internal/core: search harder for BinExprs in toposort

Finding explicit unifications (`a & b`) is essential for correct
construction of the graph of nodes, which is central to toposort. By
searching through a vertex's structinfo's Decls, we can find more
BinExprs, and so build more correct graphs.

Signed-off-by: Matthew Sackman <matthew@cue.works>
Change-Id: Id19b772617b59853e38b4291560e9689b6e2e111
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1207585
Reviewed-by: Marcel van Lohuizen <mpvl@gmail.com>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>

internal/core/toposort/testdata/t.txtar

@@ -202,10 +202,10 @@ k2: {
 		t:  10
 	}
 	d6: {
-		z:  1
-		y:  2
 		x:  3
 		w:  4
+		z:  1
+		y:  2
 		za: 11
 		t:  10
 	}
@@ -414,10 +414,10 @@ diff old new
 -		w:  4
 -		z:  1
 -		y:  2
-+		z:  1
-+		y:  2
 +		x:  3
 +		w:  4
++		z:  1
++		y:  2
 +		za: 11
  		t:  10
  	}

internal/core/toposort/vertex.go

@@ -291,29 +291,39 @@ func analyseStructs(v *adt.Vertex, builder *GraphBuilder) ([]*structMeta, map[ad
 		})
 	}
 
-	// Explore our own conjuncts to find explicit unifications and
-	// record as appropriate in the structMetas.
+	// Explore our own conjuncts, and the decls from our StructList, to
+	// find explicit unifications, and mark structMetas accordingly.
+	var worklist []adt.Expr
 	v.VisitLeafConjuncts(func(c adt.Conjunct) bool {
 		debug("self conjunct field %p :: %T, expr %p :: %T\n",
 			c.Field(), c.Field(), c.Expr(), c.Expr())
-		worklist := []adt.Expr{c.Expr()}
-		for len(worklist) != 0 {
-			expr := worklist[0]
-			worklist = worklist[1:]
-
-			binExpr, ok := expr.(*adt.BinaryExpr)
-			if !ok || binExpr.Op != adt.AndOp {
-				continue
+		worklist = append(worklist, c.Expr())
+		return true
+	})
+	for _, si := range structInfos {
+		for _, decl := range si.StructLit.Decls {
+			if expr, ok := decl.(adt.Expr); ok {
+				worklist = append(worklist, expr)
 			}
-			for _, expr := range []adt.Expr{binExpr.X, binExpr.Y} {
-				for _, sMeta := range nodeToStructMeta[expr] {
-					sMeta.isExplicit = true
-				}
+		}
+	}
+
+	for len(worklist) != 0 {
+		expr := worklist[0]
+		worklist = worklist[1:]
+
+		binExpr, ok := expr.(*adt.BinaryExpr)
+		if !ok || binExpr.Op != adt.AndOp {
+			continue
+		}
+		for _, expr := range []adt.Expr{binExpr.X, binExpr.Y} {
+			for _, sMeta := range nodeToStructMeta[expr] {
+				sMeta.isExplicit = true
+				debug(" now explicit: %v\n", sMeta)
 			}
-			worklist = append(worklist, binExpr.X, binExpr.Y)
 		}
-		return true
-	})
+		worklist = append(worklist, binExpr.X, binExpr.Y)
+	}
 
 	return roots, outgoing
 }