Do not show a warning about too new client version when server and cl…

…ient are on the same major version

lib/client/api.go

@@ -4257,8 +4257,17 @@ Future versions of tsh will fail when incompatible versions are detected.
 			versions.MinClient, versions.Client, versions.MinClient), nil
 	}
 
-	if !utils.MeetsMaxVersion(versions.Client, versions.Server) {
-		serverVersionWithWildcards, err := utils.MajorSemverWithWildcards(versions.Server)
+	clientMajorVersion, err := utils.MajorSemver(versions.Client)
+	if err != nil {
+		return "", trace.Wrap(err)
+	}
+	serverMajorVersion, err := utils.MajorSemver(versions.Server)
+	if err != nil {
+		return "", trace.Wrap(err)
+	}
+
+	if !utils.MeetsMaxVersion(clientMajorVersion, serverMajorVersion) {
+		serverVersionWithWildcards, err := utils.MajorSemverWithWildcards(serverMajorVersion)
 		if err != nil {
 			return "", trace.Wrap(err)
 		}

lib/client/api_test.go

@@ -29,6 +29,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/coreos/go-semver/semver"
 	"github.com/google/go-cmp/cmp"
 	"github.com/gravitational/trace"
 	"github.com/stretchr/testify/assert"
@@ -1390,3 +1391,66 @@ func TestNonRetryableError(t *testing.T) {
 	assert.True(t, trace.IsAccessDenied(err))
 	assert.Equal(t, orgError, err.Unwrap())
 }
+
+func TestWarningsAboutClientVersion(t *testing.T) {
+	tests := []struct {
+		name            string
+		clientVersion   string
+		serverVersion   string
+		expectedWarning string
+	}{
+		{
+			name:          "client on a higher major version than server triggers a warning",
+			clientVersion: "17.0.0",
+			serverVersion: "16.0.0",
+			expectedWarning: `
+WARNING
+Detected potentially incompatible client and server versions.
+Maximum client version supported by the server is 16.x.x but you are using 17.0.0.
+Please downgrade tsh to 16.x.x or use the --skip-version-check flag to bypass this check.
+Future versions of tsh will fail when incompatible versions are detected.
+
+`,
+		},
+		{
+			name:          "client on a too low major version compared to server triggers a warning",
+			clientVersion: "16.4.0",
+			serverVersion: "18.0.0",
+			expectedWarning: `
+WARNING
+Detected potentially incompatible client and server versions.
+Minimum client version supported by the server is 17.0.0 but you are using 16.4.0.
+Please upgrade tsh to 17.0.0 or newer or use the --skip-version-check flag to bypass this check.
+Future versions of tsh will fail when incompatible versions are detected.
+
+`,
+		},
+		{
+			name:            "client on a higher minor version than server does not trigger a warning",
+			clientVersion:   "17.1.0",
+			serverVersion:   "17.0.0",
+			expectedWarning: "",
+		},
+		{
+			name:            "client on a lower major version than server does not trigger a warning",
+			clientVersion:   "17.0.0",
+			serverVersion:   "18.0.0",
+			expectedWarning: "",
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			minClientVersion, err := semver.NewVersion(test.serverVersion)
+			require.NoError(t, err)
+			minClientVersion.Major = minClientVersion.Major - 1
+			warning, err := getClientIncompatibilityWarning(versions{
+				MinClient: minClientVersion.String(),
+				Client:    test.clientVersion,
+				Server:    test.serverVersion,
+			})
+			require.NoError(t, err)
+			require.Equal(t, test.expectedWarning, warning)
+		})
+	}
+}