diff --git a/cabal-install-parsers/Changelog.md b/cabal-install-parsers/Changelog.md
index 93fca810..e1696505 100644
--- a/cabal-install-parsers/Changelog.md
+++ b/cabal-install-parsers/Changelog.md
@@ -1,3 +1,7 @@
+## 0.6.4
+
+- Add support for reading project files with conditionals.
+
 ## 0.6.3
 
 - Drop support for GHC prior 8.8.4
diff --git a/cabal-install-parsers/cabal-install-parsers.cabal b/cabal-install-parsers/cabal-install-parsers.cabal
index 3f51819a..54466076 100644
--- a/cabal-install-parsers/cabal-install-parsers.cabal
+++ b/cabal-install-parsers/cabal-install-parsers.cabal
@@ -1,6 +1,6 @@
 cabal-version:      2.2
 name:               cabal-install-parsers
-version:            0.6.3
+version:            0.6.4
 synopsis:           Utilities to work with cabal-install files
 description:
   @cabal-install-parsers@ provides parsers for @cabal-install@ files:
diff --git a/cabal-install-parsers/src/Cabal/Index.hs b/cabal-install-parsers/src/Cabal/Index.hs
index fbf761a8..03661b83 100644
--- a/cabal-install-parsers/src/Cabal/Index.hs
+++ b/cabal-install-parsers/src/Cabal/Index.hs
@@ -399,7 +399,7 @@ indexMetadata indexFilepath mindexState = do
 
                 f :: Maybe TmpPackageInfo -> Maybe TmpPackageInfo
                 f Nothing = Just TmpPackageInfo
-                    { tmpPiVersions  = Map.singleton ver TmpReleaseInfo 
+                    { tmpPiVersions  = Map.singleton ver TmpReleaseInfo
                         { tmpRiRevision    = 0
                         , tmpRiTarOffset   = offset
                         , tmpRiCabalHash   = Just digest
diff --git a/cabal-install-parsers/src/Cabal/Project.hs b/cabal-install-parsers/src/Cabal/Project.hs
index d8e907f8..0815eae1 100644
--- a/cabal-install-parsers/src/Cabal/Project.hs
+++ b/cabal-install-parsers/src/Cabal/Project.hs
@@ -1,10 +1,11 @@
-{-# LANGUAGE CPP               #-}
-{-# LANGUAGE DeriveFoldable    #-}
-{-# LANGUAGE DeriveFunctor     #-}
-{-# LANGUAGE DeriveGeneric     #-}
-{-# LANGUAGE DeriveTraversable #-}
-{-# LANGUAGE MultiWayIf        #-}
-{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE CPP                 #-}
+{-# LANGUAGE DeriveFoldable      #-}
+{-# LANGUAGE DeriveFunctor       #-}
+{-# LANGUAGE DeriveGeneric       #-}
+{-# LANGUAGE DeriveTraversable   #-}
+{-# LANGUAGE MultiWayIf          #-}
+{-# LANGUAGE OverloadedStrings   #-}
+{-# LANGUAGE ScopedTypeVariables #-}
 -- | License: GPL-3.0-or-later AND BSD-3-Clause
 --
 module Cabal.Project (
@@ -15,6 +16,8 @@ module Cabal.Project (
     -- * Parse project
     readProject,
     parseProject,
+    readProjectWithConditionals,
+    parseProjectWithConditionals,
     -- * Resolve project
     resolveProject,
     ResolveError (..),
@@ -25,6 +28,7 @@ module Cabal.Project (
 
 import Control.DeepSeq            (NFData (..))
 import Control.Exception          (Exception (..), throwIO)
+import Control.Monad              (unless)
 import Control.Monad.IO.Class     (liftIO)
 import Control.Monad.Trans.Except (ExceptT, runExceptT, throwE)
 import Data.Bifoldable            (Bifoldable (..))
@@ -55,6 +59,7 @@ import qualified Data.Map.Strict                 as M
 import qualified Distribution.CabalSpecVersion   as C
 import qualified Distribution.FieldGrammar       as C
 import qualified Distribution.Fields             as C
+import qualified Distribution.Fields.ConfVar     as C
 import qualified Distribution.PackageDescription as C
 import qualified Distribution.Parsec             as C
 
@@ -71,6 +76,12 @@ infixl 1 <&>
 
 -- $setup
 -- >>> :set -XOverloadedStrings
+-- >>> import Data.String (fromString)
+-- >>> import qualified Distribution.PackageDescription as C
+-- >>> import Text.Show (showListWith)
+-- >>> import Data.Functor.Classes (liftShowsPrec)
+-- >>> let sB (C.CondBranch c t f) = showString "CondBranch _ " . showParen True (sT t) . showChar ' ' . liftShowsPrec (\_ -> sT) undefined 11 f; sT (C.CondNode x c xs) = showString "CondTree " . showsPrec 11 x . showString " _ " . showListWith sB xs
+-- >>> pp x = putStrLn (either show (flip sT "") x)
 
 -- | @cabal.project@ file
 data Project uri opt pkg = Project
@@ -152,7 +163,7 @@ instance (NFData c, NFData b, NFData a) => NFData (Project c b a) where
         rnf x7 `seq` rnf x8 `seq` rnf x9 `seq`
         rnfList rnfPrettyField x10
       where
-        rnfList :: (a -> ()) -> [a] -> ()
+        rnfList :: (x -> ()) -> [x] -> ()
         rnfList _ []     = ()
         rnfList f (x:xs) = f x `seq` rnfList f xs
 
@@ -179,6 +190,13 @@ readProject fp = do
     prj1 <- resolveProject fp prj0 >>= either throwIO return
     readPackagesOfProject prj1 >>= either throwIO return
 
+readProjectWithConditionals :: FilePath -> IO (C.CondTree C.ConfVar () (Project URI Void (FilePath, C.GenericPackageDescription)))
+readProjectWithConditionals fp = do
+    contents <- BS.readFile fp
+    prj0 <- either throwIO return (parseProjectWithConditionals fp contents)
+    prj1 <- traverse (\p -> resolveProject fp p >>= either throwIO return) prj0
+    traverse (\p -> readPackagesOfProject p >>= either throwIO return) prj1
+
 -- | Parse project file. Extracts only few fields.
 --
 -- >>> fmap prjPackages $ parseProject "cabal.project" "packages: foo bar/*.cabal"
@@ -207,6 +225,46 @@ parseProject = parseWith $ \fields0 -> do
 
     parseSec _ = return id
 
+-- | Parse project files with conditionals.
