digestset: deprecate package in favor of go-digest/digestset

This package was only used for the deprecated "shortid" syntax. Now that
support for this syntax was removed, we can also remove this package.

This patch deprecates and removes the package, adding temporary aliases pointing
to the new location to ease migration from docker/distribution to the new
distribution/distribution/v3. We should remove those aliases in a future update.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit 7b651a9)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

digestset/deprecated.go

@@ -0,0 +1,51 @@
+package digestset
+
+import (
+	"github.com/opencontainers/go-digest"
+	"github.com/opencontainers/go-digest/digestset"
+)
+
+// ErrDigestNotFound is used when a matching digest
+// could not be found in a set.
+//
+// Deprecated: use [digestset.ErrDigestNotFound].
+var ErrDigestNotFound = digestset.ErrDigestNotFound
+
+// ErrDigestAmbiguous is used when multiple digests
+// are found in a set. None of the matching digests
+// should be considered valid matches.
+//
+// Deprecated: use [digestset.ErrDigestAmbiguous].
+var ErrDigestAmbiguous = digestset.ErrDigestAmbiguous
+
+// Set is used to hold a unique set of digests which
+// may be easily referenced by a string
+// representation of the digest as well as short representation.
+// The uniqueness of the short representation is based on other
+// digests in the set. If digests are omitted from this set,
+// collisions in a larger set may not be detected, therefore it
+// is important to always do short representation lookups on
+// the complete set of digests. To mitigate collisions, an
+// appropriately long short code should be used.
+//
+// Deprecated: use [digestset.Set].
+type Set = digestset.Set
+
+// NewSet creates an empty set of digests
+// which may have digests added.
+//
+// Deprecated: use [digestset.NewSet].
+func NewSet() *digestset.Set {
+	return digestset.NewSet()
+}
+
+// ShortCodeTable returns a map of Digest to unique short codes. The
+// length represents the minimum value, the maximum length may be the
+// entire value of digest if uniqueness cannot be achieved without the
+// full value. This function will attempt to make short codes as short
+// as possible to be unique.
+//
+// Deprecated: use [digestset.ShortCodeTable].
+func ShortCodeTable(dst *digestset.Set, length int) map[digest.Digest]string {
+	return digestset.ShortCodeTable(dst, length)
+}