NO BUG - Document common build system targets, add requirements.txt

DONTBUILD (NPOTB)

build/docs/build-targets.rst

@@ -0,0 +1,56 @@
+.. _build_targets:
+
+=============
+Build Targets
+=============
+
+When you build with ``mach build``, there are some special targets that can be
+built. This page attempts to document them.
+
+Partial Tree Targets
+====================
+
+The targets in this section only build part of the tree. Please note that
+partial tree builds can be unreliable. Use at your own risk.
+
+export
+   Build the *export* tier. The *export* tier builds everything that is
+   required for C/C++ compilation. It stages all header files, processes
+   IDLs, etc.
+
+compile
+   Build the *compile* tier. The *compile* tier compiles all C/C++ files.
+
+libs
+   Build the *libs* tier. The *libs* tier performs linking and performs
+   most build steps which aren't related to compilation.
+
+tools
+   Build the *tools* tier. The *tools* tier mostly deals with supplementary
+   tools and compiled tests. It will link tools against libXUL, including
+   compiled test binaries.
+
+install-manifests
+   Process install manifests. Install manifests handle the installation of
+   files into the object directory.
+
+   Unless ``NO_REMOVE=1`` is defined in the environment, files not accounted
+   in the install manifests will be deleted from the object directory.
+
+install-tests
+   Processes the tests install manifest.
+
+Common Actions
+==============
+
+The targets in this section correspond to common build-related actions. Many
+of the actions in this section are effectively frontends to shell scripts.
+These actions will likely all be replaced by mach commands someday.
+
+buildsymbols
+   Create a symbols archive for the current build.
+
+   This must be performed after a successful build.
+
+check
+   Run build system tests.

build/docs/index.rst

@@ -20,6 +20,7 @@ Important Concepts
    Profile Guided Optimization <pgo>
    slow
    environment-variables
+   build-targets
    test_manifests
 
 mozbuild

build/docs/requirements.txt

@@ -0,0 +1,6 @@
+Jinja2==2.7.1
+MarkupSafe==0.18
+Pygments==1.6
+Sphinx==1.1.3
+docutils==0.11
+mdn-sphinx-theme==0.3