+--
+-- >>> pp $ fmap (fmap prjPackages) $ parseProjectWithConditionals "cabal.project" "packages: foo bar/*.cabal"
+-- CondTree ["foo","bar/*.cabal"] _ []
+--
+-- >>> pp $ fmap (fmap prjPackages) $ parseProjectWithConditionals "cabal.project" $ fromString $ unlines [ "packages: foo bar/*.cabal", "if impl(ghc >=9)", "  packages: quu" ]
+-- CondTree ["foo","bar/*.cabal"] _ [CondBranch _ (CondTree ["quu"] _ []) Nothing]
+--
+-- >>> pp $ fmap (fmap prjPackages) $ parseProjectWithConditionals "cabal.project" $ fromString $ unlines [ "packages: foo bar/*.cabal", "if impl(ghc >=9)", "  packages: quu", "if impl(ghc >=10)", "  packages: zoo" ]
+-- CondTree ["foo","bar/*.cabal"] _ [CondBranch _ (CondTree ["quu"] _ []) Nothing,CondBranch _ (CondTree ["zoo"] _ []) Nothing]
+--
+-- >>> pp $ fmap (fmap prjPackages) $ parseProjectWithConditionals "cabal.project" $ fromString $ unlines [ "packages: foo bar/*.cabal", "if impl(ghc >=9)", "  packages: quu", "else", "  packages: zoo" ]
+-- CondTree ["foo","bar/*.cabal"] _ [CondBranch _ (CondTree ["quu"] _ []) (Just CondTree ["zoo"] _ [])]
+--
+-- >>> pp $ fmap (fmap prjPackages) $ parseProjectWithConditionals "cabal.project" $ fromString $ unlines [ "packages: foo bar/*.cabal", "if impl(ghc >=9)", "  packages: quu", "elif impl(ghc >=10)", "  packages: zoo", "else", "  packages: yyz" ]
+-- CondTree ["foo","bar/*.cabal"] _ [CondBranch _ (CondTree ["quu"] _ []) (Just CondTree [] _ [CondBranch _ (CondTree ["zoo"] _ []) (Just CondTree ["yyz"] _ [])])]
+--
+parseProjectWithConditionals :: FilePath -> ByteString -> Either (ParseError NonEmpty) (C.CondTree C.ConfVar () (Project Void String String))
+parseProjectWithConditionals = parseWith $ \fields0 -> flip parseCondTree fields0 $ \fields1 sections -> do
+    let fields2  = M.filterWithKey (\k _ -> k `elem` knownFields) fields1
+    parse fields0 fields2 sections
+  where
+    knownFields = C.fieldGrammarKnownFieldList $ grammar []
+
+    parse :: [C.Field a] -> C.Fields C.Position -> [[C.Section C.Position]] -> C.ParseResult (Project Void String String)
+    parse otherFields fields sections = do
+        let prettyOtherFields = map void $ C.fromParsecFields $ filter otherFieldName otherFields
+        prj <- C.parseFieldGrammar C.cabalSpecLatest fields $ grammar prettyOtherFields
+        foldl' (&) prj <$> traverse parseSec (concat sections)
+
+    -- Special case for source-repository-package. If you add another such
+    -- special case, make sure to update otherFieldName appropriately.
+    parseSec :: C.Section C.Position -> C.ParseResult (Project Void String String -> Project Void String String)
+    parseSec (C.MkSection (C.Name _pos name) [] fields) | name == sourceRepoSectionName = do
+        let fields' = fst $ C.partitionFields fields
+        repos <- C.parseFieldGrammar C.cabalSpecLatest fields' sourceRepositoryPackageGrammar
+        return $ over prjSourceReposL (++ toList (srpFanOut repos))
+
+    parseSec _ = return id
+
 -- | Returns 'True' if a field should be a part of 'prjOtherFields'. This
 -- excludes any field that is a part of 'grammar' as well as
 -- @source-repository-package@ (see 'parseProject', which has a special case
@@ -377,3 +435,61 @@ readPackagesOfProject :: Project uri opt FilePath -> IO (Either (ParseError NonE
 readPackagesOfProject prj = runExceptT $ for prj $ \fp -> do
     contents <- liftIO $ BS.readFile fp
     either throwE (\gpd -> return (fp, gpd)) (parsePackage fp contents)
+
+-------------------------------------------------------------------------------
+-- Read package files
+-------------------------------------------------------------------------------
+
+parseCondTree
+  :: forall a. (C.Fields C.Position -> [[C.Section C.Position]] -> C.ParseResult a)  -- ^ parse
+  -> [C.Field C.Position]
+  -> C.ParseResult (C.CondTree C.ConfVar () a)
+parseCondTree subparse = go
+  where
+    go fields = do
+        let (fs, ss) = C.partitionFields fields
+        (ss', branches) <- second concat . unzip <$> traverse (goIfs id id) ss
+        x <- subparse fs ss'
+        return $ C.CondNode x () branches
+
+    goIfs
+        :: ([C.Section C.Position] -> [C.Section C.Position])
+        -> ([C.CondBranch C.ConfVar () a] -> [C.CondBranch C.ConfVar () a])
+        -> [C.Section C.Position]
+        -> C.ParseResult ([C.Section C.Position], [C.CondBranch C.ConfVar () a])
+    goIfs accS accB [] = do
+        return (accS [], accB [])
+    goIfs accS accB (C.MkSection (C.Name pos name) args fields : sections)
+        | name == "if" = do
+            test' <- C.parseConditionConfVar args
+            fields' <- go fields
+            goElse (C.CondBranch test' fields') accS accB sections
+        | name == "else" = do
+            C.parseFailure pos "standalone else"
+            return ([], [])
+        | name == "elif" = do
