cmd/docker: fail on unknown command with --version

Running "docker nonexistent --version" printed the CLI version and
exited 0, so it couldn't be used to check whether a command or plugin
is available. Without "--version" the same invocation fails with an
"unknown command" error.

When no built-in command or plugin matches, runDocker falls through to
executing the root command, and cobra handles the "--version" flag
before the root command reports the unknown command. Unset the root
command's version in that fallback, so the standard unknown-command
error is returned.

A global "--version" flag ("docker --version nonexistent") is parsed
before the command name and still prints the version, as do
"docker --version" and "docker nonexistent --help".

Signed-off-by: Nimesh Kulkarni <167794819+GitNimay@users.noreply.github.com>

cmd/docker/docker.go

@@ -580,6 +580,15 @@ func runDocker(ctx context.Context, dockerCli *command.DockerCli) error {
 			}
 			// Other missing or invalid plugins fall through to cmd.ExecuteContext(),
 			// which reports the standard unknown-command error.
+			//
+			// Cobra handles "--version" before it checks for unknown commands,
+			// so unset it to make "docker nonexistent --version" fail instead
+			// of printing the version. A global "--version" flag (as in
+			// "docker --version nonexistent") was already parsed, and still
+			// prints the version.
+			if !cmd.Flags().Changed("version") {
+				cmd.Version = ""
+			}
 		}
 	}
 

e2e/cli-plugins/run_test.go

@@ -62,6 +62,22 @@ func TestNonexistingHelp(t *testing.T) {
 	})
 }
 
+// TestNonexistingVersion ensures correct behaviour when invoking a
+// nonexistent plugin with `--version`.
+func TestNonexistingVersion(t *testing.T) {
+	run, _, cleanup := prepare(t)
+	defer cleanup()
+
+	for _, flag := range []string{"--version", "-v"} {
+		res := icmd.RunCmd(run("nonexistent", flag))
+		res.Assert(t, icmd.Expected{
+			ExitCode: 1,
+			Out:      icmd.None,
+		})
+		golden.Assert(t, res.Stderr(), "docker-nonexistent-err.golden")
+	}
+}
+
 // TestRunBad ensures correct behaviour when running an existent but invalid plugin
 func TestRunBad(t *testing.T) {
 	run, _, cleanup := prepare(t)