error[E0658]: imports can only refer to extern crate names passed with --extern on stable channel

[austinfrey]

i can not seem to get wasmtime to build.

as far as i can tell, I'm following the build instructions

details
cargo: cargo 1.31.0 (339d9f9c8 2018-11-16)
rustc: rustc 1.31.0 (abe02cefd 2018-12-04)
rustup: rustup 1.18.3 (435397f48 2019-05-22)
OS: Linux/Ubuntu 19+

git clone --recurse-submodules https://github.com/CraneStation/wasmtime.git
cargo build --release

the build fails with this error

error[E0658]: imports can only refer to extern crate names passed with `--extern` on stable channel (see issue #53130)       
   --> /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/parse.rs:48:5                           
    |                                                                                                                        
48  |   use regex;                                                                                                           
    |       ^^^^^                                                                                                            
    |                                                                                                                        
   ::: /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/lib.rs:196:1                            
    |                                                                                                                        
196 | / macro_rules! regex(                                                                                                  
197 | |     ($s:expr) => (regex::Regex::new($s).unwrap());                                                                   
198 | | );                                                                                                                   
    | |__- not an extern crate passed with `--extern`                                                                        
    |                                                                                                                        
note: this import refers to the macro defined here                                                                           
   --> /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/lib.rs:196:1                            
    |                                                                                                                        
196 | / macro_rules! regex(                                                                                                  
197 | |     ($s:expr) => (regex::Regex::new($s).unwrap());                                                                   
198 | | );                                                                                                                   
    | |__^                                                                                                                   
                                                                                                                             
error[E0603]: macro `regex` is private                                                                                       
   --> /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/parse.rs:185:41                         
    |                                                                                                                        
185 |             static ref OPTIONS: Regex = regex!(r"^\s*(?i:options:)\s*");                                               
    |                                         ^^^^^                                                                          
                                                                                                                             
error[E0603]: macro `regex` is private                                                                                       
   --> /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/parse.rs:186:40                         
    |                                                                                                                        
186 |             static ref ISFLAG: Regex = regex!(r"^(-\S|--\S)");                                                         
    |                                        ^^^^^                                                                           
                                                                                                                             
error[E0603]: macro `regex` is private                                                                                       
   --> /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/parse.rs:187:45                         
    |                                                                                                                        
187 |             static ref REMOVE_DESC: Regex = regex!(r"  .*$");                                                          
    |                                             ^^^^^                                                                      
                                                                                                                             
error[E0603]: macro `regex` is private                                                                                       
   --> /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/parse.rs:188:49                         
    |                                                                                                                        
188 |             static ref NORMALIZE_FLAGS: Regex = regex!(r"([^-\s]), -");                                                
    |                                                 ^^^^^                                                                  
                                                                                                                             
error[E0603]: macro `regex` is private                                                                                       
   --> /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/parse.rs:189:44                         
    |                                                                                                                        
189 |             static ref FIND_FLAGS: Regex = regex!(r"(?x)                                                               
    |                                            ^^^^^                                                                       
                                                                                                                             
error[E0603]: macro `regex` is private                                                                                       
   --> /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/parse.rs:264:46                         
    |                                                                                                                        
264 |             static ref FIND_DEFAULT: Regex = regex!(                                                                   
    |                                              ^^^^^                                                                     
                                                                                                                             
error[E0603]: macro `regex` is private                                                                                       
   --> /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/parse.rs:791:36                         
    |                                                                                                                        
791 |             static ref RE: Regex = regex!(r"^-[^-]\S*$");                                                              
    |                                    ^^^^^                                                                               
                                                                                                                             
error[E0603]: macro `regex` is private                                                                                       
   --> /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/parse.rs:798:36                         
    |                                                                                                                        
798 |             static ref RE: Regex = regex!(r"^--\S+(?:<[^>]+>)?$");                                                     
    |                                    ^^^^^                                                                               
                                                                                                                             
error[E0603]: macro `regex` is private                                                                                       
   --> /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/parse.rs:805:36                         
    |                                                                                                                        
805 |             static ref RE: Regex = regex!(r"^--\S+(=.+)?$");                                                           
    |                                    ^^^^^                                                                               
                                                                                                                             
error[E0603]: macro `regex` is private                                                                                       
   --> /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/parse.rs:812:36                         
    |                                                                                                                        
812 |             static ref RE: Regex = regex!(r"^(\p{Lu}+|<[^>]+>)$");                                                     
    |                                    ^^^^^                                                                               
                                                                                                                             
error[E0603]: macro `regex` is private                                                                                       
   --> /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/parse.rs:819:36                         
    |                                                                                                                        
819 |             static ref RE: Regex = regex!(r"^(-|--|[^-]\S*)$");                                                        
    |                                    ^^^^^                                                                               
                                                                                                                             
error[E0603]: macro `regex` is private                                                                                       
    --> /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/parse.rs:1236:45                       
     |                                                                                                                       
1236 |             static ref SPLIT_SPACE: Regex = regex!(r"\s+");                                                           
     |                                             ^^^^^                                                                     
                                                                                                                             
error[E0603]: macro `regex` is private                                                                                       
    --> /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/parse.rs:1444:40                       
     |                                                                                                                       
1444 |         static ref LONG_EQUAL: Regex = regex!("^(?P<name>[^=]+)=(?P<arg>.+)$");                                       
     |                                        ^^^^^                                                                          
                                                                                                                             
error[E0603]: macro `regex` is private                                                                                       
    --> /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/parse.rs:1461:40                       
     |                                                                                                                       
1461 |         static ref LONG_EQUAL: Regex = regex!("^(?P<name>[^=]+)=(?P<arg>.*)$");                                       
     |                                        ^^^^^                                                                          
                                                                                                                             
error[E0603]: macro `regex` is private                                                                                       
    --> /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/parse.rs:1480:39                       
     |                                                                                                                       
1480 |         static ref NORMALIZE: Regex = regex!(r"\.\.\.|\[|\]|\(|\)|\|");                                               
     |                                       ^^^^^                                                                           
                                                                                                                             
error[E0603]: macro `regex` is private                                                                                       
    --> /home/austin/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/parse.rs:1481:35                       
     |                                                                                                                       
1481 |         static ref WORDS: Regex = regex!(r"--\S+?=<[^>]+>|<[^>]+>|\S+");                                              
     |                                   ^^^^^                                                                               
                                                                                                                             
error: aborting due to 17 previous errors                                                                                    
                                                                                                                             
Some errors occurred: E0603, E0658.                                                                                          
For more information about an error, try `rustc --explain E0603`.                                                            
error: Could not compile `docopt`.                                                                                           
warning: build failed, waiting for other jobs to finish...
error: build failed

[austinfrey]

switched to the nightly toolchain and all is well.

[kubkon]

You don’t need nightly to be able to build Wasmtime. However, looking at the info you submitted (thanks!), your Rust version might simply be too old. Wasmtime requires Rust stable version at least 1.32, while you were trying to compile with 1.31. Could you try updating your stable toolchain with rustup update and try again?