gentoo-x86/eclass/haskell-cabal.eclass

# Copyright 1999-2015 Gentoo Foundation
# Distributed under the terms of the GNU General Public License v2
# $Header: /var/cvsroot/gentoo-x86/eclass/haskell-cabal.eclass,v 1.46 2014/06/27 07:26:18 slyfox Exp $

# @ECLASS: haskell-cabal.eclass
# @MAINTAINER:
# Haskell herd <haskell@gentoo.org>
# @AUTHOR:
# Original author: Andres Loeh <kosmikus@gentoo.org>
# Original author: Duncan Coutts <dcoutts@gentoo.org>
# @BLURB: for packages that make use of the Haskell Common Architecture for Building Applications and Libraries (cabal)
# @DESCRIPTION:
# Basic instructions:
#
# Before inheriting the eclass, set CABAL_FEATURES to
# reflect the tools and features that the package makes
# use of.
#
# Currently supported features:
#   haddock    --  for documentation generation
#   hscolour   --  generation of colourised sources
#   hoogle     --  generation of documentation search index
#   alex       --  lexer/scanner generator
#   happy      --  parser generator
#   c2hs       --  C interface generator
#   cpphs      --  C preprocessor clone written in Haskell
#   profile    --  if package supports to build profiling-enabled libraries
#   bootstrap  --  only used for the cabal package itself
#   bin        --  the package installs binaries
#   lib        --  the package installs libraries
#   nocabaldep --  don't add dependency on cabal.
#                  only used for packages that _must_ not pull the dependency
#                  on cabal, but still use this eclass (e.g. haskell-updater).
#   ghcdeps    --  constraint dependency on package to ghc onces
#                  only used for packages that use libghc internally and _must_
#                  not pull upper versions
#   test-suite --  add support for cabal test-suites (introduced in Cabal-1.8)

inherit eutils ghc-package multilib multiprocessing

# @ECLASS-VARIABLE: CABAL_EXTRA_CONFIGURE_FLAGS
# @DESCRIPTION:
# User-specified additional parameters passed to 'setup configure'.
# example: /etc/portage/make.conf: CABAL_EXTRA_CONFIGURE_FLAGS=--enable-shared
: ${CABAL_EXTRA_CONFIGURE_FLAGS:=}

# @ECLASS-VARIABLE: CABAL_EXTRA_BUILD_FLAGS
# @DESCRIPTION:
# User-specified additional parameters passed to 'setup build'.
# example: /etc/portage/make.conf: CABAL_EXTRA_BUILD_FLAGS=-v
: ${CABAL_EXTRA_BUILD_FLAGS:=}

# @ECLASS-VARIABLE: GHC_BOOTSTRAP_FLAGS
# @DESCRIPTION:
# User-specified additional parameters for ghc when building
# _only_ 'setup' binary bootstrap.
# example: /etc/portage/make.conf: GHC_BOOTSTRAP_FLAGS=-dynamic to make
# linking 'setup' faster.
: ${GHC_BOOTSTRAP_FLAGS:=}

# @ECLASS-VARIABLE: CABAL_DEBUG_LOOSENING
# @DESCRIPTION:
# Show debug output for 'cabal_chdeps' function if set.
# Needs working 'diff'.
: ${CABAL_DEBUG_LOOSENING:=}

HASKELL_CABAL_EXPF="pkg_setup src_compile src_test src_install pkg_postinst pkg_postrm"

# 'dev-haskell/cabal' passes those options with ./configure-based
# configuration, but most packages don't need/don't accept it:
# #515362, #515362
QA_CONFIGURE_OPTIONS+=" --with-compiler --with-hc --with-hc-pkg --with-gcc"

case "${EAPI:-0}" in
        2|3|4|5) HASKELL_CABAL_EXPF+=" src_configure" ;;
        *) ;;
esac

