Help: Add documentation for default generator environment variables

Documentation for environment variables that control the default
generator selection:

* CMAKE_GENERATOR
* CMAKE_GENERATOR_INSTANCE
* CMAKE_GENERATOR_PLATFORM
* CMAKE_GENERATOR_TOOLSET

4 files changed, 13 insertions, 5 deletions

diff --git a/Help/variable/CMAKE_GENERATOR.rst b/Help/variable/CMAKE_GENERATOR.rst
index cce04c1..ec52cd4 100644
--- a/Help/variable/CMAKE_GENERATOR.rst
+++ b/Help/variable/CMAKE_GENERATOR.rst
@@ -5,3 +5,8 @@ The generator used to build the project.  See :manual:`cmake-generators(7)`.
 
 The name of the generator that is being used to generate the build
 files.  (e.g.  ``Unix Makefiles``, ``Ninja``, etc.)
+
+The value of this variable should never be modified by project code.
+A generator may be selected via the :manual:`cmake(1)` ``-G`` option,
+interactively in :manual:`cmake-gui(1)`, or via the :envvar:`CMAKE_GENERATOR`
+environment variable.
diff --git a/Help/variable/CMAKE_GENERATOR_INSTANCE.rst b/Help/variable/CMAKE_GENERATOR_INSTANCE.rst
index 78c81b1..3657ed4 100644
--- a/Help/variable/CMAKE_GENERATOR_INSTANCE.rst
+++ b/Help/variable/CMAKE_GENERATOR_INSTANCE.rst
@@ -5,9 +5,10 @@ Generator-specific instance specification provided by user.
 
 Some CMake generators support selection of an instance of the native build
 system when multiple instances are available.  If the user specifies an
-instance (e.g. by setting this cache entry), or after a default instance is
-chosen when a build tree is first configured, the value will be available in
-this variable.
+instance (e.g. by setting this cache entry or via the
+:envvar:`CMAKE_GENERATOR_INSTANCE` environment variable), or after a default
+instance is chosen when a build tree is first configured, the value will be
+available in this variable.
 
 The value of this variable should never be modified by project code.
 A toolchain file specified by the :variable:`CMAKE_TOOLCHAIN_FILE`
diff --git a/Help/variable/CMAKE_GENERATOR_PLATFORM.rst b/Help/variable/CMAKE_GENERATOR_PLATFORM.rst
index 963f0a4..2c115a3 100644
--- a/Help/variable/CMAKE_GENERATOR_PLATFORM.rst
+++ b/Help/variable/CMAKE_GENERATOR_PLATFORM.rst
@@ -6,7 +6,8 @@ Generator-specific target platform specification provided by user.
 Some CMake generators support a target platform name to be given
 to the native build system to choose a compiler toolchain.
 If the user specifies a platform name (e.g. via the :manual:`cmake(1)` ``-A``
-option) the value will be available in this variable.
+option or via the :envvar:`CMAKE_GENERATOR_PLATFORM` environment variable)
+the value will be available in this variable.
 
 The value of this variable should never be modified by project code.
 A toolchain file specified by the :variable:`CMAKE_TOOLCHAIN_FILE`
diff --git a/Help/variable/CMAKE_GENERATOR_TOOLSET.rst b/Help/variable/CMAKE_GENERATOR_TOOLSET.rst
index e77f211..a01a8b7 100644
--- a/Help/variable/CMAKE_GENERATOR_TOOLSET.rst
+++ b/Help/variable/CMAKE_GENERATOR_TOOLSET.rst
@@ -5,7 +5,8 @@ Native build system toolset specification provided by user.
 
 Some CMake generators support a toolset specification to tell the
 native build system how to choose a compiler.  If the user specifies
-a toolset (e.g.  via the :manual:`cmake(1)` ``-T`` option) the value
+a toolset (e.g. via the :manual:`cmake(1)` ``-T`` option or via
+the :envvar:`CMAKE_GENERATOR_TOOLSET` environment variable) the value
 will be available in this variable.
 
 The value of this variable should never be modified by project code.