Support for low-impact updaters; some SF.net boilerplate helper.

Added support code for comfortable writing of upstream data update
expressions that do not require change of layout of the updated
expressions (although they make assumptions about single assignment per
line). Also added a default for choosing file to update (it is supposed
to be default.nix in the same directory) and a one-liner for typical
sourceforge redirects (and sourceforge mirror:// handling).

pkgs/build-support/upstream-updater/update-walker-service-specific.sh

@@ -0,0 +1,5 @@
+SF_redirect () {
+  redirect
+  process 'http://[a-z]+[.]dl[.]sourceforge[.]net/' 'mirror://sourceforge/'
+  process '[?].*' ''
+}

pkgs/build-support/upstream-updater/update-walker.sh

@@ -16,11 +16,13 @@ version_unpack () {
     s/-(gamma)/ -2 \1 /g; 
     s/-(beta)/ -3 \1 /g; 
     s/-(alpha)/ -4 \1 /g;
+    s/[-]/ - /g; 
     '
 }
 
 version_repack () {
   sed -re '
+    s/ - /-/g;
     s/ -[0-9]+ ([a-z]+) /-\1/g;
     s@ / @/@g
     s/ /./g; 
@@ -29,7 +31,7 @@ version_repack () {
 
 version_sort () {
   version_unpack | 
-    sort -t ' ' -k 1n -k 2n -k 3n -k 4n -k 5n -k 6n -k 7n -n | tac |
+    sort -t ' ' -n $(for i in $(seq 30); do echo " -k${i}n" ; done) | tac |
     version_repack
 }
 
@@ -80,6 +82,10 @@ ensure_version () {
   [ -z "$CURRENT_VERSION" ] && version '.*-([0-9.]+)[-._].*' '\1'
 }
 
+ensure_target () {
+  [ -z "$CURRENT_TARGET" ] && target default.nix
+}
+
 hash () {
   CURRENT_HASH="$(nix-prefetch-url "$CURRENT_URL")"
 }
@@ -127,6 +133,36 @@ do_write_expression () {
   echo "$2"
 }
 
+line_position () {
+  file="$1"
+  regexp="$2"
+  count="${3:-1}"
+  grep -E "$regexp" -m "$count" -B 999999 "$file" | wc -l
+}
+
+replace_once () {
+  file="$1"
+  regexp="$2"
+  replacement="$3"
+  instance="${4:-1}"
+
+  position="$(line_position "$file" "$regexp" "$instance")"
+  sed -re "${position}s	$regexp	$replacement	" -i "$file"
+}
+
+set_var_value () {
+  var="${1}"
+  value="${2}"
+  instance="${3:-1}"
+  file="${4:-$CURRENT_TARGET}"
+  no_quotes="${5:-0}"
+
+  quote='"'
+  let "$no_quotes" && quote=""
+
+  replace_once "$file" "${var} *= *.*" "${var} = ${quote}${value}${quote};"
+}
+
 do_regenerate () {
   BEFORE="$(cat "$1" | grep -F "$BEGIN_EXPRESSION" -B 999999;)"
   AFTER_EXPANDED="$(cat "$1" | grep -F "$BEGIN_EXPRESSION" -A 999999 | grep -E '^ *[}] *; *$' -A 999999;)"
@@ -151,7 +187,10 @@ process_config () {
   BEGIN_EXPRESSION='# Generated upstream information';
   retrieve_version
   ensure_version
+  ensure_target
   update_found && do_overwrite "$CURRENT_TARGET"
 }
 
+source "$own_dir/update-walker-service-specific.sh"
+
 process_config "$1"