[release-branch.go1.18] cmd/go: error out of 'go work use' if no directories are given

Otherwise, the behavior of 'go work use -r' (without arguments)
may be surprising.

For #51448.

Change-Id: I50cf1339591720ec5bd333146b89c9944ce420d5
Reviewed-on: https://go-review.googlesource.com/c/go/+/389855
Trust: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
(cherry picked from commit 4f8094386c)
Reviewed-on: https://go-review.googlesource.com/c/go/+/389299
Trust: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>

src/cmd/go/alldocs.go

@@ -1535,7 +1535,7 @@
 //
 // Usage:
 //
-// 	go work use [-r] [moddirs]
+// 	go work use [-r] moddirs
 //
 // Use provides a command-line interface for adding
 // directories, optionally recursively, to a go.work file.

src/cmd/go/internal/workcmd/use.go

@@ -20,7 +20,7 @@ import (
 )
 
 var cmdUse = &base.Command{
-	UsageLine: "go work use [-r] [moddirs]",
+	UsageLine: "go work use [-r] moddirs",
 	Short:     "add modules to workspace file",
 	Long: `Use provides a command-line interface for adding
 directories, optionally recursively, to a go.work file.
@@ -101,6 +101,9 @@ func runUse(ctx context.Context, cmd *base.Command, args []string) {
 		keepDirs[absDir] = dir
 	}
 
+	if len(args) == 0 {
+		base.Fatalf("go: 'go work use' requires one or more directory arguments")
+	}
 	for _, useDir := range args {
 		if !*useR {
 			lookDir(useDir)

src/cmd/go/testdata/script/work_use_noargs.txt

@@ -0,0 +1,11 @@
+# For now, 'go work use' requires arguments.
+# (Eventually, we may may it implicitly behave like 'go work use .'.
+
+! go work use
+stderr '^go: ''go work use'' requires one or more directory arguments'
+
+! go work use -r
+stderr '^go: ''go work use'' requires one or more directory arguments'
+
+-- go.work --
+go 1.18