Urgh I made some wrong amends and I'm too tired to separate the commits out this time

ancestor: Split out of reachability
mergebase: Add merge base routines
internal/commitquery: Add commit query context engine thingy
internal/peel: Shared tag peeling
errors: Shared object query errors
internal/testgit: Add rooted repo helpers; remove raw path access
objectstore/memory: Add in-memory object store
objectid: Add Compare helper

1 files changed, 43 insertions, 0 deletions

diff --git a/internal/commitquery/generation.go b/internal/commitquery/generation.go
new file mode 100644
index 00000000..c5edcd9f
--- /dev/null
+++ b/internal/commitquery/generation.go
@@ -0,0 +1,43 @@
+package commitquery
+
+import (
+	"math"
+
+	"codeberg.org/lindenii/furgit/objectid"
+)
+
+// EffectiveGeneration returns one node's generation value.
+func (ctx *Context) EffectiveGeneration(idx NodeIndex) uint64 {
+	if !ctx.nodes[idx].hasGeneration {
+		return generationInfinity
+	}
+
+	return ctx.nodes[idx].generation
+}
+
+const (
+	generationInfinity = uint64(math.MaxUint64)
+)
+
+func compareByGeneration(ctx *Context) func(NodeIndex, NodeIndex) int {
+	return func(left, right NodeIndex) int {
+		leftGeneration := ctx.EffectiveGeneration(left)
+		rightGeneration := ctx.EffectiveGeneration(right)
+
+		switch {
+		case leftGeneration < rightGeneration:
+			return -1
+		case leftGeneration > rightGeneration:
+			return 1
+		}
+
+		switch {
+		case ctx.nodes[left].commitTime < ctx.nodes[right].commitTime:
+			return -1
+		case ctx.nodes[left].commitTime > ctx.nodes[right].commitTime:
+			return 1
+		}
+
+		return objectid.Compare(ctx.nodes[left].id, ctx.nodes[right].id)
+	}
+}