BUG report: unicode normalization on APFS (Mac OS High Sierra)

From: Elijah Newren <newren@gmail.com>
Date: Apr 26, 2018, 16:48 UTC
Message-ID: <CABPp-BEe+BK6Ew0ZLnkgCn=1J6kyJa5VTaibuJOEVeDdgLd_Ow@mail.gmail.com>

On HFS (which appears to be the default Mac filesystem prior to High Sierra), unicode names are "normalized" before recording. Thus with a script like:

    mkdir tmp
    cd tmp

    auml=$(printf "\303\244")
    aumlcdiar=$(printf "\141\314\210")
    >"$auml"

    echo "auml:          " $(echo -n "$auml" | xxd)
    echo "aumlcdiar:     " $(echo -n "$aumlcdiar" | xxd)
    echo "Dir contents:  " $(echo -n * | xxd)

    echo "Stat auml:     " "$(stat -f "%i   %Sm   %Su %N" "$auml")"
    echo "Stat aumlcdiar:" "$(stat -f "%i   %Sm   %Su %N" "$aumlcdiar")"

We see output like:

    auml:           00000000: c3a4 ..
    aumlcdiar:      00000000: 61cc 88 a..
    Dir contents:   00000000: 61cc 88 a..
    Stat auml:      857473   Apr 26 09:40:40 2018   newren ä
    Stat aumlcdiar: 857473   Apr 26 09:40:40 2018   newren ä

On APFS, which appears to be the new default filesystem in Mac OS High Sierra, we instead see:

    auml:           00000000: c3a4 ..
    aumlcdiar:      00000000: 61cc 88 a..
    Dir contents:   00000000: c3a4 ..
    Stat auml:      8591766636   Apr 26 09:40:59 2018   newren ä
    Stat aumlcdiar: 8591766636   Apr 26 09:40:59 2018   newren ä

i.e. APFS appears to record the filename as specified by the user, but continues to allow the user to access it via any name that normalizes to the same thing. This difference causes t0050-filesystem.sh to fail the final two tests. I could change the "UTF8_NFD_TO_NFC" flag checking in test-lib.sh to instead test the exit code of stat to make it pass these two tests, but I have no idea if there are problems elsewhere that this would just be papering over.

I dislike Mac OS and avoid it, so I'd prefer to find someone else motivated to fix this. If no one is, I may eventually try to fix this up...in a year or three from now. But is someone else interested? Would this serve as a good microproject for our microprojects list (or are the internals hairy enough that this is too big of a project for that list)?

Elijah