diff --git a/src/dylib_flag.rs b/src/dylib_flag.rs
index e3a38a2..dcaba3e 100644
--- a/src/dylib_flag.rs
+++ b/src/dylib_flag.rs
@@ -66,7 +66,7 @@ impl RustFunction {
 
         let source_path = file.path().join("source.rs");
 
-        std::fs::write(&source_path, &full_file).context("writing source")?;
+        std::fs::write(&source_path, full_file).context("writing source")?;
 
         let mut rustc = Command::new("rustc");
         rustc.arg(source_path);
diff --git a/src/processor/checker.rs b/src/processor/checker.rs
new file mode 100644
index 0000000..cf10600
--- /dev/null
+++ b/src/processor/checker.rs
@@ -0,0 +1,194 @@
+use std::{collections::BTreeSet, mem};
+
+use self::worklist::Worklist;
+
+use super::AstPath;
+
+#[derive(Debug)]
+pub(crate) struct PassController {
+    state: PassControllerState,
+}
+
+#[derive(Debug)]
+enum PassControllerState {
+    InitialCollection {
+        candidates: Vec<AstPath>,
+    },
+    Bisecting {
+        committed: BTreeSet<AstPath>,
+        failed: BTreeSet<AstPath>,
+        current: BTreeSet<AstPath>,
+        worklist: Worklist,
+    },
+    Success,
+}
+
+mod worklist {
+    use super::AstPath;
+
+    /// A worklist that ensures that the inner list is never empty.
+    #[derive(Debug)]
+    pub(super) struct Worklist(Vec<Vec<AstPath>>);
+
+    impl Worklist {
+        pub(super) fn new() -> Self {
+            Self(Vec::new())
+        }
+
+        pub(super) fn push(&mut self, next: Vec<AstPath>) {
+            if !next.is_empty() {
+                self.0.push(next);
+            }
+        }
+
+        pub(super) fn pop(&mut self) -> Option<Vec<AstPath>> {
+            self.0.pop()
+        }
+    }
+}
+
+// copied from `core` because who needs stable features anyways
+pub const fn div_ceil(lhs: usize, rhs: usize) -> usize {
+    let d = lhs / rhs;
+    let r = lhs % rhs;
+    if r > 0 && rhs > 0 {
+        d + 1
+    } else {
+        d
+    }
+}
+
+fn split_owned<T, From: IntoIterator<Item = T>, A: FromIterator<T>, B: FromIterator<T>>(
+    vec: From,
+) -> (A, B) {
+    let candidates = vec.into_iter().collect::<Vec<_>>();
+    let half = div_ceil(candidates.len(), 2);
+
+    let mut candidates = candidates.into_iter();
+
+    let first_half = candidates.by_ref().take(half).collect();
+    let second_half = candidates.collect();
+
+    (first_half, second_half)
+}
+
+impl PassController {
+    pub fn new() -> Self {
+        Self {
+            state: PassControllerState::InitialCollection {
+                candidates: Vec::new(),
+            },
+        }
+    }
+
+    pub fn reproduces(&mut self) {
+        match &mut self.state {
+            PassControllerState::InitialCollection { .. } => {
+                self.state = PassControllerState::Success;
+            }
+            PassControllerState::Bisecting {
+                committed,
+                failed: _,
+                current,
+                worklist: _,
+            } => {
+                committed.extend(mem::take(current));
+
+                self.next_in_worklist();
+            }
+            PassControllerState::Success => unreachable!("Processed after success"),
+        }
+    }
+
+    pub fn does_not_reproduce(&mut self) {
+        match &mut self.state {
+            PassControllerState::InitialCollection { candidates } => {
+                let (current, first_worklist_item) = split_owned(mem::take(candidates));
+
+                let mut worklist = Worklist::new();
+                worklist.push(first_worklist_item);
+
+                self.state = PassControllerState::Bisecting {
+                    committed: BTreeSet::new(),
