Index: Mk/Uses/compiler.mk
===================================================================
--- Mk/Uses/compiler.mk
+++ Mk/Uses/compiler.mk
@@ -8,6 +8,8 @@
 # c++11-lang:	The port needs a compiler understanding C++11
 # c++14-lang:	The port needs a compiler understanding C++14
 # c++17-lang:	The port needs a compiler understanding C++17
+# c++20-lang:	The port needs a compiler understanding C++20
+# c++2b-lang:	The port needs a compiler understanding C++2b
 # gcc-c++11-lib:The port needs g++ compiler with a C++11 library
 # c++11-lib:	The port needs a compiler understanding C++11 and with a C++11 ready standard library
 # c11:		The port needs a compiler understanding C11
@@ -50,6 +52,10 @@
 _COMPILER_ARGS+=	features c++14-lang
 .  elif ${compiler_ARGS} == c++17-lang
 _COMPILER_ARGS+=	features c++17-lang
+.  elif ${compiler_ARGS} == c++20-lang
+_COMPILER_ARGS+=	features c++20-lang
+.  elif ${compiler_ARGS} == c++2b-lang
+_COMPILER_ARGS+=	features c++2b-lang
 .  elif ${compiler_ARGS} == c11
 _COMPILER_ARGS+=	features c11
 .  elif ${compiler_ARGS} == features
@@ -129,7 +135,8 @@
 .    endif
 
 CSTD=	c89 c99 c11 gnu89 gnu99 gnu11
-CXXSTD=	c++98 c++0x c++11 c++14 c++17 gnu++98 gnu++11 gnu++14 gnu++17
+CXXSTD=	c++98 c++0x c++11 c++14 c++17 c++20 c++2b \
+	gnu++98 gnu++11 gnu++14 gnu++17 gnu++20 gnu++2b
 
 .    for std in ${CSTD} ${CXXSTD}
 _LANG=c
@@ -159,25 +166,41 @@
 .    endif
 .  endif
 
-.  if (${_COMPILER_ARGS:Mc++17-lang} && !${COMPILER_FEATURES:Mc++17}) || \
+.  if (${_COMPILER_ARGS:Mc++2b-lang} && !${COMPILER_FEATURES:Mc++2b}) || \
+(${_COMPILER_ARGS:Mc++20-lang} && !${COMPILER_FEATURES:Mc++20}) || \
+(${_COMPILER_ARGS:Mc++17-lang} && !${COMPILER_FEATURES:Mc++17}) || \
 (${_COMPILER_ARGS:Mc++14-lang} && !${COMPILER_FEATURES:Mc++14}) || \
 (${_COMPILER_ARGS:Mc++11-lang} && !${COMPILER_FEATURES:Mc++11}) || \
 (${_COMPILER_ARGS:Mc++0x} && !${COMPILER_FEATURES:Mc++0x}) || \
 (${_COMPILER_ARGS:Mc11} && !${COMPILER_FEATURES:Mc11})
+.    if ${_COMPILER_ARGS:Mc++20-lang}
+_LLVM_MINVER=	11
+.    elif ${_COMPILER_ARGS:Mc++2b-lang}
+_LLVM_MINVER=	14
+.    else
+_LLVM_MINVER=	0
+.    endif
 .    if (defined(FAVORITE_COMPILER) && ${FAVORITE_COMPILER} == gcc) || (${ARCH} != amd64 && ${ARCH} != i386) # clang not always supported on Tier-2
 USE_GCC=	yes
 CHOSEN_COMPILER_TYPE=	gcc
-.    elif ${COMPILER_TYPE} == gcc
-.      if ${ALT_COMPILER_TYPE} == clang
+.    elif ${COMPILER_TYPE} == gcc || \
+	(${COMPILER_VERSION:C/[0-9]$//}<${_LLVM_MINVER})
+.      if ${ALT_COMPILER_TYPE} == clang && \
+	(${ALT_COMPILER_VERSION:C/[0-9]$//}>=${_LLVM_MINVER})
 CPP=	clang-cpp
 CC=	clang
 CXX=	clang++
 CHOSEN_COMPILER_TYPE=	clang
 .      else
-BUILD_DEPENDS+=	${LOCALBASE}/bin/clang10:devel/llvm10
-CPP=	${LOCALBASE}/bin/clang-cpp10
-CC=	${LOCALBASE}/bin/clang10
-CXX=	${LOCALBASE}/bin/clang++10
+.        if ${LLVM_DEFAULT:C/^[789]0$/0/}<${_LLVM_MINVER}
+_LLVM_REQ=	${_LLVM_MINVER}
+.        else
+_LLVM_REQ=	${LLVM_DEFAULT}
+.        endif
+BUILD_DEPENDS+=	clang${_LLVM_REQ}:devel/llvm${_LLVM_REQ}
+CPP=	${LOCALBASE}/bin/clang-cpp${_LLVM_REQ}
+CC=	${LOCALBASE}/bin/clang${_LLVM_REQ}
+CXX=	${LOCALBASE}/bin/clang++${_LLVM_REQ}
 CHOSEN_COMPILER_TYPE=	clang
 .      endif
 .    endif