cmd/cue: deprecate cue somecmd in favor of cue cmd somecmd

v0.9.0-alpha.1 will be released with the deprecation warning to stderr,
and a future release like v0.10 or v0.11 can remove support entirely.

Note that even when we remove support for the short form,
this shouldn't be a hard breakage for any users, as they can switch
to the long form by adding the "cmd" argument.

Also rewrite a few tests which didn't need to use the short form.
Only one other test case remains with the short form,
as it explicitly tests for an edge case bug relating to the short form.
That test case can be removed entirely once we drop support.

Updates #2519.

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: I04aa48b048bb3f1c397f8b95a36933d797734930
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1185473
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
Reviewed-by: Paul Jolly <paul@myitcv.io>
TryBot-Result: CUEcueckoo <cueckoo@gmail.com>

cmd/cue/cmd/cmd.go

@@ -175,6 +175,10 @@ Run "cue help commands" for more details on tasks and commands.
 			}
 			// Presumably the *cobra.Command argument should be cmd.Command,
 			// as that is the one which will have the right settings applied.
+			if isRootCmd {
+				cmd.PrintErrf("The short-form 'cue %[1]s' is deprecated; use 'cue cmd %[1]s'.\n", args[0])
+				cmd.PrintErrf("See: https://cuelang.org/issue/2519\n")
+			}
 			return sub.RunE(cmd.Command, args[1:])
 		}),
 	}

cmd/cue/cmd/testdata/script/cmd_embed.txtar

@@ -4,11 +4,11 @@ exec cue export
 cmp stdout expect/concrete.json
 
 # Using the explicitly written command works OK.
-exec cue hello1
+exec cue cmd hello1
 stdout 'hello, world'
 
 # Using the command that's defined externally fails.
-exec cue hello
+exec cue cmd hello
 stdout 'hello, world'
 
 

cmd/cue/cmd/testdata/script/cmd_func.txtar

@@ -1,5 +1,5 @@
 # Issue #578
-exec cue dump ./...
+exec cue cmd dump ./...
 cmp stdout stdout-expect
 -- k1.cue --
 package kube

cmd/cue/cmd/testdata/script/cmd_short.txtar

@@ -0,0 +1,19 @@
+exec cue cmd hello
+stdout 'Hello world!'
+! stderr .
+
+exec cue hello
+stdout 'Hello world!'
+cmp stderr stderr-warning
+
+-- stderr-warning --
+The short-form 'cue hello' is deprecated; use 'cue cmd hello'.
+See: https://cuelang.org/issue/2519
+-- task_tool.cue --
+package home
+
+import "tool/cli"
+
+command: hello: cli.Print & {
+	text: "Hello world!"
+}