src: Make the new format cache actually work

Err, oops, the new caching code wasn't actually wired in at all. Good jorb
testing by me.

Author: pkgw

src/driver.rs

@@ -770,6 +770,10 @@ impl ProcessingSession {
             return Err(ErrorKind::Msg("cannot create formats without using a bundle".to_owned()).into())
         }
 
+        if self.io.format_cache.is_none() {
+            return Err(ErrorKind::Msg("cannot create formats having a place to save them".to_owned()).into())
+        }
+
         // PathBuf.file_stem() doesn't do what we want since it only strips
         // one extension. As of 1.17, the compiler needs a type annotation for
         // some reason, which is why we use the `r` variable.
@@ -804,7 +808,7 @@ impl ProcessingSession {
         // principle we could stream the format file directly to the staging
         // area as we ran the TeX engine, but we don't bother.
 
-        let bundle = &mut *self.io.bundle.as_mut().unwrap();
+        let format_cache = &mut *self.io.format_cache.as_mut().unwrap();
 
         for (name, contents) in &*self.io.mem.files.borrow() {
             if name == self.io.mem.stdout_key() {
@@ -818,7 +822,7 @@ impl ProcessingSession {
             }
 
             // Note that we intentionally pass 'stem', not 'name'.
-            ctry!(bundle.write_format(stem, contents, status); "cannot write format file {}", sname);
+            ctry!(format_cache.write_format(stem, contents, status); "cannot write format file {}", sname);
         }
 
         // All done. Clear the memory layer since this was a special preparatory step.

src/io/setup.rs

@@ -24,7 +24,7 @@ pub struct IoSetup {
     pub bundle: Option<Box<Bundle>>,
     pub mem: MemoryIo,
     filesystem: FilesystemIo,
-    format_cache: Option<FormatCache>,
+    pub format_cache: Option<FormatCache>,
     genuine_stdout: Option<GenuineStdoutIo>,
     format_primary: Option<BufferedPrimaryIo>,
 }