File systems (System.IO.Abstractions)

dotnet add package Nullean.Entities.FileSystem
dotnet add package Nullean.Entities.CsCheck.FileSystem

1. the rules
2. tests only: generated file systems

If the model holds IFileInfo, IDirectoryInfo or IFileSystem, Nullean.Entities.FileSystem has the file rules: Files<T>.Exist, DirectoriesExist, StayInside, NotSymlink, NoHiddenSegments and HaveExtension. Each reads the file system the path came from, so a test on a MockFileSystem checks the code that runs against the disk, and each reports every offending path as evidence:

var rules = ConstraintSet.From(
	("ImagesExist", Files<Docset>.Exist(d => d.Images)),
	("ImagesStayInRoot", Files<Docset>.StayInside(d => d.Root, d => d.Images))
);

ImagesExist (Images): '/docs/missing.png' does not exist.
ImagesStayInRoot (Images): '/elsewhere/secret.png' is outside '/docs'.

.. is resolved before the comparison, so /docs/../elsewhere/secret.png is reported as /elsewhere/secret.png. The package depends only on Nullean.Entities and System.IO.Abstractions, and is trim and AOT clean.

IFileSystem has no constructor and what matters is what is on the disk, so GenAuto cannot build one by shape. Nullean.Entities.CsCheck.FileSystem teaches it: o.UseFileSystem() builds one MockFileSystem world per value, with missing, symlinked, hidden and outside-the-root files, so Probe finds counter-examples without a hand-written file system:

var gen = GenAuto.Of<Docset>(AutoMode.Mixed, o => o.UseFileSystem());

var report = Rules.Probe(gen, samples: 1500, throwOnContradiction: false);

1. report.NeverViolated names a rule no world could break

It uses reflection through GenAuto, so it is for test projects. The package READMEs on nuget.org, Nullean.Entities.FileSystem and Nullean.Entities.CsCheck.FileSystem, have complete programs, and examples/Apps has a docs build over a file system.