+            C.parseFailure pos "standalone elif"
+            goIfs accS accB sections
+    goIfs accS accB (section : sections) = do
+        goIfs (accS . (section :)) accB sections
+
+    goElse
+        :: (Maybe (C.CondTree C.ConfVar () a) -> C.CondBranch C.ConfVar () a)
+        -> ([C.Section C.Position] -> [C.Section C.Position])
+        -> ([C.CondBranch C.ConfVar () a] -> [C.CondBranch C.ConfVar () a])
+        -> [C.Section C.Position]
+        -> C.ParseResult ([C.Section C.Position], [C.CondBranch C.ConfVar () a])
+    goElse make accS accB (C.MkSection (C.Name pos name) args fields : sections)
+        | name == "else" = do
+            unless (null args) $ C.parseFailure pos "arguments passed to else"
+            fields' <- go fields
+            let condTree = make (Just fields')
+            goIfs accS (accB . (condTree :)) sections
+        | name == "elif" = do
+            test' <- C.parseConditionConfVar args
+            fields' <- go fields
+            emptyA <- subparse mempty []
+            goElse (make . Just . C.CondNode emptyA () . pure .  C.CondBranch test' fields') accS accB sections
+    goElse make accS accB sections = do
+        let condTree = make Nothing
+        goIfs accS (accB . (condTree :)) sections
diff --git a/fixtures/conditionals.args b/fixtures/conditionals.args
new file mode 100644
index 00000000..e69de29b
diff --git a/fixtures/conditionals.bash b/fixtures/conditionals.bash
new file mode 100644
index 00000000..bef079e5
--- /dev/null
+++ b/fixtures/conditionals.bash
@@ -0,0 +1,527 @@
+# SUCCESS
+# *INFO* Generating Bash script for testing for GHC versions: 8.0.1 8.0.2 8.2.1 8.2.2 8.4.1 8.4.2 8.4.3 8.4.4 8.6.1 8.6.2 8.6.3 8.6.4 8.6.5 8.8.1 8.8.2 8.8.3 8.8.4 8.10.1 8.10.2 8.10.3 8.10.4 8.10.5 8.10.6 8.10.7
+#!/bin/bash
+# shellcheck disable=SC2086,SC2016,SC2046
+# REGENDATA ["bash","conditionals.project"]
+
+set -o pipefail
+
+# Mode
+##############################################################################
+
+if [ "$1" = "indocker" ]; then
+    INDOCKER=true
+    shift
+else
+    INDOCKER=false
+fi
+
+# Run configuration
+##############################################################################
+
+CFG_CABAL_STORE_CACHE=""
+CFG_CABAL_REPO_CACHE=""
+CFG_JOBS="8.10.7 8.10.6 8.10.5 8.10.4 8.10.3 8.10.2 8.10.1 8.8.4 8.8.3 8.8.2 8.8.1 8.6.5 8.6.4 8.6.3 8.6.2 8.6.1 8.4.4 8.4.3 8.4.2 8.4.1 8.2.2 8.2.1 8.0.2 8.0.1"
+CFG_CABAL_UPDATE=false
+
+SCRIPT_NAME=$(basename "$0")
+START_TIME="$(date +'%s')"
+
+XDG_CONFIG_HOME=${XDG_CONFIG_HOME:-$HOME/.config}
+
+# Job configuration
+##############################################################################
+
+GHC_VERSION="non-existing"
+CABAL_VERSION=3.2
+HEADHACKAGE=false
+
+# Locale
+##############################################################################
+
+export LC_ALL=C.UTF-8
+
+# Utilities
+##############################################################################
+
+SGR_RED='\033[1;31m'
+SGR_GREEN='\033[1;32m'
+SGR_BLUE='\033[1;34m'
+SGR_CYAN='\033[1;96m'
+SGR_RESET='\033[0m' # No Color
+
+put_info() {
+    printf "$SGR_CYAN%s$SGR_RESET\n" "### $*"
+}
+
+put_error() {
+    printf "$SGR_RED%s$SGR_RESET\n" "!!! $*"
+}
+
+run_cmd() {
+    local PRETTYCMD="$*"
+    local PROMPT
+    if $INDOCKER; then
+        PROMPT="$(pwd) >>>"
+    else
+        PROMPT=">>>"
+    fi
+
+    printf "$SGR_BLUE%s %s$SGR_RESET\n" "$PROMPT" "$PRETTYCMD"
+
+    local start_time end_time cmd_duration total_duration
+    start_time=$(date +'%s')
+
+    "$@"
+    local RET=$?
+
+    end_time=$(date +'%s')
+    cmd_duration=$((end_time - start_time))
+    total_duration=$((end_time - START_TIME))
+
+    cmd_min=$((cmd_duration / 60))
+    cmd_sec=$((cmd_duration % 60))
+
+    total_min=$((total_duration / 60))
+    total_sec=$((total_duration % 60))
+
+    if [ $RET -eq 0 ]; then
+        printf "$SGR_GREEN%s$SGR_RESET (%dm%02ds; %dm%02ds)\n" "<<< $PRETTYCMD" "$cmd_min" "$cmd_sec" "$total_min" "$total_sec"
+    else
+        printf "$SGR_RED%s$SGR_RESET\n" "!!! $PRETTYCMD"
+        exit 1
+    fi
+}
+
+run_cmd_if() {
+    local COND=$1
+    shift
+
+    if [ $COND -eq 1 ]; then
+        run_cmd "$@"
+    else
+        local PRETTYCMD="$*"
+        local PROMPT
+        PROMPT="$(pwd) (skipping) >>>"
+
+        printf "$SGR_BLUE%s %s$SGR_RESET\n" "$PROMPT" "$PRETTYCMD"
+    fi
+}
+
+run_cmd_unchecked() {
+    local PRETTYCMD="$*"
+    local PROMPT
+    if $INDOCKER; then
+        PROMPT="$(pwd) >>>"
+    else
+        PROMPT=">>>"
+    fi
+
+    printf "$SGR_BLUE%s %s$SGR_RESET\n" "$PROMPT" "$PRETTYCMD"
+
+    local start_time end_time cmd_duration total_duration cmd_min cmd_sec total_min total_sec
+    start_time=$(date +'%s')
+
+    "$@"
+
+    end_time=$(date +'%s')
+    cmd_duration=$((end_time - start_time))
+    total_duration=$((end_time - START_TIME))
+
+    cmd_min=$((cmd_duration / 60))
