diff --git a/Mk/Uses/cabal.mk b/Mk/Uses/cabal.mk
index d0bae62f0b76..bc576b73d091 100644
--- a/Mk/Uses/cabal.mk
+++ b/Mk/Uses/cabal.mk
@@ -1,227 +1,267 @@
 # Provide support for building Haskell packages using Cabal.
 #
 # Feature:	cabal
 # Usage:	USES=cabal or USES=cabal:ARGS
 # Valid ARGS:	hpack, nodefault
 #
 # hpack:	The port doesn't have a .cabal file and needs devel/hs-hpack to
 #		generate it from package.yaml file
 # nodefault:	Do not fetch the default distribution file from Hackage. If
 #		USE_GITHUB or USE_GITLAB is specified in the port, this argument
 #		is implied.
 #
 # Variables, which can be set by the port:
 #
 #  USE_CABAL		List of Haskell packages required to build a port.
 #			Should be listed along with version, like profunctors-5.3
 #			Package revision can be specified too with
 #			usual "_" syntax: invariant-0.5.1_1
 #			When creating a new port, the initial list can be built
 #			using make-use-cabal auxiliary target.
 #
 #  CABAL_FLAGS		List of Cabal flags to be passed verbatim into --flags
 #			argument of cabal-install utility. Used for both
 #			cabal configure and cabal build.
 #
 #  EXECUTABLES		List of executable Cabal targets to be built and installed.
 #					default: ${PORTNAME}
 #
 #  opt_USE_CABAL	Variant of USE_CABAL to be used with options framework.
 #  opt_CABAL_FLAGS	Variant of CABAL_FLAGS to be used with options framework.
 #			Note that it works a bit differently from CABAL_FLAGS:
 #			it appends "${opt_CABAL_FLAGS}" when the option is enabled
 #			and "-${opt_CABAL_FLAGS}" otherwise.
 #  opt_EXECUTABLES	Variant of EXECUTABLES to be used with options framework.
 #
 #  FOO_DATADIR_VARS     Additional environment vars to add to FOO executable's
 #                       wrapper script.
 #
+#  CABAL_PROJECT	Sets how to treat existing cabal.project file. Possible
+#			values are "remove" and "append".
+#
 # MAINTAINER: haskell@FreeBSD.org
 
 .if !defined(_INCLUDE_USES_CABAL_MK)
 _INCLUDE_USES_CABAL_MK=    yes
 
-_valid_ARGS=	hpack nodefault
+_valid_ARGS=			hpack nodefault
+_cabal_project_valid_VALUES=	append remove
 
 .  for arg in ${cabal_ARGS}
 .    if !${_valid_ARGS:M${arg}}
 IGNORE=		USES=cabal: invalid arguments: ${arg}
 .    endif
 .  endfor
 
+.  if defined(CABAL_PROJECT) && !${_cabal_project_valid_VALUES:M${CABAL_PROJECT}}
+IGNORE=		CABAL_PROJECT: invalid value: ${CABAL_PROJECT}
+.  endif
+
 PKGNAMEPREFIX?=	hs-
 
 EXECUTABLES?=	${PORTNAME}
 
 CABAL_HOME=	${WRKDIR}/cabal-home
 CABAL_LIBEXEC=	libexec/cabal
 CABAL_EXTRACT_SUFX=	.tar.gz
 CABAL_ARCH=	${ARCH:S/amd64/x86_64/:C/armv.*/arm/:S/powerpc64/ppc64/}
+CABAL_DEPSDIR=	${WRKSRC}/${CABAL_DEPS_SUBDIR}
+CABAL_DEPS_SUBDIR=	_cabal_deps
 
 .  if !defined(CABAL_BOOTSTRAP)
 BUILD_DEPENDS+=	cabal:devel/hs-cabal-install \
 		ghc:lang/ghc
 .  endif
 
