Doesn't build on Rust 1.18 and 1.19

[hcpl]

Currently synstructure uses break with value (a 1.19 feature) in

synstructure/src/lib.rs

Lines 2102 to 2111 in dad0b18

 let ((unsafe_kw, bound, body, mut generics), after) = loop { 
     if let Ok((gi, c2)) = parse_gen_impl(c) { 
         break (gi, c2.token_stream()); 
     } else if let Some((tt, c2)) = c.token_tree() { 
         c = c2; 
         before.push(tt); 
     } else { 
         panic!("Expected a gen impl block"); 
     } 
 }; 

and Option::get_or_insert (a 1.20 feature) in

synstructure/src/lib.rs

Lines 282 to 286 in dad0b18

 let mut to_clause = into.where_clause.get_or_insert(WhereClause { 
     where_token: Default::default(), 
     predicates: punctuated::Punctuated::new(), 
 }); 
 to_clause.predicates.extend(from_clause.predicates.iter().cloned()); 

I see that 1.15 was failing in Travis so it was disabled and some non-1.15 features slipped into the library. But that was months ago, should it be re-enabled again or Rust version has to be bumped?

[hcpl]

There is a case about Option::get_or_insert_with which has a workaround:

synstructure/src/lib.rs

Lines 1508 to 1517 in dad0b18

 // Ensure we have a where clause, because we need to use it. We 
 // can't use `get_or_insert_with`, because it isn't supported on all 
 // rustc versions we support. 
 if where_clause.is_none() { 
     *where_clause = Some(WhereClause { 
         where_token: Default::default(), 
         predicates: punctuated::Punctuated::new(), 
     }); 
 } 
 let clause = where_clause.as_mut().unwrap(); 

[Nika Layzell]

I'd love a PR which re-enables the 1.15 tests, because I'd like to have the same minimum version as syn. It was disabled originally because I didn't have enough time to figure out what was wrong.

[hcpl]

Alright, I've changed those parts a bit and now it passes on 1.15 locally. I'll set up a PR a bit later.

[Nika Layzell]

You kindly fixed this for me in #15 🎉