[Trivial] std.path: fix a -dip1000 compilable issue

[carblue]

Without this fix and
string relativePath(CaseSensitive cs = CaseSensitive.osDefault)
(string path, lazy string base = getcwd()) temporarily attributed @safe
the reported errors are:
std/path.d(1742): Error: scope variable result may not be returned
std/path.d(1748): Error: template instance std.path.buildNormalizedPath!char error instantiating
std/path.d(1800): while evaluating: static assert(buildNormalizedPath(["/foo/..", "/bar/./baz"][]) == "/bar/baz")
std/path.d(2873): Error: @safe function std.path.relativePath!cast(CaseSensitive)true.relativePath cannot call @System function std.conv.to!string.to!(ChooseResult!(ByCodeUnitImpl, Result)).to

Thus the remainder will be an error from std.conv.to!string.to only.

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[wilzbach]

LGTM

(FWIW this piece looks like it could use an appender)

[wilzbach]

Thinking about it: wouldn't assumeUnique be better here to avoid an unnecessary allocation?
I know the loop is already horrible with .array on every iteration, but that's not an argument to make it even worse?
To ensure that the new content is freshly allocated, we could check this after the loop is then and only idup then...

[MartinNowak]

You need return scope or abbreviated (w/o ref) you can just use return on the paths parameter, as you're returning/escaping a parameter. Please file a bug report with the [scope] tag if something is fishy about variadic arguments. Just repainting the returned array can leak the passed in parameter without letting the compiler know.

[carblue]

I won't pursue this PR any more, just closing it

[WalterBright]

I redid this as #6357 but I don't see how this PR makes it any more DIP1000 compatible. The return value of the function is always copied into fresh memory.