EXPORT_FUNCTIONS ${HASKELL_CABAL_EXPF}

for feature in ${CABAL_FEATURES}; do
        case ${feature} in
                haddock)    CABAL_USE_HADDOCK=yes;;
                hscolour)   CABAL_USE_HSCOLOUR=yes;;
                hoogle)     CABAL_USE_HOOGLE=yes;;
                alex)       CABAL_USE_ALEX=yes;;
                happy)      CABAL_USE_HAPPY=yes;;
                c2hs)       CABAL_USE_C2HS=yes;;
                cpphs)      CABAL_USE_CPPHS=yes;;
                profile)    CABAL_USE_PROFILE=yes;;
                bootstrap)  CABAL_BOOTSTRAP=yes;;
                bin)        CABAL_HAS_BINARIES=yes;;
                lib)        CABAL_HAS_LIBRARIES=yes;;
                nocabaldep) CABAL_FROM_GHC=yes;;
                ghcdeps)    CABAL_GHC_CONSTRAINT=yes;;
                test-suite) CABAL_TEST_SUITE=yes;;
                *) CABAL_UNKNOWN="${CABAL_UNKNOWN} ${feature}";;
        esac
done

if [[ -n "${CABAL_USE_HADDOCK}" ]]; then
        IUSE="${IUSE} doc"
        # don't require depend on itself to build docs.
        # ebuild bootstraps docs from just built binary
        [[ ${CATEGORY}/${PN} = "dev-haskell/haddock" ]] || DEPEND="${DEPEND} doc? ( dev-haskell/haddock )"
fi

if [[ -n "${CABAL_USE_HSCOLOUR}" ]]; then
        IUSE="${IUSE} hscolour"
        DEPEND="${DEPEND} hscolour? ( dev-haskell/hscolour )"
fi

if [[ -n "${CABAL_USE_HOOGLE}" ]]; then
        # enabled only in ::gentoo-haskell
        :
fi

if [[ -n "${CABAL_USE_ALEX}" ]]; then
        DEPEND="${DEPEND} dev-haskell/alex"
fi

if [[ -n "${CABAL_USE_HAPPY}" ]]; then
        DEPEND="${DEPEND} dev-haskell/happy"
fi

if [[ -n "${CABAL_USE_C2HS}" ]]; then
        DEPEND="${DEPEND} dev-haskell/c2hs"
fi

if [[ -n "${CABAL_USE_CPPHS}" ]]; then
        DEPEND="${DEPEND} dev-haskell/cpphs"
fi

if [[ -n "${CABAL_USE_PROFILE}" ]]; then
        IUSE="${IUSE} profile"
fi

if [[ -n "${CABAL_TEST_SUITE}" ]]; then
        IUSE="${IUSE} test"
fi

# We always use a standalone version of Cabal, rather than the one that comes
# with GHC. But of course we can't depend on cabal when building cabal itself.
if [[ -z ${CABAL_MIN_VERSION} ]]; then
        CABAL_MIN_VERSION=1.1.4
fi
if [[ -z "${CABAL_BOOTSTRAP}" && -z "${CABAL_FROM_GHC}" ]]; then
        DEPEND="${DEPEND} >=dev-haskell/cabal-${CABAL_MIN_VERSION}"
fi

# returns the version of cabal currently in use
_CABAL_VERSION_CACHE=""
cabal-version() {
        if [[ -z "${_CABAL_VERSION_CACHE}" ]]; then
                if [[ "${CABAL_BOOTSTRAP}" ]]; then
                        # We're bootstrapping cabal, so the cabal version is the version
                        # of this package itself.
                        _CABAL_VERSION_CACHE="${PV}"
                elif [[ "${CABAL_FROM_GHC}" ]]; then
                        _CABAL_VERSION_CACHE="$(ghc-cabal-version)"
                else
                        # We ask portage, not ghc, so that we only pick up
                        # portage-installed cabal versions.
                        _CABAL_VERSION_CACHE="$(ghc-extractportageversion dev-haskell/cabal)"
                fi
        fi
        echo "${_CABAL_VERSION_CACHE}"
}

cabal-bootstrap() {
        local setupmodule
        local cabalpackage
        if [[ -f "${S}/Setup.lhs" ]]; then
                setupmodule="${S}/Setup.lhs"
        elif [[ -f "${S}/Setup.hs" ]]; then
                setupmodule="${S}/Setup.hs"
        else
                die "No Setup.lhs or Setup.hs found"
        fi

        if [[ -z "${CABAL_BOOTSTRAP}" && -z "${CABAL_FROM_GHC}" ]] && ! ghc-sanecabal "${CABAL_MIN_VERSION}"; then
                eerror "The package dev-haskell/cabal is not correctly installed for"
                eerror "the currently active version of ghc ($(ghc-version)). Please"
                eerror "run haskell-updater or re-build dev-haskell/cabal."
                die "cabal is not correctly installed"
        fi