+                    failed: BTreeSet::new(),
+                    current,
+                    worklist,
+                };
+            }
+            PassControllerState::Bisecting {
+                committed: _,
+                failed,
+                current,
+                worklist,
+            } => {
+                if current.len() == 1 {
+                    // We are at a leaf. This is a failure.
+                    // FIXME: We should retry the failed ones until a fixpoint is reached.
+                    failed.extend(mem::take(current));
+                } else {
+                    // Split it further and add it to the worklist.
+                    let (first_half, second_half) = split_owned(mem::take(current));
+
+                    worklist.push(first_half);
+                    worklist.push(second_half);
+                }
+
+                self.next_in_worklist()
+            }
+            PassControllerState::Success => unreachable!("Processed after success"),
+        }
+    }
+
+    pub fn no_change(&mut self) {
+        match &self.state {
+            PassControllerState::InitialCollection { candidates } => {
+                assert!(
+                    candidates.is_empty(),
+                    "No change but received candidates: {candidates:?}"
+                );
+                self.state = PassControllerState::Success;
+            }
+            PassControllerState::Bisecting { current, .. } => {
+                unreachable!("No change while bisecting, current was empty somehow: {current:?}");
+            }
+            PassControllerState::Success => {}
+        }
+    }
+
+    pub fn is_finished(&mut self) -> bool {
+        match &mut self.state {
+            PassControllerState::InitialCollection { .. } => false,
+            PassControllerState::Bisecting { .. } => false,
+            PassControllerState::Success => true,
+        }
+    }
+
+    pub fn can_process(&mut self, path: &[String]) -> bool {
+        match &mut self.state {
+            PassControllerState::InitialCollection { candidates } => {
+                candidates.push(AstPath(path.to_owned()));
+                true
+            }
+            PassControllerState::Bisecting { current, .. } => current.contains(path),
+            PassControllerState::Success => {
+                unreachable!("Processed further after success");
+            }
+        }
+    }
+
+    fn next_in_worklist(&mut self) {
+        match &mut self.state {
+            PassControllerState::Bisecting {
+                current, worklist, ..
+            } => match worklist.pop() {
+                Some(next) => {
+                    *current = next.into_iter().collect();
+                }
+                None => {
+                    self.state = PassControllerState::Success;
+                }
+            },
+            _ => unreachable!("next_in_worklist called on non-bisecting state"),
+        }
+    }
+}
diff --git a/src/processor/mod.rs b/src/processor/mod.rs
index c3efcd3..2cb6ce0 100644
--- a/src/processor/mod.rs
+++ b/src/processor/mod.rs
@@ -1,17 +1,14 @@
+mod checker;
 mod files;
 mod reaper;
+
 pub(crate) use self::files::SourceFile;
-use self::worklist::Worklist;
 use crate::{build::Build, processor::files::Changes, Options};
 use anyhow::{Context, Result};
 use owo_colors::OwoColorize;
-use std::{
-    borrow::Borrow,
-    collections::{BTreeSet, HashSet},
-    ffi::OsStr,
-    fmt::Debug,
-    mem,
-};
+use std::{borrow::Borrow, collections::HashSet, ffi::OsStr, fmt::Debug};
+
+pub(crate) use self::checker::PassController;
 
