template: Replace process substitution with pipe

After digging deeper into process substitution vs. pipes during the
implementation of `@go.mirror_directory` from `lib/fileutil`, I
realized a few things:

* The same number of processes are spawned.
* There's little benefit to a process substitution for straightforward
  pipes when the output isn't consumed by the shell process.
* It's not straightforward to get the status from a process
  substitution, and neither '$!' nor `wait` help.
* The 'PIPESTATUS' variable is available to check the status of each
  process in the pipe, without the need for `set -o pipefail`.

Also adds a test case for `tar` failure. The 'fail to download ...' test
cases required a little tweaking to ensure they properly cover the cases
where `${download_cmd[@]}` fails.

go-template

@@ -19,7 +19,7 @@
 # Make sure the variables within this script are configured as necessary for
 # your program. You can add any other initialization or configuration between:
 #
-#   . "$_GO_SCRIPT_BASH_CORE_DIR/go-core.bash" "$GO_SCRIPTS_DIR"`
+#   . "$GO_SCRIPT_BASH_CORE_DIR/go-core.bash" "$GO_SCRIPTS_DIR"`
 #   `@go "$@"`
 
 # Set to 'true' if your script is a standalone program, i.e. not bound to
@@ -50,7 +50,6 @@ declare GO_SCRIPT_BASH_DOWNLOAD_URL="${GO_SCRIPT_BASH_DOWNLOAD_URL:-${GO_SCRIPT_
 download_go_script_bash_tarball() {
   # GitHub removes the leading 'v' from the archive's output directory.
   local unpacked_dir="go-script-bash-${GO_SCRIPT_BASH_VERSION#v}"
-  local unpacked_core="$unpacked_dir/go-core.bash"
   local core_dir_parent="${GO_SCRIPT_BASH_CORE_DIR%/*}"
   local url="$GO_SCRIPT_BASH_DOWNLOAD_URL"
   local protocol="${url%%://*}"
@@ -84,7 +83,8 @@ download_go_script_bash_tarball() {
   fi
   printf "Downloading framework from '%s'...\n" "$url"
 
-  if ! tar -xzf - < <("${download_cmd[@]}") || [[ ! -f "$unpacked_core" ]]; then
+  if ! "${download_cmd[@]}" | tar -xzf - ||
+    [[ "${PIPESTATUS[0]}" -ne '0' ]]; then
     printf "Failed to download from '%s'.\n" "$url" >&2
     return 1
   elif [[ ! -d "$core_dir_parent" ]] && ! mkdir -p "$core_dir_parent" ; then

tests/template.bats

@@ -130,7 +130,7 @@ run_with_download_program() {
 
   # We're forcing a local tarball "download" here.
   TEST_USE_REAL_URL= create_fake_tarball_if_not_using_real_url
-  GO_SCRIPT_BASH_DOWNLOAD_URL="file://$TEST_GO_ROOTDIR/archive" \
+  GO_SCRIPT_BASH_DOWNLOAD_URL="$TEST_ARCHIVE_URL" \
     PATH="$BATS_TEST_BINDIR" run "$BASH" "$TEST_GO_ROOTDIR/go-template"
   restore_bats_shell_options
 }
@@ -234,7 +234,7 @@ run_with_download_program() {
 }
 
 @test "$SUITE: fail to download a nonexistent repo" {
-  local url='https://bogus-url-that-does-not-exist'
+  local url="$GO_SCRIPT_BASH_DOWNLOAD_URL/bogus-url-that-does-not-exist"
   local repo='bogus-repo-that-does-not-exist'
 
   skip_if_none_present_on_system 'curl' 'fetch' 'wget'
@@ -251,13 +251,15 @@ run_with_download_program() {
 }
 
 @test "$SUITE: fail to download a nonexistent version" {
-  local url="$GO_SCRIPT_BASH_DOWNLOAD_URL/vnonexistent.tar.gz"
+  local url="$GO_SCRIPT_BASH_DOWNLOAD_URL"
   local branch='vnonexistent'
 
   skip_if_none_present_on_system 'curl' 'fetch' 'wget'
   skip_if_system_missing 'git' 'tar'
   GO_SCRIPT_BASH_VERSION="$branch" run "$TEST_GO_ROOTDIR/go-template"
-  assert_failure
+
+  assert_output_matches "Downloading framework from '$url/${branch}.tar.gz'"
+  assert_output_matches "Failed to download from '$url/${branch}.tar.gz'"
   assert_output_matches 'Using git clone as fallback'
   assert_output_matches "Cloning framework from '$GO_SCRIPT_BASH_REPO_URL'"
   assert_output_matches "Cloning into '$CLONE_DIR'"
@@ -314,6 +316,27 @@ run_with_download_program() {
     "Clone of '$GO_SCRIPT_BASH_REPO_URL' successful\."$'\n\n'
 }
 
+@test "$SUITE: tar failure uses git clone" {
+  skip_if_none_present_on_system 'curl' 'fetch' 'wget'
+  skip_if_system_missing 'git' 'tar'
+
+  TEST_USE_REAL_URL= create_fake_tarball_if_not_using_real_url
+  stub_program_in_path 'tar' \
+    "$(command -v 'tar') \"\$@\"" \
+    'exit 1'
+
+  GO_SCRIPT_BASH_DOWNLOAD_URL="$TEST_ARCHIVE_URL" \
+    run "$BASH" "$TEST_GO_ROOTDIR/go-template"
+  restore_program_in_path 'tar'
+
+  assert_output_matches "Downloading framework from '$EXPECTED_URL'\.\.\."
+  assert_output_matches "Failed to download from '$LOCAL_DOWNLOAD_URL'"
+  assert_output_matches "Using git clone as fallback"
+  assert_output_matches "Cloning framework from '$GO_SCRIPT_BASH_REPO_URL'"
+  assert_output_matches "Cloning into '$CLONE_DIR'"
+  assert_output_matches "Clone of '$GO_SCRIPT_BASH_REPO_URL' successful\."
+}
+
 @test "$SUITE: fail to create directory uses git clone" {
   skip_if_none_present_on_system 'curl' 'fetch' 'wget'
   skip_if_system_missing 'git' 'tar'