub fn has_any_extension(&self, exts: &[&str]) -> bool {
+        exts.iter().any(|ext| self.has_extension(ext))
     }
 
     fn get_shell() -> Shell {
@@ -196,7 +270,7 @@ pub struct Repo {
 // A struct of Criteria which will be used to verify current PathBuf is
 // of X language, criteria can be set via the builder pattern
 pub struct ScanDir<'a> {
-    dir_files: &'a Vec<PathBuf>,
+    dir_contents: &'a DirContents,
     files: &'a [&'a str],
     folders: &'a [&'a str],
     extensions: &'a [&'a str],
@@ -221,48 +295,12 @@ impl<'a> ScanDir<'a> {
     /// based on the current Pathbuf check to see
     /// if any of this criteria match or exist and returning a boolean
     pub fn is_match(&self) -> bool {
-        self.dir_files.iter().any(|path| {
-            if path.is_dir() {
-                path_has_name(path, self.folders)
-            } else {
-                path_has_name(path, self.files) || has_extension(path, self.extensions)
-            }
-        })
+        self.dir_contents.has_any_extension(self.extensions)
+            || self.dir_contents.has_any_folder(self.folders)
+            || self.dir_contents.has_any_file_name(self.files)
     }
 }
 
-/// checks to see if the pathbuf matches a file or folder name
-pub fn path_has_name<'a>(dir_entry: &PathBuf, names: &'a [&'a str]) -> bool {
-    let found_file_or_folder_name = names.iter().find(|file_or_folder_name| {
-        dir_entry
-            .file_name()
-            .and_then(OsStr::to_str)
-            .unwrap_or_default()
-            == **file_or_folder_name
-    });
-
-    match found_file_or_folder_name {
-        Some(name) => !name.is_empty(),
-        None => false,
-    }
-}
-
-/// checks if pathbuf doesn't start with a dot and matches any provided extension
-pub fn has_extension<'a>(dir_entry: &PathBuf, extensions: &'a [&'a str]) -> bool {
-    if let Some(file_name) = dir_entry.file_name() {
-        if file_name.to_string_lossy().starts_with('.') {
-            return false;
-        }
-        return extensions.iter().any(|ext| {
-            dir_entry
-                .extension()
-                .and_then(OsStr::to_str)
-                .map_or(false, |e| e == *ext)
-        });
-    }
-    false
-}
-
 fn get_current_branch(repository: &Repository) -> Option<String> {
     let head = repository.head().ok()?;
     let shorthand = head.shorthand();
@@ -284,69 +322,73 @@ pub enum Shell {
 mod tests {
     use super::*;
 
-    #[test]
-    fn test_path_has_name() {
-        let mut buf = PathBuf::from("/");
-        let files = vec!["package.json"];
-
-        assert_eq!(path_has_name(&buf, &files), false);
-
-        buf.set_file_name("some-file.js");
-        assert_eq!(path_has_name(&buf, &files), false);
-
-        buf.set_file_name("package.json");
-        assert_eq!(path_has_name(&buf, &files), true);
+    fn testdir(paths: &[&str]) -> Result<tempfile::TempDir, std::io::Error> {
+        let dir = tempfile::tempdir()?;
+        for path in paths {
+            let p = dir.path().join(Path::new(path));
+            if let Some(parent) = p.parent() {
+                fs::create_dir_all(parent)?;
+            }
+            fs::File::create(p)?.sync_all()?;
+        }
+        Ok(dir)
     }
 
     #[test]
-    fn test_has_extension() {
-        let mut buf = PathBuf::from("/");
-        let extensions = vec!["js"];
+    fn test_scan_dir() -> Result<(), Box<dyn std::error::Error>> {
+        let empty = testdir(&[])?;
+        let empty_dc = DirContents::from_path(&PathBuf::from(empty.path()))?;
 
-        assert_eq!(has_extension(&buf, &extensions), false);
+        assert_eq!(
+            ScanDir {
+                dir_contents: &empty_dc,
+                files: &["package.json"],
+                extensions: &["js"],
+                folders: &["node_modules"],
+            }
+            .is_match(),
+            false
+        );
 