        # We build the setup program using the latest version of
        # cabal that we have installed
        cabalpackage=Cabal-$(cabal-version)
        einfo "Using cabal-$(cabal-version)."

        make_setup() {
                set -- -package "${cabalpackage}" --make "${setupmodule}" \
                        ${HCFLAGS} \
                        ${GHC_BOOTSTRAP_FLAGS} \
                        "$@" \
                        -o setup
                echo $(ghc-getghc) "$@"
                $(ghc-getghc) "$@"
        }
        if $(ghc-supports-shared-libraries); then
                # # some custom build systems might use external libraries,
                # # for which we don't have shared libs, so keep static fallback
                # bug #411789, http://hackage.haskell.org/trac/ghc/ticket/5743#comment:3
                # http://hackage.haskell.org/trac/ghc/ticket/7062
                # http://hackage.haskell.org/trac/ghc/ticket/3072
                # ghc does not set RPATH for extralibs, thus we do it ourselves by hands
                einfo "Prepending $(ghc-libdir) to LD_LIBRARY_PATH"
                if [[ ${CHOST} != *-darwin* ]]; then
                        LD_LIBRARY_PATH="$(ghc-libdir)${LD_LIBRARY_PATH:+:}${LD_LIBRARY_PATH}"
                        export LD_LIBRARY_PATH
                else
                        DYLD_LIBRARY_PATH="$(ghc-libdir)${DYLD_LIBRARY_PATH:+:}${DYLD_LIBRARY_PATH}"
                        export DYLD_LIBRARY_PATH
                fi
                { make_setup -dynamic "$@" && ./setup --help >/dev/null; } ||
                make_setup "$@" || die "compiling ${setupmodule} failed"
        else
                make_setup "$@" || die "compiling ${setupmodule} failed"
        fi
}

cabal-mksetup() {
        local setupdir=${1:-${S}}
        local setup_src=${setupdir}/Setup.hs

        rm -vf "${setupdir}"/Setup.{lhs,hs}
        elog "Creating 'Setup.hs' for 'Simple' build type."

        echo 'import Distribution.Simple; main = defaultMainWithHooks defaultUserHooks' \
                > "${setup_src}" || die "failed to create default Setup.hs"
}

cabal-hscolour() {
        set -- hscolour "$@"
        echo ./setup "$@"
        ./setup "$@" || die "setup hscolour failed"
}

cabal-haddock() {
        set -- haddock "$@"
        echo ./setup "$@"
        ./setup "$@" || die "setup haddock failed"
}

cabal-hoogle() {
        ewarn "hoogle USE flag requires doc USE flag, building without hoogle"
}

cabal-hscolour-haddock() {
        # --hyperlink-source implies calling 'setup hscolour'
        set -- haddock --hyperlink-source
        echo ./setup "$@"
        ./setup "$@" --hyperlink-source || die "setup haddock --hyperlink-source failed"
}

cabal-hoogle-haddock() {
        set -- haddock --hoogle
        echo ./setup "$@"
        ./setup "$@" || die "setup haddock --hoogle failed"
}

cabal-hoogle-hscolour-haddock() {
        cabal-hscolour-haddock
        cabal-hoogle-haddock
}

cabal-hoogle-hscolour() {
        ewarn "hoogle USE flag requires doc USE flag, building without hoogle"
        cabal-hscolour
}

cabal-die-if-nonempty() {
        local breakage_type=$1
        shift

        [[ "${#@}" == 0 ]] && return 0
        eerror "Detected ${breakage_type} packages: ${@}"
        die "//==-- Please, run 'haskell-updater' to fix ${breakage_type} packages --==//"
}

