framework: Add new USES=llvm to more easily depend on one an llvm port

USES=llvm supports two kinds of arguments:

* mode
	<none>:		defaults to build
	build:		add a BUILD_DEPENDS on chosen llvm-port
	run:		add a RUN_DEPENDS on chosen llvm-port
	lib:		add a LIB_DEPENDS on chosen llvm-port

* version
	<none>:		defaults to ${LLVM_DEFAULT}
	number:		use explicitly the specified version
	min=number:	use specified min if ${LLVM_DEFAULT} is lower
	max=number:	use specified max if ${LLVM_DEFAULT} is higher

An example usage might be:
	USES=	llvm
  or
	USES=	llvm:13,build
  or
	USES=	llvm:min=14,lib

The following variables are exposed to be used in the ports tree at the moment:
	* LLVM_VERSION  version chosen from the arguments to llvm.mk
	* LLVM_PORT     chosen llvm port
	* LLVM_CONFIG   llvm-config of the chosen port
	* LLVM_LIBLLVM  libLLVM.so of the chosen port
	* LLVM_PREFIX   installation prefix of the chosen port

Reviewed by:		manu, bapt
Differential Revision:	https://reviews.freebsd.org/D37728

2 files changed, 131 insertions, 0 deletions

diff --git a/CHANGES b/CHANGES
index 2cbcf2bd6a31..35c4205aee0b 100644
--- a/CHANGES
+++ b/CHANGES
@@ -10,6 +10,39 @@ in the release notes and/or placed into UPDATING.
 
 All ports committers are allowed to commit to this file.
 
