go/types, types2: ensure that the reportCycle has a deterministic output

Fixes #71254

Author: wingrez

src/cmd/compile/internal/types2/initorder.go

@@ -9,6 +9,7 @@ import (
 	"container/heap"
 	"fmt"
 	. "internal/types/errors"
+	"maps"
 	"slices"
 )
 
@@ -139,10 +140,18 @@ func findPath(objMap map[Object]*declInfo, from, to Object, seen map[Object]bool
 	}
 	seen[from] = true
 
-	for d := range objMap[from].deps {
-		if d == to {
-			return []Object{d}
-		}
+	if _, found := objMap[from].deps[to]; found {
+		return []Object{to}
+	}
+
+	// findPath is only called in cases where a cycle is indicated,
+	// so performance is not critical.
+	// Sort `deps` here in order to return a deterministic path,
+	// thereby guaranteeing consistent output in the `reportCycle`.
+	deps := slices.SortedFunc(maps.Keys(objMap[from].deps), func(x, y Object) int {
+		return cmp.Compare(x.order(), y.order())
+	})
+	for _, d := range deps {
 		if P := findPath(objMap, d, to, seen); P != nil {
 			return append(P, d)
 		}