AS10: the assignment graph finds a cycle among the waits within one step and says it

Builds: design 47 G §272, §356 Claude-Session: https://claude.ai/code/session_01NcbgfGKaxw984XyAPfLm4h
2026-11-12 06:02:18 +01:00
parent 6ce46884d5
commit de06949121
4 changed files with 120 additions and 0 deletions
@@ -34,6 +34,8 @@ type graphKeeper struct {
 	source int64
 	ok     bool
 	said   string
+	// cycled is the cycles last said (assigngraph.Cycles).
+	cycled string
 	// pins removes a revision that ceased to be current once nothing pins it (pins.go); nil keeps every revision.
 	pins *pinKeeper
 	// computed is the revision computed by the last pass, with its entries: the edges the wants wait on (actingwaits.go).
@@ -60,6 +62,12 @@ func (p *passer) keepGraph(ctx context.Context) {
 			p.logf("the assignment graph leaves out %s", u)
 		}
 	}
+	if cycles := strings.Join(c.Cycles, "; "); cycles != g.cycled {
+		g.cycled = cycles
+		if cycles != "" {
+			p.logf("the assignment graph holds a cycle among the waits within one step, and its entries wait for each other: %s", cycles)
+		}
+	}
 	if g.has && g.ok && assigngraph.Same(g.last, c.Revision) {
 		return
 	}
@@ -48,6 +48,8 @@ type Computed struct {
 	// Uncomputed is each placed module whose entry could not be computed, as "<node>/<module>: why", sorted: it is said,
 	// never left out in silence.
 	Uncomputed []string
+	// Cycles are the cycles among the waits within one step (Cycles, design 47 G §272): said, never left in silence.
+	Cycles []string
 }

 // placedAt is one placed module with what its entry is computed from.
@@ -212,6 +214,7 @@ func Compute(in Inputs) Computed {
 		rev.Entries = append(rev.Entries, meshwants.NodeEntryRef{Node: p.node, Module: p.placed.Module, Digest: d})
 	}
 	out.Revision = rev
+	out.Cycles = Cycles(slices.Collect(maps.Values(out.Entries)))
 	slices.Sort(out.Uncomputed)
 	return out
 }
@@ -0,0 +1,73 @@
+package assigngraph
+
+import (
+	"fmt"
+	"maps"
+	"slices"
+	"strings"
+
+	"git.novox.be/novox/mesh-delivery/modules/mesh-delivery-contracts/go/seats/meshwants"
+)
+
+// Cycles are the cycles among the waits within one step (design 47 G §272, ADR 0656): an entry waits for its acting parts in the step an
+// edge names, so two acting parts acting on each other in one step wait for each other for ever. Each is `<step>: a -> b -> a`, by
+// node and module, sorted. Edges of two steps never close a cycle together: the indexer taking in the checker and the checker checking
+// the indexer are none, and a holder's own inputs are no edge here (the graph gives an acting edge only from a part to the entries it
+// acts on, never to what the part is built from).
+func Cycles(entries []meshwants.AssignmentEntry) []string {
+	type key struct{ step, at string }
+	next := map[key][]string{}
+	steps := map[string]bool{}
+	for _, e := range entries {
+		for _, edge := range e.Edges {
+			if edge.Kind != EdgeActing {
+				continue
+			}
+			k := key{edge.Step, e.Node + "/" + e.Module}
+			next[k] = append(next[k], edge.Node+"/"+edge.Module)
+			steps[edge.Step] = true
+		}
+	}
+	var out []string
+	for _, step := range slices.Sorted(maps.Keys(steps)) {
+		const (
+			open = iota + 1
+			done
+		)
+		state := map[string]int{}
+		var path []string
+		var walk func(at string)
+		walk = func(at string) {
+			state[at] = open
+			path = append(path, at)
+			for _, to := range next[key{step, at}] {
+				switch state[to] {
+				case 0:
+					walk(to)
+				case open:
+					from := slices.Index(path, to)
+					cycle := slices.Clone(path[from:])
+					// start at the smallest member so one cycle is said once, whichever member is met first
+					lowest := slices.Index(cycle, slices.Min(cycle))
+					cycle = append(cycle[lowest:], cycle[:lowest]...)
+					out = append(out, fmt.Sprintf("%s: %s -> %s", step, strings.Join(cycle, " -> "), cycle[0]))
+				}
+			}
+			path = path[:len(path)-1]
+			state[at] = done
+		}
+		starts := map[string]bool{}
+		for k := range next {
+			if k.step == step {
+				starts[k.at] = true
+			}
+		}
+		for _, at := range slices.Sorted(maps.Keys(starts)) {
+			if state[at] == 0 {
+				walk(at)
+			}
+		}
+	}
+	slices.Sort(out)
+	return slices.Compact(out)
+}
@@ -0,0 +1,36 @@
+package assigngraph
+
+import (
+	"slices"
+	"testing"
+
+	"git.novox.be/novox/mesh-delivery/modules/mesh-delivery-contracts/go/seats/meshwants"
+)
+
+// Design 47 G §272 (AS10): a cycle among the waits within one step is found; an acting part acting on itself's other module, two parts
+// acting on each other in different steps, and a chain are none.
+func TestACycleAmongTheWaitsWithinOneStepIsFound(t *testing.T) {
+	act := func(node, module, step string) meshwants.Edge {
+		return meshwants.Edge{Kind: EdgeActing, Node: node, Module: module, Step: step}
+	}
+	entry := func(module string, edges ...meshwants.Edge) meshwants.AssignmentEntry {
+		return meshwants.AssignmentEntry{Node: "ace", Module: module, Edges: edges}
+	}
+	for _, c := range []struct {
+		name    string
+		entries []meshwants.AssignmentEntry
+		want    []string
+	}{
+		{"two parts on each other in one step", []meshwants.AssignmentEntry{entry("a", act("ace", "b", "compose")), entry("b", act("ace", "a", "compose"))},
+			[]string{"compose: ace/a -> ace/b -> ace/a"}},
+		{"three in a ring, said once", []meshwants.AssignmentEntry{entry("c", act("ace", "a", "build")), entry("a", act("ace", "b", "build")), entry("b", act("ace", "c", "build"))},
+			[]string{"build: ace/a -> ace/b -> ace/c -> ace/a"}},
+		{"the indexer taking in the checker, the checker checking the indexer", []meshwants.AssignmentEntry{entry("checker", act("ace", "indexer", "take-in")), entry("indexer", act("ace", "checker", "check"))}, nil},
+		{"a chain", []meshwants.AssignmentEntry{entry("a", act("ace", "b", "compose")), entry("b", act("ace", "c", "compose")), entry("c")}, nil},
+		{"provisioning edges are no wait of a step", []meshwants.AssignmentEntry{entry("a", meshwants.Edge{Kind: EdgeProvisioning, Node: "ace", Module: "b"}), entry("b", meshwants.Edge{Kind: EdgeProvisioning, Node: "ace", Module: "a"})}, nil},
+	} {
+		if got := Cycles(c.entries); !slices.Equal(got, c.want) {
+			t.Errorf("%s: cycles %v, want %v", c.name, got, c.want)
+		}
+	}
+}