Simplify checkers and add solhint

[landakram]

Hi again. I made this branch a while ago when I started on a project that uses solhint. I added solhint support and also reworked the flycheck checker initialization.

The main reason I wanted to rework flycheck checker initialization is that flycheck has its own logic to enable or disable checkers based on the presence of the :command binary, and also handles locally installed linters with its flycheck-some-checker-executable variables. So we can simplify this package's configuration by always defining the checker, and letting flycheck handle enabling/disabling it.

The second reason is basically #41. I'd expect to be able to require the package and set variables it defines after it is loaded. The changes in this PR mean I don't need to set the solidity-flycheck-some-checker-active variables at all. But for other configuration, I can set them after loading the package itself (I'm using use-package here, but it should work with regular require too):

(use-package solidity-flycheck
    :straight (solidity-flycheck :type git :host github :repo "ethereum/emacs-solidity")
    :hook solidity-mode
    :config
    (setq solidity-flycheck-chaining-error-level t)
    (setq solidity-flycheck-use-project t))

Note: this would be a breaking change. If you're onboard with the direction, I can invest a little more time in updating the readme / thoroughly testing, though I've been running it fine with the above configuration for a few months. Otherwise, I could split the solhint support into a separate PR. I just happened to combine the changes when I implemented this many months ago.

---

Commit messages copied here:

• Add a checker for solhint
• Simplify checkers. This commit removes some of the load-time logic that
  determined whether to define the flycheck checkers. Flycheck has its own logic to
  enable or disable checkers based on the presence of the :command binary, making
  these checks redundant. Some of the other checks done at load time have been
  moved into (eval ...) forms, so that the binaries can be customized after load-time
  with flycheck's pre-defined vars e.g. `flycheck-solium-checker-executable'. This is
  useful when linting binaries are installed locally in a project.

[LefterisJP]

Oh wow thanks a lot for the big PR.

I unfortunately don't have time to actually test it as I don't use solidity a lot lately.

I would not mind the approach personally so if you could test it more and add docs that would be great. Also perhaps if you can check some other user who would use it and see it does not break everything that would make things simpler for merging.

[clarkhenry]

Suggested change

	"Path to the solium binary."
	"Path to the solhint binary."

[clarkhenry]

Suggested change

	:command `(,solidity-solhint-path "-f" "visualstudio" source-inplace)
	:command `(,solidity-solhint-path "-f" "unix" source-inplace)

I don't see visualstudio among the formatter options. Although when it works when I run solhint -f visualstudio ./**/*.sol, would it make more sense here to use the unix formatted output?

Then the error-patterns would be something like:

  :error-patterns `((error
                     line-start (file-name) ":"  line ":" column ":" (zero-or-more " ")
                     "error" (zero-or-more " ") (message))
                    (warning
                     line-start (file-name) ":"  line ":" column ":" (zero-or-more " ")
                     "warning" (zero-or-more " ") (message)))

[landakram]

I had to tweak your suggestion slightly to differentiate between errors and warnings. But should be good to go.

[clarkhenry]

@landakram - could you check on my suggestions? Would love to get this merged. This PR works for me.

[landakram]

@clarkhenry Apologies for the delay. I've made your suggested fixes and I believe the PR is ready to merge now.

[hrkrshnn]

@clarkhenry, @GokhanPolat can you review this PR and approve it? I can merge it after that.

[GokhanPolat]

These changes exactly same as my PR (it was already @landakram's code) which are I walked same way with same steps. @landakram did a good job.

[hrkrshnn]

Thanks @GokhanPolat for the review. I'll proceed to merge this.