Do not enforce type Symbol for argument mod

[devmotion]

Hej!

I noticed that as soon as options are specified in the YAML header of a file, it is not possible anymore to weave in a module such as Main. The problem is that during parsing and merging of the header arguments mod is converted to a Symbol in https://github.com/mpastell/Weave.jl/blob/master/src/config.jl#L112, but https://github.com/mpastell/Weave.jl/blob/master/src/run.jl#L57 requires mod to be a Module.

As an example, for a simple file test.jmd such as

---
options:
  out_path: test.md
  doctype: github
---

This is a test.

the command

weave("test.jmd", mod = Main)

fails with the error message

ERROR: MethodError: no method matching eval(::Symbol, ::Expr)
Closest candidates are:
  eval(::Module, ::Any) at boot.jl:328
Stacktrace:
 [1] #run#29(::String, ::Symbol, ::String, ::Dict{Any,Any}, ::String, ::Nothing, ::String, ::Symbol, ::Bool, ::typeof(run), ::Weave.WeaveDoc) at /home/david/.julia/packages/Weave/L0NNS/src/run.jl:57
 [2] (::getfield(Base, Symbol("#kw##run")))(::NamedTuple{(:doctype, :mod, :out_path, :args, :fig_path, :fig_ext, :cache_path, :cache, :throw_errors),Tuple{String,Symbol,String,Dict{Any,Any},String,Nothing,String,Symbol,Bool}}, ::typeof(run), ::Weave.WeaveDoc) at ./none:0
 [3] #weave#16(::Symbol, ::Symbol, ::Symbol, ::Dict{Any,Any}, ::Module, ::String, ::Nothing, ::String, ::Symbol, ::Bool, ::Nothing, ::Nothing, ::Nothing, ::Array{String,1}, ::String, ::typeof(weave), ::String) at /home/david/.julia/packages/Weave/L0NNS/src/Weave.jl:121
 [4] (::getfield(Weave, Symbol("#kw##weave")))(::NamedTuple{(:mod,),Tuple{Module}}, ::typeof(weave), ::String) at ./none:0
 [5] top-level scope at none:0

This PR fixes that issue (and replaces getvalue with the equivalent get) - however, I'm wondering whether a mod option in the header should be handled differently. It seems "sandbox" is the only valid option since everything else will fail due to the same issue? Maybe one should explicitly check if it is set to "Main"?

[coveralls]

Coverage decreased (-0.2%) to 81.877% when pulling d5d954f on devmotion:mod into c9a8147 on mpastell:master.

[mpastell]

Thanks! Probably it would be good to check whether it is set to sandbox as that is the only valid "non-module" option. It is possible to use other modules that Main. The only possibly useful situation I can think of is to use the same sandbox module for several documents.

Could you make the change?

[devmotion]

With the latest commit the following behaviour is enforced:

• For the file test.jmd

  ---
  options:
    out_path: test.md
    doctype: github
    mod: sandbox
  ---
  
  This is a test.
  

  the module specified on the command line is used, i.e.,

  weave("test.jmd")

  and

  weave("test.jmd", mod = :sandbox)

  run in a sandbox module whereas e.g.

  weave("test.jmd", mod = Main)

  uses the Main module.

• For the file

  ---
  options:
    out_path: test.md
    doctype: github
    mod: sandbox
  ---
  
  This is a test.
  

  a sandbox module is used, regardless of the setting of mod on the command line.

• For the file

  ---
  options:
    out_path: test.md
    doctype: github
    mod: sandbox2
  ---
  
  This is a test.
  

  a warning is displayed, the header option is ignored, and the module that is specified on the command line is used.

[mpastell]

It would be better to set mod = Module(Symbol(m)) here. I don't think there is any reason not to be able to specify module name in header.

[devmotion]

Ah sorry, I misunderstood your previous comment. I assumed it should be restricted to ":sandbox" only.

In that case I think it's more reasonable to handle all mod options of type Symbol in the run method, such that weave("test.jmd", mod = :sandbox3) for a file test.jmd without header arguments and weave("test_headers.jmd") for a file test_headers.jmd with header arguments mod: sandbox3 behave the same.