go/types, types2: ensure deterministic output when reporting an init cycle

Fixes #71254

Author: wingrez

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

@@ -10,6 +10,7 @@ import (
 	"fmt"
 	. "internal/types/errors"
 	"slices"
+	"sort"
 )
 
 // initOrder computes the Info.InitOrder for package variables.
@@ -139,7 +140,16 @@ func findPath(objMap map[Object]*declInfo, from, to Object, seen map[Object]bool
 	}
 	seen[from] = true
 
+	// sort deps for deterministic result
+	var deps []Object
 	for d := range objMap[from].deps {
+		deps = append(deps, d)
+	}
+	sort.Slice(deps, func(i, j int) bool {
+		return deps[i].order() < deps[j].order()
+	})
+
+	for _, d := range deps {
 		if d == to {
 			return []Object{d}
 		}

src/cmd/compile/internal/types2/testdata/local/issue71254.go

@@ -0,0 +1,14 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+const (
+	B /* ERROR "initialization cycle: B refers to itself" */ = A + B
+	A /* ERRORx "initialization cycle for A\\s+.*A refers to B\\s+.*B refers to A" */ = A + B
+
+	C /* ERRORx "initialization cycle for C\\s+.*C refers to D\\s+.*D refers to C" */ = E + D
+	D /* ERRORx "initialization cycle for D\\s+.*D refers to C\\s+.*C refers to D" */ = E + C
+	E = D + C
+)