Split helix_core::find_root and helix_loader::find_local_config_dirs (#3929)

* Split helix_core::find_root and helix_loader::find_local_config_dirs

The documentation of find_root described the following priority for
detecting a project root:
- Top-most folder containing a root marker in current git repository
- Git repository root if no marker detected
- Top-most folder containing a root marker if not git repository detected
- Current working directory as fallback

The commit contained in https://github.com/helix-editor/helix/pull/1249
extracted and changed the implementation of find_root in find_root_impl,
actually reversing its result order (since that is the order that made
sense for the local configuration merge, from innermost to outermost
ancestors).

Since the two uses of find_root_impl have different requirements (and
it's not a matter of reversing the order of results since, e.g., the top
repository dir should be used by find_root only if there's not marker in
other dirs), this PR splits the two implementations in two different
specialized functions.

In doing so, find_root_impl is removed and the implementation is moved
back in find_root, moving it closer to the documented behaviour thus
making it easier to verify it's actually correct

* helix-core: remove Option from find_root return type

It always returns some result, so Option is not needed

1 files changed, 3 insertions, 2 deletions

diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index a5203352..c87ad0ca 100644
--- a/helix-term/src/commands.rs
+++ b/helix-term/src/commands.rs
@@ -2225,8 +2225,9 @@ fn append_mode(cx: &mut Context) {
 }
 
 fn file_picker(cx: &mut Context) {
-    // We don't specify language markers, root will be the root of the current git repo
-    let root = find_root(None, &[]).unwrap_or_else(|| PathBuf::from("./"));
+    // We don't specify language markers, root will be the root of the current
+    // git repo or the current dir if we're not in a repo
+    let root = find_root(None, &[]);
     let picker = ui::file_picker(root, &cx.editor.config());
     cx.push_layer(Box::new(overlayed(picker)));
 }