libfetchers: Actually percentDecode path when using the path from fil…

[xokdvium]

…e:// URI

Motivation

Special characters like + e.t.c. are pct-encoded.
cc @dramforever. There's also a very stupid issue that leads to test failures because of regexes of all things:

nix/src/libstore/local-overlay-store.cc

Line 52 in e44e1cc

auto regex = std::regex(R"((^|\n)overlay )" + config->realStoreDir.get() + R"( .*(\n|$))");

, but that's on Linux. With this change the tests pass on darwin with --build-dir "/nix/var/nix/builds/build-1". Not sure what your issue was when testing it out.

Context

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[dramforever]

cc @vcunat how did you repro it?

in any case #14751 doesn't seem like it was related to fetchers?

[xokdvium]

The local-overlay-store failures from #14751 is due to the regex issue I mentioned. But those tests are not run on Darwin.

[vcunat]

How is this related to me?

[dramforever]

@vcunat From this comment NixOS/nixpkgs#468208 (comment) and NixOS/nixpkgs#469207

I never figured out how to reproduce the appendPatches problem unfortunately, but given this patch it seems to be related to when the test suite is run under a path with + in it?

So it should also fail on Linux. I can give that a try myself but it wouldn't be clear whether that fixes the problems on Darwin

[xokdvium]

Yes, I did reproduce that on my linux machine with a different sandbox-build-dir. There's another unrelated issue that leads to the test suite failing, but this patch fixes the tarball one.

I can try poking around more and see if there are more issues with Darwin, but this should be good to merge regardless, since it fixes a bug.