+    cmd_sec=$((cmd_duration % 60))
+
+    total_min=$((total_duration / 60))
+    total_sec=$((total_duration % 60))
+
+    printf "$SGR_GREEN%s$SGR_RESET (%dm%02ds; %dm%02ds)\n" "<<< $PRETTYCMD" "$cmd_min" "$cmd_sec" "$total_min" "$total_sec"
+}
+
+change_dir() {
+    local DIR=$1
+    if [ -d "$DIR" ]; then
+        printf "$SGR_BLUE%s$SGR_RESET\n" "change directory to $DIR"
+        cd "$DIR" || exit 1
+    else
+        printf "$SGR_RED%s$SGR_RESET\n" "!!! cd $DIR"
+        exit 1
+    fi
+}
+
+change_dir_if() {
+    local COND=$1
+    local DIR=$2
+
+    if [ $COND -ne 0 ]; then
+        change_dir "$DIR"
+    fi
+}
+
+echo_to() {
+    local DEST=$1
+    local CONTENTS=$2
+
+    echo "$CONTENTS" >> "$DEST"
+}
+
+echo_if_to() {
+    local COND=$1
+    local DEST=$2
+    local CONTENTS=$3
+
+    if [ $COND -ne 0 ]; then
+        echo_to "$DEST" "$CONTENTS"
+    fi
+}
+
+install_cabalplan() {
+    put_info "installing cabal-plan"
+
+    if [ ! -e $CABAL_REPOCACHE/downloads/cabal-plan ]; then
+        curl -L https://github.com/haskell-hvr/cabal-plan/releases/download/v0.6.2.0/cabal-plan-0.6.2.0-x86_64-linux.xz > /tmp/cabal-plan.xz || exit 1
+        (cd /tmp && echo "de73600b1836d3f55e32d80385acc055fd97f60eaa0ab68a755302685f5d81bc  cabal-plan.xz" | sha256sum -c -)|| exit 1
+        mkdir -p $CABAL_REPOCACHE/downloads
+        xz -d < /tmp/cabal-plan.xz > $CABAL_REPOCACHE/downloads/cabal-plan || exit 1
+        chmod a+x $CABAL_REPOCACHE/downloads/cabal-plan || exit 1
+    fi
+
+    mkdir -p $CABAL_DIR/bin || exit 1
+    ln -s $CABAL_REPOCACHE/downloads/cabal-plan $CABAL_DIR/bin/cabal-plan || exit 1
+}
+
+# Help
+##############################################################################
+
+show_usage() {
+cat <<EOF
+./haskell-ci.sh - build & test
+
+Usage: ./haskell-ci.sh [options]
+  A script to run automated checks locally (using Docker)
+
+Available options:
+  --jobs JOBS               Jobs to run (default: $CFG_JOBS)
+  --cabal-store-cache PATH  Directory to use for cabal-store-cache
+  --cabal-repo-cache PATH   Directory to use for cabal-repo-cache
+  --skip-cabal-update       Skip cabal update (useful with --cabal-repo-cache)
+  --no-skip-cabal-update
+  --help                    Print this message
+
+EOF
+}
+
+# getopt
+#######################################################################
+
+process_cli_options() {
+    while [ $# -gt 0 ]; do
+        arg=$1
+        case $arg in
+            --help)
+                show_usage
+                exit
+                ;;
+            --jobs)
+                CFG_JOBS=$2
+                shift
+                shift
+                ;;
+            --cabal-store-cache)
+                CFG_CABAL_STORE_CACHE=$2
+                shift
+                shift
+                ;;
+            --cabal-repo-cache)
+                CFG_CABAL_REPO_CACHE=$2
+                shift
+                shift
+                ;;
+            --skip-cabal-update)
+                CFG_CABAL_UPDATE=false
+                shift
+                ;;
+            --no-skip-cabal-update)
+                CFG_CABAL_UPDATE=true
+                shift
+                ;;
+            *)
+                echo "Unknown option $arg"
+                exit 1
+        esac
+    done
+}
+
+process_indocker_options () {
+    while [ $# -gt 0 ]; do
+        arg=$1
+
+        case $arg in
+            --ghc-version)
+                GHC_VERSION=$2
+                shift
+                shift
+                ;;
+            --cabal-version)
+                CABAL_VERSION=$2
+                shift
+                shift
+                ;;
+            --start-time)
+                START_TIME=$2
+                shift
+                shift
+                ;;
+            --cabal-update)
+                CABAL_UPDATE=$2
+                shift
+                shift
+                ;;
+            *)
+                echo "Unknown option $arg"
+                exit 1
+        esac
+    done
+}
+
+if $INDOCKER; then
+    process_indocker_options "$@"
+
+else
+    if [ -f "$XDG_CONFIG_HOME/haskell-ci/bash.config" ]; then
+        process_cli_options $(cat "$XDG_CONFIG_HOME/haskell-ci/bash.config")
+    fi
+
+    process_cli_options "$@"
+
+    put_info "jobs:              $CFG_JOBS"
+    put_info "cabal-store-cache: $CFG_CABAL_STORE_CACHE"
+    put_info "cabal-repo-cache:  $CFG_CABAL_REPO_CACHE"
+    put_info "cabal-update:      $CFG_CABAL_UPDATE"
+fi
+
+# Constants
+##############################################################################
+
+SRCDIR=/hsci/src
+BUILDDIR=/hsci/build
+CABAL_DIR="$BUILDDIR/cabal"
+CABAL_REPOCACHE=/hsci/cabal-repocache
+CABAL_STOREDIR=/hsci/store
+
+# Docker invoke
+##############################################################################
+
+# if cache directory is specified, use it.
