Add glob FAQ entry

Change-Id: I5463c8ea6578ff2af0d72a19df48bce44afb08de
Reviewed-by: Petr Hosek <>
Commit-Queue: Brett Wilson <>
diff --git a/docs/ b/docs/
index d300c90..41a178d 100644
--- a/docs/
+++ b/docs/
@@ -171,6 +171,22 @@
 the additions of new files to the source directory will not trigger the build
 step and that addition will not be reflected in an incremental build.
+## How can I reference all files in a directory (glob)?
+Sometimes people want to automatically refer to all files in a directory,
+typically something like `"*.cc"` for the sources. This is called a "glob."
+Globs are not supported in GN. In order for Ninja to know when to re-run
+GN, it would need to check the directory modification times of any
+directories being globbed. Directory modification times that reflect
+additions and removals of files are not as reliably implemented across
+platforms and filesystems as file modification times (for example, it is
+not supported on Windows FAT32 drives).
+Even if directory modification times work properly on your build systems,
+GN's philosophy prefers a very explicit build specification style that
+is contrary to globs.
 ## Why does "gn check" complain about conditionally included headers?
 The "gn check" feature (see `gn help check`) validates that the source code's