[wip] Refactor depth behavior.

src/token/mod.rs

@@ -21,7 +21,7 @@ use crate::token::walk::{BranchFold, Fold, FoldMap, Starting, TokenEntry};
 use crate::{StrExt as _, PATHS_ARE_CASE_INSENSITIVE};
 
 pub use crate::token::parse::{parse, ParseError, ROOT_SEPARATOR_EXPRESSION};
-pub use crate::token::variance::bound::NaturalRange;
+pub use crate::token::variance::bound::{NaturalRange, VariantRange};
 pub use crate::token::variance::invariant::{Breadth, Depth, GlobVariance, Invariant, Size, Text};
 pub use crate::token::variance::Variance;
 

src/walk/glob.rs

@@ -193,44 +193,48 @@ impl<'t> Glob<'t> {
                 Some(prefix.into())
             }
         };
-        // Establish the root directory and any prefix in that root path that is not a part of the
-        // glob expression. The directory tree is traversed from `root`, which may include an
-        // invariant prefix from the glob. The `prefix` is an integer that specifies how many
-        // components from the end of the root path must be popped to get the portion of the root
-        // path that is not present in the glob. The prefix may be empty or may be the entirety of
-        // `root` depending on `directory` and the glob.
+        // Establish the root path and any pivot in that root path from the given directory and any
+        // invariant prefix in the glob. The file system is traversed from this root path. The
+        // pivot partitions the root path into the given directory and any invariant prefix by
+        // specifying how many components from the end of the root path must be popped to restore
+        // the given directory. The popped components form the invariant prefix of the glob. Either
+        // partition of the root path may be empty depending on the given directory and the glob
+        // pattern. In this way, any invariant prefix of the glob becomes a postfix in the root
+        // path.
         //
-        // Note that a rooted glob, like in `Path::join`, replaces `directory` when establishing
-        // the root path. In this case, there is no prefix, as the entire root path is present in
-        // the glob expression.
-        let (root, prefix) = match prefix {
+        // Note that a rooted glob, like in `Path::join`, replaces the given directory when
+        // establishing the root path. In this case, there is no invariant prefix (the pivot is
+        // zero), as the entire root path is present in the glob expression and the given directory
+        // is completely discarded.
+        let (root, pivot) = match prefix {
             Some(prefix) => directory.join_and_get_depth(prefix),
             _ => (directory, 0),
         };
-        Anchor { root, prefix }
+        Anchor { root, pivot }
     }
 }
 
-/// Root path and prefix of a `Glob` when walking a particular path.
+/// Root path and pivot of a `Glob` when walking a particular directory.
 #[derive(Clone, Debug)]
 struct Anchor {
-    /// The root (starting) directory of the walk.
+    /// The root (starting) path of the walk.
     root: PathBuf,
-    // TODO: Is there a better name for this? This is a prefix w.r.t. a glob but is a suffix w.r.t.
-    //       the root directory. This can be a bit confusing since either perspective is reasonable
-    //       (and in some contexts one may be more intuitive than the other).
-    /// The number of components from the end of `root` that are present in the `Glob`'s
-    /// expression.
-    prefix: usize,
+    /// The number of components from the end of `root` that are present in any invariant prefix of
+    /// the glob expression.
+    ///
+    /// The pivot partitions the root path into a target directory and any invariant prefix in the
+    /// `Glob` (this prefix becomes a postfix in the root path or, when rooted, replaces any target
+    /// directory).
+    pivot: usize,
 }
 
 impl Anchor {
     pub fn root_prefix_paths(&self) -> (&Path, &Path) {
-        self.root.split_at_depth(self.prefix)
+        self.root.split_at_depth(self.pivot)
     }
 
     pub fn walk_with_behavior(self, behavior: impl Into<WalkBehavior>) -> WalkTree {
-        WalkTree::with_prefix_and_behavior(self.root, self.prefix, behavior)
+        WalkTree::with_pivot_and_behavior(self.root, self.pivot, behavior)
     }
 }