diff --git a/gengo-bin/src/cli.rs b/gengo-bin/src/cli.rs
index 5493f08c..89e2cf6f 100644
--- a/gengo-bin/src/cli.rs
+++ b/gengo-bin/src/cli.rs
@@ -1,6 +1,6 @@
 use clap::Error as ClapError;
 use clap::Parser;
-use gengo::{analysis::SummaryOpts, Analysis, Builder};
+use gengo::{analysis::SummaryOpts, Analysis, Builder, Git};
 use indexmap::IndexMap;
 use std::io::{self, Write};
 
@@ -43,9 +43,14 @@ pub struct CLI {
 
 impl CLI {
     pub fn run<Out: Write, Err: Write>(&self, mut out: Out, mut err: Err) -> Result<(), io::Error> {
-        let gengo = Builder::new(&self.repository, &self.revision)
-            .read_limit(self.read_limit)
-            .build();
+        let git = match Git::new(&self.repository, &self.revision) {
+            Ok(git) => git,
+            Err(e) => {
+                writeln!(err, "failed to create git instance: {}", e)?;
+                return Ok(());
+            }
+        };
+        let gengo = Builder::new(git).read_limit(self.read_limit).build();
         let gengo = match gengo {
             Ok(gengo) => gengo,
             Err(e) => {
diff --git a/gengo/benches/run_on_self.rs b/gengo/benches/run_on_self.rs
index 8186f2f2..23a7f56e 100644
--- a/gengo/benches/run_on_self.rs
+++ b/gengo/benches/run_on_self.rs
@@ -1,21 +1,20 @@
 use criterion::{criterion_group, criterion_main, Criterion};
-use gengo::Builder;
+use gengo::{Builder, Git};
 
-fn head_benchmark(c: &mut Criterion) {
+fn git_benchmark(c: &mut Criterion) {
     let revs = {
         let mut revs: Vec<_> = (0..3).map(|n| format!("HEAD{}", "^".repeat(n))).collect();
         revs.extend_from_slice(&["test/javascript".into()]);
         revs
     };
     for rev in revs {
-        let gengo = Builder::new(env!("CARGO_MANIFEST_DIR"), &rev)
-            .build()
-            .unwrap();
+        let git = Git::new(env!("CARGO_MANIFEST_DIR"), &rev).unwrap();
+        let gengo = Builder::new(git).build().unwrap();
         c.bench_function(&format!("run on {}", rev), |b| {
             b.iter(|| gengo.analyze().unwrap())
         });
     }
 }
 
-criterion_group!(benches, head_benchmark);
+criterion_group!(benches, git_benchmark);
 criterion_main!(benches);
diff --git a/gengo/src/builder.rs b/gengo/src/builder.rs
index 2646d5fc..81d2d848 100644
--- a/gengo/src/builder.rs
+++ b/gengo/src/builder.rs
@@ -4,32 +4,22 @@ use super::vendored::Vendored;
 use super::Analyzers;
 use super::Gengo;
 
-use crate::file_source::Git;
+use crate::file_source::FileSource;
 use std::error::Error as ErrorTrait;
-use std::path::Path;
 
 /// Builds a new `Gengo` instance.
-///
-/// # Example
-///
-/// ```no_run
-/// use gengo::Builder;
-/// let gengo = Builder::new("path/to/repo", "HEAD").build().unwrap();
-/// ```
-pub struct Builder<P: AsRef<Path>> {
-    repository_path: P,
-    rev: String,
+pub struct Builder<FS: for<'fs> FileSource<'fs>> {
+    file_source: FS,
     analyzers: Option<Analyzers>,
     read_limit: Option<usize>,
 }
 
-impl<P: AsRef<Path>> Builder<P> {
+impl<FS: for<'fs> FileSource<'fs>> Builder<FS> {
     pub const DEFAULT_READ_LIMIT: usize = 1 << 20;
 
-    pub fn new(repository_path: P, rev: &str) -> Self {
+    pub fn new(file_source: FS) -> Self {
         Self {
-            repository_path,
-            rev: rev.to_owned(),
+            file_source,
             analyzers: None,
             read_limit: None,
         }
@@ -50,8 +40,8 @@ impl<P: AsRef<Path>> Builder<P> {
         self
     }
 
-    pub fn build(self) -> Result<Gengo<Git>, Box<dyn ErrorTrait>> {
-        let file_source = Git::new(self.repository_path, &self.rev)?;
+    pub fn build(self) -> Result<Gengo<FS>, Box<dyn ErrorTrait>> {
+        let file_source = self.file_source;
         let analyzers = self.analyzers.unwrap_or_default();
         let read_limit = self.read_limit.unwrap_or(Self::DEFAULT_READ_LIMIT);
         let documentation = Documentation::new();
diff --git a/gengo/src/lib.rs b/gengo/src/lib.rs
index e64f5589..575a2916 100644
--- a/gengo/src/lib.rs
+++ b/gengo/src/lib.rs
@@ -1,9 +1,20 @@
-//! Gengo is a language detection library for Git repositories.
+//! Gengo is a language detection library for collections of files.
+//! Currently, it supports reading from git repositories.
+//!
+//! # Example
+//!
+//! ```no_run
+//! use gengo::{Builder, Git};
+//! let git = Git::new("path/to/repo", "HEAD").unwrap();
+//! let gengo = Builder::new(git).build().unwrap();
+//! let results = gengo.analyze().unwrap();
+//! ```
+//! # Built-in Languages
+//!
 //! While it is possible to provide your own definitions for
 //! language detection, Gengo comes with a set of built-in
 //! definitions.
 //!
-//! # Built-in Languages
 #![doc = include_str!(concat!(env!("OUT_DIR"), "/language-list.md"))]
 
 pub use analysis::Analysis;
@@ -13,7 +24,7 @@ use documentation::Documentation;
 pub use error::{Error, ErrorKind};
 use generated::Generated;
 
-pub use file_source::FileSource;
+pub use file_source::{FileSource, Git};
 use glob::MatchOptions;
 pub use languages::analyzer::Analyzers;
 use languages::Category;
diff --git a/gengo/tests/gengo_test.rs b/gengo/tests/gengo_test.rs
index afcee0ab..a3c3ba5d 100644
--- a/gengo/tests/gengo_test.rs
+++ b/gengo/tests/gengo_test.rs
@@ -1,5 +1,4 @@
-use gengo::Analyzers;
-use gengo::Builder;
+use gengo::{Analyzers, Builder, Git};
 const ROOT: &str = env!("CARGO_MANIFEST_DIR");
 
 mod util;
@@ -10,10 +9,8 @@ fn test_javascript() {
     // guarantee order. Improve this test.
     let analyzers = fixture_str!("test_javascript-analyzers.yaml");
     let analyzers = Analyzers::from_yaml(analyzers).unwrap();
-    let gengo = Builder::new(ROOT, "test/javascript")
-        .analyzers(analyzers)
-        .build()
-        .unwrap();
+    let git = Git::new(ROOT, "test/javascript").unwrap();
+    let gengo = Builder::new(git).analyzers(analyzers).build().unwrap();
     let results = gengo.analyze().unwrap();
     insta::assert_debug_snapshot!(results);
 }