Switch gcc download mechanism to ftp

"./build gcc --default" now results in the download of a 5.3.0 release
tar ball from the nearest mirror, instead of the previous svn checkout
of the trunk (6.0.0).  Any gcc build launched by install.sh now
installs release 5.3.0.  When invoking "build" by other means, e.g.,
at the command line, a development branch can be built by specifying
the branch name (e.g., "./build gcc gcc-5-branch").  Not specifying a
branch is equivalent to "./build gcc trunk".

Author: Damian Rouson

install.sh

@@ -408,14 +408,20 @@ find_or_install()
         stack_push dependency_pkg "bison"
         stack_push dependency_exe "yacc"
         stack_push dependency_path `./build bison --default --query-path`
-
       else
         printf "no.\n"
         printf "$this_script: Using the $executable found in the PATH.\n"
         export FLEX=$executable
         stack_push acceptable_in_path $package $executable
-        # Halt the recursion by removing flex from the dependency stack and indicating
-        # that none of the prerequisites required to build flex are needed.
+        # Remove $package from the dependency stack
+        stack_pop dependency_pkg package_done
+        stack_pop dependency_exe executable_done
+        stack_pop dependency_path package_done_path
+        # Put $package onto the script_installed log
+        stack_push script_installed package_done
+        stack_push script_installed executable_done
+        stack_push script_installed package_done_path
+        # Halt the recursion and signal that none of $package's prerequisites need to be built
         stack_push dependency_pkg "none"
         stack_push dependency_exe "none"
         stack_push dependency_path "none"

install_prerequisites/build

@@ -57,22 +57,52 @@ usage()
     echo ""
     echo "[exit 10]"
     exit 10
+ 
+# Private usage information
+#
+# The following arguments are intentionally not documented in the above public usage information because
+# they are intended for use by ../install.sh only rather than for use interactively at the command line:
+#    Argument $2  Argument $3      Description 
+#    --default                     install the default version for the corresponding package
+#    --default    --query-path     return the default installation location for the package
+#    --default    --query-version  return the default version for the package
+#    --default    --query-url      return the default download location for the package
+#
+#   Example: ./build gcc --default --query-path
+#
+#  With the exception of gcc, all uses of "--default" refer to the package version that would be downloaded
+#  if no version is specified, e.g., "./build mpich". By contrast, "./build gcc" downloads the latest 
+#  pre-release, development branch (the "trunk"), whereas "./build gcc --default" downloads a released 
+#  version of gcc.
+#
+# The following argument works only with gcc and is mutually exclusive with the above private arguments 
+# (it could be extended to work with any svn download):
+#    Argument $2  Description 
+#    --avail      list the development branches available for checkout
+#    -a           same as --avail
+#
+#   Example: ./build gcc --avail
 }
 
 # If the package name is recognized, then set the default version.
 # Otherwise, list the allowable package names and default versions and then exit.
 set_default_version()
 {
+  version_requested=$2
   if [[ $package_to_build == "--list" || $package_to_build == "-l" ]]; then
        printf "\n"
        printf "The '$this_script' script can build the following packages:\n"
+  elif [[ $package_to_build == "gcc" && $version_requested == "--default" ]]; then
+    gcc_version="5.3.0"
+  else
+    gcc_version="trunk"
   fi
   # This is a bash 3 hack standing in for a bash 4 hash (bash 3 is the lowest common
   # denominator because, for licensing reasons, OS X only has bash 3 by default.)
   # See http://stackoverflow.com/questions/1494178/how-to-define-hash-tables-in-bash
   package_version=(
     "cmake:3.4.0"
-    "gcc:gcc-5-branch"
+    "gcc:$gcc_version"
     "mpich:3.1.4"
     "wget:1.16.3"
     "flex:2.6.0"
@@ -100,7 +130,7 @@ set_default_version()
      elif [[ $package_to_build == "$KEY" ]]; then
        # We recognize the package name so we set the default version:
        verbosity=$1
-       if [[ $verbosity != "quietly" ]]; then
+       if [[ $2 != "--default" ]]; then
          printf "Using default version $VALUE\n"
        fi
        default_version=$VALUE
@@ -116,11 +146,16 @@ set_default_version()
 
 check_prerequisites()
 {
+  if [[ $package_to_build == "gcc" && $version_requested == "--default" ]]; then
+    gcc_fetch="ftp"
+  else
+    gcc_fetch="svn"
+  fi
   # This is a bash 3 hack standing in for a bash 4 hash (bash 3 is the lowest common
   # denominator because, for licensing reasons, OS X only has bash 3 by default.)
   # See http://stackoverflow.com/questions/1494178/how-to-define-hash-tables-in-bash
   package_download_mechanism=(
-    "gcc:svn"
+    "gcc:$gcc_fetch"
     "wget:ftp"
     "cmake:wget"
     "mpich:wget"
@@ -166,9 +201,13 @@ set_url()
 {
   if [[ $package_to_build == 'cmake' ]]; then
     major_minor="${version_to_build%.*}"
+  elif [[ "$package_to_build" == "gcc" && "$version_to_build" == "$default_version" ]]; then
+    gcc_url_head="http://ftpmirror.gnu.org/gcc/gcc-5.3.0/"
+  else
+    gcc_url_head="svn://gcc.gnu.org/svn/gcc/"
   fi
   package_url_head=(
-    "gcc;svn://gcc.gnu.org/svn/gcc/"
+    "gcc;$gcc_url_head"
     "wget;ftp.gnu.org:/gnu/wget/"
     "m4;ftp.gnu.org:/gnu/m4/"
     "pkg-config;http://pkgconfig.freedesktop.org/releases/"
@@ -202,7 +241,7 @@ set_url()
     elif [[ $version_to_build == '--avail' || $version_to_build == '-a' ]]; then
       gcc_tail='branches'
     else
-      gcc_tail=/branches/$version_to_build
+      gcc_tail="gcc-$version_to_build.tar.bz2"
     fi
   fi
   package_url_tail=(
@@ -299,6 +338,7 @@ download_if_necessary()
     printf "Downloading $package_to_build $version_to_build to the following location:\n"
     printf "$download_path/$package_source_directory \n"
     printf "Download command: $fetch $args $url\n"
+    printf "Depending on the file size and network bandwidth, this could take several minutes or longer."
     $fetch $args $url
     if [[ $version_to_build == '--avail' || $version_to_build == '-a' ]]; then
       # In this case, args="ls" and the list of available versions has been printed so we can move on.
@@ -390,11 +430,8 @@ package_to_build=$1
 
 # Interpret the second command-line argument, if present, as the package version.
 # Otherwise, set the default package version.
-if [[ -z $2 ]]; then
-  set_default_version
-  version_to_build=$default_version
-elif [[ $2 == "--default" ]]; then
-  set_default_version "quietly"
+if [[ -z $2 || $2 == "--default"  ]]; then
+  set_default_version $*
   version_to_build=$default_version
 else
   version_to_build=$2
@@ -446,7 +483,7 @@ elif [[ $1 == '-v' || $1 == '-V' || $1 == '--version' ]]; then
 else
   # Download, unpack, and build CMake
   download_path=${PWD}
-  check_prerequisites &&
+  check_prerequisites $* &&
   download_if_necessary &&
   unpack_if_necessary &&
   CC=$CC CXX=$CXX build_and_install $package_to_build $version_to_build $install_path $num_threads $download_path \