StackOverflow error using tuple types as type parameter

[daanhb]

The following code produces a StackOverflowError on 0.6 RC2:

bar(::Type{Val{Tuple{T,T}}}) where {T} = 1
bar(::Type{Val{Tuple{Int,T}}}) where {T} = 2

Output when running julia foo.jl with the above two lines as contents:

ERROR: LoadError: StackOverflowError:
Stacktrace:
 [1] include_from_node1(::String) at ./loading.jl:569
 [2] include(::String) at ./sysimg.jl:14
 [3] process_options(::Base.JLOptions) at ./client.jl:305
 [4] _start() at ./client.jl:371
while loading /tmp/foo.jl, in expression starting on line 2

Yet, everything works fine if the order of the two lines is reversed!

• The problem goes away if you remove the extra complexity of the Val above, i.e. the tuple types have to be type parameters. Maybe that is not a valid thing to do? The above is a MWE, the context was code to convert between nested tuples and flat tuples.
• The second line matches the first if T=Int, but that is not essential. You can replace the Int with Tuple{T,T} so it never matches the first line, and the problem remains.

Version info:

julia> versioninfo()
Julia Version 0.6.0-rc2.0
Commit 68e911b (2017-05-18 02:31 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Core(TM) i5-3570 CPU @ 3.40GHz
  WORD_SIZE: 64
  BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY Sandybridge)
  LAPACK: libopenblas64_
  LIBM: libopenlibm
  LLVM: libLLVM-3.9.1 (ORCJIT, ivybridge)

[daanhb]

The above example now indeed works on 0.6.0 - thanks! - but unfortunately after more tests the code that led to this issue still produces a similar error. The minimal working example is now more complicated:

bar(::Type{Val{Tuple{Tuple{T},T}}}, ::Val{T}) where {T} = 1
bar(::Type{Val{Tuple{T,Tuple{T}}}}, ::Val{T}) where {T} = 2

I can't reduce this any further without making the problem go away. In particular, the second argument seems important, as well as the nested tuple.

The exact error message is the same StackOverflowError:

ERROR: LoadError: StackOverflowError:
Stacktrace:
 [1] include_from_node1(::String) at ./loading.jl:569
 [2] include(::String) at ./sysimg.jl:14
 [3] process_options(::Base.JLOptions) at ./client.jl:305
 [4] _start() at ./client.jl:371
while loading /tmp/foo2.jl, in expression starting on line 2

Version info (0.6.0 as released):

julia> versioninfo()
Julia Version 0.6.0
Commit 9036443 (2017-06-19 13:05 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Core(TM) i5-3570 CPU @ 3.40GHz
  WORD_SIZE: 64
  BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY Sandybridge)
  LAPACK: libopenblas64_
  LIBM: libopenlibm
  LLVM: libLLVM-3.9.1 (ORCJIT, ivybridge)

[daanhb]

Here is another example that is less nested but produces a similar error:

bar(::Type{Tuple{T,Val{T}}}, ::Val{T}) where {T} = 1
bar(::Type{Tuple{Val{T},T}}, ::Val{T}) where {T} = 2

[martinholters]

julia> typeintersect(Tuple{Type{Tuple{T,Val{T}}}, Val{T}} where T, Tuple{Type{Tuple{Val{T},T}}, Val{T}} where T)
ERROR: StackOverflowError:
Stacktrace:
 [1] typeintersect(::Any, ::Any) at ./reflection.jl:314