+# Otherwise use another tmpfs host
+if [ -z "$CFG_CABAL_STORE_CACHE" ]; then
+    CABALSTOREARG="--tmpfs $CABAL_STOREDIR:exec"
+else
+    CABALSTOREARG="--volume $CFG_CABAL_STORE_CACHE:$CABAL_STOREDIR"
+fi
+
+if [ -z "$CFG_CABAL_REPO_CACHE" ]; then
+    CABALREPOARG="--tmpfs $CABAL_REPOCACHE:exec"
+else
+    CABALREPOARG="--volume $CFG_CABAL_REPO_CACHE:$CABAL_REPOCACHE"
+fi
+
+echo_docker_cmd() {
+    local GHCVER=$1
+
+    # TODO: mount /hsci/src:ro (readonly)
+    echo docker run \
+        --tty \
+        --interactive \
+        --rm \
+        --label haskell-ci \
+        --volume "$(pwd):/hsci/src" \
+        $CABALSTOREARG \
+        $CABALREPOARG \
+        --tmpfs /tmp:exec \
+        --tmpfs /hsci/build:exec \
+        --workdir /hsci/build \
+        "phadej/ghc:$GHCVER-bionic" \
+        "/bin/bash" "/hsci/src/$SCRIPT_NAME" indocker \
+        --ghc-version "$GHCVER" \
+        --cabal-update "$CFG_CABAL_UPDATE" \
+        --start-time "$START_TIME"
+}
+
+# if we are not in docker, loop through jobs
+if ! $INDOCKER; then
+    for JOB in $CFG_JOBS; do
+        put_info "Running in docker: $JOB"
+        run_cmd $(echo_docker_cmd "$JOB")
+    done
+
+    run_cmd echo "ALL OK"
+    exit 0
+fi
+
+# Otherwise we are in docker, and the rest of script executes
+put_info "In docker"
+
+# Environment
+##############################################################################
+
+GHCDIR=/opt/ghc/$GHC_VERSION
+
+HC=$GHCDIR/bin/ghc
+HCPKG=$GHCDIR/bin/ghc-pkg
+HADDOCK=$GHCDIR/bin/haddock
+
+CABAL=/opt/cabal/$CABAL_VERSION/bin/cabal
+
+CABAL="$CABAL -vnormal+nowrap"
+
+export CABAL_DIR
+export CABAL_CONFIG="$BUILDDIR/cabal/config"
+
+PATH="$CABAL_DIR/bin:$PATH"
+
+# HCNUMVER
+HCNUMVER=$(${HC} --numeric-version|perl -ne '/^(\d+)\.(\d+)\.(\d+)(\.(\d+))?$/; print(10000 * $1 + 100 * $2 + ($3 == 0 ? $5 != 1 : $3))')
+GHCJSARITH=0
+
+put_info "HCNUMVER: $HCNUMVER"
+
+# Args for shorter/nicer commands
+if [ 1 -ne 0 ] ; then ARG_TESTS=--enable-tests; else ARG_TESTS=--disable-tests; fi
+if [ 1 -ne 0 ] ; then ARG_BENCH=--enable-benchmarks; else ARG_BENCH=--disable-benchmarks; fi
+ARG_COMPILER="--ghc --with-compiler=$HC"
+
+put_info "tests/benchmarks: $ARG_TESTS $ARG_BENCH"
+
+# Apt dependencies
+##############################################################################
+
+
+# Cabal config
+##############################################################################
+
+mkdir -p $BUILDDIR/cabal
+
+cat > $BUILDDIR/cabal/config <<EOF
+remote-build-reporting: anonymous
+write-ghc-environment-files: always
+remote-repo-cache: $CABAL_REPOCACHE
+logs-dir:          $CABAL_DIR/logs
+world-file:        $CABAL_DIR/world
+extra-prog-path:   $CABAL_DIR/bin
+symlink-bindir:    $CABAL_DIR/bin
+installdir:        $CABAL_DIR/bin
+build-summary:     $CABAL_DIR/logs/build.log
+store-dir:         $CABAL_STOREDIR
+install-dirs user
+  prefix: $CABAL_DIR
+repository hackage.haskell.org
+  url: http://hackage.haskell.org/
+EOF
+
+if $HEADHACKAGE; then
+    put_error "head.hackage is not implemented"
+    exit 1
+fi
+
+run_cmd cat "$BUILDDIR/cabal/config"
+
+# Version
+##############################################################################
+
+put_info "Versions"
+run_cmd $HC --version
+run_cmd_unchecked $HC --print-project-git-commit-id
+run_cmd $CABAL --version
+
+# Build script
+##############################################################################
+
+# update cabal index
+if $CABAL_UPDATE; then
+    put_info "Updating Hackage index"
+    run_cmd $CABAL v2-update -v
+fi
+
+# install cabal-plan
+install_cabalplan
+run_cmd cabal-plan --version
+
+# initial cabal.project for sdist
+put_info "initial cabal.project for sdist"
+change_dir "$BUILDDIR"
+run_cmd touch cabal.project
+echo_to cabal.project "packages: $SRCDIR/servant"
+echo_to cabal.project "packages: $SRCDIR/servant-client"
+run_cmd cat cabal.project
+
+# sdist
+put_info "sdist"
+run_cmd mkdir -p "$BUILDDIR/sdist"
+run_cmd $CABAL sdist all --output-dir "$BUILDDIR/sdist"
+
+# unpack
+put_info "unpack"
+change_dir "$BUILDDIR"
+run_cmd mkdir -p "$BUILDDIR/unpacked"
+run_cmd find "$BUILDDIR/sdist" -maxdepth 1 -type f -name '*.tar.gz' -exec tar -C "$BUILDDIR/unpacked" -xzvf {} \;
+
+# generate cabal.project
+put_info "generate cabal.project"
+PKGDIR_servant="$(find "$BUILDDIR/unpacked" -maxdepth 1 -type d -regex '.*/servant-[0-9.]*')"
+PKGDIR_servant_client="$(find "$BUILDDIR/unpacked" -maxdepth 1 -type d -regex '.*/servant-client-[0-9.]*')"
+run_cmd touch cabal.project
+run_cmd touch cabal.project.local
+echo_to cabal.project "packages: ${PKGDIR_servant}"
+echo_to cabal.project "packages: ${PKGDIR_servant_client}"
+echo_if_to $((HCNUMVER >= 80200)) cabal.project "package servant"
+echo_if_to $((HCNUMVER >= 80200)) cabal.project "    ghc-options: -Werror=missing-methods"
+echo_if_to $((HCNUMVER >= 80200)) cabal.project "package servant-client"
+echo_if_to $((HCNUMVER >= 80200)) cabal.project "    ghc-options: -Werror=missing-methods"
+cat >> cabal.project <<EOF
+EOF
+$HCPKG list --simple-output --names-only | perl -ne 'for (split /\s+/) { print "constraints: $_ installed\n" unless /^(servant|servant-client)$/; }' >> cabal.project.local
+run_cmd cat cabal.project
+run_cmd cat cabal.project.local
+
+# dump install plan
+put_info "dump install plan"
+run_cmd $CABAL v2-build $ARG_COMPILER $ARG_TESTS $ARG_BENCH --dry-run all
+run_cmd cabal-plan
+
+# install dependencies
+put_info "install dependencies"
+run_cmd $CABAL v2-build $ARG_COMPILER --disable-tests --disable-benchmarks --dependencies-only -j all
+run_cmd $CABAL v2-build $ARG_COMPILER $ARG_TESTS $ARG_BENCH --dependencies-only -j all
+
+# build w/o tests
+put_info "build w/o tests"
+run_cmd $CABAL v2-build $ARG_COMPILER --disable-tests --disable-benchmarks all