 .  if ${cabal_ARGS:Mhpack}
 EXTRACT_DEPENDS+=	hpack:devel/hs-hpack
 .  endif
 
 # Inherited via lang/ghc we need to depend on iconv and libgmp.so (stage q/a)
 iconv_ARGS=	translit
 .include "${USESDIR}/iconv.mk"
 LIB_DEPENDS+=	libgmp.so:math/gmp \
 		libffi.so:devel/libffi
 
 DIST_SUBDIR?=	cabal
 
 .  if !defined(USE_GITHUB) && !defined(USE_GITLAB) && !${cabal_ARGS:Mnodefault}
 _hackage_is_default=	yes
 .  else
 _hackage_is_default=	no
 .  endif
 
 .  if ${_hackage_is_default} == yes
 MASTER_SITES=	https://hackage.haskell.org/package/${PORTNAME}-${PORTVERSION}/ \
 		http://hackage.haskell.org/package/${PORTNAME}-${PORTVERSION}/
 DISTFILES+=	${PORTNAME}-${PORTVERSION}${CABAL_EXTRACT_SUFX}
 EXTRACT_ONLY+=	${PORTNAME}-${PORTVERSION}${CABAL_EXTRACT_SUFX}
 .  else
 .    if defined(USE_GITHUB) && !defined(DISTFILES) && !${USE_GITHUB:Mnodefault}
 EXTRACT_ONLY+=	${DISTNAME_DEFAULT}${_GITHUB_EXTRACT_SUFX}
 .    endif
 .    if defined(USE_GITLAB) && !defined(DISTFILES) && !${USE_GITLAB:Mnodefault}
 EXTRACT_ONLY+=	${DISTNAME}${_GITLAB_EXTRACT_SUFX}
 .    endif
 .  endif
 
 _USES_extract=	701:cabal-post-extract
 _USES_patch=	701:cabal-post-patch
+_USES_configure=301:cabal-pre-configure
 _USES_stage=	751:cabal-post-install-script
 
 BUILD_TARGET?=	${EXECUTABLES:S/^/exe:&/}
 
 .  if defined(USE_LOCALE)
 LOCALE_ENV=	LANG=${USE_LOCALE} LC_ALL=${USE_LOCALE}
 .  endif
 
 _use_cabal=	${USE_CABAL:O:u}
 
 .  for package in ${_use_cabal}
 _PKG_GROUP=		${package:C/[\.-]//g}
 _PKG_WITHOUT_REV=	${package:C/_[0-9]+//}
 _REV=			${package:C/[^_]*//:S/_//}
 
 MASTER_SITES+=	https://hackage.haskell.org/package/:${package:C/[\.-]//g} \
 		http://hackage.haskell.org/package/:${package:C/[\.-]//g}
 DISTFILES+=	${package:C/_[0-9]+//}/${package:C/_[0-9]+//}${CABAL_EXTRACT_SUFX}:${package:C/[\.-]//g}
 
 .    if !defined(CABAL_BOOTSTRAP)
 EXTRACT_ONLY+=	${package:C/_[0-9]+//}/${package:C/_[0-9]+//}${CABAL_EXTRACT_SUFX}
 .    endif
 
 .    if ${package:C/[^_]*//:S/_//} != ""
 DISTFILES+=	${package:C/_[0-9]+//}/revision/${package:C/[^_]*//:S/_//}.cabal:${package:C/[\.-]//g}
 .    endif
 
 .  endfor
 
 
+# Auxiliary targets used during port creation/updating.
+
 # Fetches and unpacks package source from Hackage using only PORTNAME and PORTVERSION.
 cabal-extract: ${WRKDIR}
 	${RM} -rf ${CABAL_HOME}/.cabal
 	${SETENV} HOME=${CABAL_HOME} cabal new-update
 .  if ${_hackage_is_default} == yes
 	cd ${WRKDIR} && \
 		${SETENV} ${LOCALE_ENV} HOME=${CABAL_HOME} cabal get ${PORTNAME}-${PORTVERSION}
 .  else
 	${MV} ${CABAL_HOME} /tmp/${PORTNAME}-cabal-home
 	cd ${.CURDIR} && ${MAKE} extract CABAL_BOOTSTRAP=yes
 	${RM} -rf ${CABAL_HOME}
 	${MV} /tmp/${PORTNAME}-cabal-home ${CABAL_HOME}
 .  endif
 