-        buf.set_file_name("some-file.rs");
-        assert_eq!(has_extension(&buf, &extensions), false);
+        let rust = testdir(&["README.md", "Cargo.toml", "src/main.rs"])?;
+        let rust_dc = DirContents::from_path(&PathBuf::from(rust.path()))?;
+        assert_eq!(
+            ScanDir {
+                dir_contents: &rust_dc,
+                files: &["package.json"],
+                extensions: &["js"],
+                folders: &["node_modules"],
+            }
+            .is_match(),
+            false
+        );
 
-        buf.set_file_name(".some-file.js");
-        assert_eq!(has_extension(&buf, &extensions), false);
+        let java = testdir(&["README.md", "src/com/test/Main.java", "pom.xml"])?;
+        let java_dc = DirContents::from_path(&PathBuf::from(java.path()))?;
+        assert_eq!(
+            ScanDir {
+                dir_contents: &java_dc,
+                files: &["package.json"],
+                extensions: &["js"],
+                folders: &["node_modules"],
+            }
+            .is_match(),
+            false
+        );
 
-        buf.set_file_name("some-file.js");
-        assert_eq!(has_extension(&buf, &extensions), true)
-    }
+        let node = testdir(&["README.md", "node_modules/lodash/main.js", "package.json"])?;
+        let node_dc = DirContents::from_path(&PathBuf::from(node.path()))?;
+        assert_eq!(
+            ScanDir {
+                dir_contents: &node_dc,
+                files: &["package.json"],
+                extensions: &["js"],
+                folders: &["node_modules"],
+            }
+            .is_match(),
+            true
+        );
 
-    #[test]
-    fn test_criteria_scan_fails() {
-        let failing_criteria = ScanDir {
-            dir_files: &vec![PathBuf::new()],
-            files: &["package.json"],
-            extensions: &["js"],
-            folders: &["node_modules"],
-        };
-
-        // fails if buffer does not match any criteria
-        assert_eq!(failing_criteria.is_match(), false);
-
-        let failing_dir_criteria = ScanDir {
-            dir_files: &vec![PathBuf::from("/package.js/dog.go")],
-            files: &["package.json"],
-            extensions: &["js"],
-            folders: &["node_modules"],
-        };
-
-        // fails when passed a pathbuf dir matches extension path
-        assert_eq!(failing_dir_criteria.is_match(), false);
-    }
-
-    #[test]
-    fn test_criteria_scan_passes() {
-        let passing_criteria = ScanDir {
-            dir_files: &vec![PathBuf::from("package.json")],
-            files: &["package.json"],
-            extensions: &["js"],
-            folders: &["node_modules"],
-        };
-
-        assert_eq!(passing_criteria.is_match(), true);
+        Ok(())
     }
 }
diff --git a/src/modules/dotnet.rs b/src/modules/dotnet.rs
index 738e38a9..5ca4d636 100644
--- a/src/modules/dotnet.rs
+++ b/src/modules/dotnet.rs
@@ -165,8 +165,8 @@ fn get_pinned_sdk_version(json: &str) -> Option<Version> {
 
 fn get_local_dotnet_files<'a>(context: &'a Context) -> Result<Vec<DotNetFile<'a>>, std::io::Error> {
     Ok(context
-        .get_dir_files()?
-        .iter()
+        .dir_contents()?
+        .files()
         .filter_map(|p| {
             get_dotnet_file_type(p).map(|t| DotNetFile {
                 path: p.as_ref(),
diff --git a/src/modules/rust.rs b/src/modules/rust.rs
index b18692b8..e11fa430 100644
--- a/src/modules/rust.rs
+++ b/src/modules/rust.rs
@@ -1,4 +1,3 @@
-use std::ffi::OsStr;
 use std::path::Path;
 use std::process::{Command, Output};
 use std::{env, fs};
@@ -107,13 +106,11 @@ fn find_rust_toolchain_file(context: &Context) -> Option<String> {
         Some(line.trim().to_owned())
     }
 
-    if let Some(path) = context
-        .get_dir_files()
-        .ok()?
-        .iter()
-        .find(|p| p.file_name() == Some(OsStr::new("rust-toolchain")))
+    if let Ok(true) = context
+        .dir_contents()
+        .map(|dir| dir.has_file("rust-toolchain"))
     {
-        if let Some(toolchain) = read_first_line(path) {
+        if let Some(toolchain) = read_first_line(Path::new("rust-toolchain")) {
             return Some(toolchain);
         }
     }