Auto merge of #23857 - phildawes:libsyntax_nopanic, r=nikomatsakis

Hello! 

I've been working towards a libsyntax without panics. See:
http://internals.rust-lang.org/t/changing-libsyntax-to-use-result-instead-of-panic/1670

This patch changes the internals of parser.rs to use Result<> rather than panicing. It keeps the following old-style panicing functions as a facade:
parse_expr, parse_item, parse_pat, parse_arm, parse_ty, parse_stmt

I left these functions because I wasn't sure what to do about the quote_* macros or how many syntax-extensions would break if these and quoting macros returned Result.

The gyst of the rest of the patch is:

 - Functions in parse/parser.rs return PResult<> rather than panicing
 - Other functions in libsyntax call panic! explicitly if they rely on panicing behaviour.
 - I added a macro 'panictry!()' to act as scaffolding for callers while converting panicing functions. (This does the same as 'unwrap()' but is easier to grep for and turn into try!()).

Am I on the right track?  I'd quite like to get something merged soon as keeping this rebased in the face of libsyntax changes is a lot of work. Please let me know what changes you'd like to see to make this happen.

Thanks!, Phil

1 files changed, 2 insertions, 2 deletions

diff --git a/src/libsyntax/ext/source_util.rs b/src/libsyntax/ext/source_util.rs
index 31d8b207bb9..a4c2d2dc030 100644
--- a/src/libsyntax/ext/source_util.rs
+++ b/src/libsyntax/ext/source_util.rs
@@ -117,11 +117,11 @@ pub fn expand_include<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[ast::TokenTree
             while self.p.token != token::Eof {
                 match self.p.parse_item() {
                     Some(item) => ret.push(item),
-                    None => self.p.span_fatal(
+                    None => panic!(self.p.span_fatal(
                         self.p.span,
                         &format!("expected item, found `{}`",
                                  self.p.this_token_to_string())
-                    )
+                    ))
                 }
             }
             Some(ret)