diff --git a/fixtures/matrix-extra.args b/fixtures/matrix-extra.args
new file mode 100644
index 00000000..6b69595d
--- /dev/null
+++ b/fixtures/matrix-extra.args
@@ -0,0 +1,2 @@
+--matrix-extra=abc:1,2,3
+--matrix-extra=foo:bar,baz
diff --git a/fixtures/matrix-extra.bash b/fixtures/matrix-extra.bash
new file mode 100644
index 00000000..3cf447b1
--- /dev/null
+++ b/fixtures/matrix-extra.bash
@@ -0,0 +1,513 @@
+# SUCCESS
+# *INFO* Generating Bash script for testing for GHC versions: 8.0.2 8.2.2 8.4.4 8.6.5 8.8.4 8.10.3
+#!/bin/bash
+# shellcheck disable=SC2086,SC2016,SC2046
+# REGENDATA ["--matrix-extra=abc:1,2,3","--matrix-extra=foo:bar,baz","bash","matrix-extra.project"]
+
+set -o pipefail
+
+# Mode
+##############################################################################
+
+if [ "$1" = "indocker" ]; then
+    INDOCKER=true
+    shift
+else
+    INDOCKER=false
+fi
+
+# Run configuration
+##############################################################################
+
+CFG_CABAL_STORE_CACHE=""
+CFG_CABAL_REPO_CACHE=""
+CFG_JOBS="8.10.3 8.8.4 8.6.5 8.4.4 8.2.2 8.0.2"
+CFG_CABAL_UPDATE=false
+
+SCRIPT_NAME=$(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 $CABAL v2-update -v
+fi
+
+# install cabal-plan
+install_cabalplan
+run_cmd cabal-plan --version
+
+# sdist
+put_info "sdist"
+change_dir "$SRCDIR"
+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_notmuch="$(find "$BUILDDIR/unpacked" -maxdepth 1 -type d -regex '.*/notmuch-[0-9.]*')"
+run_cmd touch cabal.project
+run_cmd touch cabal.project.local
+echo_to cabal.project "packages: ${PKGDIR_notmuch}"
+echo_if_to $((HCNUMVER >= 80200)) cabal.project "package notmuch"
+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: $_ installed\n" unless /^(notmuch)$/; }' >> 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 $ARG_BENCH all
+
+# tests
+put_info "tests"
+
+# cabal check
+put_info "cabal check"
+change_dir "${PKGDIR_notmuch}"
+run_cmd ${CABAL} -vnormal check
+change_dir "$BUILDDIR"
+
+# haddock
+put_info "haddock"
+run_cmd $CABAL v2-haddock $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/matrix-extra.github b/fixtures/matrix-extra.github
new file mode 100644
index 00000000..f7c806c5
--- /dev/null
+++ b/fixtures/matrix-extra.github
@@ -0,0 +1,300 @@
+# SUCCESS
+# *INFO* Generating GitHub config for testing for GHC versions: 8.0.2 8.2.2 8.4.4 8.6.5 8.8.4 8.10.3
+# This GitHub workflow config has been generated by a script via
+#
+#   haskell-ci '--matrix-extra=abc:1,2,3' '--matrix-extra=foo:bar,baz' 'github' 'matrix-extra.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 ["--matrix-extra=abc:1,2,3","--matrix-extra=foo:bar,baz","github","matrix-extra.project"]
+#
+name: Haskell-CI
+on:
+  - push
+  - pull_request
+jobs:
+  linux:
+    name: Haskell-CI Linux - GHC ${{ matrix.ghc }}
+    runs-on: ubuntu-18.04
+    container:
+      image: buildpack-deps:bionic
+    continue-on-error: ${{ matrix.allow-failure }}
+    strategy:
+      matrix:
+        include:
+          - ghc: 8.10.3
+            allow-failure: false
+            abc: "1"
+            foo: bar
+          - ghc: 8.8.4
+            allow-failure: false
+            abc: "1"
+            foo: bar
+          - ghc: 8.6.5
+            allow-failure: false
+            abc: "1"
+            foo: bar
+          - ghc: 8.4.4
+            allow-failure: false
+            abc: "1"
+            foo: bar
+          - ghc: 8.2.2
+            allow-failure: false
+            abc: "1"
+            foo: bar
+          - ghc: 8.0.2
+            allow-failure: false
+            abc: "1"
+            foo: bar
+          - ghc: 8.10.3
+            allow-failure: false
+            abc: "1"
+            foo: baz
+          - ghc: 8.8.4
