A better error message when the specified style is not found

[Fil]

No description provided.

[Fil]

ok I've tried several things (like checking that the source is an actual file and not a directory) — however they only add complexity.

What we want here is only to let the user to know that this problem is due to the style option, which is not obvious from the current message.

bundle docs/ → ✘ [ERROR] Could not resolve "docs/"

A possibility might be to change the message slightly into:

bundle style option docs/ → ✘ [ERROR] Could not resolve "docs/"

We could also catch the error and then add one line of log to say the style option ${style.path} must reference a valid file, then throw. Note that this error is not distinguishable from other potential errors (no error type or errcode that I can see).

[Fil]

related: #525

[mythmon]

This is crashing build specifically, right? Does it show up when you run "yarn build", or only deploy?

This provides more evidence that we should be separating build and deploy.

[Fil]

yes, it crashes the build. In this case it's a good thing that the build errors, but the error message was unclear and it took me a moment to find why it was erroring.

[mbostock]

To clarify the issue description: it’s expected that the build crashes if you reference a stylesheet that does not exist (including the empty string); but we want a better error message when this happens. So this is not a bug (the crashing is desired), but we should enhance the error message.