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, 1 insertions, 1 deletions

diff --git a/src/libsyntax/util/parser_testing.rs b/src/libsyntax/util/parser_testing.rs
index ec608646327..c6646fe93a2 100644
--- a/src/libsyntax/util/parser_testing.rs
+++ b/src/libsyntax/util/parser_testing.rs
@@ -44,7 +44,7 @@ fn with_error_checking_parse<T, F>(s: String, f: F) -> T where
 /// Parse a string, return a crate.
 pub fn string_to_crate (source_str : String) -> ast::Crate {
     with_error_checking_parse(source_str, |p| {
-        p.parse_crate_mod()
+        panictry!(p.parse_crate_mod())
     })
 }