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/parse/lexer/mod.rs b/src/libsyntax/parse/lexer/mod.rs
index 78470f00207..22b7d5c9f1d 100644
--- a/src/libsyntax/parse/lexer/mod.rs
+++ b/src/libsyntax/parse/lexer/mod.rs
@@ -116,7 +116,7 @@ impl<'a> Reader for TtReader<'a> {
         r
     }
     fn fatal(&self, m: &str) -> ! {
-        self.sp_diag.span_fatal(self.cur_span, m);
+        panic!(self.sp_diag.span_fatal(self.cur_span, m));
     }
     fn err(&self, m: &str) {
         self.sp_diag.span_err(self.cur_span, m);
@@ -181,7 +181,7 @@ impl<'a> StringReader<'a> {
 
     /// Report a fatal lexical error with a given span.
     pub fn fatal_span(&self, sp: Span, m: &str) -> ! {
-        self.span_diagnostic.span_fatal(sp, m)
+        panic!(self.span_diagnostic.span_fatal(sp, m))
     }
 
     /// Report a lexical error with a given span.