Replace GAP's ExecuteProcess by Julia code

This is a step towards getting rid of the GAP SIGCHLD handler

gap/exec.g

@@ -0,0 +1,4 @@
+BindGlobal("_ORIG_ExecuteProcess", ExecuteProcess);
+MakeReadWriteGlobal("ExecuteProcess");
+ExecuteProcess := Julia.GAP.GAP_ExecuteProcess;
+MakeReadOnlyGlobal("ExecuteProcess");

src/GAP.jl

@@ -153,6 +153,7 @@ function initialize(argv::Vector{String})
     end
 
     GAP.Globals.Read(GapObj(joinpath(@__DIR__, "..", "gap", "pkg.g")))
+    GAP.Globals.Read(GapObj(joinpath(@__DIR__, "..", "gap", "exec.g")))
 
     # If we are in "stand-alone mode", stop here
     if handle_signals
@@ -287,6 +288,7 @@ include("utils.jl")
 include("help.jl")
 include("packages.jl")
 include("prompt.jl")
+include("exec.jl")
 include("doctestfilters.jl")
 
 end

src/exec.jl

@@ -0,0 +1,40 @@
+# Replacement for the GAP kernel function ExecuteProcess
+const use_orig_ExecuteProcess = Ref{Bool}(false)
+function GAP_ExecuteProcess(dir::GapObj, prg::GapObj, in::Int, out::Int, args::GapObj)
+    if use_orig_ExecuteProcess[]
+        return GAP.Globals._ORIG_ExecuteProcess(dir, prg, in, out, args)
+    end
+    return GAP_ExecuteProcess(String(dir), String(prg), in, out, Vector{String}(args))
+end
+
+function GAP_ExecuteProcess(dir::String, prg::String, fin::Int, fout::Int, args::Vector{String})
+    # TODO: the GAP kernel function `ExecuteProcess` also handles so-called
+    # "window mode" but this function currently does not
+
+    if fin < 0
+        fin = Base.devnull
+    else
+        fin = ccall((:SyBufFileno, libgap), Int, (Culong, ), fin)
+        if fin == -1
+            error("fin invalid")
+        end
+        fin = RawFD(fin)
+    end
+
+    if fout < 0
+        fout = Base.devnull
+    else
+        fout = ccall((:SyBufFileno, libgap), Int, (Culong, ), fout)
+        if fout == -1
+            error("fout invalid")
+        end
+        fout = RawFD(fout)
+    end
+
+
+    # TODO: verify `dir` is a valid dir?
+    cd(dir) do
+        res = run(pipeline(`$prg $args`, stdin=fin, stdout=fout))
+        return res == 255 ? GAP.Globals.Fail : res
+    end
+end