Building: Option to cache dependencies

[alubbe]

We're running snowpack build quite a lot on CI, and only rarely were the dependencies changed since the last run - and building them takes over 2 minutes vs. the 10 seconds to build our own files. We can't use snowpack build --watch, since we cannot keep processes across CI runs, but we can (and do) keep cache files. It would be great if there was a build cache folder similar to dev mode, where most of the time, it can just reuse the previous build and build everything in 10 seconds rather than 2 minutes and 10 seconds.

Maybe something like snowpack build --cache?

[FredKSchott]

+1, we have an issue out that is strongly related to this: #1052

snowpack build --cache is interesting as an opt-in, because even without #1052 it would put a bit of the responsibility on you as the user. "I haven't touched config myself, therefore I feel comfortable reusing cached build values". But, it would be nice to tackle #1052 first and then potentially turn this on for everyone, by default.

[alubbe]

If you think #1052 will be solid enough to be trusted by snowpack build, then I'm all for it :)

[cmalven]

I just started experimenting with using snowpack build without a dev server on a recent PHP project, and have found the slow, recurring building dependencies times to wipe out any gains from using snowpack. The actual build (using esbuild) takes only 1 second, but bundling dependencies takes almost 30 seconds, which on its own is about 20 seconds longer than webpack took to bundle the same project.

Likewise, when using snowpack build --watch, the build times on subsequent file change are very fast, but first you have to wait 30 seconds for dependencies.