Crash when defining a convert method for NTuple #29321
Description
The following code:
Base.convert(tp, x::NTuple{N, T}) where {N, T} = x
foo()
crashes when executed both in Julia 1.0 and nightly (Version 1.1.0-DEV.263 (2018-09-15), commit e2c9878) on MacOS 10.13.6. In Julia 1.0 the error is:
fatal: error thrown and no exception handler available.
MethodError(f=typeof(Base.convert)(), args=(Tuple{}, ()), world=0x00000000000061af)
rec_backtrace at /Users/osx/buildbot/slave/package_osx64/build/src/stackwalk.c:94
record_backtrace at /Users/osx/buildbot/slave/package_osx64/build/src/task.c:246 [inlined]
jl_throw at /Users/osx/buildbot/slave/package_osx64/build/src/task.c:577
jl_method_error_bare at /Users/osx/buildbot/slave/package_osx64/build/src/gf.c:1614
jl_method_error at /Users/osx/buildbot/slave/package_osx64/build/src/gf.c:1632
jl_lookup_generic_ at /Users/osx/buildbot/slave/package_osx64/build/src/gf.c:2159
jl_apply_generic at /Users/osx/buildbot/slave/package_osx64/build/src/gf.c:2179
Type at ./iterators.jl:169
pairs at ./iterators.jl:226
#printstyled at ./none:0
jl_fptr_trampoline at /Users/osx/buildbot/slave/package_osx64/build/src/gf.c:1829
display_error at ./client.jl:93
jl_fptr_trampoline at /Users/osx/buildbot/slave/package_osx64/build/src/gf.c:1829
display_error at ./client.jl:102
jl_fptr_trampoline at /Users/osx/buildbot/slave/package_osx64/build/src/gf.c:1829
jl_apply at /Users/osx/buildbot/slave/package_osx64/build/src/./julia.h:1536 [inlined]
jl_f__apply at /Users/osx/buildbot/slave/package_osx64/build/src/builtins.c:556
jl_f__apply_latest at /Users/osx/buildbot/slave/package_osx64/build/src/builtins.c:594
#invokelatest#1 at ./essentials.jl:686 [inlined]
invokelatest at ./essentials.jl:685 [inlined]
_start at ./client.jl:423
true_main at /Applications/Julia-1.0.app/Contents/Resources/julia/bin/julia (unknown line)
main at /Applications/Julia-1.0.app/Contents/Resources/julia/bin/julia (unknown line)
For v1.1 the error is similar, with some differences in line numbers.