feat: add checking against multiple statements per line (#123)

[arichard4]

No description provided.

[arichard4]

Note that we can't use "code_lines"- it's a boolean, and it can't be made numeric because it has potential false positives here. (It tracks "line" as well as "state.lexer.line", potentially the same or next line.)

[arichard4]

@alerque Oh, I see you tested one other case- this current technically passes this case, but only by flatly ignoring anything not at the top level of the AST, so it misses almost everything. Good catch, I can fix that up by checking over each block of statements instead.

[arichard4]

@alerque Updated.

For the sort of case you were looking at, the following will not trigger the new warning:

function () print("a") end
if true then; bar = 42; end

However, if you stick multiple statements on the same line inside those blocks, they will emit warnings now. There is one case in luacheck's existing code which fails, which I have modified:

   parser:flag("-v --version", "Show version info and exit.")
      :action(function() print(version.string) os.exit(exit_codes.ok) end)

The new lint flags that the print and exit statements are on the same line; I've put them on different lines.

[arichard4]

The latter case is, I think, wrong regardless; but we might want to add an explicit escape hatch to ignore multiple semicolon separated statements per line. I've changed it to this:

   parser:flag("-v --version", "Show version info and exit.")
      :action(function()
         print(version.string)
         os.exit(exit_codes.ok)
      end)

I'm not sure if we'd want this lint to explicitly permit this:

   parser:flag("-v --version", "Show version info and exit.")
      :action(function() print(version.string); os.exit(exit_codes.ok); end)