cmd/cue: deduplicate logic to implement command groups

That is, the logic that gives useful errors when `cue mod` or
`cue mod unknown` are executed.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I4029b3d3c81596fe3609f81f65dd5b090befeb0f
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1211266
Unity-Result: CUE porcuepine <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Roger Peppe <[email protected]>

Author: mvdan

cmd/cue/cmd/exp.go

@@ -15,16 +15,14 @@
 package cmd
 
 import (
-	"fmt"
-
 	"cuelang.org/go/cue/load"
 	"cuelang.org/go/internal/encoding/gotypes"
 
 	"github.com/spf13/cobra"
 )
 
 func newExpCmd(c *Command) *cobra.Command {
-	cmd := &cobra.Command{
+	cmd := commandGroup(c, &cobra.Command{
 		// Experimental commands are hidden by design.
 		Hidden: true,
 
@@ -36,17 +34,7 @@ exp groups commands which are still in an experimental stage.
 Experimental commands may be changed or removed at any time,
 as the objective is to gain experience and then move the feature elsewhere.
 `[1:],
-		RunE: mkRunE(c, func(cmd *Command, args []string) error {
-			stderr := cmd.Stderr()
-			if len(args) == 0 {
-				fmt.Fprintln(stderr, "exp must be run as one of its subcommands")
-			} else {
-				fmt.Fprintf(stderr, "exp must be run as one of its subcommands: unknown subcommand %q\n", args[0])
-			}
-			fmt.Fprintln(stderr, "Run 'cue help exp' for known subcommands.")
-			return ErrPrintedError
-		}),
-	}
+	})
 
 	cmd.AddCommand(newExpGenGoTypesCmd(c))
 	return cmd

cmd/cue/cmd/get.go

@@ -15,13 +15,11 @@
 package cmd
 
 import (
-	"fmt"
-
 	"github.com/spf13/cobra"
 )
 
 func newGetCmd(c *Command) *cobra.Command {
-	cmd := &cobra.Command{
+	cmd := commandGroup(c, &cobra.Command{
 		Use:   "get <language> [packages]",
 		Short: "add non-CUE dependencies to the current module",
 		Long: `Get downloads packages or modules for non-CUE languages
@@ -37,17 +35,7 @@ For information on native CUE modules:
 
     cue help modules
 `,
-		RunE: mkRunE(c, func(cmd *Command, args []string) error {
-			stderr := cmd.Stderr()
-			if len(args) == 0 {
-				fmt.Fprintln(stderr, "get must be run as one of its subcommands")
-			} else {
-				fmt.Fprintf(stderr, "get must be run as one of its subcommands: unknown subcommand %q\n", args[0])
-			}
-			fmt.Fprintln(stderr, "Run 'cue help get' for known subcommands.")
-			return ErrPrintedError
-		}),
-	}
+	})
 	cmd.AddCommand(newGoCmd(c))
 	return cmd
 }

cmd/cue/cmd/mod.go

@@ -15,13 +15,11 @@
 package cmd
 
 import (
-	"fmt"
-
 	"github.com/spf13/cobra"
 )
 
 func newModCmd(c *Command) *cobra.Command {
-	cmd := &cobra.Command{
+	cmd := commandGroup(c, &cobra.Command{
 		Use:   "mod <cmd> [arguments]",
 		Short: "module maintenance",
 		Long: `Mod groups commands which operate on CUE modules.
@@ -32,17 +30,7 @@ just 'cue mod'.
 See also:
 	cue help modules
 `,
-		RunE: mkRunE(c, func(cmd *Command, args []string) error {
-			stderr := cmd.Stderr()
-			if len(args) == 0 {
-				fmt.Fprintln(stderr, "mod must be run as one of its subcommands")
-			} else {
-				fmt.Fprintf(stderr, "mod must be run as one of its subcommands: unknown subcommand %q\n", args[0])
-			}
-			fmt.Fprintln(stderr, "Run 'cue help mod' for known subcommands.")
-			return ErrPrintedError
-		}),
-	}
+	})
 
 	cmd.AddCommand(newModEditCmd(c))
 	cmd.AddCommand(newModFixCmd(c))

cmd/cue/cmd/refactor.go

@@ -15,13 +15,11 @@
 package cmd
 
 import (
-	"fmt"
-
 	"github.com/spf13/cobra"
 )
 
 func newRefactorCmd(c *Command) *cobra.Command {
-	cmd := &cobra.Command{
+	cmd := commandGroup(c, &cobra.Command{
 		// Experimental so far.
 		Hidden: true,
 
@@ -31,17 +29,7 @@ func newRefactorCmd(c *Command) *cobra.Command {
 This command groups together commands relating
 to altering code within the current CUE module.
 `[1:],
-		RunE: mkRunE(c, func(cmd *Command, args []string) error {
-			stderr := cmd.Stderr()
-			if len(args) == 0 {
-				fmt.Fprintln(stderr, "refactor must be run as one of its subcommands")
-			} else {
-				fmt.Fprintf(stderr, "refactor must be run as one of its subcommands: unknown subcommand %q\n", args[0])
-			}
-			fmt.Fprintln(stderr, "Run 'cue help refactor' for known subcommands.")
-			return ErrPrintedError
-		}),
-	}
+	})
 
 	cmd.AddCommand(newRefactorImportsCmd(c))
 	return cmd

cmd/cue/cmd/root.go

@@ -85,6 +85,25 @@ type Stats struct {
 	}
 }
 
+// commandGroup makes cmd runnable in a way that implements commands grouping more subcommands,
+// such as `cue mod` or `cue refactor`. Note that the user can't actually run these commands to
+// do anything useful, but we need RunE for good error messages, as Cobra itself is lacking:
+// https://github.com/spf13/cobra/issues/706
+func commandGroup(c *Command, cmd *cobra.Command) *cobra.Command {
+	name := cmd.Name()
+	cmd.RunE = mkRunE(c, func(cmd *Command, args []string) error {
+		stderr := cmd.Stderr()
+		if len(args) == 0 {
+			fmt.Fprintf(stderr, "%s must be run as one of its subcommands\n", name)
+		} else {
+			fmt.Fprintf(stderr, "%s must be run as one of its subcommands: unknown subcommand %q\n", name, args[0])
+		}
+		fmt.Fprintf(stderr, "Run 'cue help %s' for known subcommands.\n", name)
+		return ErrPrintedError
+	})
+	return cmd
+}
+
 func mkRunE(c *Command, f runFunction) func(*cobra.Command, []string) error {
 	return func(cmd *cobra.Command, args []string) error {
 		c.Command = cmd