makerepropkg: use correct devtools makepkg.conf files from dist

Use the recorded buildtool in order to download the matching dist
package and use the appropriate makepkg.conf for reproducing the
package. This is required as the flags are not recorded in the BUILDINFO
hence we need to provide the matching config that declared those flags.

Makefile

 V=20210202
+BUILDTOOLVER ?= $(V)-git
 
 PREFIX = /usr/local
 MANDIR = $(PREFIX)/share/man
@@ -92,7 +93,7 @@ edit = sed -e "s|@pkgdatadir[@]|$(PREFIX)/share/devtools|g"
 %: %.in Makefile lib/common.sh
 	@echo "GEN $@"
 	@$(RM) "$@"
-	@{ echo -n 'm4_changequote([[[,]]])'; cat $@.in; } | m4 -P --define=m4_devtools_version=$V | $(edit) >$@
+	@{ echo -n 'm4_changequote([[[,]]])'; cat $@.in; } | m4 -P --define=m4_devtools_version=$(BUILDTOOLVER) | $(edit) >$@
 	@chmod a-w "$@"
 	@chmod +x "$@"
 	@bash -O extglob -n "$@"

README.md

@@ -14,6 +14,17 @@ as following.
 git config format.subjectprefix 'devtools] [PATCH'
 ```
 
+## Building
+
+When building official distro packages the `BUILDTOOLVER` needs to be set to the
+exact label of the release package in order to allow to detect the exactly used
+devtools version. This is required for reproducible builds to fetch the according
+files like `makepkg.conf`.
+
+```sh
+BUILDTOOLVER="${pkgver}-${pkgrel}-${arch}" make all
+```
+
 ## Releasing
 
 1. bump the version in the Makefile

makerepropkg.in

@@ -81,6 +81,18 @@ get_pkgfile() {
     return 1
 }
 
+get_makepkg_conf() {
+    local fname=${1}
+    local makepkg_conf="${2}"
+    if ! buildtool_file=$(get_pkgfile "${fname}"); then
+        error "failed to retrieve ${fname}"
+        return 1
+    fi
+    msg2 "using makepkg.conf from ${fname}"
+    bsdtar xOqf "${buildtool_file/file:\/\//}" usr/share/devtools/makepkg-x86_64.conf > "${makepkg_conf}"
+    return 0
+}
+
 usage() {
     cat << __EOF__
 usage: ${BASH_SOURCE[0]##*/} [options] <package_file>
@@ -185,7 +197,26 @@ for fname in "${installed[@]}"; do
         exit 1
     fi
 done
-printf '%s\n' "${allpkgfiles[@]}" | mkarchroot -M @pkgdatadir@/makepkg-x86_64.conf -U "${archroot_args[@]}" "${buildroot}"/root - || exit 1
+
+trap 'rm -rf $TEMPDIR' EXIT INT TERM QUIT
+TEMPDIR=$(mktemp -d --tmpdir makerepropkg.XXXXXXXXXX)
+
+makepkg_conf="${TEMPDIR}/makepkg.conf"
+# anything before buildtool support is pinned to the last none buildtool aware release
+if [[ -z "${BUILDTOOL}" ]]; then
+    get_makepkg_conf "devtools-20210202-3-any" "${makepkg_conf}" || exit 1
+# prefere to assume devtools up until matching makepkg version so repository packages remain reproducible
+elif [[ "${BUILDTOOL}" = makepkg ]] && (( $(vercmp "${BUILDTOOLVER}" 6.0.1) <= 0 )); then
+    get_makepkg_conf "devtools-20210202-3-any" "${makepkg_conf}" || exit 1
+# all devtools builds
+elif [[ "${BUILDTOOL}" = devtools ]] && get_makepkg_conf "${BUILDTOOL}-${BUILDTOOLVER}" "${makepkg_conf}"; then
+    true
+# fallback to current makepkg.conf
+else
+    warning "Unknown buildtool (${BUILDTOOL}-${BUILDTOOLVER}), using fallback"
+    makepkg_conf=@pkgdatadir@/makepkg-x86_64.conf
+fi
+printf '%s\n' "${allpkgfiles[@]}" | mkarchroot -M "${makepkg_conf}" -U "${archroot_args[@]}" "${buildroot}"/root - || exit 1
 
 # use makechrootpkg to prep the build directory
 makechrootpkg -r "${buildroot}" -l "${chroot}" -- --packagelist || exit 1