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 {

src/librustc/middle/borrowck/preserve.rs

@@ -108,7 +108,7 @@ pub impl<'self> PreserveCtxt<'self> {
                 // Maybe if we pass in the parent instead here,
                 // we can prevent the "scope not found" error
                 debug!("scope_region thing: %? ", cmt.id);
-                ty::re_scope(*self.tcx().region_map.get(&cmt.id))
+                self.tcx().region_maps.encl_region(cmt.id)
             };
 
             self.compare_scope(cmt, scope_region)
@@ -128,27 +128,27 @@ pub impl<'self> PreserveCtxt<'self> {
                     cmt.span,
                     ~"preserve() called with local and !root_managed_data");
             }
-            let local_scope_id = *self.tcx().region_map.get(&local_id);
-            self.compare_scope(cmt, ty::re_scope(local_scope_id))
+            let local_region = self.tcx().region_maps.encl_region(local_id);
+            self.compare_scope(cmt, local_region)
           }
           cat_binding(local_id) => {
             // Bindings are these kind of weird implicit pointers (cc
             // #2329).  We require (in gather_loans) that they be
             // rooted in an immutable location.
-            let local_scope_id = *self.tcx().region_map.get(&local_id);
-            self.compare_scope(cmt, ty::re_scope(local_scope_id))
+            let local_region = self.tcx().region_maps.encl_region(local_id);
+            self.compare_scope(cmt, local_region)
           }
           cat_arg(local_id) => {
             // This can happen as not all args are lendable (e.g., &&
             // modes).  In that case, the caller guarantees stability
             // for at least the scope of the fn.  This is basically a
             // deref of a region ptr.
-            let local_scope_id = *self.tcx().region_map.get(&local_id);
-            self.compare_scope(cmt, ty::re_scope(local_scope_id))
+            let local_region = self.tcx().region_maps.encl_region(local_id);
+            self.compare_scope(cmt, local_region)
           }
           cat_self(local_id) => {
-            let local_scope_id = *self.tcx().region_map.get(&local_id);
-            self.compare_scope(cmt, ty::re_scope(local_scope_id))
+            let local_region = self.tcx().region_maps.encl_region(local_id);
+            self.compare_scope(cmt, local_region)
           }
           cat_comp(cmt_base, comp_field(*)) |
           cat_comp(cmt_base, comp_index(*)) |

src/librustc/middle/check_match.rs

@@ -596,8 +596,11 @@ pub fn specialize(cx: @MatchCheckCtxt,
                                                              class_id);
                             }
                             _ => {
-                                cx.tcx.sess.span_bug(pat_span,
-                                ~"struct pattern didn't resolve to a struct");
+                                cx.tcx.sess.span_bug(
+                                    pat_span,
+                                    fmt!("struct pattern resolved to %s, \
+                                          not a struct",
+                                         ty_to_str(cx.tcx, left_ty)));
                             }
                         }
                         let args = vec::map(class_fields, |class_field| {

src/librustc/middle/kind.rs

@@ -478,13 +478,13 @@ pub fn check_durable(tcx: ty::ctxt, ty: ty::t, sp: span) -> bool {
     }
 }
 
