[tor-bugs] #24467 [Core Tor/Tor]: Enable -Wnormalized=nfkc when available to avoid source code identifier confusion

[Tor Bug Tracker & Wiki]

#24467: Enable -Wnormalized=nfkc when available to avoid source code identifier
confusion
------------------------------+--------------------------------
     Reporter:  teor          |      Owner:  (none)
         Type:  enhancement   |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.3.3.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  security-low
Actual Points:                |  Parent ID:
       Points:  0.2           |   Reviewer:
      Sponsor:                |
------------------------------+--------------------------------
 In https://people.torproject.org/~nickm/warnings.html , nickm asks:

 > We use -Wnormalized=id now; should we switch?


 Yes, we should switch to `-Wnormalized=nfkc`, as a precaution against
 patches that are submitted with similar-looking characters. Ideally, we
 would use `-Wnormalized=ban-unicode-in-identifiers`, but that's not
 something gcc has implemented yet.

 From https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

     Some characters in ISO 10646 have distinct meanings but look identical
 in some fonts or display methodologies, especially once formatting has
 been applied. For instance \u207F, “SUPERSCRIPT LATIN SMALL LETTER N”,
 displays just like a regular n that has been placed in a superscript. ISO
 10646 defines the NFKC normalization scheme to convert all these into a
 standard form as well, and GCC warns if your code is not in NFKC if you
 use -Wnormalized=nfkc. This warning is comparable to warning about every
 identifier that contains the letter O because it might be confused with
 the digit 0, and so is not the default, but may be useful as a local
 coding convention if the programming environment cannot be fixed to
 display these characters distinctly.

 clang hasn't implemented -Wnormalized yet:

 https://clang.llvm.org/docs/DiagnosticsReference.html

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24467>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online