Add config validation for empty network and forking url

[kshyun28]

• Because this PR includes a bug fix, relevant tests have been included.
• Because this PR includes a new feature, the change was previously discussed on an Issue or with someone from the team.
• I didn't do anything of this.

---

Considering the discussions in the related issue, this PR adds empty string validation such as:

• empty strings ""
• empty strings with at least 1 whitespace " "

for the following configs:

• [CUSTOM_NETWORK].url
• [HARDHAT_NETWORK_NAME].forking.url

To improve the error message, instead of using the default invalid error message, I also added an empty error message. This can be up for debate since we can just use invalid error message which makes the code simpler.

This closes #2730

Screenshot of sample config error

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[fvictorio]

Thank you @kshyun28, this looks good! I just left a minor comment.

[fvictorio]

Uhm, thinking about this a bit more, I'm afraid this change will break some existing projects that use an empty string as a placeholder, like this template.

This is not your fault, my initial description in the issue was a mistake 😞

Instead of that, I think we should validate the URL here:

hardhat/packages/hardhat-core/src/internal/core/providers/http.ts

Line 52 in a207463

const url = new URL(this._url);

(This is used both by normal networks and by the forking feature.)

This means adding a new general error here and throwing it there when url.trim() is empty. The error message should say something about trying to connect to an empty URL, and suggesting that this can be caused by an empty forking or network URL (we can't know for sure because it's a shared code).

I'm sorry for asking you to discard what you did so far, but I think doing this when the URL is actually used is the right thing to do here.

[kshyun28]

Hello @fvictorio, I understand that if this implementation of the fix would break some existing projects, better not go with this approach.

And no worries, it's not really discarding since the issue is moving and allows us to see potential issues.

I'll try to reimplement the fixes in the HttpProvider. Actually that was the first thing that came to mind for me, but considered the config validation approach. At least we now know that config validation won't work. :)

Thanks for the guidance!