Try to avoid adding Setup non-globally

ext/PkgExt.jl

@@ -27,7 +27,11 @@ const STACK_SPEC = Pkg.REPLMode.CommandSpec(
 Stack another environment.
 """,
     description = "Stack another environment",
-    completions = Pkg.REPLMode.complete_activate,
+    completions = if VERSION <= v"1.10"
+        Pkg.REPLMode.complete_activate
+    else
+        Pkg.REPLMode.get_complete_function(:complete_activate)
+    end,
     should_splat = false,
     arg_count = 0 => Inf)
 

src/Setup.jl

@@ -46,13 +46,16 @@ function ensureglobalpkg(pkg::String)
     if isnothing(Base.find_package(pkg))
         Pkg = lazypkg()
         oldproj = Base.current_project()
-        Pkg.activate()
-        @info "Installing $pkg"
-        lazypkg().add(pkg)
-        if isnothing(oldproj)
+        try
             Pkg.activate()
-        else
-            Pkg.activate(oldproj)
+            @info "Installing $pkg"
+            Pkg.add(pkg)
+        finally
+            if isnothing(oldproj)
+                Pkg.activate()
+            else
+                Pkg.activate(oldproj)
+            end
         end
     end
 end

src/install.jl

@@ -13,7 +13,18 @@ else
     catch e
         if e isa ArgumentError && isnothing(Base.find_package("Setup")) # Package not found in current path
             let pkg_id = Base.PkgId(Base.UUID("44cfe95a-1eb2-52ea-b672-e2afdf69b78f"), "Pkg")
-                Base.require(pkg_id).develop(path=joinpath(@__DIR__, "Setup"))
+                Pkg = Base.require(pkg_id)
+                cproj = Base.current_project()
+                try
+                    Pkg.activate()
+                    Pkg.develop(path=joinpath(@__DIR__, "Setup"))
+                finally
+                    if isnothing(cproj)
+                        Pkg.activate()
+                    else
+                        Pkg.activate(cproj)
+                    end
+                end
             end
             using Setup
         else