fix BoundsError of args[1] when args is empty (#1014)

* fix BoundsError of args[1] when args is empty

if `args` on L101 is empty, then `args[1]` in `isexpr()` would throw `BoundsError: attempt to access 0-element Vector{Any} at index [1]`

* add unit tests for empty arguments

* Update src/pyfncall.jl

* Update src/pyfncall.jl

Co-authored-by: Steven G. Johnson <[email protected]>

Author: szcf-weiya

src/pyfncall.jl

@@ -99,7 +99,7 @@ macro pycall(ex)
     end
     func = ex.args[1].args[1]
     args, kwargs = ex.args[1].args[2:end], []
-    if isexpr(args[1],:parameters)
+    if !isempty(args) && isexpr(args[1],:parameters)
         kwargs, args = args[1], args[2:end]
     end
     T = ex.args[2]

test/runtests.jl

@@ -530,6 +530,8 @@ const PyInt = pyversion < v"3" ? Int : Clonglong
 
     # @pycall macro expands correctly
     _pycall = GlobalRef(PyCall,:pycall)
+    @test macroexpand(@__MODULE__, :(@pycall foo()::T)) == :($(_pycall)(foo, T))
+    @test macroexpand(@__MODULE__, :(@pycall foo(; kwargs...)::T)) == :($(_pycall)(foo, T; kwargs...))
     @test macroexpand(@__MODULE__, :(@pycall foo(bar)::T)) == :($(_pycall)(foo, T, bar))
     @test macroexpand(@__MODULE__, :(@pycall foo(bar, args...)::T)) == :($(_pycall)(foo, T, bar, args...))
     @test macroexpand(@__MODULE__, :(@pycall foo(bar; kwargs...)::T)) == :($(_pycall)(foo, T, bar; kwargs...))