[@typescript-eslint/typedef] variableDeclaration broken with for..of loops

[octogonz]

Repro

{
  "rules": {
    "@typescript-eslint/typedef": [
      "error",
      {
        "variableDeclaration": true
      },
    ],
  }
}

// error @typescript-eslint/typedef : expected item to have a type annotation
for (const item of ['a', 'b']) {
}

Expected Result

The error should not be reported for a for..of loop variable.

Actual Result

The error is reported. The error is impossible to fix, because TypeScript does not allow type annotations here.

Additional Info

TSLint encountered this same problem as palantir/tslint#743.

Their fix is here and might be relevant: palantir/tslint#745

Versions

package	version
@typescript-eslint/eslint-plugin	2.0.0-alpha.4
@typescript-eslint/parser	1.13.0
TypeScript	3.5.3
ESLint	6.1.0

[octogonz]

@JoshuaKGoldberg TSLint does it like this:

    public visitVariableDeclaration(node: ts.VariableDeclaration) {
        // AFAIK, variable declarations will always have a grandparent, 
        // but check that to be on the safe side.
        // catch statements will be the parent of the variable declaration
        // for-in/for-of loops will be the gradparent of the variable declaration
        if (node.parent != null && node.parent.parent != null
                && node.parent.kind !== ts.SyntaxKind.CatchClause
                && node.parent.parent.kind !== ts.SyntaxKind.ForInStatement
                && node.parent.parent.kind !== ts.SyntaxKind.ForOfStatement) {
            this.checkTypeAnnotation("variable-declaration", node.name.getEnd(), node.type, node.name);
        }
        super.visitVariableDeclaration(node);
    }

That same idea should work for @typescript-eslint/typedef, right?

[octogonz]

Here's a PR: #787