+            allow-failure: false
+            abc: "1"
+            foo: baz
+          - ghc: 8.6.5
+            allow-failure: false
+            abc: "1"
+            foo: baz
+          - ghc: 8.4.4
+            allow-failure: false
+            abc: "1"
+            foo: baz
+          - ghc: 8.2.2
+            allow-failure: false
+            abc: "1"
+            foo: baz
+          - ghc: 8.0.2
+            allow-failure: false
+            abc: "1"
+            foo: baz
+          - ghc: 8.10.3
+            allow-failure: false
+            abc: "2"
+            foo: bar
+          - ghc: 8.8.4
+            allow-failure: false
+            abc: "2"
+            foo: bar
+          - ghc: 8.6.5
+            allow-failure: false
+            abc: "2"
+            foo: bar
+          - ghc: 8.4.4
+            allow-failure: false
+            abc: "2"
+            foo: bar
+          - ghc: 8.2.2
+            allow-failure: false
+            abc: "2"
+            foo: bar
+          - ghc: 8.0.2
+            allow-failure: false
+            abc: "2"
+            foo: bar
+          - ghc: 8.10.3
+            allow-failure: false
+            abc: "2"
+            foo: baz
+          - ghc: 8.8.4
+            allow-failure: false
+            abc: "2"
+            foo: baz
+          - ghc: 8.6.5
+            allow-failure: false
+            abc: "2"
+            foo: baz
+          - ghc: 8.4.4
+            allow-failure: false
+            abc: "2"
+            foo: baz
+          - ghc: 8.2.2
+            allow-failure: false
+            abc: "2"
+            foo: baz
+          - ghc: 8.0.2
+            allow-failure: false
+            abc: "2"
+            foo: baz
+          - ghc: 8.10.3
+            allow-failure: false
+            abc: "3"
+            foo: bar
+          - ghc: 8.8.4
+            allow-failure: false
+            abc: "3"
+            foo: bar
+          - ghc: 8.6.5
+            allow-failure: false
+            abc: "3"
+            foo: bar
+          - ghc: 8.4.4
+            allow-failure: false
+            abc: "3"
+            foo: bar
+          - ghc: 8.2.2
+            allow-failure: false
+            abc: "3"
+            foo: bar
+          - ghc: 8.0.2
+            allow-failure: false
+            abc: "3"
+            foo: bar
+          - ghc: 8.10.3
+            allow-failure: false
+            abc: "3"
+            foo: baz
+          - ghc: 8.8.4
+            allow-failure: false
+            abc: "3"
+            foo: baz
+          - ghc: 8.6.5
+            allow-failure: false
+            abc: "3"
+            foo: baz
+          - ghc: 8.4.4
+            allow-failure: false
+            abc: "3"
+            foo: baz
+          - ghc: 8.2.2
+            allow-failure: false
+            abc: "3"
+            foo: baz
+          - ghc: 8.0.2
+            allow-failure: false
+            abc: "3"
+            foo: baz
+      fail-fast: false
+    steps:
+      - name: apt
+        run: |
+          apt-get update
+          apt-get install -y --no-install-recommends gnupg ca-certificates dirmngr curl git software-properties-common
+          apt-add-repository -y 'ppa:hvr/ghc'
+          apt-get update
+          apt-get install -y ghc-$GHC_VERSION cabal-install-3.2
+        env:
+          GHC_VERSION: ${{ matrix.ghc }}
+      - name: Set PATH and environment variables
+        run: |
+          echo "$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" >> $GITHUB_ENV
+          HC=/opt/ghc/$GHC_VERSION/bin/ghc
+          echo "HC=$HC" >> $GITHUB_ENV
+          echo "HCPKG=/opt/ghc/$GHC_VERSION/bin/ghc-pkg" >> $GITHUB_ENV
+          echo "HADDOCK=/opt/ghc/$GHC_VERSION/bin/haddock" >> $GITHUB_ENV