cabal-show-brokens() {
        elog "ghc-pkg check: 'checking for other broken packages:'"
        # pretty-printer
        $(ghc-getghcpkg) check 2>&1 \
                | egrep -v '^Warning: haddock-(html|interfaces): ' \
                | egrep -v '^Warning: include-dirs: ' \
                | head -n 20

        cabal-die-if-nonempty 'broken' \
                $($(ghc-getghcpkg) check --simple-output)
}

cabal-show-old() {
        cabal-die-if-nonempty 'outdated' \
                $("${EPREFIX}"/usr/sbin/haskell-updater --quiet --upgrade --list-only)
}

cabal-show-brokens-and-die() {
        cabal-show-brokens
        cabal-show-old

        die "$@"
}

cabal-configure() {
        local cabalconf=()
        has "${EAPI:-0}" 0 1 2 && ! use prefix && EPREFIX=

        if [[ -n "${CABAL_USE_HADDOCK}" ]] && use doc; then
                cabalconf+=(--with-haddock=${EPREFIX}/usr/bin/haddock)
        fi
        if [[ -n "${CABAL_USE_PROFILE}" ]] && use profile; then
                cabalconf+=(--enable-library-profiling)
        fi
        if [[ -n "${CABAL_USE_ALEX}" ]]; then
                cabalconf+=(--with-alex=${EPREFIX}/usr/bin/alex)
        fi

        if [[ -n "${CABAL_USE_HAPPY}" ]]; then
                cabalconf+=(--with-happy=${EPREFIX}/usr/bin/happy)
        fi

        if [[ -n "${CABAL_USE_C2HS}" ]]; then
                cabalconf+=(--with-c2hs=${EPREFIX}/usr/bin/c2hs)
        fi
        if [[ -n "${CABAL_USE_CPPHS}" ]]; then
                cabalconf+=(--with-cpphs=${EPREFIX}/usr/bin/cpphs)
        fi
        if [[ -n "${CABAL_TEST_SUITE}" ]]; then
                cabalconf+=($(use_enable test tests))
        fi

        if [[ -n "${CABAL_GHC_CONSTRAINT}" ]]; then
                cabalconf+=($(cabal-constraint "ghc"))
        fi

        local option
        for option in ${HCFLAGS}
        do
                cabalconf+=(--ghc-option="$option")
        done

        # parallel on all available cores
        if ghc-supports-parallel-make; then
                local max_jobs=$(makeopts_jobs)

                # limit to very small value, as parallelism
                # helps slightly, but makes things severely worse
                # when amount of threads is Very Large.
                [[ ${max_jobs} -gt 4 ]] && max_jobs=4

                cabalconf+=(--ghc-option=-j"$max_jobs")
        fi

        # Building GHCi libs on ppc64 causes "TOC overflow".
        if use ppc64; then
                cabalconf+=(--disable-library-for-ghci)
        fi

        # currently cabal does not respect CFLAGS and LDFLAGS on it's own (bug #333217)
        # so translate LDFLAGS to ghc parameters (without filtering)
        local flag
        for flag in $LDFLAGS; do cabalconf+=(--ghc-option="-optl$flag"); done

        # disable executable stripping for the executables, as portage will
        # strip by itself, and pre-stripping gives a QA warning.
        # cabal versions previous to 1.4 does not strip executables, and does
        # not accept the flag.
        # this fixes numerous bugs, amongst them;
        # bug #251881, bug #251882, bug #251884, bug #251886, bug #299494
        cabalconf+=(--disable-executable-stripping)

        cabalconf+=(--docdir="${EPREFIX}"/usr/share/doc/${PF})
        # As of Cabal 1.2, configure is quite quiet. For diagnostic purposes
        # it's better if the configure chatter is in the build logs:
        cabalconf+=(--verbose)

        # We build shared version of our Cabal where ghc ships it's shared
        # version of it. We will link ./setup as dynamic binary againt Cabal later.
        [[ ${CATEGORY}/${PN} == "dev-haskell/cabal" ]] && \
                $(ghc-supports-shared-libraries) && \
                        cabalconf+=(--enable-shared)

        if $(ghc-supports-shared-libraries); then
                # maybe a bit lower
                if $(ghc-supports-dynamic-by-default); then
                        cabalconf+=(--enable-shared)
                fi
        fi

