cmd/go: replace uses of ioutil.ReadFile with renameio.ReadFile

Windows does not have atomic renames; instead, it produces one of a
handful of errors in case a read races with a rename.

CL 180219 added a utility function that retries those errors in most
cases; this change updates the locations that use renameio for writes
to also use the new renameio.ReadFile function for reads.

It remains possible for a renameio.ReadFile to fail with a spurious
ERROR_FILE_NOT_FOUND, but with retries in place for the other errors
(and practical limits on write concurrency) such failures are unlikely
in practice.

Fixes #32188

Change-Id: I78c81051cc871325c1e3229e696b921b0fcd865a
Reviewed-on: https://go-review.googlesource.com/c/go/+/180517
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

src/cmd/go/internal/cache/cache.go

@@ -261,7 +261,7 @@ func (c *Cache) Trim() {
 	// We maintain in dir/trim.txt the time of the last completed cache trim.
 	// If the cache has been trimmed recently enough, do nothing.
 	// This is the common case.
-	data, _ := ioutil.ReadFile(filepath.Join(c.dir, "trim.txt"))
+	data, _ := renameio.ReadFile(filepath.Join(c.dir, "trim.txt"))
 	t, err := strconv.ParseInt(strings.TrimSpace(string(data)), 10, 64)
 	if err == nil && now.Sub(time.Unix(t, 0)) < trimInterval {
 		return

src/cmd/go/internal/modfetch/cache.go

@@ -482,7 +482,7 @@ func readDiskCache(path, rev, suffix string) (file string, data []byte, err erro
 	if err != nil {
 		return "", nil, errNotCached
 	}
-	data, err = ioutil.ReadFile(file)
+	data, err = renameio.ReadFile(file)
 	if err != nil {
 		return file, nil, errNotCached
 	}
@@ -576,7 +576,7 @@ func rewriteVersionList(dir string) {
 		buf.WriteString(v)
 		buf.WriteString("\n")
 	}
-	old, _ := ioutil.ReadFile(listFile)
+	old, _ := renameio.ReadFile(listFile)
 	if bytes.Equal(buf.Bytes(), old) {
 		return
 	}

src/cmd/go/internal/modfetch/fetch.go

@@ -293,7 +293,7 @@ func initGoSum() bool {
 
 	goSum.m = make(map[module.Version][]string)
 	goSum.checked = make(map[modSum]bool)
-	data, err := ioutil.ReadFile(GoSumFile)
+	data, err := renameio.ReadFile(GoSumFile)
 	if err != nil && !os.IsNotExist(err) {
 		base.Fatalf("go: %v", err)
 	}
@@ -303,7 +303,7 @@ func initGoSum() bool {
 	// Add old go.modverify file.
 	// We'll delete go.modverify in WriteGoSum.
 	alt := strings.TrimSuffix(GoSumFile, ".sum") + ".modverify"
-	if data, err := ioutil.ReadFile(alt); err == nil {
+	if data, err := renameio.ReadFile(alt); err == nil {
 		migrate := make(map[module.Version][]string)
 		readGoSum(migrate, alt, data)
 		for mod, sums := range migrate {
@@ -363,7 +363,7 @@ func checkMod(mod module.Version) {
 	if err != nil {
 		base.Fatalf("verifying %s@%s: %v", mod.Path, mod.Version, err)
 	}
-	data, err := ioutil.ReadFile(ziphash)
+	data, err := renameio.ReadFile(ziphash)
 	if err != nil {
 		if os.IsNotExist(err) {
 			// This can happen if someone does rm -rf GOPATH/src/cache/download. So it goes.
@@ -490,7 +490,7 @@ func Sum(mod module.Version) string {
 	if err != nil {
 		return ""
 	}
-	data, err := ioutil.ReadFile(ziphash)
+	data, err := renameio.ReadFile(ziphash)
 	if err != nil {
 		return ""
 	}
@@ -538,7 +538,7 @@ func WriteGoSum() {
 	if !goSum.overwrite {
 		// Re-read the go.sum file to incorporate any sums added by other processes
 		// in the meantime.
-		data, err := ioutil.ReadFile(GoSumFile)
+		data, err := renameio.ReadFile(GoSumFile)
 		if err != nil && !os.IsNotExist(err) {
 			base.Fatalf("go: re-reading go.sum: %v", err)
 		}

src/cmd/go/internal/modload/init.go

@@ -316,7 +316,7 @@ func InitMod() {
 	}
 
 	gomod := filepath.Join(modRoot, "go.mod")
-	data, err := ioutil.ReadFile(gomod)
+	data, err := renameio.ReadFile(gomod)
 	if err != nil {
 		base.Fatalf("go: %v", err)
 	}
@@ -696,7 +696,7 @@ func WriteGoMod() {
 	defer unlock()
 
 	file := filepath.Join(modRoot, "go.mod")
-	old, err := ioutil.ReadFile(file)
+	old, err := renameio.ReadFile(file)
 	if !bytes.Equal(old, modFileData) {
 		if bytes.Equal(old, new) {
 			// Some other process wrote the same go.mod file that we were about to write.