 # Fetches and unpacks dependencies sources for a cabal-extract'ed package.
 # Builds them as side-effect.
 cabal-extract-deps:
 .  if ${cabal_ARGS:Mhpack}
 	cd ${WRKSRC} && ${SETENV} HOME=${CABAL_HOME} hpack
 .  endif
 	cd ${WRKSRC} && \
 		${SETENV} ${LOCALE_ENV} HOME=${CABAL_HOME} cabal new-configure --disable-benchmarks --disable-tests --flags="${CABAL_FLAGS}" ${CONFIGURE_ARGS}
 	cd ${WRKSRC} && \
 		${SETENV} ${LOCALE_ENV} HOME=${CABAL_HOME} cabal new-build --disable-benchmarks --disable-tests --dependencies-only ${BUILD_ARGS}
 
 # Generates USE_CABAL= ... line ready to be pasted into the port based on artifacts of cabal-extract-deps.
 make-use-cabal:
 	@echo ====================
 	@echo -n USE_CABAL=
 	@find ${CABAL_HOME} -name '*.conf' -exec basename {} + | sed -E 's|-[0-9a-z]{64}\.conf||' | sort | sed 's/$$/ \\/'
 	@find ${CABAL_HOME} -name 'hsc2hs*.tar.gz' -exec basename {} + | sed -E 's|\.tar\.gz||' | sed 's/$$/ \\/'
 	@find ${CABAL_HOME} -name 'alex*.tar.gz' -exec basename {} + | sed -E 's|\.tar\.gz||' | sed 's/$$/ \\/'
 	@find ${CABAL_HOME} -name 'happy*.tar.gz' -exec basename {} + | sed -E 's|\.tar\.gz||' | sed 's/$$/ \\/'
 
 # Re-generates USE_CABAL items to have revision numbers.
 make-use-cabal-revs:
 .  for package in ${_use_cabal}
 	@(${SETENV} HTTP_ACCEPT="application/json" fetch -q -o - http://hackage.haskell.org/package/${package:C/_[0-9]+//}/revisions/ | sed -Ee 's/.*":([0-9]+)}\]/${package:C/_[0-9]+//}_\1 /' -e 's/_0//')
 	@echo '\'
 .  endfor
 
 .  if !defined(CABAL_BOOTSTRAP)
 
+# Main targets implementation.
+
 cabal-post-extract:
-	@/bin/test ! -f ${WRKSRC}/cabal.project || (echo "cabal.project file already present in WRKSRC!" && false)
-	echo -n "packages: . " > ${WRKSRC}/cabal.project
+# Remove the project file as requested
+.    if "${CABAL_PROJECT}" == "remove"
+	${RM} ${WRKSRC}/cabal.project
+.    endif
+# Save the original project file so that users can patch them
+.    if "${CABAL_PROJECT}" == "append"
+	${MV} ${WRKSRC}/cabal.project ${WRKSRC}/cabal.project.${PORTNAME}
+.    endif
+
+	@/bin/test ! -f ${WRKSRC}/cabal.project || (echo "cabal.project file is already present in WRKSRC! Set CABAL_PROJECT variable." && false)
+
+# Move extracted dependencies into ${CABAL_DEPSDIR} directory
+	${MKDIR} ${CABAL_DEPSDIR}
 .    for package in ${_use_cabal}
-	echo -n "${package:C/_[0-9]+//} " >> ${WRKSRC}/cabal.project
+# Copy revised .cabal file if present
 .      if ${package:C/[^_]*//:S/_//} != ""
 		cp ${DISTDIR}/${DIST_SUBDIR}/${package:C/_[0-9]+//}/revision/${package:C/[^_]*//:S/_//}.cabal `find ${WRKDIR}/${package:C/_[0-9]+//} -name '*.cabal' -depth 1`
 .      endif
+# Move the dependency source itself
 	cd ${WRKDIR} && \
-		mv ${package:C/_[0-9]+//} ${WRKSRC}/
+		mv ${package:C/_[0-9]+//} ${CABAL_DEPSDIR}/
 .    endfor
-	mkdir -p ${CABAL_HOME}/.cabal
-	echo "jobs: ${MAKE_JOBS_NUMBER}" > ${CABAL_HOME}/.cabal/config
+# Create the cabal-install config
+	${MKDIR} ${CABAL_HOME}/.cabal
+	${ECHO_CMD} "jobs: ${MAKE_JOBS_NUMBER}" > ${CABAL_HOME}/.cabal/config
 
