Bug 15276 – Allow specification of shell for spawnShell/executeShell/pipeShell

We should allow callers to specify a particular shell to be used, be it sh, bash, zsh, or what the user has in their SHELL environment variable. One of the things that made the fix for https://issues.dlang.org/show_bug.cgi?id=14282 so jarring is that there's no easy way to work around it to achieve the old behavior. That fix ended up being reverted.

Commits pushed to master at https://github.com/D-Programming-Language/phobos https://github.com/D-Programming-Language/phobos/commit/963f7e4170fd02aa07c95562f2554807a8fe9178 Issue 15276: Allow users to specify shell for executeShell, pipeShell, spawnShell This diff: This diff makes it possible to specify your preferred shell for the various `*shell` functions in `std.process`. By default it uses the new `nativeShell` function. `nativeShell` to always returns the native system shell (see the "some history" section for why this is the default value). I chose to create `nativeShell` rather than changeing `userShell` because I think it is still valuable to have something like `userShell` around in Phobos. The one part of this diff I'm not super thrilled by is the use of variadic arguments (easier to see than to explain); if you have a suggestion for something better I'd love to hear it :). Note: The default shell is a breaking change for Windows, which probably *should have* been broken same as posix in the diffs listed in the history section below, but I suspect was overlooked. Find rationale behind making a breaking change at all here: https://issues.dlang.org/show_bug.cgi?id=15000. Some history: https://github.com/D-Programming-Language/phobos/commit/a524a3571b18e440c4dd751fcf4e2d00b834fb22 and https://github.com/D-Programming-Language/phobos/commit/f537cb50b5f8f9ad6d841db14b2e0a6cb845d008 Tried to move us from a world where we preferred the shell specified in the SHELL environment variable to a world where we always went with the native system shell, /bin/sh for posix. The former of those revisions was reverted in: https://github.com/D-Programming-Language/phobos/commit/5b2b1fb59450cfc32ecec3252f543a9f6f34c2a4 Because the documentation was not updated to reflect the change. Presently: we are in a state of schism, whereby `userShell` has behavior that does not align with what is actually used in `executeShell`, `pipeShell`, and `spawnShell`. This is something we *must* resolve. Personal pain: This bit me when one of my scripts at work stopped working because it dependend on features that don't exist in `sh` (but do in `bash`, `zsh`, etc). It was really frustrating that there was no simple way to work around this and specify my preferred shell; it is, of course, possible to leverage the various `escape*` functions from `std.process` and `spawnProcess` to use whichever shell I prefer, but this seems like something warranting first class support. I was sad to not have something like this after a breaking change. https://github.com/D-Programming-Language/phobos/commit/9284ee864c38eb062a4bcd57b4a44556fe878b94 Merge pull request #3900 from markisaa/issue_15276 Issue 15276: Allow users to specify shell for executeShell, pipeShell, spawnShell

Commits pushed to stable at https://github.com/D-Programming-Language/phobos https://github.com/D-Programming-Language/phobos/commit/963f7e4170fd02aa07c95562f2554807a8fe9178 Issue 15276: Allow users to specify shell for executeShell, pipeShell, spawnShell https://github.com/D-Programming-Language/phobos/commit/9284ee864c38eb062a4bcd57b4a44556fe878b94 Merge pull request #3900 from markisaa/issue_15276