On Fri, Jan 12, 2018 at 10:24:28AM -0800, Junio C Hamano wrote: > Jeff King <p...@peff.net> writes: > > >> + /* > >> + * Do we have a sequence of "unset GIT_DIR; GIT_DIR=foo"? > >> + * Then don't bother with the unset thing. > >> + */ > >> + if (i + 1 < envs.nr && > >> + !strcmp(env, envs.items[i + 1].string)) > >> continue; > > > > Are we guaranteed that "FOO" and "FOO=bar" appear next to each other in the > > sorted list? I think "FOO123=bar" could come between. > > At this point, envs is a string list whose key is FOO for both "FOO" > (unset) and "FOO=bar" (set); "FOO123=bar" would sort after these two.
Ah, right, I didn't notice that we took just the key name. > But I did not see anything that attempts to guarantee that "FOO" > sorts before "FOO=bar" with string_list_sort(). If the sort used in > the function is stable, and if the case we care about is unset > followed by set, then the above would catch the case, but even if > that were the case, it is unclear what we want to do when a set of > FOO is followed by an unset of FOO. The actual prep_childenv() code looks like it would always do last-one-wins, so we should treat FOO as unset in that final case. But that only kicks in on non-Windows. On Windows we feed cmd->env straight to mingw_spawnvpe(). That ends up in make_environment_block(), which looks like it does something similar. It's too bad the prep code is not shared, since then we could probably just ask _it_ which deltas it applied. I suspect it would be possible to share it, since mingw_spawnvpe is our own compat thing (so we could change its interface to take the whole prepared environment block). But I won't blame Duy if he doesn't want to refactor all of the cross-platform exec code. ;) > And if the sort is not stable, then the above code is just simply > broken. Agreed. > > > I also think this is a special case of a more general problem. FOO could > > appear any number of times in the "env" array, as a deletion or with > > multiple values. Our prep_childenv() would treat that as "last one > > wins", I think. Could we just do the same here? > > Yeah, if the last one is to set FOO=bar, then it feels sufficient to > just check if FOO is set to bar in the original and deciding to show > or hide; similarly if the last one is to unset FOO, it does not matter > if the caller sets it to some other value before unsetting, so it > feels sufficient to just check if FOO is set to anything in the > original environment. Yep, agreed again. -Peff
