pyc: replace data in place

This is in preparation for future changes. The code for 'struct Pyc'
is put together in one place, separate from the more general code for
PycParser.

parser.clear_unused_flag_refs() modifies parser in place. A scratch
copy of the data is still used, so that modifications can be discarder
on failure. Returning a new copy of data would be awkward if we want
to do further processing on that data.

src/handlers/pyc.rs

@@ -296,16 +296,6 @@ pub fn pyc_python_version(buf: &[u8; 4]) -> Result<((u32, u32), usize)> {
     }
 }
 
-pub struct Pyc {
-    config: Rc<options::Config>,
-}
-
-impl Pyc {
-    pub fn boxed(config: &Rc<options::Config>) -> Box<dyn super::Processor> {
-        Box::new(Self { config: config.clone() })
-    }
-}
-
 #[derive(Debug)]
 #[allow(dead_code)]   // Right now, we only use dbg! to print the object.
 enum Object {
@@ -697,7 +687,7 @@ impl PycParser {
         Ok(Object::Dict(dict))
     }
 
-    fn clear_unused_flag_refs(&mut self) -> Result<(bool, Vec<u8>)> {
+    fn clear_unused_flag_refs(&mut self) -> Result<bool> {
         // Sequence of flag_refs and irefs ordered by number of byte in a file
         let final_list =
             iter::zip(self.flag_refs.iter(), iter::repeat(true))
@@ -743,7 +733,22 @@ impl PycParser {
 
         debug!("{}: removed {} unused FLAG_REFs", self.input_path.display(), removed_count);
         assert_eq!(data == self.data, removed_count == 0);
-        Ok((removed_count > 0, data))
+        if removed_count > 0 {
+            self.data = data;
+        }
+
+        Ok(removed_count > 0)
+    }
+}
+
+
+pub struct Pyc {
+    config: Rc<options::Config>,
+}
+
+impl Pyc {
+    pub fn boxed(config: &Rc<options::Config>) -> Box<dyn super::Processor> {
+        Box::new(Self { config: config.clone() })
     }
 }
 
@@ -766,10 +771,10 @@ impl super::Processor for Pyc {
 
         parser.read_object()?;
 
-        let (have_mod, data) = parser.clear_unused_flag_refs()?;
+        let have_mod = parser.clear_unused_flag_refs()?;
         if have_mod {
             io.open_output()?;
-            io.output.as_mut().unwrap().write_all(&data)?;
+            io.output.as_mut().unwrap().write_all(&parser.data)?;
         }
 
         io.finalize(have_mod)