Reason about nested free variables that appear in a function

signature.  In a nutshell, the idea is to (1) report an error if, for
a region pointer `'a T`, the lifetime `'a` is longer than any
lifetimes that appear in `T` (in other words, if a borrowed pointer
outlives any portion of its contents) and then (2) use this to assume
that in a function like `fn(self: &'a &'b T)`, the relationship `'a <=
'b` holds. This is needed for rust-lang#5656.  Fixes rust-lang#5728.

Author: nikomatsakis

src/libcore/cmp.rs

@@ -116,6 +116,19 @@ totalord_impl!(i64)
 totalord_impl!(int)
 totalord_impl!(uint)
 
+pub fn cmp2<A:TotalOrd,B:TotalOrd>(
+    a1: &A, b1: &B,
+    a2: &A, b2: &B) -> Ordering
+{
+    //! Compares (a1, b1) against (a2, b2), where the a values are more significant.
+
+    match a1.cmp(a2) {
+        Less => Less,
+        Greater => Greater,
+        Equal => b1.cmp(b2)
+    }
+}
+
 /**
 * Trait for values that can be compared for a sort-order.
 *
@@ -193,6 +206,14 @@ mod test {
         assert_eq!(12.cmp(-5), Greater);
     }
 
+    #[test]
+    fn test_cmp2() {
+        assert_eq!(cmp2(1, 2, 3, 4), Less);
+        assert_eq!(cmp2(3, 2, 3, 4), Less);
+        assert_eq!(cmp2(5, 2, 3, 4), Greater);
+        assert_eq!(cmp2(5, 5, 5, 4), Greater);
+    }
+
     #[test]
     fn test_int_totaleq() {
         assert!(5.equals(&5));

src/libcore/str.rs

@@ -301,7 +301,11 @@ pub fn slice_shift_char<'a>(s: &'a str) -> (char, &'a str) {
 
 /// Prepend a char to a string
 pub fn unshift_char(s: &mut ~str, ch: char) {
-    *s = from_char(ch) + *s;
+    // This could be more efficient.
+    let mut new_str = ~"";
+    new_str.push_char(ch);
+    new_str.push_str(*s);
+    *s = new_str;
 }
 
 /**

src/libcore/tuple.rs

@@ -161,7 +161,6 @@ impl<A:Ord> Ord for (A,) {
     fn gt(&self, other: &(A,)) -> bool { other.lt(&(*self))  }
 }
 
-
 #[cfg(notest)]
 impl<A:Eq,B:Eq> Eq for (A, B) {
     #[inline(always)]

src/librustc/metadata/tydecode.rs

@@ -239,7 +239,8 @@ fn parse_region(st: @mut PState) -> ty::Region {
         assert!(next(st) == '|');
         let br = parse_bound_region(st);
         assert!(next(st) == ']');
-        ty::re_free(id, br)
+        ty::re_free(ty::FreeRegion {scope_id: id,
+                                    bound_region: br})
       }
       's' => {
         let id = parse_int(st);

src/librustc/metadata/tyencode.rs

@@ -146,12 +146,12 @@ fn enc_region(w: @io::Writer, cx: @ctxt, r: ty::Region) {
         w.write_char('b');
         enc_bound_region(w, cx, br);
       }
-      ty::re_free(id, br) => {
+      ty::re_free(ref fr) => {
         w.write_char('f');
         w.write_char('[');
-        w.write_int(id);
+        w.write_int(fr.scope_id);
         w.write_char('|');
-        enc_bound_region(w, cx, br);
+        enc_bound_region(w, cx, fr.bound_region);
         w.write_char(']');
       }
       ty::re_scope(nid) => {

src/librustc/middle/astencode.rs

@@ -475,9 +475,12 @@ impl tr for ty::Region {
     fn tr(&self, xcx: @ExtendedDecodeContext) -> ty::Region {
         match *self {
             ty::re_bound(br) => ty::re_bound(br.tr(xcx)),
-            ty::re_free(id, br) => ty::re_free(xcx.tr_id(id), br.tr(xcx)),
             ty::re_scope(id) => ty::re_scope(xcx.tr_id(id)),
             ty::re_static | ty::re_infer(*) => *self,
+            ty::re_free(ref fr) => {
+                ty::re_free(ty::FreeRegion {scope_id: xcx.tr_id(fr.scope_id),
+                                            bound_region: fr.bound_region.tr(xcx)})
+            }
         }
     }
 }

src/librustc/middle/borrowck/check_loans.rs

@@ -128,9 +128,9 @@ pub impl CheckLoanCtxt {
               Some(e) => return Some(pc_cmt(*e))
             }
 
