replace Chunk/Markers with LaneSlot enum

Author: philocalyst

asyncgit/src/graph/chunk.rs

@@ -1,15 +1,61 @@
-use super::AliasId;
+use super::{CommitAlias, UnwalkedAlias};
 
+/// A lane's occupant at one point in the walk.
 #[derive(Clone, Debug, PartialEq, Eq)]
-pub enum Markers {
-	Uncommitted,
-	Commit,
+pub enum LaneSlot {
+	/// A walked commit flowing down to its first parent.
+	Flowing {
+		alias: CommitAlias,
+		parent: UnwalkedAlias,
+	},
+
+	/// A flowing lane that still owes a bridge to a second parent
+	FlowingMerge {
+		alias: CommitAlias,
+		parent: UnwalkedAlias,
+		second: UnwalkedAlias,
+	},
+
+	/// A root commit: draws its node, nothing continues below.
+	Settled { alias: CommitAlias },
+
+	/// Reserved for a merge's second parent that hasn't been reached
+	/// by the walk yet. Once that parent is processed, the
+	/// reservation is replaced by the parent's own slot.
+	Reserved { parent: UnwalkedAlias },
 }
 
-#[derive(Clone, Debug, PartialEq, Eq)]
-pub struct Chunk {
-	pub alias: Option<AliasId>,
-	pub parent_a: Option<AliasId>,
-	pub parent_b: Option<AliasId>,
-	pub marker: Markers,
+impl LaneSlot {
+	/// The commit this lane currently belongs to, `None` for a
+	/// reserved placeholder.
+	pub const fn alias(&self) -> Option<CommitAlias> {
+		match self {
+			Self::Flowing { alias, .. }
+			| Self::FlowingMerge { alias, .. }
+			| Self::Settled { alias } => Some(*alias),
+			Self::Reserved { .. } => None,
+		}
+	}
+
+	/// The parent whose placement this lane waits on; the lane stays
+	/// open (drawing a vertical line) until that commit is walked.
+	pub const fn awaits(&self) -> Option<CommitAlias> {
+		match self {
+			Self::Flowing { parent, .. }
+			| Self::FlowingMerge { parent, .. }
+			| Self::Reserved { parent } => Some(parent.get()),
+			Self::Settled { .. } => None,
+		}
+	}
+
+	/// The pending second parent of a merge that hasn't been given
+	/// its own lane.
+	pub const fn second(&self) -> Option<CommitAlias> {
+		match self {
+			Self::FlowingMerge { second, .. } => Some(second.get()),
+			Self::Flowing { .. }
+			| Self::Settled { .. }
+			| Self::Reserved { .. } => None,
+		}
+	}
 }