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Purify CanonPath

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The core `CanonPath` constructors were using `absPath`, but `absPath` in
some situations does IO which is not appropriate. It turns out that
these constructors avoided those situations, and thus were pure, but it
was far from obvious this was the case.

To remedy the situation, abstract the core algorithm from `canonPath` to
use separately in `CanonPath` without any IO. No we know by-construction
that those constructors are pure.

That leaves `CanonPath::fromCWD` as the only operation which uses IO /
is impure. Add docs on it, and `CanonPath` as a whole, explaining the
situation.

This is also necessary to support Windows paths on windows without
messing up `CanonPath`. But, I think it is good even without that.

Co-authored-by: Eelco Dolstra <edolstra@gmail.com>
Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
This commit is contained in:
John Ericson 2024-01-13 01:11:49 -05:00
parent d53c8901ef
commit d17e1d9737
5 changed files with 155 additions and 57 deletions
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18
tests/unit/libutil/canon-path.cc
View file

@ -41,6 +41,24 @@ namespace nix {
}
}
TEST(CanonPath, from_existing) {
CanonPath p0("foo//bar/");
{
CanonPath p("/baz//quux/", p0);
ASSERT_EQ(p.abs(), "/baz/quux");
ASSERT_EQ(p.rel(), "baz/quux");
ASSERT_EQ(*p.baseName(), "quux");
ASSERT_EQ(*p.dirOf(), "/baz");
}
{
CanonPath p("baz//quux/", p0);
ASSERT_EQ(p.abs(), "/foo/bar/baz/quux");
ASSERT_EQ(p.rel(), "foo/bar/baz/quux");
ASSERT_EQ(*p.baseName(), "quux");
ASSERT_EQ(*p.dirOf(), "/foo/bar/baz");
}
}
TEST(CanonPath, pop) {
CanonPath p("foo/bar/x");
ASSERT_EQ(p.abs(), "/foo/bar/x");