Fixes #153.

The zero-or-one alternation (i.e., `?`) was not being patched correctly.
It was erroneously assuming that one of its holes always pointed to a
subsequently instruction. This is not the case when it is itself at the
end of an enclosing alternation.

We fix this by exposing that hole so that it is patched with the correct
instruction by the enclosing alternation.

Author: BurntSushi

regex_macros/tests/tests.rs

@@ -384,6 +384,10 @@ fn regression_captures_rep() {
     assert_eq!(caps.name("foo").unwrap(), "x");
 }
 
+// Regression test for https://github.com/rust-lang-nursery/regex/issues/153
+mat!(regression_alt_in_alt1, r"ab?|$", "az", Some((0, 1)));
+mat!(regression_alt_in_alt2, r"^(.*?)(\n|\r\n?|$)", "ab\rcd", Some((0, 3)));
+
 // A whole mess of tests from Glenn Fowler's regex test suite.
 // Generated by the 'src/etc/regex-match-tests' program.
 #[path = "matches.rs"]

src/compile.rs

@@ -187,15 +187,14 @@ impl Compiler {
     ) -> CompileResult {
         let split = self.push_split_hole();
         let goto1 = self.insts.len();
-        let hole = try!(self.c(expr));
-        let goto2 = self.insts.len();
+        let hole1 = try!(self.c(expr));
 
-        if greedy {
-            self.fill_split(split, Some(goto1), Some(goto2));
+        let hole2 = if greedy {
+            self.fill_split(split, Some(goto1), None)
         } else {
-            self.fill_split(split, Some(goto2), Some(goto1));
-        }
-        Ok(hole)
+            self.fill_split(split, None, Some(goto1))
+        };
+        Ok(Hole::Many(vec![hole1, hole2]))
     }
 
     fn c_repeat_zero_or_more(