auto merge of #5125 : nikomatsakis/rust/issue-4846-lifetime-defaults, r=nikomatsakis

Work towards #4846.

- Institute new region defaults where all omitted regions get a fresh lifetime.
- Require explicit region names except in functions.
- Fix a bug in region parameterization inference.  I've been putting this off because it will not be important when we remove RP inference in favor of explicit declarations, but then it was blocking this patch.

r? @pcwalton

1 files changed, 33 insertions, 9 deletions

diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 5013b2c919f..f71f07655f2 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -599,6 +599,12 @@ pub impl Parser {
         }
     }
 
+    fn region_from_lifetime(&self, l: &ast::Lifetime) -> @region {
+        // eventually `ast::region` should go away in favor of
+        // `ast::Lifetime`.  For now we convert between them.
+        self.region_from_name(Some(l.ident))
+    }
+
     fn parse_ty(&self, colons_before_params: bool) -> @Ty {
         maybe_whole!(self, nt_ty);
 
@@ -944,7 +950,7 @@ pub impl Parser {
 
         // Parse the region parameter, if any, which will
         // be written "foo/&x"
-        let rp = {
+        let rp_slash = {
             // Hack: avoid parsing vstores like /@ and /~.  This is painful
             // because the notation for region bounds and the notation for
             // vstores is... um... the same.  I guess that's my fault.  This
@@ -961,9 +967,23 @@ pub impl Parser {
         };
 
         // Parse any lifetime or type parameters which may appear:
-        let tps = self.parse_generic_values();
+        let (lifetimes, tps) = self.parse_generic_values();
         let hi = self.span.lo;
 
+        let rp = match (&rp_slash, &lifetimes) {
+            (&Some(_), _) => rp_slash,
+            (&None, v) => {
+                if v.len() == 0 {
+                    None
+                } else if v.len() == 1 {
+                    Some(self.region_from_lifetime(v.get(0)))
+                } else {
+                    self.fatal(fmt!("Expected at most one \
+                                     lifetime name (for now)"));
+                }
+            }
+        };
+
         @ast::path { span: mk_sp(lo, hi),
                      rp: rp,
                      types: tps,
@@ -1316,11 +1336,11 @@ pub impl Parser {
                   token::IDENT(i, _) => {
                     hi = self.span.hi;
                     self.bump();
-                    let tys = if self.eat(&token::MOD_SEP) {
+                    let (_, tys) = if self.eat(&token::MOD_SEP) {
                         self.expect(&token::LT);
                         self.parse_generic_values_after_lt()
                     } else {
-                        ~[]
+                        (opt_vec::Empty, ~[])
                     };
 
                     // expr.f() method call
@@ -2776,20 +2796,24 @@ pub impl Parser {
         }
     }
 
-    fn parse_generic_values(&self) -> ~[@Ty] {
+    fn parse_generic_values(
+        &self) -> (OptVec<ast::Lifetime>, ~[@Ty])
+    {
         if !self.eat(&token::LT) {
-            ~[]
+            (opt_vec::Empty, ~[])
         } else {
             self.parse_generic_values_after_lt()
         }
     }
 
-    fn parse_generic_values_after_lt(&self) -> ~[@Ty] {
-        let _lifetimes = self.parse_lifetimes();
+    fn parse_generic_values_after_lt(
+        &self) -> (OptVec<ast::Lifetime>, ~[@Ty])
+    {
+        let lifetimes = self.parse_lifetimes();
         let result = self.parse_seq_to_gt(
             Some(token::COMMA),
             |p| p.parse_ty(false));
-        opt_vec::take_vec(result)
+        (lifetimes, opt_vec::take_vec(result))
     }
 
     fn parse_fn_decl(&self, parse_arg_fn: fn(&Parser) -> arg_or_capture_item)