I think the existing logic is correct in its intent to track only for new and deleted files, but not for changes.
BUT, most IDE annihilate that effort by creating a temporary file when saving a file.
If we merge this PR, we will introduce a new bug: deleted/new files won't be tracked anymore.
This means we should find a better way to track new/removed files only.

Then I probably misunderstood the mechanics.

Here's how to reproduce my issue:

symfony --quiet demo test
cd test
# run symfony to warm up cache
bin/console --quiet about
# see container modification time
date -r var/cache/dev/appDevDebugProjectContainer.php
# this is to see later the difference in seconds
sleep 2
# create a twig file
touch app/Resources/views/test.html.twig
# run command again and I expect here the container to be not recompiled
bin/console --quiet about
# it actually recompiles, because the modification time is now different
date -r var/cache/dev/appDevDebugProjectContainer.php

This happens because of this call in TwigExtension which creates a FileResource for the app/Resources/views directory although $trackContents = false.

Am I right that TwigBundle keeps track of all bundle directories to recompile container in case these directories appear or get removed?

The actual problem is that dx becomes worse when you are waiting for n seconds after just changing a template...

With current code there's no possibility to prevent directory tracking even by doing ContainerBuilder::fileExists('/path/to/dir', false). Is this valid?

@nicolas-grekas , I've checked, with my changes new and deleted files are still tracked correctly.
But the Twig issue disappears

@vudaltsov the problem with your patch is that removing the app/Ressources/views will non longer trigger a recompile of the container leading to a fatal error because twig throw an exception when adding an inexistent path to the FileSystem loader.

@vudaltsov can you try this?

--- a/src/Symfony/Component/DependencyInjection/ContainerBuilder.php
+++ b/src/Symfony/Component/DependencyInjection/ContainerBuilder.php
@@ -407,9 +407,13 @@ class ContainerBuilder extends Container implements TaggedContainerInterface
             return $exists;
         }
 
-        if ($trackContents && is_dir($path)) {
-            $this->addResource(new DirectoryResource($path, is_string($trackContents) ? $trackContents : null));
-        } elseif ($trackContents || is_dir($path)) {
+        if (is_dir($path)) {
+            if ($trackContents) {
+                $this->addResource(new DirectoryResource($path, is_string($trackContents) ? $trackContents : null));
+            } else {
+                $this->addResource(new GlobResource($path, '/*', false));
+            }
+        } elseif ($trackContents) {
             $this->addResource(new FileResource($path));
         }

If it works, you can take the patch for your PR (and add a test case if possible.)

@nicolas-grekas, this makes things better. Now editing existing templates doesn't make the container recompile. New templates still do. Which makes sense because GlobResource notices the change in the file structure.

Is it possible to improve it even more? As @jvasseur pointed out, we only need to track for directory's existence in case of TwigExtension.

I'll try to experiment a little with this next week.

@nicolas-grekas , awesome news! Thank you. I din't have time to look at this yet.

Thank you @vudaltsov.