Modules/readme.txt - third_party/cmake - Git at Google

 Note to authors of FindXXX.cmake files

 We would like all FindXXX.cmake files to produce consistent variable names.

 Please use the following consistent variable names for general use.

 XXX_INCLUDE_DIR        	Where to find xxx.h, etc. If for some reason, you really need two paths, then that shouldn't be a problem - however, consider if you really should have two different FindXXX.cmake files. (XXX_INCLUDE_PATH was considered bad because a path includes an actual filename.)
 XXX_LIBRARIES          	The libraries to link against to use XXX. These should include full paths.
 XXX_DEFINITIONS        	Definitions to use when compiling code that uses XXX. This really shouldn't include options such as (-DHAS_JPEG)that a client source-code file uses to decide whether to #include <jpeg.h>
 XXX_EXECUTABLE         	Where to find the XXX tool.
 XXX_YYY_EXECUTABLE     	Where to find the YYY tool that comes with XXX.
 XXX_ROOT_DIR           	Where to find the base directory of XXX.
 XXX_VERSION_YY		Expect Version YY if true. Make sure at most one of these is ever true.
 XXX_WRAP_YY		If False, do not try to use the relevent CMake wrapping command.
 XXX_YY_FOUND           	If False, optional YY part of XXX sytem is not available.
 XXX_FOUND              	Set to false, or undefined, if we haven't found, or don't want to use XXX.

 You do not have to provide all of the above variables. You should provide XXX_FOUND under most circumstances. If XXX is a library, then  XXX_LIBRARIES, should also be defined, and XXX_INCLUDE_DIR should usually be defined (I guess libm.a might be an exception)

 The following names should not usually be used in CMakeLists.txt files, but they may be usefully modified in users' CMake Caches to control stuff.

 XXX_LIBRARY		Name of XXX Library. A User may set this and XXX_INCLUDE_DIR to ignore to force non-use of XXX.
 XXX_YY_LIBRARY		Name of YY library that is part of the XXX system. It may or may not be required to use XXX.

 For tidiness's sake, try to keep as many options as possible out of the cache, leaving at least one option which can be used to disable use of the module, or locate a not-found library (e.g. XXX_ROOT_DIR). For the same reason, mark most cache options as advanced.

 If you need other commands to do special things then it should still begin with XXX_. This gives a sort of namespace effect and keeps things tidy for the user. You should put comments describing all the exported settings, plus descriptions of any the users can use to control stuff.

 You really should also provide backwards compatibility any old settings that were actually in use. Make sure you comment them as deprecated, so that no-one starts using them.

 To correctly document a module, create a comment block at the top with # comments.  There are three types of comments that can be in the block:

 1. The brief description of the module, this is done by:
 # - a small description

 2. A paragraph of text.  This is done with all text that has a single
 space between the # and the text.  To create a new paragraph, just
 put a # with no text on the line.

 3. A verbatim line.  This is done with two spaces between the # and the text.

 For example:

 # - This is a cool module
 # This module does really cool stuff.
 # It can do even more than you think.
 #
 # It even needs to paragraphs to tell you about it.
 # And it defines the following variables:
 #  VAR_COOL - this is greate isn't it?
 #  VAR_REALLY_COOL - cool right?
 #

 To have a .cmake file in this directory NOT show up in the
 modules documentation, you should start the file with a blank
 line.

 A FindXXX.cmake module will typically be loaded by the command

   FIND_PACKAGE(XXX [QUIET] [REQUIRED [components...]])

 If the QUIET option is given to the command it will set the variable
 XXX_FIND_QUIETLY to true before loading the FindXXX.cmake module.  If
 this variable is set the module should not complain about not being
 able to find the package and should never issue a FATAL_ERROR.  If the
 REQUIRED option is given to the command it will set the variable
 XXX_FIND_REQUIRED to true before loading the FindXXX.cmake module.  If
 this variable is set the module should issue a FATAL_ERROR if the
 package cannot be found.  For each package-specific component, say
 YYY, listed after the REQUIRED option a variable XXX_FIND_REQUIRED_YYY
 to true.  This can be used by the FindXXX.cmake module to determine
 which sub-components of the package must be found.  If neither the
 QUIET nor REQUIRED options are given then the FindXXX.cmake module
 should look for the package and complain without error if the module
 is not found.
	Note to authors of FindXXX.cmake files

	We would like all FindXXX.cmake files to produce consistent variable names.