        # --sysconfdir appeared in Cabal-1.18+
        if ./setup configure --help | grep -q -- --sysconfdir; then
                cabalconf+=(--sysconfdir="${EPREFIX}"/etc)
        fi

        # appeared in Cabal-1.18+ (see '--disable-executable-stripping')
        if ./setup configure --help | grep -q -- --disable-library-stripping; then
                cabalconf+=(--disable-library-stripping)
        fi

        set -- configure \
                --ghc --prefix="${EPREFIX}"/usr \
                --with-compiler="$(ghc-getghc)" \
                --with-hc-pkg="$(ghc-getghcpkg)" \
                --prefix="${EPREFIX}"/usr \
                --libdir="${EPREFIX}"/usr/$(get_libdir) \
                --libsubdir=${P}/ghc-$(ghc-version) \
                --datadir="${EPREFIX}"/usr/share/ \
                --datasubdir=${P}/ghc-$(ghc-version) \
                "${cabalconf[@]}" \
                ${CABAL_CONFIGURE_FLAGS} \
                ${CABAL_EXTRA_CONFIGURE_FLAGS} \
                "$@"
        echo ./setup "$@"
        ./setup "$@" || cabal-show-brokens-and-die "setup configure failed"
}

cabal-build() {
        set --  build ${CABAL_EXTRA_BUILD_FLAGS} "$@"
        echo ./setup "$@"
        ./setup "$@" \
                || die "setup build failed"
}

cabal-copy() {
        has "${EAPI:-0}" 0 1 2 && ! use prefix && ED=${D}

        set -- copy --destdir="${D}" "$@"
        echo ./setup "$@"
        ./setup "$@" || die "setup copy failed"

        # cabal is a bit eager about creating dirs,
        # so remove them if they are empty
        rmdir "${ED}/usr/bin" 2> /dev/null
}

cabal-pkg() {
        # This does not actually register since we're using true instead
        # of ghc-pkg. So it just leaves the .conf file and we can
        # register that ourselves (if it exists).

        if [[ -n ${CABAL_HAS_LIBRARIES} ]]; then
                # Newer cabal can generate a package conf for us:
                ./setup register --gen-pkg-config="${T}/${P}.conf"
                ghc-install-pkg "${T}/${P}.conf"
        fi
}

# Some cabal libs are bundled along with some versions of ghc
# eg filepath-1.0 comes with ghc-6.6.1
# by putting CABAL_CORE_LIB_GHC_PV="6.6.1" in an ebuild we are declaring that
# when building with this version of ghc, the ebuild is a dummy that is it will
# install no files since the package is already included with ghc.
# However portage still records the dependency and we can upgrade the package
# to a later one that's not included with ghc.
# You can also put a space separated list, eg CABAL_CORE_LIB_GHC_PV="6.6 6.6.1".
cabal-is-dummy-lib() {
        for version in ${CABAL_CORE_LIB_GHC_PV[*]}; do
                [[ "$(ghc-version)" == ${version} ]] && return 0
        done
        return 1
}

# exported function: check if cabal is correctly installed for
# the currently active ghc (we cannot guarantee this with portage)
haskell-cabal_pkg_setup() {
        if [[ -n ${CABAL_HAS_LIBRARIES} ]]; then
                [[ ${RDEPEND} == *dev-lang/ghc* ]] || eqawarn "QA Notice: A library does not have runtime dependency on dev-lang/ghc."
        fi
        if [[ -z "${CABAL_HAS_BINARIES}" ]] && [[ -z "${CABAL_HAS_LIBRARIES}" ]]; then
                eqawarn "QA Notice: Neither bin nor lib are in CABAL_FEATURES."
        fi
        if [[ -n "${CABAL_UNKNOWN}" ]]; then
                eqawarn "QA Notice: Unknown entry in CABAL_FEATURES: ${CABAL_UNKNOWN}"
        fi
        if cabal-is-dummy-lib; then
                einfo "${P} is included in ghc-${CABAL_CORE_LIB_GHC_PV}, nothing to install."
        fi
}

