Print missing semicolon warning for type-inferred ints

We only printed the extra semicolon warning if the type of the last
statement was the same as the return type of the function.

If a semicolon was appended, then the code

fn foo() -> u16 {
    1234;
}

Would not print the extra semicolon warning because without knowing
that 1234 is the return value, the inference engine would take 1234 to
be an i32.

This adds extra logic to recognize this case.

Author: Dylan McKay

src/librustc/middle/liveness.rs

@@ -1483,7 +1483,14 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
                         None if !body.stmts.is_empty() =>
                             match body.stmts.first().unwrap().node {
                                 hir::StmtSemi(ref e, _) => {
-                                    self.ir.tcx.expr_ty(&**e) == t_ret
+                                    match (&self.ir.tcx.expr_ty(&**e).sty, &t_ret.sty) {
+                                        // Type inference causes unsuffixed integer literals
+                                        // to be evaluated as i32 values. We still want to
+                                        // inform the user of a semicolon in this case.
+                                        (&ty::TyInt(ast::TyI32),&ty::TyInt(..)) => true,
+                                        (&ty::TyInt(ast::TyI32),&ty::TyUint(..)) => true,
+                                        (a,b) => (a == b),
+                                    }
                                 },
                                 _ => false
                             },

src/test/compile-fail/missing-semicolon.rs

@@ -0,0 +1,17 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// error-pattern:consider removing this semicolon
+
+fn foo() -> u16 {
+    1234;
+}
+
+fn main() { }