 cabal-post-patch:
+# Create our own cabal.project
+	${ECHO_CMD} "packages: ." > ${WRKSRC}/cabal.project
+.    for package in ${_use_cabal}
+	${ECHO_CMD} "        ${CABAL_DEPS_SUBDIR}/${package:C/_[0-9]+//}" >> ${WRKSRC}/cabal.project
+.    endfor
+# Append the (possibly patched) original cabal.project, if requested
+.    if "${CABAL_PROJECT}" == "append"
+	${CAT} ${WRKSRC}/cabal.project.${PORTNAME} >> ${WRKSRC}/cabal.project
+.    endif
+
+cabal-pre-configure:
+# Generate .cabal file with hpack if requested
 .    if ${cabal_ARGS:Mhpack}
 	cd ${WRKSRC} && ${SETENV} HOME=${CABAL_HOME} hpack
 .    endif
 
 .    if !target(do-build)
 do-build:
 	cd ${WRKSRC} && \
 		${SETENV} ${MAKE_ENV} HOME=${CABAL_HOME} cabal new-build --offline --disable-benchmarks --disable-tests --flags "${CABAL_FLAGS}" ${BUILD_ARGS} ${BUILD_TARGET}
 .    endif
 
 .    if !target(do-install)
 do-install:
 	${MKDIR} ${STAGEDIR}${PREFIX}/${CABAL_LIBEXEC}
 .      for exe in ${EXECUTABLES}
 	${INSTALL_PROGRAM} \
 		$$(find ${WRKSRC}/dist-newstyle -name ${exe} -type f -perm +111) \
 		${STAGEDIR}${PREFIX}/${CABAL_LIBEXEC}/${exe}
 	${ECHO_CMD} '#!/bin/sh' > ${STAGEDIR}${PREFIX}/bin/${exe}
 	${ECHO_CMD} '' >> ${STAGEDIR}${PREFIX}/bin/${exe}
 	${ECHO_CMD} 'export ${exe:S/-/_/}_datadir=${DATADIR}' >> ${STAGEDIR}${PREFIX}/bin/${exe}
 .         for dep in ${${exe}_DATADIR_VARS}
 	${ECHO_CMD} 'export ${dep:S/-/_/}_datadir=${DATADIR}' >> ${STAGEDIR}${PREFIX}/bin/${exe}
 .         endfor
 	${ECHO_CMD} '' >> ${STAGEDIR}${PREFIX}/bin/${exe}
 	${ECHO_CMD} 'exec ${PREFIX}/${CABAL_LIBEXEC}/${exe} "$$@"' >> ${STAGEDIR}${PREFIX}/bin/${exe}
 	${CHMOD} +x ${STAGEDIR}${PREFIX}/bin/${exe}
 .      endfor
 .    endif
 
 .    if !defined(SKIP_CABAL_PLIST)
 cabal-post-install-script:
 .      for exe in ${EXECUTABLES}
 		${ECHO_CMD} 'bin/${exe}' >> ${TMPPLIST}
 		${ECHO_CMD} '${CABAL_LIBEXEC}/${exe}' >> ${TMPPLIST}
 .      endfor
 .    endif
 
 .  endif # !defined(CABAL_BOOTSTRAP)
 
 .endif