Improve attribute name matching

[dbanck]

This PR improves the attribute name matching in two ways:

• We now match a whole word with the negative lookahead instead of just the first letter
• We only match null, false, and true when they are followed by whitespace, so words like nullable are matched correctly.

UX

Before

After

Fixes hashicorp/vscode-terraform#1286

[radeksimko]

I'm guessing the reason we also still match null, true and false as some kind of "special" attribute names, although they are not really special, is pure pragmatism as it would be harder not to highlight, due to the regexp-based matching in TextMate, right?

With that in mind, LGTM.

[radeksimko]

Oh, actually, one more note/suggestion - AFAICT technically this would be valid (although mis-formatted) config:

variable "foo" {
  nullable=true
  falseyy=""
  trueyy=""
}

Wouldn't that suffer from the same problem?

[dbanck]

I'm guessing the reason we also still match null, true and false as some kind of "special" attribute names, although they are not really special, is pure pragmatism as it would be harder not to highlight, due to the regexp-based matching in TextMate, right?

We match null, true, and false as constant.language.hcl (Language Constants) here, although they aren't valid constants here. I think turning the constant matching off for attribute names would be hard.

Wouldn't that suffer from the same problem?

Good catch! I've updated the Regex and the test case for attributes without whitespace before the =.