internal/core/adt: fix processing of additional disjunctions

Sometimes evaluating disjunctions is triggered before all
conjuncts have been added. If then another disjunction was
added, these results were not properly merged with previously
computed disjunctions. This change fixes that.

Issue #2851
Issue #2884

Signed-off-by: Marcel van Lohuizen <[email protected]>
Change-Id: I248b9ecc4694b2cb9a1e478343d9a8d233e14929

cue/testdata/eval/conjuncts.txtar

@@ -69,15 +69,15 @@ issue2355: {
 }
 
 -- out/evalalpha/stats --
-Leaks:  234
-Freed:  42
-Reused: 42
-Allocs: 234
+Leaks:  236
+Freed:  38
+Reused: 38
+Allocs: 236
 Retain: 0
 
 Unifications: 46
-Conjuncts:    467
-Disjuncts:    184
+Conjuncts:    463
+Disjuncts:    180
 -- out/evalalpha --
 Errors:
 issue2351.let.param: conflicting values [{}] and "foo" (mismatched types list and string):
@@ -163,18 +163,18 @@ diff old new
 -Reused: 59
 -Allocs: 18
 -Retain: 22
-+Leaks:  234
-+Freed:  42
-+Reused: 42
-+Allocs: 234
++Leaks:  236
++Freed:  38
++Reused: 38
++Allocs: 236
 +Retain: 0
 
 -Unifications: 45
 -Conjuncts:    135
 -Disjuncts:    86
 +Unifications: 46
-+Conjuncts:    467
-+Disjuncts:    184
++Conjuncts:    463
++Disjuncts:    180
 -- diff/-out/evalalpha<==>+out/eval --
 diff old new
 --- old

internal/core/adt/disjunct2.go

@@ -311,19 +311,23 @@ func (n *nodeContext) processDisjunctions() *Bottom {
 		cross, results = results, cross[:0]
 	}
 
-	switch len(cross) {
+	// Note it is under some circumstances possible that the disjunctions of a
+	// node are evaluated before all conjuncts are known. This could cause this
+	// method to be called more than once for a single node. In this case, we
+	// must properly merge disjuncts with existing disjunctions.
+	for _, x := range cross {
+		n.disjuncts = appendDisjunct(n.ctx, n.disjuncts, x)
+	}
+
+	switch a := n.disjuncts; len(a) {
 	case 0:
 		panic("unreachable: empty disjunction already handled above")
 
 	case 1:
-		d := cross[0].node
+		d := a[0].node
 		n.node.BaseValue = d
-		n.defaultMode = cross[0].defaultMode
-
-	default:
-		// append, rather than assign, to allow reusing the memory of
-		// a pre-existing slice.
-		n.disjuncts = append(n.disjuncts, cross...)
+		n.defaultMode = a[0].defaultMode
+		n.disjuncts = n.disjuncts[:0]
 	}
 
 	return nil
@@ -333,8 +337,6 @@ func (n *nodeContext) processDisjunctions() *Bottom {
 // with an existing set of results.
 func (n *nodeContext) crossProduct(dst, cross []*nodeContext, dn *envDisjunct, mode runMode) []*nodeContext {
 	for _, p := range cross {
-		// TODO: use a partial unify instead
-		// p.completeNodeConjuncts()
 		initArcs(n.ctx, p.node)
 
 		for j, d := range dn.disjuncts {
@@ -382,6 +384,9 @@ func (n *nodeContext) doDisjunct(c Conjunct, m defaultMode, mode runMode) (*node
 	}
 	n.ctx.stats.Disjuncts++
 
+	// Be sure we use the dereferenced node. This was probably already done.
+	n = n.node.Indirect().state
+
 	oc := newOverlayContext(n.ctx)
 
 	var ccHole *closeContext