+
+# build
+put_info "build"
+run_cmd $CABAL v2-build $ARG_COMPILER $ARG_TESTS $ARG_BENCH all
+
+# tests
+put_info "tests"
+run_cmd $CABAL v2-test $ARG_COMPILER $ARG_TESTS $ARG_BENCH all --test-show-details=direct
+
+# cabal check
+put_info "cabal check"
+change_dir "${PKGDIR_servant}"
+run_cmd ${CABAL} -vnormal check
+change_dir "${PKGDIR_servant_client}"
+run_cmd ${CABAL} -vnormal check
+change_dir "$BUILDDIR"
+
+# haddock
+put_info "haddock"
+run_cmd $CABAL v2-haddock --haddock-all $ARG_COMPILER --with-haddock $HADDOCK $ARG_TESTS $ARG_BENCH all
+
+# unconstrained build
+put_info "unconstrained build"
+run_cmd rm -f cabal.project.local
+run_cmd $CABAL v2-build $ARG_COMPILER --disable-tests --disable-benchmarks all
+
+
+# Done
+run_cmd echo OK
diff --git a/fixtures/conditionals.github b/fixtures/conditionals.github
new file mode 100644
index 00000000..4725bef1
--- /dev/null
+++ b/fixtures/conditionals.github
@@ -0,0 +1,319 @@
+# SUCCESS
+# *INFO* Generating GitHub config for testing for GHC versions: 8.0.1 8.0.2 8.2.1 8.2.2 8.4.1 8.4.2 8.4.3 8.4.4 8.6.1 8.6.2 8.6.3 8.6.4 8.6.5 8.8.1 8.8.2 8.8.3 8.8.4 8.10.1 8.10.2 8.10.3 8.10.4 8.10.5 8.10.6 8.10.7
+# This GitHub workflow config has been generated by a script via
+#
+#   haskell-ci 'github' 'conditionals.project'
+#
+# To regenerate the script (for example after adjusting tested-with) run
+#
+#   haskell-ci regenerate
+#
+# For more information, see https://github.com/haskell-CI/haskell-ci
+#
+# REGENDATA ["github","conditionals.project"]
+#
+name: Haskell-CI
+on:
+  - push
+  - pull_request
+jobs:
+  linux:
+    name: Haskell-CI - Linux - ${{ matrix.compiler }}
+    runs-on: ubuntu-24.04
+    timeout-minutes:
+      60
+    container:
+      image: buildpack-deps:jammy
+    continue-on-error: ${{ matrix.allow-failure }}
+    strategy:
+      matrix:
+        include:
+          - compiler: ghc-8.10.7
+            compilerKind: ghc
+            compilerVersion: 8.10.7
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.10.6
+            compilerKind: ghc
+            compilerVersion: 8.10.6
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.10.5
+            compilerKind: ghc
+            compilerVersion: 8.10.5
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.10.4
+            compilerKind: ghc
+            compilerVersion: 8.10.4
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.10.3
+            compilerKind: ghc
+            compilerVersion: 8.10.3
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.10.2
+            compilerKind: ghc
+            compilerVersion: 8.10.2
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.10.1
+            compilerKind: ghc
+            compilerVersion: 8.10.1
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.8.4
+            compilerKind: ghc
+            compilerVersion: 8.8.4
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.8.3
+            compilerKind: ghc
+            compilerVersion: 8.8.3
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.8.2
+            compilerKind: ghc
+            compilerVersion: 8.8.2
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.8.1
+            compilerKind: ghc
+            compilerVersion: 8.8.1
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.6.5
+            compilerKind: ghc
+            compilerVersion: 8.6.5
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.6.4
+            compilerKind: ghc
+            compilerVersion: 8.6.4
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.6.3
+            compilerKind: ghc
+            compilerVersion: 8.6.3
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.6.2
+            compilerKind: ghc
+            compilerVersion: 8.6.2
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.6.1
+            compilerKind: ghc
+            compilerVersion: 8.6.1
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.4.4
+            compilerKind: ghc
+            compilerVersion: 8.4.4
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.4.3
+            compilerKind: ghc
+            compilerVersion: 8.4.3
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.4.2
+            compilerKind: ghc
+            compilerVersion: 8.4.2
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.4.1
+            compilerKind: ghc
+            compilerVersion: 8.4.1
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.2.2
+            compilerKind: ghc
+            compilerVersion: 8.2.2
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.2.1
+            compilerKind: ghc
+            compilerVersion: 8.2.1
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.0.2
+            compilerKind: ghc
+            compilerVersion: 8.0.2
+            setup-method: ghcup
+            allow-failure: false
+          - compiler: ghc-8.0.1
+            compilerKind: ghc
+            compilerVersion: 8.0.1
+            setup-method: ghcup
+            allow-failure: false
+      fail-fast: false
+    steps:
+      - name: apt-get install
+        run: |
+          apt-get update
+          apt-get install -y --no-install-recommends gnupg ca-certificates dirmngr curl git software-properties-common libtinfo5 libnuma-dev
+      - name: Install GHCup
+        run: |
+          mkdir -p "$HOME/.ghcup/bin"
+          curl -sL https://downloads.haskell.org/ghcup/0.1.50.1/x86_64-linux-ghcup-0.1.50.1 > "$HOME/.ghcup/bin/ghcup"
+          chmod a+x "$HOME/.ghcup/bin/ghcup"
+      - name: Install cabal-install
+        run: |
+          "$HOME/.ghcup/bin/ghcup" install cabal 3.14.2.0 || (cat "$HOME"/.ghcup/logs/*.* && false)
+          echo "CABAL=$HOME/.ghcup/bin/cabal-3.14.2.0 -vnormal+nowrap" >> "$GITHUB_ENV"
