waf: update README with current status

README-WAF.md

@@ -1,71 +1,183 @@
 # WAF Build #
 
-To keep access to waf convenient, use the following alias from the
+Ardupilot is gradually moving from the make-based build system to
+[Waf](https://waf.io/).
+
+To keep access to Waf convenient, use the following alias from the
 root ardupilot directory:
 
 ```bash
-    alias waf="$PWD/modules/waf/waf-light"
+alias waf="$PWD/modules/waf/waf-light"
+```
+
+You can also define the alias or create a function in your shell rc file (e.g.
+`~/.bashrc`).
+
+You can read the [Waf Book](https://waf.io/book/) if you want to learn more
+about Waf.
+
+## Calling waf ##
+
+Waf should always be called from the ardupilot's root directory.
+
+Differently from the make-based build, with Waf there's a configure step
+to choose the board to be used (default is `sitl`):
+
+```bash
+# Configure the Linux board
+waf configure --board=linux
+```
+
+Waf build system is composed of commands. For example, the above command
+(`configure`) is for configuring the build. Consequently, in order to build, a
+"build" command is issued, thus `waf build`. That is the default command, so
+calling just `waf` is enough:
+
+```bash
+# Build programs from bin group
+waf
+
+# Waf also accepts '-j' option to parallelize the build.
+waf -j8
+```
+
+To clean things up, use the `clean` or `distclean` command:
+
+```bash
+# Clean the build products, but keep configure information
+waf clean
+
+# Clean everything, will need to call configure again
+waf distclean
 ```
 
-Waf should always be called from the ardupilot's root.
+Using git to clean the files also work fine.
 
-Differently from the make-based build, with waf there's a configure step
-to choose the board to be used
+To list the task generator names that can be used for the option `--targets`,
+use the `list`command:
 
 ```bash
-    # Configure the Linux board.
-    waf configure --board=linux
+waf list
 ```
 
-by default the board used is `sitl`.
+## Program groups ##
+
+The programs in ardupilot are categorized into the following groups:
 
-To build, use the 'waf build' command. This is the default command, so
-calling just `waf` is enough
+ - bin: *the main binaries, that is, ardupilot's main products - the vehicles and
+   Antenna Tracker*
+ - tools
+ - examples: *programs that show how certain libraries are used or to simply
+   test their operation*
+ - benchmarks
+ - tests: *basically unit tests to ensure changes don't break the system's
+   logic*
+
+There's also a special group, called "all", that comprises all groups.
+
+All build files are placed under `build/<board>/`, where `<board>` represents
+the board/platform you selected during configuration. Each program group has a
+folder with its name directly under `build/<board>/`. Thus, a program will be
+stored in `build/<board>/<group/`, where `<group>` is the group the program
+belongs to. For example, for a linux build, arducopter will be located at
+`build/linux/bin/arducopter`.
+
+## Building a program group ##
+
+Ardupilot adds to waf an option called `--program-group`, which receives as
+argument the group you want it to build. For a build command, if you don't pass
+any of `--targets` or `--program-group`, then the group "bin" is selected by
+default. The option `--program-group` can be passed multiple times.
+
+Examples:
+
+```bash
+# Group bin is the default one
+waf
+
+# Build all vehicles and Antenna Tracker
+waf --program-group bin
+
+# Build all benchmarks and tests
+waf --program-group benchmarks --program-group tests
+```
+### Shortcut for program groups ###
+
+For less typing, you can use the group name as the command to waf. Examples:
 
 ```bash
-    # From the root ardupilot directory, build everything.
-    waf
+# Build all vehicles and Antenna Tracker
+waf bin
 
-    # Waf also accepts '-j' option to parallelize the build.
-    waf -j8
+# Build all examples
+waf examples
 ```
 
-It's possible to build for just a vehicle or an example by specifying it as the
-target:
+## Building a specific program ##
+
+In order to build a specific program, you just need to pass its path relative
+to `build/<board>/` to the option `--targets`. Example:
 
 ```bash
-    # From the top directory
-    waf --targets bin/ArduCopter
+# Build arducopter
+waf --targets bin/arducopter
 
-    # List all the targets available
-    waf list
+# Build vectors unit test
+waf --targets tests/test_vectors
 ```
 
-There are also shortcuts for vehicle builds, for example:
+### Shortcuts for vehicles ###
+
+Vehicles can be built in the common single program building way (example: `waf
+--targets bin/arducopter`). But that is too much typing :-), we provide
+shortcut commands for vehicles:
 
 ```bash
-    # Shortcut for waf --targets bin/ArduCopter
-    waf copter
+# Build arducopter
+waf copter
+
+# Build arduplane
+waf plane
+
+# Build ardurover
+waf rover
 ```
 
-By default all the files produced by the build will be inside the build/
-subdirectory. The binaries will also be there, with the name identifying
-the target board.
+## Checking ##
 
-To clean things up use
+The command `check` builds all programs and then run the relevant tests. In
+that context, a relevant test is a program from the group "tests" that makes
+one of the following statements true:
+
+ - it's the first time the test is built since the last cleanup or when the
+   project was cloned.
+ - the program had to be rebuilt (due to modifications in the code or
+   dependencies, for example)
+ - the test program failed in the previous check.
+
+That is, the tests are run only if necessary. If you want waf to run all tests,
+then you can use either option `--alltests` or the shortcut command
+`check-all`.
+
+Examples:
 
 ```bash
-    # Clean the build products, but keep configure information
-    waf clean
+# Build everything and run relevant tests
+waf check
 
-    # Clean everything, will need to call configure again
-    waf distclean
+# Build everything and run all tests
+waf check --alltests
+
+# Build everything and run all tests
+waf check-all
 ```
 
-using git to clean the files also work fine.
+## Make wrapper ##
 
 There's also a make wrapper called `Makefile.waf`. You can use
 `make -f Makefile.waf help` for instructions on how to use it.
 
-*TODO: Add explanation on how the build system is organized once we
-settle down.*
+## Command line help ##
+
+You can use `waf --help` to see information about commands and options built-in
+to waf as well as some quick help on those added by ardupilot.