Add support to bin/tahoe for invoking a runner command prefixed with @, with the Tahoe libraries on the PYTHONPATH. This is documented in 'tahoe debug --help'.

bin/tahoe-script.template

@@ -95,7 +95,22 @@ when you run "python setup.py install" (perhaps as "%s").
 ''' % (script, perhaps_installed_tahoe)
     sys.exit(1)
 
-command = prefix + [script] + args
+# Support indirection via another "runner" script (e.g. coverage).
+# For example: bin/tahoe @RUNNER RUNNER_ARGS @tahoe TAHOE_ARGS
+
+if len(args) >= 1 and args[0].startswith('@'):
+    runner = args[0][1:]
+    if runner.endswith('.py') or runner.endswith('.pyscript'):
+        prefix = [sys.executable]
+    else:
+        prefix = []
+
+    def _subst(a):
+        if a == '@tahoe': return script
+        return a
+    command = prefix + [runner] + map(_subst, args[1:])
+else:
+    command = prefix + [script] + args
 
 try:
     res = subprocess.call(command, env=os.environ)

src/allmydata/scripts/debug.py

@@ -846,7 +846,22 @@ Subcommands:
 
 Please run e.g. 'tahoe debug dump-share --help' for more details on each
 subcommand.
-"""
+
+Another debugging feature is that bin%stahoe allows executing an arbitrary
+"runner" command (typically an installed Python script, such as 'coverage'),
+with the Tahoe libraries on the PYTHONPATH. The runner command name is
+prefixed with '@', and any occurrences of '@tahoe' in its arguments are
+replaced by the full path to the tahoe script.
+
+For example, if 'coverage' is installed and on the PATH, you can use:
+
+    bin%stahoe @coverage run --branch @tahoe debug trial
+
+to get branch coverage for the Tahoe test suite. Or, to run python with
+the -3 option that warns about Python 3 incompatibilities:
+
+    bin%stahoe @python -3 @tahoe command [options]
+""" % (os.sep, os.sep, os.sep)
         return t
 
 subDispatch = {