auto merge of #19984 : japaric/rust/macro-expressions, r=alexcrichton

followed by a semicolon.

This allows code like `vec![1i, 2, 3].len();` to work.

This breaks code that uses macros as statements without putting
semicolons after them, such as:

    fn main() {
        ...
        assert!(a == b)
        assert!(c == d)
        println(...);
    }

It also breaks code that uses macros as items without semicolons:

    local_data_key!(foo)

    fn main() {
        println("hello world")
    }

Add semicolons to fix this code. Those two examples can be fixed as
follows:

    fn main() {
        ...
        assert!(a == b);
        assert!(c == d);
        println(...);
    }

    local_data_key!(foo);

    fn main() {
        println("hello world")
    }

RFC #378.

Closes #18635.

[breaking-change]

---

Rebased version of #18958
r? @alexcrichton 
cc @pcwalton 

1 files changed, 9 insertions, 6 deletions

diff --git a/src/libstd/rt/backtrace.rs b/src/libstd/rt/backtrace.rs
index ebbd3561313..d815a5ea4f7 100644
--- a/src/libstd/rt/backtrace.rs
+++ b/src/libstd/rt/backtrace.rs
@@ -116,7 +116,7 @@ fn demangle(writer: &mut Writer, s: &str) -> IoResult<()> {
             rest = rest.slice_to(i);
             while rest.len() > 0 {
                 if rest.starts_with("$") {
-                    macro_rules! demangle(
+                    macro_rules! demangle {
                         ($($pat:expr => $demangled:expr),*) => ({
                             $(if rest.starts_with($pat) {
                                 try!(writer.write_str($demangled));
@@ -128,7 +128,8 @@ fn demangle(writer: &mut Writer, s: &str) -> IoResult<()> {
                             }
 
                         })
-                    )
+                    }
+
                     // see src/librustc/back/link.rs for these mappings
                     demangle! (
                         "$SP$" => "@",
@@ -940,12 +941,12 @@ mod imp {
             Err(..) => return Ok(()),
         };
 
-        macro_rules! sym( ($e:expr, $t:ident) => (unsafe {
+        macro_rules! sym { ($e:expr, $t:ident) => (unsafe {
             match lib.symbol($e) {
                 Ok(f) => mem::transmute::<*mut u8, $t>(f),
                 Err(..) => return Ok(())
             }
-        }) )
+        }) }
 
         // Fetch the symbols necessary from dbghelp.dll
         let SymFromAddr = sym!("SymFromAddr", SymFromAddrFn);
@@ -1013,11 +1014,13 @@ mod imp {
 #[cfg(test)]
 mod test {
     use prelude::*;
-    macro_rules! t( ($a:expr, $b:expr) => ({
+    use io::MemWriter;
+
+    macro_rules! t { ($a:expr, $b:expr) => ({
         let mut m = Vec::new();
         super::demangle(&mut m, $a).unwrap();
         assert_eq!(String::from_utf8(m).unwrap(), $b);
-    }) )
+    }) }
 
     #[test]
     fn demangle() {