all: swap math/rand for math/rand/v2 where it doesn't affect behavior

math/rand is not and likely will never be deprecated,
but math/rand/v2 is better in many ways, so switch to it.

Apply two gopls suggested fixes along the way to use range-over-int.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: Ic4c1baff05bfef744fcd95a85d401ba982c75f89
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1216886
Reviewed-by: Roger Peppe <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

Author: mvdan

internal/core/toposort/graph_test.go

@@ -16,7 +16,7 @@ package toposort_test
 
 import (
 	"fmt"
-	"math/rand"
+	"math/rand/v2"
 	"os"
 	"slices"
 	"strconv"
@@ -138,28 +138,28 @@ func TestSortFullyConnected(t *testing.T) {
 }
 
 func TestSortRandom(t *testing.T) {
-	seed := rand.Int63()
+	seed := rand.Uint64()
 	if str := os.Getenv("SEED"); str != "" {
-		num, err := strconv.ParseInt(str, 10, 64)
+		num, err := strconv.ParseUint(str, 10, 64)
 		if err != nil {
 			t.Fatalf("Could not parse SEED env var %q: %v", str, err)
 			return
 		}
 		seed = num
 	}
 	t.Log("Seed", seed)
-	rng := rand.New(rand.NewSource(seed))
+	rng := rand.New(rand.NewPCG(seed, 123))
 
 	names := strings.Split("abcdefghijklm", "")
 	index := runtime.New()
 
-	for n := 0; n < 100; n++ {
-		inputs := make([][]string, 2+rng.Intn(4))
+	for n := range 100 {
+		inputs := make([][]string, 2+rng.IntN(4))
 		for i := range inputs {
 			names := slices.Clone(names)
 			rng.Shuffle(len(names),
 				func(i, j int) { names[i], names[j] = names[j], names[i] })
-			inputs[i] = names[:2+rng.Intn(4)]
+			inputs[i] = names[:2+rng.IntN(4)]
 		}
 
 		t.Run(fmt.Sprint(n), func(t *testing.T) {

internal/mod/semver/semver_test.go

@@ -5,7 +5,7 @@
 package semver
 
 import (
-	"math/rand"
+	"math/rand/v2"
 	"slices"
 	"strings"
 	"testing"

internal/par/work.go

@@ -7,7 +7,7 @@ package par
 
 import (
 	"errors"
-	"math/rand"
+	"math/rand/v2"
 	"sync"
 	"sync/atomic"
 )
@@ -93,7 +93,7 @@ func (w *Work[T]) runner() {
 		// to eliminate pathological contention
 		// in case items added at about the same time
 		// are most likely to contend.
-		i := rand.Intn(len(w.todo))
+		i := rand.IntN(len(w.todo))
 		item := w.todo[i]
 		w.todo[i] = w.todo[len(w.todo)-1]
 		w.todo = w.todo[:len(w.todo)-1]

mod/modcache/fetch.go

@@ -7,7 +7,7 @@ import (
 	"io"
 	"io/fs"
 	"log"
-	"math/rand"
+	"math/rand/v2"
 	"os"
 	"path/filepath"
 	"slices"
@@ -361,8 +361,8 @@ func quoteGlob(s string) string {
 
 // tempFile creates a new temporary file with given permission bits.
 func tempFile(ctx context.Context, dir, prefix string, perm fs.FileMode) (f *os.File, err error) {
-	for i := 0; i < 10000; i++ {
-		name := filepath.Join(dir, prefix+strconv.Itoa(rand.Intn(1000000000))+".tmp")
+	for range 10000 {
+		name := filepath.Join(dir, prefix+strconv.Itoa(rand.IntN(1000000000))+".tmp")
 		f, err = os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, perm)
 		if os.IsExist(err) {
 			if ctx.Err() != nil {