Forbid multiple imports in use statements

Closes #10911

src/libsyntax/parse/obsolete.rs

@@ -44,6 +44,7 @@ pub enum ObsoleteSyntax {
     ObsoleteVecDotDotWildcard,
     ObsoleteBoxedClosure,
     ObsoleteClosureType,
+    ObsoleteMultipleImport,
 }
 
 impl to_bytes::IterBytes for ObsoleteSyntax {
@@ -140,6 +141,10 @@ fn obsolete(&self, sp: Span, kind: ObsoleteSyntax) {
                 "closures are now written `|A| -> B` rather than `&fn(A) -> \
                  B`."
             ),
+            ObsoleteMultipleImport => (
+                "multiple imports",
+                "only one import is allowed per `use` statement"
+            ),
         };
 
         self.report(sp, kind, kind_str, desc);

src/libsyntax/parse/parser.rs

@@ -4923,6 +4923,7 @@ fn parse_view_paths(&self) -> ~[@view_path] {
         let mut vp = ~[self.parse_view_path()];
         while *self.token == token::COMMA {
             self.bump();
+            self.obsolete(*self.last_span, ObsoleteMultipleImport);
             vp.push(self.parse_view_path());
         }
         return vp;