2b9981a2

By: Tom Sydney Kerckhove <syd@cs-syd.eu>

Typed paths, so a path that names nothing cannot be built

packageFactsDir serialised as hopinion/. because a package directory was
joined out of two strings, and it was then handed to wholeFileSpan, which
wants a file. Both mistakes are now type errors.

RelPath wraps Path Rel File. SourceRoot carries Path Abs Dir and Maybe (Path
Rel Dir), where Nothing is a repository whose paths are already relative to it
rather than an empty string that gets joined in anyway. Discovery, module
resolution and the stray-file walk all work in typed paths, and the one place
that turns what a person typed into a path the tool can join is the command
layer, where the IO to resolve it belongs.

packageFactsDir becomes packageFactsCabal. A package has no single file, so
the no-gen-package abstention used to point at a directory; it points at the
cabal file now, which is both a real file and where a reader would look for
the gen package that is not there.

Zero-width spans are widened to their line at render time, which is where the
line length is known. A whole-file span used to render as a marker with
nothing under it, sitting in a committed golden looking broken.

The refactor found a bug the typing did not: walking a source directory a
cabal file declares and the tree does not have used to be an exception rather
than an empty answer, which killed the run on sydtest. There is a resource and
a test for it now, and the test fails without the guard.

factsForFile splits into itself and factsForSource, so the ormolu invariance
test can ask what a reformatted module attaches to without writing it to a
temporary file first.

TemplateHaskell joins the hlint allowlist for path's mkRelFile, which is how a
path literal is checked at compile time rather than parsed at runtime and
hoped about.

Timeline