haskell-cabal_src_configure() {
        cabal-is-dummy-lib && return

        pushd "${S}" > /dev/null

        cabal-bootstrap

        cabal-configure "$@"

        popd > /dev/null
}

# exported function: nice alias
cabal_src_configure() {
        haskell-cabal_src_configure "$@"
}

# exported function: cabal-style bootstrap configure and compile
cabal_src_compile() {
        # it's a common mistake when one bumps ebuild to EAPI="2" (and upper)
        # and forgets to separate src_compile() to src_configure()/src_compile().
        # Such error leads to default src_configure and we lose all passed flags.
        if ! has "${EAPI:-0}" 0 1; then
                local passed_flag
                for passed_flag in "$@"; do
                        [[ ${passed_flag} == --flags=* ]] && \
                                eqawarn "QA Notice: Cabal option '${passed_flag}' has effect only in src_configure()"
                done
        fi

        cabal-is-dummy-lib && return

        has src_configure ${HASKELL_CABAL_EXPF} || haskell-cabal_src_configure "$@"
        cabal-build

        if [[ -n "${CABAL_USE_HADDOCK}" ]] && use doc; then
                if [[ -n "${CABAL_USE_HSCOLOUR}" ]] && use hscolour; then
                        if [[ -n "${CABAL_USE_HOOGLE}" ]] && use hoogle; then
                                # hoogle, hscolour and haddock
                                cabal-hoogle-hscolour-haddock
                        else
                                # haddock and hscolour
                                cabal-hscolour-haddock
                        fi
                else
                        if [[ -n "${CABAL_USE_HOOGLE}" ]] && use hoogle; then
                                # hoogle and haddock
                                cabal-hoogle-haddock
                        else
                                # just haddock
                                cabal-haddock
                        fi
                fi
        else
                if [[ -n "${CABAL_USE_HSCOLOUR}" ]] && use hscolour; then
                        if [[ -n "${CABAL_USE_HOOGLE}" ]] && use hoogle; then
                                # hoogle and hscolour
                                cabal-hoogle-hscolour
                        else
                                # just hscolour
                                cabal-hscolour
                        fi
                else
                        if [[ -n "${CABAL_USE_HOOGLE}" ]] && use hoogle; then
                                # just hoogle
                                cabal-hoogle
                        fi
                fi
        fi
}

haskell-cabal_src_compile() {
        pushd "${S}" > /dev/null

        cabal_src_compile "$@"

        popd > /dev/null
}

haskell-cabal_src_test() {
        pushd "${S}" > /dev/null

        if cabal-is-dummy-lib; then
                einfo ">>> No tests for dummy library: ${CATEGORY}/${PF}"
        else
                einfo ">>> Test phase [cabal test]: ${CATEGORY}/${PF}"
                set -- test "$@"
                echo ./setup "$@"
                ./setup "$@" || die "cabal test failed"
        fi

        popd > /dev/null
}

# exported function: cabal-style copy and register
cabal_src_install() {
        has "${EAPI:-0}" 0 1 2 && ! use prefix && EPREFIX=

        if ! cabal-is-dummy-lib; then
                cabal-copy
                cabal-pkg
        fi

        # create a dummy local package conf file for haskell-updater
        # if it does not exist (dummy libraries and binaries w/o libraries)
        local ghc_confdir_with_prefix="$(ghc-confdir)"
        # remove EPREFIX
        dodir ${ghc_confdir_with_prefix#${EPREFIX}}
        local hint_db="${D}/$(ghc-confdir)"
        local hint_file="${hint_db}/${PF}.conf"
        mkdir -p "${hint_db}" || die
        touch "${hint_file}" || die
}