-            match self.tcx().region_map.find(&scope_id) {
+            match self.tcx().region_maps.opt_encl_scope(scope_id) {
               None => return default_purity,
-              Some(&next_scope_id) => scope_id = next_scope_id
+              Some(next_scope_id) => scope_id = next_scope_id
             }
         }
     }
@@ -146,9 +146,9 @@ pub impl CheckLoanCtxt {
                 }
             }
 
-            match self.tcx().region_map.find(&scope_id) {
+            match self.tcx().region_maps.opt_encl_scope(scope_id) {
               None => return,
-              Some(&next_scope_id) => scope_id = next_scope_id,
+              Some(next_scope_id) => scope_id = next_scope_id,
             }
         }
     }
@@ -270,7 +270,7 @@ pub impl CheckLoanCtxt {
 
         debug!("new_loans has length %?", new_loans.len());
 
-        let par_scope_id = *self.tcx().region_map.get(&scope_id);
+        let par_scope_id = self.tcx().region_maps.encl_scope(scope_id);
         for self.walk_loans(par_scope_id) |old_loan| {
             debug!("old_loan=%?", self.bccx.loan_to_repr(old_loan));
 

src/librustc/middle/borrowck/gather_loans.rs

@@ -242,7 +242,7 @@ fn req_loans_in_expr(ex: @ast::expr,
         // (if used like `a.b(...)`), the call where it's an argument
         // (if used like `x(a.b)`), or the block (if used like `let x
         // = a.b`).
-        let scope_r = ty::re_scope(*self.tcx().region_map.get(&ex.id));
+        let scope_r = self.tcx().region_maps.encl_region(ex.id);
         let rcvr_cmt = self.bccx.cat_expr(rcvr);
         self.guarantee_valid(rcvr_cmt, m_imm, scope_r);
         visit::visit_expr(ex, self, vt);
@@ -524,7 +524,10 @@ pub impl GatherLoanCtxt {
         // immutable structures, this is just the converse I suppose)
 
         let scope_id = match scope_r {
-            ty::re_scope(scope_id) | ty::re_free(scope_id, _) => scope_id,
+            ty::re_scope(scope_id) |
+            ty::re_free(ty::FreeRegion {scope_id, _}) => {
+                scope_id
+            }
             _ => {
                 self.bccx.tcx.sess.span_bug(
                     cmt.span,

src/librustc/middle/borrowck/loan.rs

@@ -130,8 +130,8 @@ pub impl LoanContext {
           }
           cat_local(local_id) | cat_arg(local_id) | cat_self(local_id) => {
               // FIXME(#4903)
-            let local_scope_id = *self.bccx.tcx.region_map.get(&local_id);
-            self.issue_loan(cmt, ty::re_scope(local_scope_id), loan_kind,
+            let local_region = self.bccx.tcx.region_maps.encl_region(local_id);
+            self.issue_loan(cmt, local_region, loan_kind,
                             owns_lent_data)
           }
           cat_stack_upvar(cmt) => {

src/librustc/middle/borrowck/mod.rs

@@ -227,7 +227,6 @@ Borrowck results in two maps.
 use core::prelude::*;
 
 use middle::mem_categorization::*;
-use middle::region;
 use middle::ty;
 use middle::typeck;
 use middle::moves;
@@ -458,7 +457,7 @@ pub fn root_map() -> root_map {
 
 pub impl BorrowckCtxt {
     fn is_subregion_of(&self, r_sub: ty::Region, r_sup: ty::Region) -> bool {
-        region::is_subregion_of(self.tcx.region_map, r_sub, r_sup)
+        self.tcx.region_maps.is_subregion_of(r_sub, r_sup)
     }
 
     fn cat_expr(&self, expr: @ast::expr) -> cmt {