Update to Go 1.17

Go 1.17 now lazy-loads dependencies when `go.mod` is version `go17`. This does not work for us for new projects started with `hugo mod init`.

Before this commit, starting a project with Go 1.17 with `hugo mod init` and then start adding dependencies with transitive dependenies to `config.toml` would treat the transitive dependencies as new, and you would potentially get a too recent version of those.

Note that this does not effect existing projects, where all dependencies are already recorded in `go.mod`.

Fixes #8930

htesting/test_helpers.go

@@ -16,7 +16,9 @@ package htesting
 import (
 	"math/rand"
 	"os"
+	"regexp"
 	"runtime"
+	"strconv"
 	"strings"
 	"time"
 
@@ -103,3 +105,28 @@ func IsGitHubAction() bool {
 func SupportsAll() bool {
 	return IsGitHubAction()
 }
+
+// GoMinorVersion returns the minor version of the current Go version,
+// e.g. 16 for Go 1.16.
+func GoMinorVersion() int {
+	return extractMinorVersionFromGoTag(runtime.Version())
+}
+
+var goMinorVersionRe = regexp.MustCompile(`go1.(\d*)`)
+
+func extractMinorVersionFromGoTag(tag string) int {
+	// The tag may be on the form go1.17, go1.17.5 go1.17rc2 -- or just a commit hash.
+	match := goMinorVersionRe.FindStringSubmatch(tag)
+
+	if len(match) == 2 {
+		i, err := strconv.Atoi(match[1])
+		if err != nil {
+			return -1
+		}
+		return i
+	}
+
+	// a commit hash, not useful.
+	return -1
+
+}

htesting/test_helpers_test.go

@@ -0,0 +1,31 @@
+// Copyright 2021 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package htesting
+
+import (
+	"testing"
+
+	qt "github.com/frankban/quicktest"
+)
+
+func TestExtractMinorVersionFromGoTag(t *testing.T) {
+
+	c := qt.New(t)
+
+	c.Assert(extractMinorVersionFromGoTag("go1.17"), qt.Equals, 17)
+	c.Assert(extractMinorVersionFromGoTag("go1.16.7"), qt.Equals, 16)
+	c.Assert(extractMinorVersionFromGoTag("go1.17beta1"), qt.Equals, 17)
+	c.Assert(extractMinorVersionFromGoTag("asdfadf"), qt.Equals, -1)
+
+}