WIP: Draft iterable hooks implementation

pluggy/callers.py

@@ -199,3 +199,62 @@ def _multicall(hook_impls, caller_kwargs, firstresult=False):
                 pass
 
         return outcome.get_result()
+
+
+def _itercall(hook_impls, caller_kwargs, specopts={}, hook=None):
+    """Execute a calls into multiple python functions/methods and yield
+    the result(s) lazily.
+
+    ``caller_kwargs`` comes from _HookCaller.__call__().
+    """
+    __tracebackhide__ = True
+    specopts = hook.spec_opts if hook else specopts
+    results = []
+    firstresult = specopts.get("firstresult")
+    excinfo = None
+    try:  # run impl and wrapper setup functions in a loop
+        teardowns = []
+        try:
+            for hook_impl in reversed(hook_impls):
+                try:
+                    args = [caller_kwargs[argname] for argname in hook_impl.argnames]
+                except KeyError:
+                    for argname in hook_impl.argnames:
+                        if argname not in caller_kwargs:
+                            raise HookCallError(
+                                "hook call must provide argument %r" % (argname,))
+
+                if hook_impl.hookwrapper:
+                    try:
+                        gen = hook_impl.function(*args)
+                        next(gen)   # first yield
+                        teardowns.append(gen)
+                    except StopIteration:
+                        _raise_wrapfail(gen, "did not yield")
+                else:
+                    res = hook_impl.function(*args)
+                    if res is not None:
+                        results.append(res)
+                        yield res
+                        if firstresult:  # halt further impl calls
+                            break
+        except GeneratorExit:
+            pass  # loop was terminated prematurely by caller
+        except BaseException:
+            excinfo = sys.exc_info()
+    finally:
+        if firstresult:  # first result hooks return a single value
+            outcome = _Result(results[0] if results else None, excinfo)
+        else:
+            outcome = _Result(results, excinfo)
+
+        # run all wrapper post-yield blocks
+        for gen in reversed(teardowns):
+            try:
+                gen.send(outcome)
+                _raise_wrapfail(gen, "has second yield")
+            except StopIteration:
+                pass
+
+        # raise any exceptions
+        outcome.get_result()

pluggy/hooks.py

@@ -168,16 +168,16 @@ def __init__(self, trace):
 
 
 class _HookCaller(object):
-    def __init__(self, name, hook_execute, specmodule_or_class=None,
-                 spec_opts=None):
+    def __init__(self, name, hook_execute, specmodule_or_class=None, spec_opts=None,
+                 iterate=False):
         self.name = name
         self._wrappers = []
         self._nonwrappers = []
         self._hookexec = hook_execute
         self._specmodule_or_class = None
         self.argnames = None
         self.kwargnames = None
-        self.multicall = _multicall
+        self.multicall = _multicall if not iterate else _itercall
         self.spec_opts = spec_opts or {}
         if specmodule_or_class is not None:
             self.set_specification(specmodule_or_class, spec_opts)

testing/test_pluginmanager.py

@@ -393,3 +393,60 @@ def example_hook():
     assert getattr(pm.hook, 'example_hook', None)  # conftest.example_hook should be collected
     assert pm.parse_hookimpl_opts(conftest, 'example_blah') is None
     assert pm.parse_hookimpl_opts(conftest, 'example_hook') == {}
+
+
+def test_iterable_hooks(pm):
+    class Hooks(object):
+        @hookspec
+        def he_method1(self, arg):
+            pass
+
+    pm.add_hookspecs(Hooks)
+
+    l = []
+
+    class Plugin1(object):
+        @hookimpl
+        def he_method1(self, arg):
+            l.append(1)
+            return 1
+
+    class Plugin2(object):
+        @hookimpl
+        def he_method1(self, arg):
+            l.append(2)
+            return 2
+
+    class Plugin3(object):
+        @hookimpl
+        def he_method1(self, arg):
+            l.append(3)
+            return 3
+
+    class Plugin4(object):
+        @hookimpl
+        def he_method1(self, arg):
+            l.append(4)
+            return 4
+
+    class PluginWrapper(object):
+        @hookimpl(hookwrapper=True)
+        def he_method1(self, arg):
+            assert not l
+            outcome = yield
+            res = outcome.get_result()
+            assert res
+            assert res == [4, 3, 2] == l
+
+    pm.register(Plugin1())
+    pm.register(Plugin2())
+    pm.register(Plugin3())
+    pm.register(Plugin4())
+    pm.register(PluginWrapper())
+
+    for result, i in zip(pm.ihook.he_method1(arg=None), reversed(range(1, 5))):
+        assert result == i
+        if result == 2:  # stop before the final iteration
+            break
+
+    assert l == [4, 3, 2]