Fix delete-unused-functions panics

The pass used to (?) track invalidated files itself,
but now that functionality has been moved up one level,
but also kinda not really.

So here we clarify this by:
- making reaper not care about tracking invalidated files anymore
- making processor yes care about tracking invalidated files, and
    ensuring that it does not call process_file again after gettin
    ProcessState::FileInvalidated, as it advertizes to do.

src/processor/reaper.rs

@@ -7,11 +7,7 @@ use anyhow::{Context, Result};
 use proc_macro2::Span;
 use quote::ToTokens;
 use rustfix::{diagnostics::Diagnostic, Suggestion};
-use std::{
-    collections::{HashMap, HashSet},
-    ops::Range,
-    path::{Path, PathBuf},
-};
+use std::{collections::HashMap, ops::Range, path::Path};
 use syn::{visit_mut::VisitMut, ImplItem, Item};
 
 fn file_for_suggestion(suggestion: &Suggestion) -> &Path {
@@ -103,16 +99,11 @@ impl Minimizer {
 struct DeleteUnusedFunctions {
     diags: Vec<Diagnostic>,
     build: Build,
-    invalid: HashSet<PathBuf>,
 }
 
 impl DeleteUnusedFunctions {
     fn new(build: Build, diags: Vec<Diagnostic>) -> Self {
-        DeleteUnusedFunctions {
-            diags,
-            build,
-            invalid: HashSet::new(),
-        }
+        DeleteUnusedFunctions { diags, build }
     }
 }
 
@@ -120,7 +111,6 @@ impl Pass for DeleteUnusedFunctions {
     fn refresh_state(&mut self) -> Result<()> {
         let (diags, _) = self.build.get_diags().context("getting diagnostics")?;
         self.diags = diags;
-        self.invalid.clear();
         Ok(())
     }
 
@@ -130,18 +120,9 @@ impl Pass for DeleteUnusedFunctions {
         file: &SourceFile,
         checker: &mut super::PassController,
     ) -> ProcessState {
-        assert!(
-            !self.invalid.contains(file.path_no_fs_interact()),
-            "processing with invalid state"
-        );
-
         let mut visitor = FindUnusedFunction::new(file, self.diags.iter(), checker);
         visitor.visit_file_mut(krate);
 
-        if visitor.process_state == ProcessState::FileInvalidated {
-            self.invalid.insert(file.path_no_fs_interact().to_owned());
-        }
-
         visitor.process_state
     }
 
@@ -235,8 +216,12 @@ impl<'a> FindUnusedFunction<'a> {
         match span_matches {
             0 => true,
             1 => {
-                self.process_state = ProcessState::FileInvalidated;
-                !self.checker.can_process(&self.current_path)
+                if self.checker.can_process(&self.current_path) {
+                    self.process_state = ProcessState::FileInvalidated;
+                    !self.checker.can_process(&self.current_path)
+                } else {
+                    true
+                }
             }
             _ => {
                 panic!("multiple dead_code spans matched identifier: {span_matches}.");