feat: Detect unexpected arguments and flags using the arguments package.

internal/command/arguments/workspace.go

@@ -32,6 +32,18 @@ func ParseWorkspace(args []string) (*Workspace, tfdiags.Diagnostics) {
 		))
 	}
 
+	// There should not be any non-flag arguments for the workspace list command.
+	// In future when other workspace subcommands start using the arguments package
+	// this code will need to change.
+	args = cmdFlags.Args()
+	if len(args) != 0 {
+		diags = diags.Append(tfdiags.Sourceless(
+			tfdiags.Error,
+			"Too many command line arguments",
+			"Expected no positional arguments.",
+		))
+	}
+
 	switch {
 	case jsonOutput:
 		return &Workspace{ViewType: ViewJSON}, diags

internal/command/arguments/workspace_test.go

@@ -0,0 +1,87 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: BUSL-1.1
+
+package arguments
+
+import (
+	"testing"
+
+	"github.com/hashicorp/terraform/internal/tfdiags"
+)
+
+func TestParseWorkspace_valid(t *testing.T) {
+	testCases := map[string]struct {
+		args []string
+		want *Workspace
+	}{
+		"defaults": {
+			nil,
+			&Workspace{
+				ViewType: ViewHuman,
+			},
+		},
+		"json": {
+			[]string{"-json"},
+			&Workspace{
+				ViewType: ViewJSON,
+			},
+		},
+	}
+
+	for name, tc := range testCases {
+		t.Run(name, func(t *testing.T) {
+			got, diags := ParseWorkspace(tc.args)
+			if len(diags) > 0 {
+				t.Fatalf("unexpected diags: %v", diags)
+			}
+			if *got != *tc.want {
+				t.Fatalf("unexpected result\n got: %#v\nwant: %#v", got, tc.want)
+			}
+		})
+	}
+}
+
+func TestParseWorkspace_invalid(t *testing.T) {
+	testCases := map[string]struct {
+		args      []string
+		want      *Workspace
+		wantDiags tfdiags.Diagnostics
+	}{
+		"unknown flag": {
+			[]string{"-boop"},
+			&Workspace{
+				ViewType: ViewHuman,
+			},
+			tfdiags.Diagnostics{
+				tfdiags.Sourceless(
+					tfdiags.Error,
+					"Failed to parse command-line flags",
+					"flag provided but not defined: -boop",
+				),
+			},
+		},
+		"too many arguments": {
+			[]string{"-json", "bar", "baz"},
+			&Workspace{
+				ViewType: ViewJSON,
+			},
+			tfdiags.Diagnostics{
+				tfdiags.Sourceless(
+					tfdiags.Error,
+					"Too many command line arguments",
+					"Expected no positional arguments.",
+				),
+			},
+		},
+	}
+
+	for name, tc := range testCases {
+		t.Run(name, func(t *testing.T) {
+			got, gotDiags := ParseWorkspace(tc.args)
+			if *got != *tc.want {
+				t.Fatalf("unexpected result\n got: %#v\nwant: %#v", got, tc.want)
+			}
+			tfdiags.AssertDiagnosticsMatch(t, gotDiags, tc.wantDiags)
+		})
+	}
+}