Display Windows NTSTATUS exit codes in hex

On Windows, "negative" exit codes are probably NTSTATUS values. For
example, if a program accesses an invalid memory location, Unix sends
a SIGSEGV signal which, if unhandled, will terminate the
process (setting some kind of non-zero exit code - for example, Linux
sets the exit code to 128 + signal number to give a fairly memorable
139). In the equivalent scenario, Windows throws an
EXCEPTION_ACCESS_VIOLATION which, if handled by the default exception
handler, will terminate the process with exit code
STATUS_ACCESS_VIOLATION. These codes are large negative numbers, which
are not terribly memorable in decimal, so for negative exit codes we
instead display them in hexadecimal as 0xc0000005 is slightly more
memorable than -1073741819.

Co-authored-by: David Allsopp <[email protected]>

master_changes.md

@@ -38,6 +38,7 @@ users)
   * Improve the messages when a package is not up-to-date on opam upgrade [#6272 @kit-ty-kate - fix #6270]
   * Use a non-underline uppercase character to denotate the default when asking a question [#6289 @hannesm @kit-ty-kate - fix #6288]
   * Do not pre-write the answer to questions with the default anwser [#6376 @kit-ty-kate]
+  * Display Windows NTSTATUS exit codes in hex [#6401 @dra27 @MisterDA]
 
 ## Switch
   * [BUG] Fix `opam switch remove <dir>` failure when it is a linked switch [#6276 @btjorge - fix #6275]

src/core/opamProcess.ml

@@ -842,10 +842,12 @@ let string_of_result ?(color=`yellow) r =
   Buffer.contents b
 
 let result_summary r =
-  Printf.sprintf "%S exited with code %d%s"
+  Printf.sprintf "%S exited with code %s%s"
     (try OpamStd.List.assoc String.equal "command" r.r_info
      with Not_found -> "command")
-    r.r_code
+    (if Sys.win32 && r.r_code < 0 then
+       Printf.sprintf "0x%08lx" (Int32.of_int r.r_code)
+     else string_of_int r.r_code)
     (if r.r_code = 0 then "" else
      match r.r_stderr, r.r_stdout with
      | [e], _ | [], [e] -> Printf.sprintf " \"%s\"" e