+      - name: Install GHC (GHCup)
+        if: matrix.setup-method == 'ghcup'
+        run: |
+          "$HOME/.ghcup/bin/ghcup" install ghc "$HCVER" || (cat "$HOME"/.ghcup/logs/*.* && false)
+          HC=$("$HOME/.ghcup/bin/ghcup" whereis ghc "$HCVER")
+          HCPKG=$(echo "$HC" | sed 's#ghc$#ghc-pkg#')
+          HADDOCK=$(echo "$HC" | sed 's#ghc$#haddock#')
+          echo "HC=$HC" >> "$GITHUB_ENV"
+          echo "HCPKG=$HCPKG" >> "$GITHUB_ENV"
+          echo "HADDOCK=$HADDOCK" >> "$GITHUB_ENV"
+        env:
+          HCKIND: ${{ matrix.compilerKind }}
+          HCNAME: ${{ matrix.compiler }}
+          HCVER: ${{ matrix.compilerVersion }}
+      - name: Set PATH and environment variables
+        run: |
+          echo "$HOME/.cabal/bin" >> $GITHUB_PATH
+          echo "LANG=C.UTF-8" >> "$GITHUB_ENV"
+          echo "CABAL_DIR=$HOME/.cabal" >> "$GITHUB_ENV"
+          echo "CABAL_CONFIG=$HOME/.cabal/config" >> "$GITHUB_ENV"
+          HCNUMVER=$(${HC} --numeric-version|perl -ne '/^(\d+)\.(\d+)\.(\d+)(\.(\d+))?$/; print(10000 * $1 + 100 * $2 + ($3 == 0 ? $5 != 1 : $3))')
+          echo "HCNUMVER=$HCNUMVER" >> "$GITHUB_ENV"
+          echo "ARG_TESTS=--enable-tests" >> "$GITHUB_ENV"
+          echo "ARG_BENCH=--enable-benchmarks" >> "$GITHUB_ENV"
+          echo "HEADHACKAGE=false" >> "$GITHUB_ENV"
+          echo "ARG_COMPILER=--$HCKIND --with-compiler=$HC" >> "$GITHUB_ENV"
+        env:
+          HCKIND: ${{ matrix.compilerKind }}
+          HCNAME: ${{ matrix.compiler }}
+          HCVER: ${{ matrix.compilerVersion }}
+      - name: env
+        run: |
+          env
+      - name: write cabal config
+        run: |
+          mkdir -p $CABAL_DIR
+          cat >> $CABAL_CONFIG <<EOF
+          remote-build-reporting: anonymous
+          write-ghc-environment-files: never
+          remote-repo-cache: $CABAL_DIR/packages
+          logs-dir:          $CABAL_DIR/logs
+          world-file:        $CABAL_DIR/world
+          extra-prog-path:   $CABAL_DIR/bin
+          symlink-bindir:    $CABAL_DIR/bin
+          installdir:        $CABAL_DIR/bin
+          build-summary:     $CABAL_DIR/logs/build.log
+          store-dir:         $CABAL_DIR/store
+          install-dirs user
+            prefix: $CABAL_DIR
+          repository hackage.haskell.org
+            url: http://hackage.haskell.org/
+          EOF
+          cat >> $CABAL_CONFIG <<EOF
+          program-default-options
+            ghc-options: $GHCJOBS +RTS -M3G -RTS
+          EOF
+          cat $CABAL_CONFIG
+      - name: versions
+        run: |
+          $HC --version || true
+          $HC --print-project-git-commit-id || true
+          $CABAL --version || true
+      - name: update cabal index
+        run: |
+          $CABAL v2-update -v
+      - name: install cabal-plan
+        run: |
+          mkdir -p $HOME/.cabal/bin
+          curl -sL https://github.com/haskell-hvr/cabal-plan/releases/download/v0.7.3.0/cabal-plan-0.7.3.0-x86_64-linux.xz > cabal-plan.xz
+          echo 'f62ccb2971567a5f638f2005ad3173dba14693a45154c1508645c52289714cb2  cabal-plan.xz' | sha256sum -c -
+          xz -d < cabal-plan.xz > $HOME/.cabal/bin/cabal-plan
+          rm -f cabal-plan.xz
+          chmod a+x $HOME/.cabal/bin/cabal-plan
+          cabal-plan --version
+      - name: checkout
+        uses: actions/checkout@v4
+        with:
+          path: source
+      - name: initial cabal.project for sdist
+        run: |
+          touch cabal.project
+          echo "packages: $GITHUB_WORKSPACE/source/servant" >> cabal.project
+          echo "packages: $GITHUB_WORKSPACE/source/servant-client" >> cabal.project
+          cat cabal.project
+      - name: sdist
+        run: |
+          mkdir -p sdist
+          $CABAL sdist all --output-dir $GITHUB_WORKSPACE/sdist
+      - name: unpack
+        run: |
+          mkdir -p unpacked
+          find sdist -maxdepth 1 -type f -name '*.tar.gz' -exec tar -C $GITHUB_WORKSPACE/unpacked -xzvf {} \;
+      - name: generate cabal.project
+        run: |
+          PKGDIR_servant="$(find "$GITHUB_WORKSPACE/unpacked" -maxdepth 1 -type d -regex '.*/servant-[0-9.]*')"
+          echo "PKGDIR_servant=${PKGDIR_servant}" >> "$GITHUB_ENV"
+          PKGDIR_servant_client="$(find "$GITHUB_WORKSPACE/unpacked" -maxdepth 1 -type d -regex '.*/servant-client-[0-9.]*')"
+          echo "PKGDIR_servant_client=${PKGDIR_servant_client}" >> "$GITHUB_ENV"
+          rm -f cabal.project cabal.project.local
+          touch cabal.project
+          touch cabal.project.local
+          echo "packages: ${PKGDIR_servant}" >> cabal.project
+          echo "packages: ${PKGDIR_servant_client}" >> cabal.project
+          if [ $((HCNUMVER >= 80200)) -ne 0 ] ; then echo "package servant" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 80200)) -ne 0 ] ; then echo "    ghc-options: -Werror=missing-methods" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 80200)) -ne 0 ] ; then echo "package servant-client" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 80200)) -ne 0 ] ; then echo "    ghc-options: -Werror=missing-methods" >> cabal.project ; fi
+          cat >> cabal.project <<EOF
+          EOF
+          $HCPKG list --simple-output --names-only | perl -ne 'for (split /\s+/) { print "constraints: any.$_ installed\n" unless /^(servant|servant-client)$/; }' >> cabal.project.local
+          cat cabal.project
+          cat cabal.project.local
+      - name: dump install plan
+        run: |
+          $CABAL v2-build $ARG_COMPILER $ARG_TESTS $ARG_BENCH --dry-run all
+          cabal-plan
+      - name: restore cache
+        uses: actions/cache/restore@v4
+        with:
+          key: ${{ runner.os }}-${{ matrix.compiler }}-${{ github.sha }}