+          echo "CABAL=/opt/cabal/3.2/bin/cabal -vnormal+nowrap" >> $GITHUB_ENV
+          HCNUMVER=$(${HC} --numeric-version|perl -ne '/^(\d+)\.(\d+)\.(\d+)(\.(\d+))?$/; 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" >> $GITHUB_ENV
+          echo "ARG_COMPILER=--ghc --with-compiler=/opt/ghc/$GHC_VERSION/bin/ghc" >> $GITHUB_ENV
+          echo "GHCJSARITH=0" >> $GITHUB_ENV
+        env:
+          GHC_VERSION: ${{ matrix.ghc }}
+      - 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
+      - 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/v0.6.2.0/cabal-plan-0.6.2.0-x86_64-linux.xz > cabal-plan.xz
+          echo 'de73600b1836d3f55e32d80385acc055fd97f60eaa0ab68a755302685f5d81bc  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@v2
+        with:
+          path: source
+      - name: sdist
+        run: |
+          mkdir -p sdist
+          cd source || false
+          $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 $GITHUB_WORKSPACE/unpacked -xzvf {} \;
+      - name: generate cabal.project
+        run: |
+          PKGDIR_notmuch="$(find "$GITHUB_WORKSPACE/unpacked" -maxdepth 1 -type d -regex '.*/notmuch-[0-9.]*')"
+          echo "PKGDIR_notmuch=${PKGDIR_notmuch}" >> $GITHUB_ENV
+          touch cabal.project
+          touch cabal.project.local
+          echo "packages: ${PKGDIR_notmuch}" >> cabal.project
+          if [ $((HCNUMVER >= 80200)) -ne 0 ] ; then echo "package notmuch" >> 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: $_ installed\n" unless /^(notmuch)$/; }' >> 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: cache
+        uses: actions/cache@v2
+        with:
+          key: ${{ runner.os }}-${{ matrix.ghc }}-${{ github.sha }}
+          path: ~/.cabal/store
+          restore-keys: ${{ runner.os }}-${{ matrix.ghc }}-
+      - 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: cabal check
+        run: |
+          cd ${PKGDIR_notmuch} || false
+          ${CABAL} -vnormal check
+      - name: haddock
+        run: |
+          $CABAL v2-haddock $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
diff --git a/fixtures/matrix-extra.project b/fixtures/matrix-extra.project
new file mode 100644
index 00000000..393d9ee5
--- /dev/null
+++ b/fixtures/matrix-extra.project
@@ -0,0 +1 @@
+packages: notmuch
diff --git a/fixtures/matrix-extra.travis b/fixtures/matrix-extra.travis
new file mode 100644
index 00000000..e11b24e2
--- /dev/null
+++ b/fixtures/matrix-extra.travis
@@ -0,0 +1,150 @@
+# SUCCESS
+# *INFO* Generating Travis-CI config for testing for GHC versions: 8.0.2 8.2.2 8.4.4 8.6.5 8.8.4 8.10.3
+# This Travis job script has been generated by a script via
+#
+#   haskell-ci '--matrix-extra=abc:1,2,3' '--matrix-extra=foo:bar,baz' 'travis' 'matrix-extra.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
+#
+version: ~> 1.0
+language: c
+os: linux
+dist: xenial
+git:
+  # whether to recursively clone submodules
+  submodules: false
+cache:
+  directories:
+    - $HOME/.cabal/packages
+    - $HOME/.cabal/store
+    - $HOME/.hlint
+before_cache:
+  - rm -fv $CABALHOME/packages/hackage.haskell.org/build-reports.log
+  # remove files that are regenerated by 'cabal update'
+  - rm -fv $CABALHOME/packages/hackage.haskell.org/00-index.*
+  - rm -fv $CABALHOME/packages/hackage.haskell.org/*.json
+  - rm -fv $CABALHOME/packages/hackage.haskell.org/01-index.cache
+  - rm -fv $CABALHOME/packages/hackage.haskell.org/01-index.tar
+  - rm -fv $CABALHOME/packages/hackage.haskell.org/01-index.tar.idx
+  - rm -rfv $CABALHOME/packages/head.hackage
+jobs:
+  include:
+    - compiler: ghc-8.10.3
