Grammar with action is broken when defined in another package

[Kolaru]

Assume I have a simple package with StringParserPEG (master branch) as dependency, and containing the following

module TestPEG

using StringParserPEG

greet() = print("Hello World!")

const g = Grammar("""
    start => 'a' {(r,v,f,l,c) -> v}
""")

end # module

then after activating the package and trying to import it I get the following

(@v1.5) pkg> activate TestPEG/
 Activating environment at `~/Documents/TestPEG/Project.toml`

julia> using TestPEG
[ Info: Precompiling TestPEG [958ec1b8-d9f0-43ac-bfa4-8d89bc9a0955]
ERROR: LoadError: Evaluation into the closed module `StringParserPEG` breaks incremental compilation because the side effects will not be permanent. This is likely due to some other module mutating `StringParserPEG` with `eval` during precompilation - don't do this.
Stacktrace:
 [1] eval at ./boot.jl:331 [inlined]
 [2] eval at /home/benoit/.julia/dev/StringParserPEG/src/StringParserPEG.jl:1 [inlined]
 [3] togrammar(::StringParserPEG.Node, ::Array{Any,1}, ::StringParserPEG.MatchRule{:SINGLE}) at /home/benoit/.julia/dev/StringParserPEG/src/grammarparsing.jl:82
 [4] transform(::typeof(StringParserPEG.togrammar), ::StringParserPEG.Node) at /home/benoit/.julia/dev/StringParserPEG/src/transform.jl:20
 [5] (::StringParserPEG.var"#4#5"{typeof(StringParserPEG.togrammar)})(::StringParserPEG.Node) at ./none:0
 [6] iterate at ./generator.jl:47 [inlined]
 [7] collect_to!(::Array{Symbol,1}, ::Base.Generator{Array{Any,1},StringParserPEG.var"#4#5"{typeof(StringParserPEG.togrammar)}}, ::Int64, ::Int64) at ./array.jl:732
 [8] collect_to_with_first!(::Array{Symbol,1}, ::Symbol, ::Base.Generator{Array{Any,1},StringParserPEG.var"#4#5"{typeof(StringParserPEG.togrammar)}}, ::Int64) at ./array.jl:710
 [9] collect(::Base.Generator{Array{Any,1},StringParserPEG.var"#4#5"{typeof(StringParserPEG.togrammar)}}) at ./array.jl:691
 [10] transform(::typeof(StringParserPEG.togrammar), ::StringParserPEG.Node) at /home/benoit/.julia/dev/StringParserPEG/src/transform.jl:10
 [11] (::StringParserPEG.var"#4#5"{typeof(StringParserPEG.togrammar)})(::StringParserPEG.Node) at ./none:0
 [12] iterate at ./generator.jl:47 [inlined]
 [13] collect(::Base.Generator{Array{Any,1},StringParserPEG.var"#4#5"{typeof(StringParserPEG.togrammar)}}) at ./array.jl:686
 [14] transform(::typeof(StringParserPEG.togrammar), ::StringParserPEG.Node) at /home/benoit/.julia/dev/StringParserPEG/src/transform.jl:10
 [15] StringParserPEG.Grammar(::String) at /home/benoit/.julia/dev/StringParserPEG/src/grammar.jl:18
 [16] top-level scope at /home/benoit/Documents/TestPEG/src/TestPEG.jl:7
 [17] include(::Function, ::Module, ::String) at ./Base.jl:380
 [18] include(::Module, ::String) at ./Base.jl:368
 [19] top-level scope at none:2
 [20] eval at ./boot.jl:331 [inlined]
 [21] eval(::Expr) at ./client.jl:467
 [22] top-level scope at ./none:3
in expression starting at /home/benoit/Documents/TestPEG/src/TestPEG.jl:7
ERROR: Failed to precompile TestPEG [958ec1b8-d9f0-43ac-bfa4-8d89bc9a0955] to /home/benoit/.julia/compiled/v1.5/TestPEG/zafuC_oC3oL.ji.
Stacktrace:
 [1] error(::String) at ./error.jl:33
 [2] compilecache(::Base.PkgId, ::String) at ./loading.jl:1290
 [3] _require(::Base.PkgId) at ./loading.jl:1030
 [4] require(::Base.PkgId) at ./loading.jl:928
 [5] require(::Module, ::Symbol) at ./loading.jl:923

Everything works fine however when I'm simply running a file with the grammar, instead of including it in a module.
Also I get no error if I don't define an action in the grammar.