Adding new TREE folder option

chapters/features/ides.md

@@ -2,7 +2,7 @@
 
 In general, IDEs are already supported by a standard CMake project. There are just a few extra things that can help IDEs perform even better.
 
-## Folders
+## Folders for targets
 
 Some IDEs, like Xcode, support folders. You have to manually enable the `USE_FOLDERS` global property to allow CMake to organize your files by folders:
 
@@ -16,13 +16,32 @@ Then, you can add targets to folders when after you create them:
 set_property(TARGET MyFile PROPERTY FOLDER "Scripts")
 ```
 
-Folders can be nested with `/`. You can control how files show up in each folder with regular expressions or explicit listings in [`source_group`](https://cmake.org/cmake/help/latest/command/source_group.html):
+Folders can be nested with `/`.
 
-```
-source_group("Source Files" REGULAR_EXPRESSION ".*\\.c[ucp]p?")
+
+
+You can control how files show up in each folder with regular expressions or explicit listings in [`source_group`](https://cmake.org/cmake/help/latest/command/source_group.html):
+
+## Folders for files
+
+You can also control how the folders inside targets appear. There are two ways, both using the «command:source_group» command. The traditional way is 
+
+```cmake
+source_group("Source Files\\New Directory" REGULAR_EXPRESSION ".*\\.c[ucp]p?")
 ```
 
-Take a look at [this blog post][sorting] for tips on ways to automatically sort folders to match your source code layout.
+You can explicitly list files with `FILES`, or use a `REGULAR_EXPRESSION`. This way you have complete control over the folder structure. However, if your on-disk layout is well designed, you might just want to mimic that. In CMake 3.8+, you can do so very easily with a new version of the «command:source_group» command:
+
+```cmake
+source_group(TREE /full/path/to/start/at PREFIX "Header Files" FILES ${FILE_LIST})
+```
+
+For the `TREE` option, you should usually give a full path starting with something like `${CMAKE_CURRENT_SOURCE_DIR}/`(because the command interprets paths relative to the build directory).
+The prefix tells you where it puts it into the IDE structure, and the `FILES` option takes a list of files.
+CMake will strip the `TREE` path from the `FILE_LIST` path, it will add `PREFIX`, and that will be the IDE folder structure.
+
+> Note: If you need to support CMake < 3.8, I would recommend just protecting the above command, and only supporting nice folder layout on CMake 3.8+. For older methods to do this folder layout, see
+> [this blog post][sorting].
 
 ## Running with an IDE
 

chapters/intro/newcmake.md

@@ -97,6 +97,7 @@ This adds CUDA as a language, as well as `cxx_std_11` as a compiler meta-feature
 * `COMPILE_FLAGS` now supports generator expression
 * `*_CPPLINT` added
 * `$<IF:cond,true-value,false-value>` added (wow!)
+* `source_group(TREE` added (finally allowing IDE's to reflect the project folder structure!)
 
 ## [CMake 3.9][] : IPO