Fix ICE in decimal_literal_representation lint

[phansch]

Handling the integer parsing properly instead of just unwrapping.

Note that the test is not catching the ICE because plain UI tests
currently hide ICEs. Once that issue is fixed, this
test would fail properly again.

Fixes #3891

[phansch]

For some reason rustfmt is triggering the same rust warning: https://travis-ci.com/rust-lang/rust-clippy/jobs/191281098#L1664
I didn't know that running rustfmt will trigger rustc errors as well and I'm not sure how to properly test this then? #![rustfmt::skip] has no effect either.

[flip1995]

Maybe use the old hack and exclude the test file here:

rust-clippy/ci/base-tests.sh

Line 62 in 949f584

for file in `find tests | grep "\.rs$"` ; do

rustfmt only triggers parsing errors, since the file needs to be parsed for rustfmt to run.

[phansch]

I re-added the old hack to exclude the file from rustfmt. I think in this specific case it makes sense to be excluded.

[flip1995]

One last thing: All these if statements should be collapsible into the if_chain! macro:

if_chain! {
    if let LitKind::Int(..) = lit.node;
    if let Some(src) = snippet_opt(cx, lit.span);
    if let Some(firstch) = src.chars().next();
    if char::to_digit(firstch, 10).is_some();
    let digit_info = DigitInfo::new(&src, false);
    if digit_info.radix == Radix::Decimal;
    if let Ok(val) = digit_info.digits;
    if val >= u128::from(self.threshold);
    then {
        let hex = format!("{:#X}", val);
        let digit_info = DigitInfo::new(&hex, false);
        let _ = Self::do_lint(digit_info.digits).map_err(|warning_type| {
            warning_type.display(&digit_info.grouping_hint(), cx, lit.span)
        });
    }
}

---

(For some reason I wasn't able to comment directly on the code)

[phansch]

Yup, that worked =)

[flip1995]

@bors r+

[bors]

📌 Commit ab6b949 has been approved by flip1995

[bors]

⌛ Testing commit ab6b949 with merge 2278814...

[bors]

☀️ Test successful - checks-travis, status-appveyor
Approved by: flip1995
Pushing 2278814 to master...