fix(branch): disallow branch before subcommand

The command line parsing for `stg branch` was such that specifying a
branch name before a subcommand was being allowed, **but** that early
branch name argument **was not** known or used by the subcommand; i.e.
any branch name argument before the subcommand was silently ignored.

This allowed certain valid command lines to lead to pathological
behavior. For example:

    stg branch foo --delete --force

would delete the current branch, not branch "foo".

The fix is to enable clap's args_conflicts_with_subcommands for `stg
branch`, which disallows non-subcommand arguments to precede  a
subcommand argument. This is consistent with the intended usage of
`stg branch`.

Fixes: #447

src/cmd/branch/mod.rs

@@ -44,6 +44,7 @@ fn make() -> clap::Command {
              result in an error.",
         )
         .disable_help_subcommand(true)
+        .args_conflicts_with_subcommands(true)
         .override_usage(super::make_usage(
             "stg branch",
             &[

t/t1000-branch-create.sh

@@ -78,7 +78,7 @@ test_expect_success 'Attempt switching to current branch' '
 
 test_expect_success 'Attempt no branch command' '
     general_error stg branch foo bar 2>err &&
-    grep "unexpected argument .bar." err
+    grep "the subcommand .bar. cannot be used with ..branch.." err
 '
 
 test_expect_success 'Invalid num arguments to branch list' '

t/t1005-branch-delete.sh

@@ -29,6 +29,15 @@ test_expect_success 'Attempt to delete branch with patches' '
     grep -e "delete not permitted: the series still contains patches" err
 '
 
+test_expect_success 'Delete subcommand ordering' '
+    general_error stg branch master --delete --force &&
+    stg branch >out &&
+    cat >expected <<-\EOF &&
+	foo
+	EOF
+    test_cmp expected out
+'
+
 test_expect_success 'Force delete branch with patches' '
     stg branch --delete --force master
 '