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libutil: Create empty directory at the root for makeEmptySourceAccessor

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This is my SNAFU. Accidentally broken in 02c9ac445f.

There's very dubious behavior for 'builtins.readDir /.':

{
  outputs =
    { ... }:
    {
      lib.a = builtins.readDir /.;
    };
}

nix eval /tmp/test-flake#lib.a

Starting from 2.27 this now returns an empty set. This really isn't supposed
to happen, but this change in the semantics of makeEmptySourceAccessor accidentally
changed the behavior of this.
This commit is contained in:
Sergei Zimmerman 2025-09-29 23:16:28 +03:00
parent 8a968c599d
commit 1830f5f967
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1 changed files with 10 additions and 5 deletions
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15
src/libutil/memory-source-accessor.cc
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@ -208,11 +208,16 @@ void MemorySink::createSymlink(const CanonPath & path, const std::string & targe
ref<SourceAccessor> makeEmptySourceAccessor()
{
static auto empty = make_ref<MemorySourceAccessor>().cast<SourceAccessor>();
/* Don't forget to clear the display prefix, as the default constructed
SourceAccessor has the «unknown» prefix. Since this accessor is supposed
to mimic an empty root directory the prefix needs to be empty. */
empty->setPathDisplay("");
static auto empty = []() {
auto empty = make_ref<MemorySourceAccessor>();
MemorySink sink{*empty};
sink.createDirectory(CanonPath::root);
/* Don't forget to clear the display prefix, as the default constructed
SourceAccessor has the «unknown» prefix. Since this accessor is supposed
to mimic an empty root directory the prefix needs to be empty. */
empty->setPathDisplay("");
return empty.cast<SourceAccessor>();
}();
return empty;
}