StringIndexError when indexing String with Umlauts

[axsk]

julia> ("xöb")[3]
ERROR: StringIndexError("xöb", 3)
Stacktrace:
 [1] string_index_err(::String, ::Int64) at ./strings/string.jl:12
 [2] getindex_continued(::String, ::Int64, ::UInt32) at ./strings/string.jl:216
 [3] getindex(::String, ::Int64) at ./strings/string.jl:209
 [4] top-level scope at none:0

julia> versioninfo()
Julia Version 1.0.1
Commit 0d713926f8 (2018-09-29 19:05 UTC)
Platform Info:
  OS: macOS (x86_64-apple-darwin14.5.0)
  CPU: Intel(R) Core(TM) i5-7267U CPU @ 3.10GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-6.0.0 (ORCJIT, skylake)

Stumbled upon this when debugging a still unexplained segfault

julia> myFunctionInvolvingTheAboveWithASecretString() Unreachable reached at 0x1324555d6

signal (4): Illegal instruction: 4
in expression starting at no file:0
Type at ./dict.jl:696
jl_fptr_trampoline at /Users/osx/buildbot/slave/package_osx64/build/src/gf.c:1831
Type at ./show.jl:193
Type at ./show.jl:271 [inlined]
show_default at ./show.jl:325
show at ./show.jl:315
jl_fptr_trampoline at /Users/osx/buildbot/slave/package_osx64/build/src/gf.c:1831
show_delim_array at ./show.jl:695
show_delim_array at ./show.jl:680 [inlined]
show at ./show.jl:714
jl_fptr_trampoline at /Users/osx/buildbot/slave/package_osx64/build/src/gf.c:1831
show_default at ./show.jl:332
jl_fptr_trampoline at /Users/osx/buildbot/slave/package_osx64/build/src/gf.c:1831
show at ./show.jl:315 [inlined]
print at ./strings/io.jl:31
jl_fptr_trampoline at /Users/osx/buildbot/slave/package_osx64/build/src/gf.c:1831
print_to_string at ./strings/io.jl:122
string at ./strings/io.jl:155 [inlined]
macro expansion at ./logging.jl:321 [inlined]
parsedata at /Users/alex/home/dev/winston/src/webcrawl.jl:77
jl_fptr_trampoline at /Users/osx/buildbot/slave/package_osx64/build/src/gf.c:1831
macro expansion at ./logging.jl:308 [inlined]
#search#1 at /Users/alex/home/dev/winston/src/webcrawl.jl:46
unknown function (ip: 0x132439283)
jl_fptr_trampoline at /Users/osx/buildbot/slave/package_osx64/build/src/gf.c:1831
#search at ./none:0 [inlined]
#crawl#1 at /Users/alex/home/dev/winston/src/webcrawl.jl:137
jl_fptr_trampoline at /Users/osx/buildbot/slave/package_osx64/build/src/gf.c:1831
#crawl at ./none:0
jl_fptr_trampoline at /Users/osx/buildbot/slave/package_osx64/build/src/gf.c:1831
do_call at /Users/osx/buildbot/slave/package_osx64/build/src/interpreter.c:324
eval_stmt_value at /Users/osx/buildbot/slave/package_osx64/build/src/interpreter.c:363 [inlined]
eval_body at /Users/osx/buildbot/slave/package_osx64/build/src/interpreter.c:682
jl_interpret_toplevel_thunk_callback at /Users/osx/buildbot/slave/package_osx64/build/src/interpreter.c:795
unknown function (ip: 0xfffffffffffffffe)
unknown function (ip: 0x11f7f734f)
unknown function (ip: 0x6)
jl_interpret_toplevel_thunk at /Users/osx/buildbot/slave/package_osx64/build/src/interpreter.c:804
jl_toplevel_eval_flex at /Users/osx/buildbot/slave/package_osx64/build/src/toplevel.c:813
jl_toplevel_eval_in at /Users/osx/buildbot/slave/package_osx64/build/src/builtins.c:622
eval at ./boot.jl:319
eval_user_input at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/REPL/src/REPL.jl:85
macro expansion at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/REPL/src/REPL.jl:117 [inlined]
#28 at ./task.jl:259
jl_apply at /Users/osx/buildbot/slave/package_osx64/build/src/./julia.h:1537 [inlined]
start_task at /Users/osx/buildbot/slave/package_osx64/build/src/task.c:268
Allocations: 92944920 (Pool: 92915632; Big: 29288); GC: 232
[1] 21238 illegal hardware instruction julia

[stev47]

From the documentation:

String literals are encoded using the UTF-8 encoding. UTF-8 is a variable-width encoding, meaning that not all characters are encoded in the same number of bytes. In UTF-8, ASCII characters – i.e. those with code points less than 0x80 (128) – are encoded as they are in ASCII, using a single byte, while code points 0x80 and above are encoded using multiple bytes – up to four per character. This means that not every byte index into a UTF-8 string is necessarily a valid index for a character. If you index into a string at such an invalid byte index, an error is thrown