gopls/internal/util/goversion: warn about EOL for Go 1.18

Gopls v0.15.0 will be the final gopls version to support Go 1.18, so
include a warning, as is our practice.

Fixes golang/go#64407

Change-Id: I215631420c05ad1922312f1b1009d15577ddb01e
Reviewed-on: https://go-review.googlesource.com/c/tools/+/549115
Reviewed-by: Alan Donovan <adonovan@google.com>
Auto-Submit: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

gopls/internal/util/goversion/goversion.go

@@ -14,8 +14,17 @@ import (
 //
 // Exposed for testing.
 type Support struct {
-	GoVersion           int
-	DeprecatedVersion   string // if unset, the version is already deprecated
+	// GoVersion is the Go version to which these settings relate.
+	GoVersion int
+
+	// DeprecatedVersion is the first version of gopls that no longer supports
+	// this Go version.
+	//
+	// If unset, the version is already deprecated.
+	DeprecatedVersion string
+
+	// InstallGoplsVersion is the latest gopls version that supports this Go
+	// version without warnings.
 	InstallGoplsVersion string
 }
 
@@ -29,12 +38,15 @@ type Support struct {
 var Supported = []Support{
 	{12, "", "v0.7.5"},
 	{15, "", "v0.9.5"},
-	{16, "v0.13.0", "v0.11.0"},
-	{17, "v0.13.0", "v0.11.0"},
+	{16, "", "v0.11.0"},
+	{17, "", "v0.11.0"},
+	{18, "v0.16.0", "v0.14.2"},
 }
 
 // OldestSupported is the last X in Go 1.X that this version of gopls
-// supports.
+// supports without warnings.
+//
+// Exported for testing.
 func OldestSupported() int {
 	return Supported[len(Supported)-1].GoVersion + 1
 }

gopls/internal/util/goversion/goversion_test.go

@@ -5,27 +5,55 @@
 package goversion_test
 
 import (
+	"fmt"
 	"strings"
 	"testing"
 
 	"golang.org/x/tools/gopls/internal/util/goversion"
 )
 
 func TestMessage(t *testing.T) {
+	// Note(rfindley): this test is a change detector, as it must be updated
+	// whenever we deprecate a version.
+	//
+	// However, I chose to leave it as is since it gives us confidence in error
+	// messages served for Go versions that we no longer support (and therefore
+	// no longer run in CI).
+	type test struct {
+		goVersion    int
+		fromBuild    bool
+		wantContains []string // string fragments that we expect to see
+		wantIsError  bool     // an error, not a mere warning
+	}
+
+	deprecated := func(goVersion int, lastVersion string) test {
+		return test{
+			goVersion: goVersion,
+			fromBuild: false,
+			wantContains: []string{
+				fmt.Sprintf("Found Go version 1.%d", goVersion),
+				"not supported",
+				fmt.Sprintf("upgrade to Go 1.%d", goversion.OldestSupported()),
+				fmt.Sprintf("install gopls %s", lastVersion),
+			},
+			wantIsError: true,
+		}
+	}
+
 	tests := []struct {
 		goVersion    int
 		fromBuild    bool
 		wantContains []string // string fragments that we expect to see
 		wantIsError  bool     // an error, not a mere warning
 	}{
 		{-1, false, nil, false},
-		{12, false, []string{"1.12", "not supported", "upgrade to Go 1.18", "install gopls v0.7.5"}, true},
-		{13, false, []string{"1.13", "not supported", "upgrade to Go 1.18", "install gopls v0.9.5"}, true},
-		{15, false, []string{"1.15", "not supported", "upgrade to Go 1.18", "install gopls v0.9.5"}, true},
-		{15, true, []string{"Gopls was built with Go version 1.15", "not supported", "upgrade to Go 1.18", "install gopls v0.9.5"}, true},
-		{16, false, []string{"1.16", "will be unsupported by gopls v0.13.0", "upgrade to Go 1.18", "install gopls v0.11.0"}, false},
-		{17, false, []string{"1.17", "will be unsupported by gopls v0.13.0", "upgrade to Go 1.18", "install gopls v0.11.0"}, false},
-		{17, true, []string{"Gopls was built with Go version 1.17", "will be unsupported by gopls v0.13.0", "upgrade to Go 1.18", "install gopls v0.11.0"}, false},
+		deprecated(12, "v0.7.5"),
+		deprecated(13, "v0.9.5"),
+		deprecated(15, "v0.9.5"),
+		deprecated(16, "v0.11.0"),
+		deprecated(17, "v0.11.0"),
+		{18, false, []string{"Found Go version 1.18", "unsupported by gopls v0.16.0", "upgrade to Go 1.19", "install gopls v0.14.2"}, false},
+		{18, true, []string{"Gopls was built with Go version 1.18", "unsupported by gopls v0.16.0", "upgrade to Go 1.19", "install gopls v0.14.2"}, false},
 	}
 
 	for _, test := range tests {