+          path: ~/.cabal/store
+          restore-keys: ${{ runner.os }}-${{ matrix.compiler }}-
+      - name: install dependencies
+        run: |
+          $CABAL v2-build $ARG_COMPILER --disable-tests --disable-benchmarks --dependencies-only -j2 all
+          $CABAL v2-build $ARG_COMPILER $ARG_TESTS $ARG_BENCH --dependencies-only -j2 all
+      - name: build w/o tests
+        run: |
+          $CABAL v2-build $ARG_COMPILER --disable-tests --disable-benchmarks all
+      - name: build
+        run: |
+          $CABAL v2-build $ARG_COMPILER $ARG_TESTS $ARG_BENCH all --write-ghc-environment-files=always
+      - name: tests
+        run: |
+          $CABAL v2-test $ARG_COMPILER $ARG_TESTS $ARG_BENCH all --test-show-details=direct
+      - name: cabal check
+        run: |
+          cd ${PKGDIR_servant} || false
+          ${CABAL} -vnormal check
+          cd ${PKGDIR_servant_client} || false
+          ${CABAL} -vnormal check
+      - name: haddock
+        run: |
+          $CABAL v2-haddock --disable-documentation --haddock-all $ARG_COMPILER --with-haddock $HADDOCK $ARG_TESTS $ARG_BENCH all
+      - name: unconstrained build
+        run: |
+          rm -f cabal.project.local
+          $CABAL v2-build $ARG_COMPILER --disable-tests --disable-benchmarks all
+      - name: save cache
+        if: always()
+        uses: actions/cache/save@v4
+        with:
+          key: ${{ runner.os }}-${{ matrix.compiler }}-${{ github.sha }}
+          path: ~/.cabal/store
diff --git a/fixtures/conditionals.project b/fixtures/conditionals.project
new file mode 100644
index 00000000..99fad6b4
--- /dev/null
+++ b/fixtures/conditionals.project
@@ -0,0 +1,3 @@
+packages: servant
+if impl(ghc >=8.6)
+  packages: servant-client
diff --git a/haskell-ci.cabal b/haskell-ci.cabal
index edd2535d..37de0c40 100644
--- a/haskell-ci.cabal
+++ b/haskell-ci.cabal
@@ -1,6 +1,6 @@
 cabal-version:      2.2
 name:               haskell-ci
-version:            0.19.20250605
+version:            0.19.20250630
 synopsis:           Haskell CI script generator
 description:
   Script generator (@haskell-ci@) for
@@ -176,7 +176,7 @@ library haskell-ci-internal
     , attoparsec                     ^>=0.14.1
     , base-compat                    ^>=0.14.0
     , base16-bytestring              ^>=1.0.1.0
-    , cabal-install-parsers          ^>=0.6.3
+    , cabal-install-parsers          ^>=0.6.4
     , cryptohash-sha256              ^>=0.11.101.0
     , exceptions                     ^>=0.10.0
     , generic-lens-lite              ^>=0.1
diff --git a/src/HaskellCI.hs b/src/HaskellCI.hs
index 6a3058ee..6c45e52a 100644
--- a/src/HaskellCI.hs
+++ b/src/HaskellCI.hs
@@ -35,6 +35,7 @@ import System.Process        (readProcessWithExitCode)
 
 import Distribution.PackageDescription (GenericPackageDescription, package, packageDescription, testedWith)
 import Distribution.Text
+import Distribution.Types.CondTree     (CondBranch (..), CondTree (..))
 import Distribution.Version
 
 import qualified Data.ByteString       as BS
@@ -360,13 +361,38 @@ getCabalFiles
     -> m (Project URI Void (FilePath, GenericPackageDescription))
 getCabalFiles InputTypeProject path = do
     contents <- liftIO $ BS.readFile path
-    prj0 <- either (putStrLnErr . renderParseError) return $ parseProject path contents
-    prj1 <- either (putStrLnErr . renderResolveError) return =<< liftIO (resolveProject path prj0)
+    prj0 <- either (putStrLnErr . renderParseError) return $ parseProjectWithConditionals path contents
+    let prj0' :: Project Void String String
+        prj0' = simplifyProject prj0
+    prj1 <- either (putStrLnErr . renderResolveError) return =<< liftIO (resolveProject path prj0')
     either (putStrLnErr . renderParseError) return =<< liftIO (readPackagesOfProject prj1)
 getCabalFiles InputTypePackage path = do
     e <- liftIO $ readPackagesOfProject (emptyProject & field @"prjPackages" .~ [path])
     either (putStrLnErr . renderParseError) return e
 
+simplifyProject :: CondTree c d (Project Void String String) -> Project Void String String
+simplifyProject (CondNode a _ ifs) =
+  foldl (<<>>) a $ map simplifyProject' ifs
+
+simplifyProject' :: CondBranch v d (Project Void String String) -> Project Void String String
+simplifyProject' (CondBranch _ t Nothing)  = simplifyProject t
+simplifyProject' (CondBranch _ t (Just e)) = simplifyProject t <<>> simplifyProject e
+
+-- TODO: we preserve only top-level structure and packages specs.
+(<<>>) :: Project pkg opt uri -> Project pkg opt uri -> Project pkg opt uri
+x <<>> y = Project
+    { prjPackages     = prjPackages x <> prjPackages y
+    , prjOptPackages  = prjOptPackages x <> prjOptPackages y
+    , prjUriPackages  = prjUriPackages x <> prjUriPackages y
+    , prjConstraints  = prjConstraints x
+    , prjAllowNewer   = prjAllowNewer x
+    , prjReorderGoals = prjReorderGoals x
+    , prjMaxBackjumps = prjMaxBackjumps x
+    , prjOptimization = prjOptimization x
+    , prjSourceRepos  = prjSourceRepos x
+    , prjOtherFields  = prjOtherFields x
+    }
+
 -------------------------------------------------------------------------------
 -- Config
 -------------------------------------------------------------------------------
diff --git a/test/Tests.hs b/test/Tests.hs
index 6017158d..f23048ba 100644
--- a/test/Tests.hs
+++ b/test/Tests.hs
@@ -34,6 +34,7 @@ main = do
             , fixtureGoldenTest "enabled-jobs"
             , fixtureGoldenTest "doctest"
             , fixtureGoldenTest "doctest-version"
+            , fixtureGoldenTest "conditionals"
             , testGroup "copy-fields"
                 [ fixtureGoldenTest "copy-fields-all"
                 , fixtureGoldenTest "copy-fields-some"