+      addons: {"apt":{"sources":[{"sourceline":"deb http://ppa.launchpad.net/hvr/ghc/ubuntu xenial main","key_url":"https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x063dab2bdc0b3f9fcebc378bff3aeacef6f88286"}],"packages":["ghc-8.10.3","cabal-install-3.4"]}}
+      os: linux
+    - compiler: ghc-8.8.4
+      addons: {"apt":{"sources":[{"sourceline":"deb http://ppa.launchpad.net/hvr/ghc/ubuntu xenial main","key_url":"https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x063dab2bdc0b3f9fcebc378bff3aeacef6f88286"}],"packages":["ghc-8.8.4","cabal-install-3.4"]}}
+      os: linux
+    - compiler: ghc-8.6.5
+      addons: {"apt":{"sources":[{"sourceline":"deb http://ppa.launchpad.net/hvr/ghc/ubuntu xenial main","key_url":"https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x063dab2bdc0b3f9fcebc378bff3aeacef6f88286"}],"packages":["ghc-8.6.5","cabal-install-3.4"]}}
+      os: linux
+    - compiler: ghc-8.4.4
+      addons: {"apt":{"sources":[{"sourceline":"deb http://ppa.launchpad.net/hvr/ghc/ubuntu xenial main","key_url":"https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x063dab2bdc0b3f9fcebc378bff3aeacef6f88286"}],"packages":["ghc-8.4.4","cabal-install-3.4"]}}
+      os: linux
+    - compiler: ghc-8.2.2
+      addons: {"apt":{"sources":[{"sourceline":"deb http://ppa.launchpad.net/hvr/ghc/ubuntu xenial main","key_url":"https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x063dab2bdc0b3f9fcebc378bff3aeacef6f88286"}],"packages":["ghc-8.2.2","cabal-install-3.4"]}}
+      os: linux
+    - compiler: ghc-8.0.2
+      addons: {"apt":{"sources":[{"sourceline":"deb http://ppa.launchpad.net/hvr/ghc/ubuntu xenial main","key_url":"https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x063dab2bdc0b3f9fcebc378bff3aeacef6f88286"}],"packages":["ghc-8.0.2","cabal-install-3.4"]}}
+      os: linux
+before_install:
+  - HC=$(echo "/opt/$CC/bin/ghc" | sed 's/-/\//')
+  - WITHCOMPILER="-w $HC"
+  - HADDOCK=$(echo "/opt/$CC/bin/haddock" | sed 's/-/\//')
+  - HCPKG="$HC-pkg"
+  - unset CC
+  - CABAL=/opt/ghc/bin/cabal
+  - CABALHOME=$HOME/.cabal
+  - export PATH="$CABALHOME/bin:$PATH"
+  - TOP=$(pwd)
+  - "HCNUMVER=$(${HC} --numeric-version|perl -ne '/^(\\d+)\\.(\\d+)\\.(\\d+)(\\.(\\d+))?$/; print(10000 * $1 + 100 * $2 + ($3 == 0 ? $5 != 1 : $3))')"
+  - echo $HCNUMVER
+  - CABAL="$CABAL -vnormal+nowrap"
+  - set -o pipefail
+  - TEST=--enable-tests
+  - BENCH=--enable-benchmarks
+  - HEADHACKAGE=false
+  - rm -f $CABALHOME/config
+  - |
+    echo "verbose: normal +nowrap +markoutput"          >> $CABALHOME/config
+    echo "remote-build-reporting: anonymous"            >> $CABALHOME/config
+    echo "write-ghc-environment-files: never"           >> $CABALHOME/config
+    echo "remote-repo-cache: $CABALHOME/packages"       >> $CABALHOME/config
+    echo "logs-dir:          $CABALHOME/logs"           >> $CABALHOME/config
+    echo "world-file:        $CABALHOME/world"          >> $CABALHOME/config
+    echo "extra-prog-path:   $CABALHOME/bin"            >> $CABALHOME/config
+    echo "symlink-bindir:    $CABALHOME/bin"            >> $CABALHOME/config
+    echo "installdir:        $CABALHOME/bin"            >> $CABALHOME/config
+    echo "build-summary:     $CABALHOME/logs/build.log" >> $CABALHOME/config
+    echo "store-dir:         $CABALHOME/store"          >> $CABALHOME/config
+    echo "install-dirs user"                            >> $CABALHOME/config
+    echo "  prefix: $CABALHOME"                         >> $CABALHOME/config
+    echo "repository hackage.haskell.org"               >> $CABALHOME/config
+    echo "  url: http://hackage.haskell.org/"           >> $CABALHOME/config
+install:
+  - ${CABAL} --version
+  - echo "$(${HC} --version) [$(${HC} --print-project-git-commit-id 2> /dev/null || echo '?')]"
