librustc: Implement the fully-expanded, UFCS form of explicit self.

This makes two changes to region inference: (1) it allows region
inference to relate early-bound regions; and (2) it allows regions to be
related before variance runs. The former is needed because there is no
relation between the two regions before region substitution happens,
while the latter is needed because type collection has to run before
variance. We assume that, before variance is inferred, that lifetimes
are invariant. This is a conservative overapproximation.

This relates to #13885. This does not remove `~self` from the language
yet, however.

[breaking-change]

src/libsyntax/parse/parser.rs

@@ -45,7 +45,7 @@ use ast::{RetStyle, Return, BiShl, BiShr, Stmt, StmtDecl};
 use ast::{StmtExpr, StmtSemi, StmtMac, StructDef, StructField};
 use ast::{StructVariantKind, BiSub};
 use ast::StrStyle;
-use ast::{SelfRegion, SelfStatic, SelfUniq, SelfValue};
+use ast::{SelfExplicit, SelfRegion, SelfStatic, SelfUniq, SelfValue};
 use ast::{TokenTree, TraitMethod, TraitRef, TTDelim, TTSeq, TTTok};
 use ast::{TTNonterminal, TupleVariantKind, Ty, Ty_, TyBot, TyBox};
 use ast::{TypeField, TyFixedLengthVec, TyClosure, TyProc, TyBareFn};
@@ -3843,7 +3843,15 @@ impl<'a> Parser<'a> {
                 }
             }
             token::IDENT(..) if self.is_self_ident() => {
-                SelfValue(self.expect_self_ident())
+                let self_ident = self.expect_self_ident();
+
+                // Determine whether this is the fully explicit form, `self:
+                // TYPE`.
+                if self.eat(&token::COLON) {
+                    SelfExplicit(self.parse_ty(false), self_ident)
+                } else {
+                    SelfValue(self_ident)
+                }
             }
             token::BINOP(token::STAR) => {
                 // Possibly "*self" or "*mut self" -- not supported. Try to avoid
@@ -3851,7 +3859,9 @@ impl<'a> Parser<'a> {
                 self.bump();
                 let _mutability = if Parser::token_is_mutability(&self.token) {
                     self.parse_mutability()
-                } else { MutImmutable };
+                } else {
+                    MutImmutable
+                };
                 if self.is_self_ident() {
                     let span = self.span;
                     self.span_err(span, "cannot pass self by unsafe pointer");
@@ -3863,7 +3873,15 @@ impl<'a> Parser<'a> {
             _ if Parser::token_is_mutability(&self.token) &&
                     self.look_ahead(1, |t| token::is_keyword(keywords::Self, t)) => {
                 mutbl_self = self.parse_mutability();
-                SelfValue(self.expect_self_ident())
+                let self_ident = self.expect_self_ident();
+
+                // Determine whether this is the fully explicit form, `self:
+                // TYPE`.
+                if self.eat(&token::COLON) {
+                    SelfExplicit(self.parse_ty(false), self_ident)
+                } else {
+                    SelfValue(self_ident)
+                }
             }
             _ if Parser::token_is_mutability(&self.token) &&
                     self.look_ahead(1, |t| *t == token::TILDE) &&
@@ -3914,8 +3932,8 @@ impl<'a> Parser<'a> {
             }
             SelfValue(id) => parse_remaining_arguments!(id),
             SelfRegion(_,_,id) => parse_remaining_arguments!(id),
-            SelfUniq(id) => parse_remaining_arguments!(id)
-
+            SelfUniq(id) => parse_remaining_arguments!(id),
+            SelfExplicit(_,id) => parse_remaining_arguments!(id),
         };