haskell-cabal_src_install() {
        pushd "${S}" > /dev/null

        cabal_src_install

        popd > /dev/null
}

haskell-cabal_pkg_postinst() {
        ghc-package_pkg_postinst
}

haskell-cabal_pkg_postrm() {
        ghc-package_pkg_postrm
}

# @FUNCTION: cabal_flag
# @DESCRIPTION:
# ebuild.sh:use_enable() taken as base
#
# Usage examples:
#
#     CABAL_CONFIGURE_FLAGS=$(cabal_flag gui)
#  leads to "--flags=gui" or "--flags=-gui" (useflag 'gui')
#
#     CABAL_CONFIGURE_FLAGS=$(cabal_flag gtk gui)
#  also leads to "--flags=gui" or " --flags=-gui" (useflag 'gtk')
#
cabal_flag() {
        if [[ -z "$1" ]]; then
                echo "!!! cabal_flag() called without a parameter." >&2
                echo "!!! cabal_flag() <USEFLAG> [<cabal_flagname>]" >&2
                return 1
        fi

        local UWORD=${2:-$1}

        if use "$1"; then
                echo "--flags=${UWORD}"
        else
                echo "--flags=-${UWORD}"
        fi

        return 0
}

# @FUNCTION: cabal_chdeps
# @DESCRIPTION:
# Allows easier patching of $CABAL_FILE (${S}/${PN}.cabal by default)
# depends
#
# Accepts argument list as pairs of substitutions: <from-string> <to-string>...
#
# Dies on error.
#
# Usage examples:
#
# src_prepare() {
#    cabal_chdeps \
#        'base >= 4.2 && < 4.6' 'base >= 4.2 && < 4.7' \
#        'containers ==0.4.*' 'containers >= 0.4 && < 0.6'
#}
# or
# src_prepare() {
#    CABAL_FILE=${S}/${MY_PN}.cabal cabal_chdeps \
#        'base >= 4.2 && < 4.6' 'base >= 4.2 && < 4.7'
#    CABAL_FILE=${S}/${MY_PN}-tools.cabal cabal_chdeps \
#        'base == 3.*' 'base >= 4.2 && < 4.7'
#}
#
cabal_chdeps() {
        local cabal_fn=${MY_PN:-${PN}}.cabal
        local cf=${CABAL_FILE:-${S}/${cabal_fn}}
        local from_ss # ss - substring
        local to_ss
        local orig_c # c - contents
        local new_c

        [[ -f $cf ]] || die "cabal file '$cf' does not exist"

        orig_c=$(< "$cf")

        while :; do
                from_pat=$1
                to_str=$2

                [[ -n ${from_pat} ]] || break
                [[ -n ${to_str} ]] || die "'${from_str}' does not have 'to' part"

                einfo "CHDEP: '${from_pat}' -> '${to_str}'"

                # escape pattern-like symbols
                from_pat=${from_pat//\*/\\*}
                from_pat=${from_pat//\[/\\[}

                new_c=${orig_c//${from_pat}/${to_str}}

                if [[ -n $CABAL_DEBUG_LOOSENING ]]; then
                        echo "${orig_c}" >"${T}/${cf}".pre
                        echo "${new_c}" >"${T}/${cf}".post
                        diff -u "${T}/${cf}".{pre,post}
                fi

                [[ "${orig_c}" == "${new_c}" ]] && die "no trigger for '${from_pat}'"
                orig_c=${new_c}
                shift
                shift
        done

        echo "${new_c}" > "$cf" ||
                die "failed to update"
}

# @FUNCTION: cabal-constraint
# @DESCRIPTION:
# Allowes to set contraint to the libraries that are
# used by specified package
cabal-constraint() {
        while read p v ; do
                echo "--constraint \"$p == $v\""
        done < $(ghc-pkgdeps ${1})
}

# @FUNCTION: replace-hcflags
# @USAGE: <old> <new>
# @DESCRIPTION:
# Replace the <old> flag with <new> in HCFLAGS. Accepts shell globs for <old>.
# The implementation is picked from flag-o-matic.eclass:replace-flags()
replace-hcflags() {
        [[ $# != 2 ]] && die "Usage: replace-hcflags <old flag> <new flag>"

        local f new=()
        for f in ${HCFLAGS} ; do
                # Note this should work with globs like -O*
                if [[ ${f} == ${1} ]]; then
                        einfo "HCFLAGS: replacing '${f}' to '${2}'"
                        f=${2}
                fi
                new+=( "${f}" )
        done
        export HCFLAGS="${new[*]}"

        return 0
}