Rebuild for tests too long

[martypdx]

Doesn't look like much single file benefit, rebuild times are high(er) than first build. Also appears to get progressively worse longer it runs.

Single file change:

gobble: build invalidated (1 file changed). restarting
gobble: 02-6to5 done in 341ms                                                                                                 
gobble: 03-esperantoBundle done in 1462ms                                                                                     
gobble: 04-sorcery done in 1810ms                                                                                             
gobble: 18-merge done in 5ms                                                                                                  
gobble: 07-merge done in 11ms                                                                                                 
gobble: 08-bundleTests done in 1273ms                                                                                         
gobble: 09-es6transpiler done in 2099ms                                                                                       
gobble: 10-map done in 42ms                                                                                                   
gobble: 16-merge done in 66ms                                                                                                 
gobble: 17-moveTo done in 1ms                                                                                                 
gobble: 19-merge done in 5ms                                                                                                  
gobble: build completed in 7203ms. Listening for changes...

Compare to initial gobble:

~/ractive>npm start

> [email protected] start /Users/marty/ractive
> gobble

gobble: server listening on port 4567
gobble: livereload server running
gobble: 02-6to5 done in 6429ms                                                                                                
gobble: 03-esperantoBundle done in 1103ms                                                                                     
gobble: 04-sorcery done in 1344ms                                                                                             
gobble: 01-moveTo done in 2ms                                                                                                 
gobble: 05-sorcery done in 4ms                                                                                                
gobble: 18-merge done in 2ms                                                                                                  
gobble: 06-moveTo done in 0ms                                                                                                 
gobble: 07-merge done in 12ms                                                                                                 
gobble: 08-bundleTests done in 1125ms                                                                                         
gobble: 09-es6transpiler done in 6620ms                                                                                       
gobble: 10-map done in 38ms                                                                                                   
gobble: 11-moveTo done in 1ms                                                                                                 
gobble: 12-include done in 4ms                                                                                                
gobble: 13-esperanto done in 34ms                                                                                             
gobble: 14-es6transpiler done in 313ms                                                                                        
gobble: 15-moveTo done in 1ms                                                                                                 
gobble: 16-merge done in 49ms                                                                                                 
gobble: 17-moveTo done in 0ms                                                                                                 
gobble: 19-merge done in 3ms                                                                                                  
gobble: build completed in 17119ms.

[Rich-Harris]

Yeah this is a pain point for me too. I tried to fix part of the problem the other day but it turned out to be a less trivial fix than I imagined.

There are (at least?) three things that need to happen:

• Source and test files should be transpiled to ES6 in one go. At the moment, test files are bundled and then transpiled - I forget the reason. (This is also why we're using es6-transpiler for that step - 6to5 babel is excruciatingly slow with large files, but es6-transpiler has certain limitations so I'd rather remove it)
• Esperanto needs to cache transformations where possible - Cache analysis/ast for incremental builds esperantojs/esperanto#72
• Ditto for sorcery if that's possible (I suspect it may not be - it's not possible to state that if a file has unchanged, its sources are also unchanged, I opened an issue for it anyway Cache analysis Rich-Harris/sorcery#2). There may be other performance optimisations for sorcery (or vlq, which does the sourcemap en/decoding) that I haven't yet investigated

[Rich-Harris]

Closing this - items 2 and 3 on the list above are still outstanding, but the build is now a good deal faster anyway