-/// This is rather subtle.  When we are casting a value to a
-/// instantiated trait like `a as trait<'r>`, regionck already ensures
-/// that any borrowed pointers that appear in the type of `a` are
-/// bounded by `&r`.  However, it is possible that there are *type
-/// parameters* in the type of `a`, and those *type parameters* may
-/// have borrowed pointers within them.  We have to guarantee that the
-/// regions which appear in those type parameters are not obscured.
+/// This is rather subtle.  When we are casting a value to a instantiated
+/// trait like `a as trait<'r>`, regionck already ensures that any borrowed
+/// pointers that appear in the type of `a` are bounded by `'r` (ed.: modulo
+/// FIXME(#5723)).  However, it is possible that there are *type parameters*
+/// in the type of `a`, and those *type parameters* may have borrowed pointers
+/// within them.  We have to guarantee that the regions which appear in those
+/// type parameters are not obscured.
 ///
 /// Therefore, we ensure that one of three conditions holds:
 ///
@@ -501,6 +501,8 @@ pub fn check_durable(tcx: ty::ctxt, ty: ty::t, sp: span) -> bool {
 ///
 /// (3) The type parameter is owned (and therefore does not contain
 /// borrowed ptrs).
+///
+/// FIXME(#5723)---This code should probably move into regionck.
 pub fn check_cast_for_escaping_regions(
     cx: Context,
     source: @expr,
@@ -509,40 +511,78 @@ pub fn check_cast_for_escaping_regions(
     // Determine what type we are casting to; if it is not an trait, then no
     // worries.
     let target_ty = ty::expr_ty(cx.tcx, target);
-    let target_substs = match ty::get(target_ty).sty {
-      ty::ty_trait(_, ref substs, _) => {(/*bad*/copy *substs)}
-      _ => { return; /* not a cast to a trait */ }
-    };
+    match ty::get(target_ty).sty {
+        ty::ty_trait(*) => {}
+        _ => { return; }
+    }
+
+    // Collect up the regions that appear in the target type.  We want to
+    // ensure that these lifetimes are shorter than all lifetimes that are in
+    // the source type.  See test `src/test/compile-fail/regions-trait-2.rs`
+    let mut target_regions = ~[];
+    ty::walk_regions_and_ty(
+        cx.tcx,
+        target_ty,
+        |r| {
+            if !r.is_bound() {
+                target_regions.push(r);
+            }
+        },
+        |_| true);
 
     // Check, based on the region associated with the trait, whether it can
     // possibly escape the enclosing fn item (note that all type parameters
-    // must have been declared on the enclosing fn item):
-    match target_substs.self_r {
-      Some(ty::re_scope(*)) => { return; /* case (1) */ }
-      None | Some(ty::re_static) | Some(ty::re_free(*)) => {}
-      Some(ty::re_bound(*)) | Some(ty::re_infer(*)) => {
-        cx.tcx.sess.span_bug(
-            source.span,
-            fmt!("bad region found in kind: %?", target_substs.self_r));
-      }
+    // must have been declared on the enclosing fn item).
+    if target_regions.any(|r| is_re_scope(*r)) {
+        return; /* case (1) */
     }
 
     // Assuming the trait instance can escape, then ensure that each parameter
-    // either appears in the trait type or is owned:
+    // either appears in the trait type or is owned.
     let target_params = ty::param_tys_in_type(target_ty);
     let source_ty = ty::expr_ty(cx.tcx, source);
-    do ty::walk_ty(source_ty) |ty| {
-        match ty::get(ty).sty {
-          ty::ty_param(source_param) => {
-            if target_params.contains(&source_param) {
-                /* case (2) */
-            } else {
-                check_durable(cx.tcx, ty, source.span); /* case (3) */
+    ty::walk_regions_and_ty(
+        cx.tcx,
+        source_ty,
+
+        |_r| {
+            // FIXME(#5723) --- turn this check on once &Objects are usable
+            //
+            // if !target_regions.any(|t_r| is_subregion_of(cx, *t_r, r)) {
+            //     cx.tcx.sess.span_err(
+            //         source.span,
+            //         fmt!("source contains borrowed pointer with lifetime \
+            //               not found in the target type `%s`",
+            //              ty_to_str(cx.tcx, target_ty)));
+            //     note_and_explain_region(
+            //         cx.tcx, "source data is only valid for ", r, "");
+            // }
+        },
+
+        |ty| {
+            match ty::get(ty).sty {
+                ty::ty_param(source_param) => {
+                    if target_params.contains(&source_param) {
+                        /* case (2) */
+                    } else {
+                        check_durable(cx.tcx, ty, source.span); /* case (3) */
+                    }
+                }
+                _ => {}
             }
-          }
-          _ => {}
+            true
+        });
+
+    fn is_re_scope(+r: ty::Region) -> bool {
+        match r {
+            ty::re_scope(*) => true,
+            _ => false
         }
     }
+
+    fn is_subregion_of(cx: Context, r_sub: ty::Region, r_sup: ty::Region) -> bool {
+        cx.tcx.region_maps.is_subregion_of(r_sub, r_sup)
+    }
 }
 
 /// Ensures that values placed into a ~Trait are copyable and sendable.