cli/command: deprecate prompt utilities that were for internal use

- The `DisableInputEcho` and `PromptForInput` utilities were added in
  c15ade0c64 as part of a bug-fix, which
  was part of v28.x. [There are no (publicly visible) users][1] of either.
- The `ErrPromptTerminated` was added in v26.x (originally added in
  10bf91a02d, later updated in commit
  7c722c08d0. [It is not used][2]
- The `PromptForConfirmation` was added in [moby@280c872] (docker v1.13.0)
  as part of the `docker <object> prune` subcommands. It was meant for
  internal use but exported to allow re-using it in the `container`,
  `image` (etc.) packages. However, a breaking change to its signature
  was made in 10bf91a02d. It currently
  does [not appear to have any (public) users][2].

This patch deprecates the `ErrPromptTerminated`, `DisableInputEcho`,
`PromptForInput`, and `PromptForConfirmation` utilities from the
`cli/command` package. The core functionality of these is still
available in the `internal/prompt` package, which we may make
public at some point, but still needs some refining / decoupling.

[moby@280c872]: 280c872366
[1]: https://grep.app/search?f.lang=Go&regexp=true&q=%5C.%28DisableInputEcho%7CPromptForInput%29%5C%28
[2]: https://grep.app/search?f.lang=Go&q=%5C.ErrPromptTerminated
[3]: https://grep.app/search?f.lang=Go&q=.PromptForConfirmation%28

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/utils.go

@@ -17,12 +17,17 @@ import (
 	"github.com/pkg/errors"
 )
 
+// ErrPromptTerminated is returned if the user terminated the prompt.
+//
+// Deprecated: this error is for internal use and will be removed in the next release.
 const ErrPromptTerminated = prompt.ErrTerminated
 
 // DisableInputEcho disables input echo on the provided streams.In.
 // This is useful when the user provides sensitive information like passwords.
 // The function returns a restore function that should be called to restore the
 // terminal state.
+//
+// Deprecated: this function is for internal use and will be removed in the next release.
 func DisableInputEcho(ins *streams.In) (restore func() error, err error) {
 	return prompt.DisableInputEcho(ins)
 }
@@ -34,6 +39,8 @@ func DisableInputEcho(ins *streams.In) (restore func() error, err error) {
 // When the prompt returns an error, the caller should propagate the error up
 // the stack and close the io.Reader used for the prompt which will prevent the
 // background goroutine from blocking indefinitely.
+//
+// Deprecated: this function is for internal use and will be removed in the next release.
 func PromptForInput(ctx context.Context, in io.Reader, out io.Writer, message string) (string, error) {
 	return prompt.ReadInput(ctx, in, out, message)
 }
@@ -48,6 +55,8 @@ func PromptForInput(ctx context.Context, in io.Reader, out io.Writer, message st
 // When the prompt returns an error, the caller should propagate the error up
 // the stack and close the io.Reader used for the prompt which will prevent the
 // background goroutine from blocking indefinitely.
+//
+// Deprecated: this function is for internal use and will be removed in the next release.
 func PromptForConfirmation(ctx context.Context, ins io.Reader, outs io.Writer, message string) (bool, error) {
 	return prompt.Confirm(ctx, ins, outs, message)
 }