Add more descriptive error to run(``) (Fixes #19094, PR #19118)

Author: SaschaMann

base/process.jl

@@ -507,6 +507,9 @@ function setup_stdio(anon::Function, stdio::StdIOSet)
 end
 
 function spawn(cmd::Cmd, stdios::StdIOSet; chain::Nullable{ProcessChain}=Nullable{ProcessChain}())
+    if isempty(cmd.exec)
+        throw(ArgumentError("cannot spawn empty command"))
+    end
     loop = eventloop()
     pp = Process(cmd, C_NULL, stdios[1], stdios[2], stdios[3])
     setup_stdio(stdios) do in, out, err

test/spawn.jl

@@ -406,6 +406,17 @@ end
 @test Base.AndCmds(`$echo abc`, `$echo def`) == Base.AndCmds(`$echo abc`, `$echo def`)
 @test Base.AndCmds(`$echo abc`, `$echo def`) != Base.AndCmds(`$echo abc`, `$echo xyz`)
 
+# test for correct error when an empty command is spawned (Issue 19094)
+@test_throws ArgumentError run(Base.Cmd(``))
+@test_throws ArgumentError run(Base.AndCmds(``, ``))
+@test_throws ArgumentError run(Base.AndCmds(``, `$echo test`))
+@test_throws ArgumentError run(Base.AndCmds(`$echo test`, ``))
+
+@test_throws ArgumentError spawn(Base.Cmd(``))
+@test_throws ArgumentError spawn(Base.AndCmds(``, ``))
+@test_throws ArgumentError spawn(Base.AndCmds(``, `$echo test`))
+@test_throws ArgumentError spawn(Base.AndCmds(`$echo test`, ``))
+
 # tests for reducing over collection of Cmd
 @test_throws ArgumentError reduce(&, Base.AbstractCmd[])
 @test_throws ArgumentError reduce(&, Base.Cmd[])