clear out a bunch of old code, reorganize

crates/memory/src/borrow.rs

@@ -0,0 +1,59 @@
+use crate::region::Region;
+
+pub struct GuestBorrows {
+    immutable: Vec<Region>,
+    mutable: Vec<Region>,
+}
+
+impl GuestBorrows {
+    pub fn new() -> Self {
+        GuestBorrows {
+            immutable: Vec::new(),
+            mutable: Vec::new(),
+        }
+    }
+
+    fn is_borrowed_immut(&self, r: Region) -> bool {
+        !self.immutable.iter().all(|b| !b.overlaps(r))
+    }
+
+    fn is_borrowed_mut(&self, r: Region) -> bool {
+        !self.mutable.iter().all(|b| !b.overlaps(r))
+    }
+
+    pub fn borrow_immut(&mut self, r: Region) -> bool {
+        if self.is_borrowed_mut(r) {
+            return false;
+        }
+        self.immutable.push(r);
+        true
+    }
+
+    pub fn unborrow_immut(&mut self, r: Region) {
+        let (ix, _) = self
+            .immutable
+            .iter()
+            .enumerate()
+            .find(|(_, reg)| r == **reg)
+            .expect("region exists in borrows");
+        self.immutable.remove(ix);
+    }
+
+    pub fn borrow_mut(&mut self, r: Region) -> bool {
+        if self.is_borrowed_immut(r) || self.is_borrowed_mut(r) {
+            return false;
+        }
+        self.mutable.push(r);
+        true
+    }
+
+    pub fn unborrow_mut(&mut self, r: Region) {
+        let (ix, _) = self
+            .mutable
+            .iter()
+            .enumerate()
+            .find(|(_, reg)| r == **reg)
+            .expect("region exists in borrows");
+        self.mutable.remove(ix);
+    }
+}