Remove check_invalid() in favor of cache_off()

contingent/contingent/projectlib.py

@@ -1,6 +1,7 @@
 """Provide a Project of related tasks that can be rebuilt when inputs change.
 
 """
+from contextlib import contextmanager
 from collections import namedtuple
 from functools import wraps
 from .graphlib import Graph
@@ -14,6 +15,7 @@ def __init__(self):
         self._graph = Graph()
         self._graph.sort_key = task_key
         self._cache = {}
+        self._cache_on = True
         self._task_stack = []
         self._todo = set()
         self._trace = None
@@ -47,9 +49,6 @@ def _add_task_to_trace(self, task, return_value):
         """Add a task to the currently running task trace."""
         tup = (len(self._task_stack), return_value is _unavailable, task)
         self._trace.append(tup)
-        if len(self._trace) > 30:
-            print(self.stop_output())
-            raise RuntimeError()
 
     def task(self, task_function):
         """Decorate a function that defines one of the tasks for this project.
@@ -72,14 +71,7 @@ def task(self, task_function):
         sure that if `task_function` invokes any further tasks, we can
         remember that it used their return values and that it will need
         to be re-invoked again in the future if any of those other tasks
-        change their return value.
-
-        The wrapper also includes a convenience function,
-        `check_invalid`, that invokes the `task_function` and updates
-        the value in the cache if the cache and the current value do not
-        match. If the cached value is determined to be invalid, the
-        consequences of the task are added to the to-do list for
-        reevaluation.
+        changes its return value.
 
         """
         @wraps(task_function)
@@ -104,13 +96,6 @@ def wrapper(*args):
 
             return return_value
 
-        def check_invalid(*args):
-            task = Task(wrapper, args)
-            current_value = task_function(*args)
-            self.set(task, current_value)
-
-        wrapper.check_invalid = check_invalid
-
         return wrapper
 
     def _get_from_cache(self, task):
@@ -120,10 +105,31 @@ def _get_from_cache(self, task):
         returns the singleton `_unavailable` instead.
 
         """
+        if not self._cache_on:
+            return _unavailable
         if task in self._todo:
             return _unavailable
         return self._cache.get(task, _unavailable)
 
+    @contextmanager
+    def cache_off(self):
+        """Context manager that forces tasks to really be invoked.
+
+        Even if the project has already cached the output of a
+        particular task, re-running the task inside of this context
+        manager will make the project re-invoke the task::
+
+            with project.cache_off():
+                my_task()
+
+        """
+        original_value = self._cache_on
+        self._cache_on = False
+        try:
+            yield
+        finally:
+            self._cache_on = original_value
+
     def set(self, task, return_value):
         """Add the `return_value` of `task` to our cache of return values.
 

contingent/example/blog_project.py

@@ -1,4 +1,4 @@
-"""Render a directory of blog posts as HTML."""
+"""Render a directory of cross-referenced blog posts as HTML."""
 
 import os
 import re
@@ -113,8 +113,9 @@ def main():
         changed_paths = looping_wait_on(paths)
         print('=' * 72)
         print('Reloading:', ' '.join(changed_paths))
-        for path in changed_paths:
-            read_text_file.check_invalid(path)
+        with project.cache_off():
+            for path in changed_paths:
+                read_text_file(path)
         project.rebuild()
 
 if __name__ == '__main__':

contingent/make.py

@@ -79,8 +79,9 @@ def chapter_doctests(path):
         optionflags=doctest.ELLIPSIS,
         )
 
-    for dot in glob('*.dot'):
-        read_text_file.check_invalid(dot)
+    with project.cache_off():
+        for dot in glob('*.dot'):
+            read_text_file(dot)
 
 
 @task
@@ -90,6 +91,7 @@ def render(path):
         png = path[:-3] + 'png'
         subprocess.call(['dot', '-Tpng', '-o', png, path])
     elif path.endswith('.rst'):
+        read_text_file(path)
         chapter_doctests(path)
         check_rst_includes(path)
         subprocess.call(['rst2html.py', 'chapter.rst', 'chapter.html'])
@@ -115,8 +117,9 @@ def main():
         changed_paths = looping_wait_on(get_paths())
         print('=' * 72)
         print('Reloading:', ' '.join(changed_paths))
-        for path in changed_paths:
-            read_text_file.check_invalid(path)
+        with project.cache_off():
+            for path in changed_paths:
+                read_text_file(path)
         project.start_tracing()
         project.rebuild()
         print(project.stop_tracing(True))