 pub(crate) trait Processor {
     fn refresh_state(&mut self) -> Result<()> {
@@ -198,195 +195,6 @@ impl Debug for AstPath {
     }
 }
 
-#[derive(Debug)]
-pub(crate) struct PassController {
-    state: PassControllerState,
-}
-
-#[derive(Debug)]
-enum PassControllerState {
-    InitialCollection {
-        candidates: Vec<AstPath>,
-    },
-    Bisecting {
-        committed: BTreeSet<AstPath>,
-        failed: BTreeSet<AstPath>,
-        current: BTreeSet<AstPath>,
-        worklist: Worklist,
-    },
-    Success,
-}
-
-mod worklist {
-    use super::AstPath;
-
-    /// A worklist that ensures that the inner list is never empty.
-    #[derive(Debug)]
-    pub(super) struct Worklist(Vec<Vec<AstPath>>);
-
-    impl Worklist {
-        pub(super) fn new() -> Self {
-            Self(Vec::new())
-        }
-
-        pub(super) fn push(&mut self, next: Vec<AstPath>) {
-            if !next.is_empty() {
-                self.0.push(next);
-            }
-        }
-
-        pub(super) fn pop(&mut self) -> Option<Vec<AstPath>> {
-            self.0.pop()
-        }
-    }
-}
-
-// copied from `core` because who needs stable features anyways
-pub const fn div_ceil(lhs: usize, rhs: usize) -> usize {
-    let d = lhs / rhs;
-    let r = lhs % rhs;
-    if r > 0 && rhs > 0 {
-        d + 1
-    } else {
-        d
-    }
-}
-
-fn split_owned<T, From: IntoIterator<Item = T>, A: FromIterator<T>, B: FromIterator<T>>(
-    vec: From,
-) -> (A, B) {
-    let candidates = vec.into_iter().collect::<Vec<_>>();
-    let half = div_ceil(candidates.len(), 2);
-
-    let mut candidates = candidates.into_iter();
-
-    let first_half = candidates.by_ref().take(half).collect();
-    let second_half = candidates.collect();
-
-    (first_half, second_half)
-}
-
-impl PassController {
-    fn new() -> Self {
-        Self {
-            state: PassControllerState::InitialCollection {
-                candidates: Vec::new(),
-            },
-        }
-    }
-
-    fn next_in_worklist(&mut self) {
-        match &mut self.state {
-            PassControllerState::Bisecting {
-                current, worklist, ..
-            } => match worklist.pop() {
-                Some(next) => {
-                    *current = next.into_iter().collect();
-                }
-                None => {
-                    self.state = PassControllerState::Success;
-                }
-            },
-            _ => unreachable!("next_in_worklist called on non-bisecting state"),
-        }
-    }
-
-    fn reproduces(&mut self) {
-        match &mut self.state {
-            PassControllerState::InitialCollection { .. } => {
-                self.state = PassControllerState::Success;
-            }
-            PassControllerState::Bisecting {
-                committed,
-                failed: _,
-                current,
-                worklist: _,
-            } => {
-                committed.extend(mem::take(current));
-
-                self.next_in_worklist();
-            }
-            PassControllerState::Success => unreachable!("Processed after success"),
-        }
-    }
-
-    fn does_not_reproduce(&mut self) {
-        match &mut self.state {
-            PassControllerState::InitialCollection { candidates } => {
-                let (current, first_worklist_item) = split_owned(mem::take(candidates));
-
-                let mut worklist = Worklist::new();
-                worklist.push(first_worklist_item);
-
-                self.state = PassControllerState::Bisecting {
-                    committed: BTreeSet::new(),
-                    failed: BTreeSet::new(),
-                    current,
-                    worklist,
-                };
-            }
-            PassControllerState::Bisecting {
-                committed: _,
-                failed,
-                current,
-                worklist,
-            } => {
-                if current.len() == 1 {
-                    // We are at a leaf. This is a failure.
-                    // FIXME: We should retry the failed ones until a fixpoint is reached.
-                    failed.extend(mem::take(current));
-                } else {
-                    // Split it further and add it to the worklist.
-                    let (first_half, second_half) = split_owned(mem::take(current));
-
-                    worklist.push(first_half);
-                    worklist.push(second_half);
-                }
-
-                self.next_in_worklist()
-            }
-            PassControllerState::Success => unreachable!("Processed after success"),
-        }
-    }
-
-    fn no_change(&mut self) {
-        match &self.state {
-            PassControllerState::InitialCollection { candidates } => {
-                assert!(
-                    candidates.is_empty(),
-                    "No change but received candidates: {candidates:?}"
-                );
-                self.state = PassControllerState::Success;
-            }
-            PassControllerState::Bisecting { current, .. } => {
-                unreachable!("No change while bisecting, current was empty somehow: {current:?}");
-            }
-            PassControllerState::Success => {}
-        }
-    }
-
-    fn is_finished(&mut self) -> bool {
-        match &mut self.state {
-            PassControllerState::InitialCollection { .. } => false,
-            PassControllerState::Bisecting { .. } => false,
-            PassControllerState::Success => true,
-        }
-    }
-
-    pub(crate) fn can_process(&mut self, path: &[String]) -> bool {
-        match &mut self.state {
-            PassControllerState::InitialCollection { candidates } => {
-                candidates.push(AstPath(path.to_owned()));
-                true
-            }
-            PassControllerState::Bisecting { current, .. } => current.contains(path),
-            PassControllerState::Success => {
-                unreachable!("Processed further after success");
-            }
-        }
-    }
-}
-
 macro_rules! tracking {
     () => {
         tracking!(visit_item_fn_mut);