	Please use the following consistent variable names for general use.

	XXX_INCLUDE_DIR Where to find xxx.h, etc. If for some reason, you really need two paths, then that shouldn't be a problem - however, consider if you really should have two different FindXXX.cmake files. (XXX_INCLUDE_PATH was considered bad because a path includes an actual filename.)
	XXX_LIBRARIES The libraries to link against to use XXX. These should include full paths.
	XXX_DEFINITIONS Definitions to use when compiling code that uses XXX. This really shouldn't include options such as (-DHAS_JPEG)that a client source-code file uses to decide whether to #include <jpeg.h>
	XXX_EXECUTABLE Where to find the XXX tool.
	XXX_YYY_EXECUTABLE Where to find the YYY tool that comes with XXX.
	XXX_ROOT_DIR Where to find the base directory of XXX.
	XXX_VERSION_YY Expect Version YY if true. Make sure at most one of these is ever true.
	XXX_WRAP_YY If False, do not try to use the relevent CMake wrapping command.
	XXX_YY_FOUND If False, optional YY part of XXX sytem is not available.
	XXX_FOUND Set to false, or undefined, if we haven't found, or don't want to use XXX.

	You do not have to provide all of the above variables. You should provide XXX_FOUND under most circumstances. If XXX is a library, then XXX_LIBRARIES, should also be defined, and XXX_INCLUDE_DIR should usually be defined (I guess libm.a might be an exception)

	The following names should not usually be used in CMakeLists.txt files, but they may be usefully modified in users' CMake Caches to control stuff.

	XXX_LIBRARY Name of XXX Library. A User may set this and XXX_INCLUDE_DIR to ignore to force non-use of XXX.
	XXX_YY_LIBRARY Name of YY library that is part of the XXX system. It may or may not be required to use XXX.

	For tidiness's sake, try to keep as many options as possible out of the cache, leaving at least one option which can be used to disable use of the module, or locate a not-found library (e.g. XXX_ROOT_DIR). For the same reason, mark most cache options as advanced.

	If you need other commands to do special things then it should still begin with XXX_. This gives a sort of namespace effect and keeps things tidy for the user. You should put comments describing all the exported settings, plus descriptions of any the users can use to control stuff.

	You really should also provide backwards compatibility any old settings that were actually in use. Make sure you comment them as deprecated, so that no-one starts using them.

	To correctly document a module, create a comment block at the top with # comments. There are three types of comments that can be in the block:

	1. The brief description of the module, this is done by:
	# - a small description

	2. A paragraph of text. This is done with all text that has a single
	space between the # and the text. To create a new paragraph, just
	put a # with no text on the line.

	3. A verbatim line. This is done with two spaces between the # and the text.

	For example:

	# - This is a cool module
	# This module does really cool stuff.
	# It can do even more than you think.
	#
	# It even needs to paragraphs to tell you about it.
	# And it defines the following variables:
	# VAR_COOL - this is greate isn't it?
	# VAR_REALLY_COOL - cool right?
	#

	To have a .cmake file in this directory NOT show up in the
	modules documentation, you should start the file with a blank
	line.

	A FindXXX.cmake module will typically be loaded by the command

	FIND_PACKAGE(XXX [QUIET] [REQUIRED [components...]])

	If the QUIET option is given to the command it will set the variable
	XXX_FIND_QUIETLY to true before loading the FindXXX.cmake module. If
	this variable is set the module should not complain about not being
	able to find the package and should never issue a FATAL_ERROR. If the
	REQUIRED option is given to the command it will set the variable
	XXX_FIND_REQUIRED to true before loading the FindXXX.cmake module. If
	this variable is set the module should issue a FATAL_ERROR if the
	package cannot be found. For each package-specific component, say
	YYY, listed after the REQUIRED option a variable XXX_FIND_REQUIRED_YYY
	to true. This can be used by the FindXXX.cmake module to determine
	which sub-components of the package must be found. If neither the
	QUIET nor REQUIRED options are given then the FindXXX.cmake module
	should look for the package and complain without error if the module
	is not found.