librustc: Make the compiler ignore purity.

For bootstrapping purposes, this commit does not remove all uses of
the keyword "pure" -- doing so would cause the compiler to no longer
bootstrap due to some syntax extensions ("deriving" in particular).
Instead, it makes the compiler ignore "pure". Post-snapshot, we can
remove "pure" from the language.

There are quite a few (~100) borrow check errors that were essentially
all the result of mutable fields or partial borrows of `@mut`. Per
discussions with Niko I think we want to allow partial borrows of
`@mut` but detect obvious footguns. We should also improve the error
message when `@mut` is erroneously reborrowed.

2 files changed, 8 insertions, 5 deletions

diff --git a/src/libsyntax/print/pp.rs b/src/libsyntax/print/pp.rs
index 7f46e452299..492ecdb3f4d 100644
--- a/src/libsyntax/print/pp.rs
+++ b/src/libsyntax/print/pp.rs
@@ -452,9 +452,10 @@ pub impl Printer {
         self.pending_indentation += amount;
     }
     fn get_top(&mut self) -> print_stack_elt {
-        let n = self.print_stack.len();
+        let print_stack = &mut *self.print_stack;
+        let n = print_stack.len();
         if n != 0u {
-            self.print_stack[n - 1u]
+            print_stack[n - 1u]
         } else {
             print_stack_elt {
                 offset: 0,
@@ -496,7 +497,8 @@ pub impl Printer {
           }
           END => {
             debug!("print END -> pop END");
-            fail_unless!((self.print_stack.len() != 0u));
+            let print_stack = &*self.print_stack;
+            fail_unless!((print_stack.len() != 0u));
             self.print_stack.pop();
           }
           BREAK(b) => {
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 5aae5570dbf..71f3de17414 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -279,9 +279,10 @@ pub fn is_bol(s: @ps) -> bool {
 }
 
 pub fn in_cbox(s: @ps) -> bool {
-    let len = s.boxes.len();
+    let boxes = &*s.boxes;
+    let len = boxes.len();
     if len == 0u { return false; }
-    return s.boxes[len - 1u] == pp::consistent;
+    return boxes[len - 1u] == pp::consistent;
 }
 
 pub fn hardbreak_if_not_bol(s: @ps) { if !is_bol(s) { hardbreak(s.s); } }