+  - |
+    echo "program-default-options"                >> $CABALHOME/config
+    echo "  ghc-options: $GHCJOBS +RTS -M6G -RTS" >> $CABALHOME/config
+  - cat $CABALHOME/config
+  - rm -fv cabal.project cabal.project.local cabal.project.freeze
+  - travis_retry ${CABAL} v2-update -v
+  # Generate cabal.project
+  - rm -rf cabal.project cabal.project.local cabal.project.freeze
+  - touch cabal.project
+  - |
+    echo "packages: notmuch" >> cabal.project
+  - if [ $((HCNUMVER >= 80200)) -ne 0 ] ; then echo 'package notmuch' >> cabal.project ; fi
+  - "if [ $((HCNUMVER >= 80200)) -ne 0 ] ; then echo '  ghc-options: -Werror=missing-methods' >> cabal.project ; fi"
+  - |
+  - "for pkg in $($HCPKG list --simple-output); do echo $pkg | sed 's/-[^-]*$//' | (grep -vE -- '^(notmuch)$' || true) | sed 's/^/constraints: /' | sed 's/$/ installed/' >> cabal.project.local; done"
+  - cat cabal.project || true
+  - cat cabal.project.local || true
+  - if [ -f "notmuch/configure.ac" ]; then (cd "notmuch" && autoreconf -i); fi
+  - ${CABAL} v2-freeze $WITHCOMPILER ${TEST} ${BENCH}
+  - "cat cabal.project.freeze | sed -E 's/^(constraints: *| *)//' | sed 's/any.//'"
+  - rm  cabal.project.freeze
+  - travis_wait 40 ${CABAL} v2-build $WITHCOMPILER ${TEST} ${BENCH} --dep -j2 all
+  - travis_wait 40 ${CABAL} v2-build $WITHCOMPILER --disable-tests --disable-benchmarks --dep -j2 all
+script:
+  - DISTDIR=$(mktemp -d /tmp/dist-test.XXXX)
+  # Packaging...
+  - ${CABAL} v2-sdist all
+  # Unpacking...
+  - mv dist-newstyle/sdist/*.tar.gz ${DISTDIR}/
+  - cd ${DISTDIR} || false
+  - find . -maxdepth 1 -type f -name '*.tar.gz' -exec tar -xvf '{}' \;
+  - find . -maxdepth 1 -type f -name '*.tar.gz' -exec rm       '{}' \;
+  - PKGDIR_notmuch="$(find . -maxdepth 1 -type d -regex '.*/notmuch-[0-9.]*')"
+  # Generate cabal.project
+  - rm -rf cabal.project cabal.project.local cabal.project.freeze
+  - touch cabal.project
+  - |
+    echo "packages: ${PKGDIR_notmuch}" >> cabal.project
+  - if [ $((HCNUMVER >= 80200)) -ne 0 ] ; then echo 'package notmuch' >> cabal.project ; fi
+  - "if [ $((HCNUMVER >= 80200)) -ne 0 ] ; then echo '  ghc-options: -Werror=missing-methods' >> cabal.project ; fi"
+  - |
+  - "for pkg in $($HCPKG list --simple-output); do echo $pkg | sed 's/-[^-]*$//' | (grep -vE -- '^(notmuch)$' || true) | sed 's/^/constraints: /' | sed 's/$/ installed/' >> cabal.project.local; done"
+  - cat cabal.project || true
+  - cat cabal.project.local || true
+  # Building...
+  # this builds all libraries and executables (without tests/benchmarks)
+  - ${CABAL} v2-build $WITHCOMPILER --disable-tests --disable-benchmarks all
+  # Building with tests and benchmarks...
+  # build & run tests, build benchmarks
+  - ${CABAL} v2-build $WITHCOMPILER ${TEST} ${BENCH} all --write-ghc-environment-files=always
+  # cabal check...
+  - (cd ${PKGDIR_notmuch} && ${CABAL} -vnormal check)
+  # haddock...
+  - ${CABAL} v2-haddock $WITHCOMPILER --with-haddock $HADDOCK ${TEST} ${BENCH} all
+  # Building without installed constraints for packages in global-db...
+  - rm -f cabal.project.local
+  - ${CABAL} v2-build $WITHCOMPILER --disable-tests --disable-benchmarks all
+
+# REGENDATA ["--matrix-extra=abc:1,2,3","--matrix-extra=foo:bar,baz","travis","matrix-extra.project"]
+# EOF
diff --git a/fixtures/notmuch/notmuch.cabal b/fixtures/notmuch/notmuch.cabal
new file mode 100644
index 00000000..c98b46a3
--- /dev/null
+++ b/fixtures/notmuch/notmuch.cabal
@@ -0,0 +1,129 @@
+-- Initial notmuch.cabal generated by cabal init.  For further 
+-- documentation, see http://haskell.org/cabal/users-guide/
+
+name:                notmuch
+version:             0.3.0.0
+synopsis:            Haskell binding to Notmuch, the mail indexer
+description:
+  Binding to the notmuch mail indexer, providing a hopefully
+  somewhat typesafe way to search your email.
