solver: fix printing progress messages after merged edges

When different LLB vertexes (eg. parallel requests referencing
local sources from different sessions) generate same cache keys
during solve they are merged together into a single operation.

Currently, when this happened the progress for the vertex that
was dropped got lost. This fixes this case by adding the
progressWriter of the redirected vertex as a target to the
source one.

This should also work with multiple levels of merged edges,
just multiple nested multiwriters as well.

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

solver/jobs.go

@@ -156,7 +156,7 @@ func (s *state) getEdge(index Index) *edge {
 	return e
 }
 
-func (s *state) setEdge(index Index, targetEdge *edge) {
+func (s *state) setEdge(index Index, targetEdge *edge, targetState *state) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	e, ok := s.edges[index]
@@ -172,6 +172,13 @@ func (s *state) setEdge(index Index, targetEdge *edge) {
 		s.edges[index] = e
 	}
 	targetEdge.takeOwnership(e)
+
+	if targetState != nil {
+		if _, ok := targetState.allPw[s.mpw]; !ok {
+			targetState.mpw.Add(s.mpw)
+			targetState.allPw[s.mpw] = struct{}{}
+		}
+	}
 }
 
 func (s *state) combinedCacheManager() CacheManager {
@@ -273,7 +280,7 @@ func NewSolver(opts SolverOpt) *Solver {
 	return jl
 }
 
-func (jl *Solver) setEdge(e Edge, newEdge *edge) {
+func (jl *Solver) setEdge(e Edge, targetEdge *edge) {
 	jl.mu.RLock()
 	defer jl.mu.RUnlock()
 
@@ -282,7 +289,10 @@ func (jl *Solver) setEdge(e Edge, newEdge *edge) {
 		return
 	}
 
-	st.setEdge(e.Index, newEdge)
+	// potentially passing nil targetSt is intentional and handled in st.setEdge
+	targetSt := jl.actives[targetEdge.edge.Vertex.Digest()]
+
+	st.setEdge(e.Index, targetEdge, targetSt)
 }
 
 func (jl *Solver) getState(e Edge) *state {

util/progress/multiwriter.go

@@ -18,6 +18,8 @@ type MultiWriter struct {
 	meta    map[string]interface{}
 }
 
+var _ rawProgressWriter = &MultiWriter{}
+
 func NewMultiWriter(opts ...WriterOption) *MultiWriter {
 	mw := &MultiWriter{
 		writers: map[rawProgressWriter]struct{}{},