+20221217:
+AUTHOR: tcberner@FreeBSD.org
+
+  USES=llvm has been added to more easily depend on llvm.
+
+  USES=llvm supports two kinds of arguments:
+
+  * mode
+	<none>:	defaults to build
+	build:	add a BUILD_DEPENDS on chosen llvm-port
+	run:	add a RUN_DEPENDS on chosen llvm-port
+	lib:	add a LIB_DEPENDS on chosen llvm-port
+
+  * version
+	<none>:		defaults to ${LLVM_DEFAULT}
+	number:		use explicitly the specified version
+	min=number:	use specified min if ${LLVM_DEFAULT} is lower
+	max=number:	use specified max if ${LLVM_DEFAULT} is higher
+
+  An example usage might be:
+	USES=	llvm
+  or
+	USES=	llvm:13,build
+  or
+	USES=	llvm:min=14,lib
+
+  The following variables are exposed to be used in the ports tree at the moment:
+	* LLVM_VERSION	version chosen from the arguments to llvm.mk
+	* LLVM_PORT	chosen llvm port
+	* LLVM_CONFIG	llvm-config of the chosen port
+	* LLVM_LIBLLVM	libLLVM.so of the chosen port
+	* LLVM_PREFIX	installation prefix of the chosen port
+
 20221026:
 AUTHOR: bapt@FreeBSD.org
   3 new features are available now: PIE, RELRO, BIND_NOW, each port can
diff --git a/Mk/Uses/llvm.mk b/Mk/Uses/llvm.mk
new file mode 100644
index 000000000000..459fd8736cb6
--- /dev/null
+++ b/Mk/Uses/llvm.mk
@@ -0,0 +1,98 @@
+# Provides support to depend on LLVM
+#
+# It chooses the llvm port to be used based on the following constraint:
+#	1) no constraints given						=> ${LLVM_DEFAULT}
+#	2) exact constraint given					=> ${exact}
+#	2) max constraint given && ${max} < ${LLVM_DEFAULT}		=> ${max}
+#	3) min constraint given && ${LLVM_DEFAULT} < ${LLVM_DEFAULT}	=> ${LLVM_DEFAULT}
+
+# Usage:
+# 	USES=	llvm			- default version chosen
+# 	USES=	llvm:15			- exact constraint
+# 	USES=	llvm:min=9		- min constraint: max(min,default)
+# 	USES=	llvm:max=10		- max constraint: min(max,default)
+# 	USES=	llvm:min=10,max=11	- all constraint: max(min(max,default),default)
+
+.if !defined(_INCLUDE_USES_LLVM_MK)
+_INCLUDE_USES_LLVM_MK=	YES
+
+_LLVM_MK_VALID_VERSIONS=	7 8 9 10 11 12 13 14 15
+_LLVM_MK_VALID_CONSTRAINTS=	min max
+_LLVM_MK_VALID_MODES=		build run lib
+
+# === parse mode arguments ===
+_LLVM_MK_MODES=	# empty
+.  for _mode in ${_LLVM_MK_VALID_MODES}
+.    if ${llvm_ARGS:M${_mode}}
+_LLVM_MK_MODES+=	${_mode}
+.    endif
+.  endfor
+.  if empty(_LLVM_MK_MODES)
+_LLVM_MK_MODES=	build
+.  endif
+
+# === parse version arguments ===
+_LLVM_MK_VERSION=	# empty
+.  for _ver in ${_LLVM_MK_VALID_VERSIONS}
+.    if ${llvm_ARGS:M${_ver}}
+.      if !empty(_LLVM_MK_VERSION)
+BROKEN=		USES=llvm:${llvm_ARGS} contains multiple version definitions
+.      else
+_LLVM_MK_VERSION=	${_ver}
+.      endif
+.    endif
+.  endfor
+.  if empty(_LLVM_MK_VERSION)
+_LLVM_MK_VERSION=	${LLVM_DEFAULT}
+.  endif
+
+# === handle constraints ===
+.  for _constraint in ${_LLVM_MK_VALID_CONSTRAINTS}
+_version=	${llvm_ARGS:M${_constraint}=[0-9]*:S/${_constraint}=//}
+.    if !empty(_version)
+_LLVM_MK_CONSTRAINT_${_constraint}=	${_version}
+.    endif
+.  endfor
+
+.  if !empty(_LLVM_MK_CONSTRAINT_min)
+.    if ${_LLVM_MK_CONSTRAINT_min} > ${_LLVM_MK_VERSION}
+_LLVM_MK_VERSION=	${_LLVM_MK_CONSTRAINT_min}
+.    endif
+.  endif
+
+.  if !empty(_LLVM_MK_CONSTRAINT_max)
+.    if ${_LLVM_MK_CONSTRAINT_max} < ${_LLVM_MK_VERSION}
+_LLVM_MK_VERSION=	${_LLVM_MK_CONSTRAINT_max}
+.    endif
+.  endif
+
+# === define helpers for the dependencies ===
+.  for _ver in ${_LLVM_MK_VALID_VERSIONS:N1[0-9]}
+_LLVM_MK_SUFFIX_${_ver}=	${_ver}0
+.  endfor
+
+.  for _ver in ${_LLVM_MK_VALID_VERSIONS}
+_LLVM_MK_SUFFIX_${_ver}?=	${_ver}
+.  endfor
+
+# === define variables to depend on and export ===
+_LLVM_MK_PORT=		devel/llvm${_LLVM_MK_SUFFIX_${_LLVM_MK_VERSION}}
+_LLVM_MK_LIBLLVM=	libLLVM-${_LLVM_MK_VERSION}.so
+_LLVM_MK_PATH=		llvm-config${_LLVM_MK_SUFFIX_${_LLVM_MK_VERSION}}
+_LLVM_MK_PREFIX=	${PREFIX}/llvm${_LLVM_MK_SUFFIX_${_LLVM_MK_VERSION}}
+
+# == add actual dependencies ===
+_LLVM_MK_PATH_lib=	${_LLVM_MK_LIBLLVM}
+.  for _mode in ${_LLVM_MK_MODES}
+_LLVM_MK_PATH_${_mode}?=	${_LLVM_MK_PATH}
+${_mode:tu}_DEPENDS+=	${_LLVM_MK_PATH_${_mode}}:${_LLVM_MK_PORT}
+.  endfor
+
+# == export config ===
+LLVM_PORT=		${_LLVM_MK_PORT}
+LLVM_CONFIG=		${_LLVM_MK_PATH}
+LLVM_LIBLLVM=		${_LLVM_MK_LIBLLVM}
+LLVM_VERSION=		${_LLVM_MK_VERSION}
+LLVM_PREFIX=		${_LLVM_MK_PREFIX}
+
+.endif