+license:             GPL-3
+license-file:        gpl-3.0.txt
+extra-source-files:
+  README.rst
+author:              Fraser Tweedale
+maintainer:          frase@frase.id.au
+copyright:           Copyright (C) 2014-2018  Fraser Tweedale
+category:            FFI
+build-type:          Simple
+cabal-version:       >=1.10
+tested-with:
+  GHC==8.0.2, GHC==8.2.2, GHC==8.4.4, GHC==8.6.5, GHC==8.8.4, GHC==8.10.3
+
+homepage:            https://github.com/purebred-mua/hs-notmuch
+bug-reports:         https://github.com/purebred-mua/hs-notmuch/issues
+source-repository head
+  type: git
+  location: https://github.com/purebred-mua/hs-notmuch.git
+
+flag demos
+  description: Build demonstration programs
+  default:     False
+
+library
+  exposed-modules:
+    Notmuch
+    Notmuch.Util
+
+  other-modules:
+    Notmuch.Binding
+    Notmuch.Binding.Constants
+    Notmuch.Search
+    Notmuch.Tag
+    Notmuch.Talloc
+
+  build-depends:
+    base >= 4.9 && <5
+    , bytestring >= 0.10 && < 0.11
+    , deepseq >= 1.4
+    , filepath >= 1.0
+    , mtl >= 2 && < 3
+    , profunctors >= 5 && < 6
+    , tagged >= 0.8 && < 1
+    , time
+    , text
+
+  build-tools:
+    c2hs >= 0.19.1
+
+  extra-libraries:
+    notmuch
+    , talloc
+
+  ghc-options:         -Wall
+  hs-source-dirs:      src
+  default-language:    Haskell2010
+
+executable hs-notmuch-files
+  if !flag(demos)
+    buildable: False
+  default-language:    Haskell2010
+  hs-source-dirs: tools
+  ghc-options: -Wall
+  main-is: Files.hs
+  build-depends:
+    base         >= 4.9
+    , mtl
+    , notmuch
+
+executable hs-notmuch-tag-message
+  if !flag(demos)
+    buildable: False
+  default-language:    Haskell2010
+  hs-source-dirs: tools
+  ghc-options: -Wall
+  main-is: TagMessage.hs
+  build-depends:
+    base         >= 4.9
+    , bytestring
+    , mtl
+    , notmuch
+
+executable hs-notmuch-tag-count
+  if !flag(demos)
+    buildable: False
+  default-language:    Haskell2010
+  hs-source-dirs: tools
+  ghc-options: -Wall
+  main-is: TagCount.hs
+  build-depends:
+    base         >= 4.9
+    , bytestring
+    , mtl
+    , containers
+    , notmuch
+
+executable hs-notmuch-tag-set
+  if !flag(demos)
+    buildable: False
+  default-language:    Haskell2010
+  hs-source-dirs: tools
+  ghc-options: -Wall
+  main-is: TagSet.hs
+  build-depends:
+    base         >= 4.9
+    , bytestring
+    , mtl
+    , notmuch
+
+executable hs-notmuch-index-file
+  if !flag(demos)
+    buildable: False
+  default-language:    Haskell2010
+  hs-source-dirs: tools
+  ghc-options: -Wall
+  main-is: IndexFile.hs
+  build-depends:
+    base         >= 4.9
+    , mtl
+    , notmuch
diff --git a/haskell-ci.cabal b/haskell-ci.cabal
index d0514c7d..b8d0018d 100644
--- a/haskell-ci.cabal
+++ b/haskell-ci.cabal
@@ -48,6 +48,7 @@ extra-source-files:
   fixtures/servant-foreign/servant-foreign.cabal
   fixtures/servant-server/servant-server.cabal
   fixtures/splitmix/splitmix.cabal
+  fixtures/notmuch/notmuch.cabal
 
 source-repository head
   type:     git
diff --git a/test/Tests.hs b/test/Tests.hs
index 61b6b252..93a46dfa 100644
--- a/test/Tests.hs
+++ b/test/Tests.hs
@@ -29,6 +29,7 @@ main = do
         , fixtureGoldenTest "messy"
         , fixtureGoldenTest "psql"
         , fixtureGoldenTest "travis-patch"
+        , fixtureGoldenTest "matrix-extra"
         , testGroup "copy-fields"
             [ fixtureGoldenTest "copy-fields-all"
             , fixtureGoldenTest "copy-fields-some"