add GetJuliaScratchspace to JuliaInterface (#1030)

pkg/JuliaInterface/gap/JuliaInterface.gd

@@ -535,3 +535,18 @@ DeclareGlobalFunction( "CallJuliaFunctionWithKeywordArguments" );
 #TODO: add the cross-references to MatElm, SetMatElm when they are documented
 
 #! @InsertChunk JuliaHelpInGAP
+
+#! @Section Utilities
+
+#! @Arguments key
+#! @Returns a string
+#! @Description
+#!  Returns the path of a &Julia; scratchspace associated to the given key.
+#!  This scratchspace gets created if it did not exist already,
+#!  one can rely on the fact that the returned path describes a writable
+#!  directory.
+#!  Subsequent calls with the same key yield the same result,
+#!  and calls with different keys yield different results.
+#!  The directory may be removed by &Julia; as soon as the &Julia; package
+#!  <C>GAP.jl</C> gets uninstalled.
+DeclareGlobalFunction( "GetJuliaScratchspace" );

pkg/JuliaInterface/gap/JuliaInterface.gi

@@ -166,3 +166,13 @@ InstallGlobalFunction( JuliaModule,
     return JuliaPointer( Julia.(name) );
 end );
 
+
+InstallGlobalFunction( GetJuliaScratchspace,
+  function( key )
+    if not IsString( key ) then
+        Error( "GetJuliaScratchspace: <key> must be a string" );
+    fi;
+    key:= Julia.Base.string( key );
+    return JuliaToGAP( IsString,
+             Julia.GAP.get_scratch_helper\!( key ) );
+end );

pkg/JuliaInterface/tst/utils.tst

@@ -97,4 +97,11 @@ gap> Unbind(Julia.Main.f00bar);
 Error, cannot unbind Julia variables
 
 ##
-gap> STOP_TEST( "utils.tst", 1 );
+gap> GetJuliaScratchspace( true);
+Error, GetJuliaScratchspace: <key> must be a string
+gap> path:= GetJuliaScratchspace( "test_scratch" );;
+gap> IsDirectoryPath( path );
+true
+
+##
+gap> STOP_TEST( "utils.tst" );

src/utils.jl

@@ -106,6 +106,14 @@ function Base.functionloc(f::GapObj)
     return (String(file), ln)
 end
 
+import Scratch: get_scratch!
+
+# Return the path of a Julia scratchspace with name `key`.
+# This scratchspace gets created if it did not exist already.
+# The scratchspace may be removed by Julia as soon as the Julia package GAP.jl
+# gets uninstalled.
+get_scratch_helper!(key::String) = get_scratch!(GAP, key)
+
 # Allow `InteractiveUtils.edit(GAP.Globals.Group)` and similar for any global
 # function. Not (yet?) useful for GAP operations, but better than nothing.
 import InteractiveUtils: edit