[SR-1724][Lexer] Handle hex letters after '.' on hex number literal

[rintaro]

What's in this pull request?

This case used to emit an error:

extension Int {
    var asUiColor: UIColor { ... }
}
0xfff.asUiColor

If [a-fA-F] follows ., it can be valid int literal followed by dot expression: e.g. 0xff.description, 0xff.fpValue

Resolved bug number: (SR-1724)

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[rintaro]

CC: @jckarter

[lattner]

The patch LGTM, but please simplify it by eliminating the "letterAfterDot" boolean. You should be able to change this condition to:

if (isDigit(PtrOnDot[1])) {

[rintaro]

Thank you! done.

[lattner]

Thanks!

[lattner]

@swift-ci please test and merge

[rintaro]

Thank you! I will add these test cases in later commit:

var fl_p: Float = 0x1p // expected-error {{expected a digit in floating point exponent}}
var fl_q: Float = 0x1p+ // expected-error {{expected a digit in floating point exponent}}
var fl_r: Float = 0x1.0fp // expected-error {{expected a digit in floating point exponent}}
var fl_s: Float = 0x1.0fp+ // expected-error {{expected a digit in floating point exponent}}

[jrose-apple]

Thanks! Can you add a test case for "hex letters but no 'p'"?

[jckarter]

@jrose-apple They already did so in #3132: https://github.com/apple/swift/pull/3132/files#diff-8be63eab29191d470b12d9177393ad1eR347

[jrose-apple]

Ah, missed that. Thanks!