Show eval expression for PowerShell on native Windows

src/state/opamEnv.ml

@@ -348,12 +348,18 @@ let is_up_to_date ?skip st =
 
 (** Returns shell-appropriate statement to evaluate [cmd]. *)
 let shell_eval_invocation shell cmd =
-  match shell with
-  | SH_fish ->
+  (* If we are running on Windows but not Cygwin or MSYS2, suggest a shell invocation for PowerShell.
+     We are running in a functioning Cygwin or MSYS2 environment if and only if `cygpath` is in the PATH.
+   *)
+  let is_native_windows = Sys.win32 && Option.is_none (OpamSystem.resolve_command "cygpath") in
+  match is_native_windows, shell with
+  | true, _ ->
+    Printf.sprintf "(& %s) -split '\\r?\\n' | ForEach-Object { Invoke-Expression ( '$env:' + ($_ -split '; export')[0] ) }" cmd
+  | _, SH_fish ->
     Printf.sprintf "eval (%s)" cmd
-  | SH_csh ->
+  | _, SH_csh ->
     Printf.sprintf "eval `%s`" cmd
-  | _ ->
+  | _, _ ->
     Printf.sprintf "eval $(%s)" cmd
 
 (** Returns "opam env" invocation string together with optional root and switch