support fresh build of jars;
prefer pushd/popd, to avoid unclarity about fail/exit within sub-shell;

--- a/Admin/build	Wed Jun 08 16:19:22 2011 +0200
+++ b/Admin/build	Wed Jun 08 17:11:00 2011 +0200
@@ -27,6 +27,7 @@
     browser         graph browser (requires jdk)
     doc             documentation (requires latex and rail)
     jars            Isabelle/Scala layer (requires Scala in \$SCALA_HOME)
+    jars_fresh      fresh build of jars
 
 EOF
   exit 1
@@ -84,7 +85,7 @@
 function build_jars ()
 {
   pushd "$ISABELLE_HOME/src/Pure" >/dev/null
-  "$ISABELLE_TOOL" env ./build-jars || exit $?
+  "$ISABELLE_TOOL" env ./build-jars "$@" || exit $?
   popd >/dev/null
 }
 
@@ -98,6 +99,7 @@
     browser) build_browser;;
     doc) build_doc;;
     jars) build_jars;;
+    jars_fresh) build_jars -f;;
     *) fail "Bad module $MODULE"
   esac
 done

--- a/src/Pure/build-jars	Wed Jun 08 16:19:22 2011 +0200
+++ b/src/Pure/build-jars	Wed Jun 08 17:11:00 2011 +0200
@@ -9,6 +9,19 @@
 
 ## diagnostics
 
+PRG="$(basename "$0")"
+
+function usage()
+{
+  echo
+  echo "Usage: isabelle $PRG [OPTIONS]"
+  echo
+  echo "  Options are:"
+  echo "    -f           fresh build"
+  echo
+  exit 1
+}
+
 function fail()
 {
   echo "$1" >&2
@@ -19,6 +32,33 @@
 [ -z "$SCALA_HOME" ] && fail "Unknown SCALA_HOME -- Scala unavailable"
 
 
+## process command line
+
+# options
+
+FRESH=""
+
+while getopts "f" OPT
+do
+  case "$OPT" in
+    f)
+      FRESH=true
+      ;;
+    \?)
+      usage
+      ;;
+  esac
+done
+
+shift $(($OPTIND - 1))
+
+
+# args
+
+[ "$#" -ne 0 ] && usage
+
+
+
 ## dependencies
 
 declare -a SOURCES=(
@@ -75,16 +115,19 @@
 
 ## main
 
-OUTDATED=false
-
-for SOURCE in "${SOURCES[@]}"
-do
-  [ ! -e "$SOURCE" ] && fail "Missing source file: $SOURCE"
-  for TARGET in "${TARGETS[@]}"
+if [ -n "$FRESH" ]; then
+  OUTDATED=true
+else
+  OUTDATED=false
+  for SOURCE in "${SOURCES[@]}"
   do
-    [ ! -e "$TARGET" -o "$SOURCE" -nt "$TARGET" ] && OUTDATED=true
+    [ ! -e "$SOURCE" ] && fail "Missing source file: $SOURCE"
+    for TARGET in "${TARGETS[@]}"
+    do
+      [ ! -e "$TARGET" -o "$SOURCE" -nt "$TARGET" ] && OUTDATED=true
+    done
   done
-done
+fi
 
 if [ "$OUTDATED" = true ]
 then
@@ -96,17 +139,20 @@
   "$SCALA_HOME/bin/scalac" -unchecked -deprecation -d classes -target:jvm-1.5 "${SOURCES[@]}" || \
     fail "Failed to compile sources"
   mkdir -p "$TARGET_DIR" || fail "Failed to create directory $TARGET_DIR"
-  (
-    cd classes
-    jar cfe "$(jvmpath "$PURE_JAR")" isabelle.GUI_Setup isabelle || \
-      fail "Failed to produce $PURE_JAR"
+
+  pushd classes
+
+  jar cfe "$(jvmpath "$PURE_JAR")" isabelle.GUI_Setup isabelle || \
+    fail "Failed to produce $PURE_JAR"
 
-    cp "$SCALA_HOME/lib/scala-swing.jar" .
-    jar xf scala-swing.jar
+  cp "$SCALA_HOME/lib/scala-swing.jar" .
+  jar xf scala-swing.jar
 
-    cp "$SCALA_HOME/lib/scala-library.jar" "$FULL_JAR"
-    jar ufe "$(jvmpath "$FULL_JAR")" isabelle.GUI_Setup isabelle scala || \
-      fail "Failed to produce $FULL_JAR"
-  )
+  cp "$SCALA_HOME/lib/scala-library.jar" "$FULL_JAR"
+  jar ufe "$(jvmpath "$FULL_JAR")" isabelle.GUI_Setup isabelle scala || \
+    fail "Failed to produce $FULL_JAR"
+
+  popd >/dev/null
+
   rm -rf classes
 fi