help: Restore IFS, handle ./go commands error

This appeared after trying to use the script with Bash 3.2.57(1)-release
(OS X 10.11.6 default) in my blog repo. The problem did not manifest
when using Bash 4.3.46(1)-release.

A seemingly related issue: apparently "temporary" assignments to `IFS`
were not meant to affect word expansions and redirections, an issue
apparently fixed in Bash 4.3:

https://lists.gnu.org/archive/html/bug-bash/2014-03/msg00065.html

Perhaps the "fix" prevents called functions from inheriting the value of
`IFS`. Certainly adheres to the principle of least surprise considering
the ubiquity and importance of `IFS`, but violates the principle of
expecting called functions to inherit variable values from their
callers. In a way, both versions were doing the "right" thing, but in
the case of 3.2, the "right" thing exposed a latent bug.

Author: mbland

libexec/help

@@ -56,16 +56,30 @@
 
 _@go.usage() {
   local cmd_paths=("${_GO_PLUGINS_PATHS[@]}" "$_GO_SCRIPTS_DIR")
+  local origIFS="$IFS"
   local IFS=':'
+  local summaries
+  local summaries_status=0
+
+  cmd_paths="${cmd_paths[*]}"
+  IFS="$origIFS"
+  summaries="$(_@go.source_builtin 'commands' --summaries "$cmd_paths")"
+
+  if [[ "$?" -ne '0' ]]; then
+    summaries="<No commands found in or error retrieving summaries from: "
+    summaries+="$cmd_paths>"
+    summaries_status=1
+  fi
 
   @go.printf "%s\n\n%s\n\n%s\n\n%s %s\n\n%s %s\n\n" \
     "Usage: $_GO_CMD <command> [arguments...]" \
     "Where <command> is one of:" \
-    "$(_@go.source_builtin 'commands' --summaries "${cmd_paths[*]}")" \
+    "$summaries" \
     "Use \"$_GO_CMD help <command>\" for more information about that command," \
     "if available." \
     "Use \"$_GO_CMD help builtins\" for help on builtin commands," \
     "and \"$_GO_CMD help aliases\" for information on shell alias commands."
+  [[ "$?" -eq '0' && "$summaries_status" -eq '0' ]]
 }
 
 _@go.help_message_for_command() {

tests/help.bats

@@ -27,12 +27,32 @@ teardown() {
 }
 
 @test "$SUITE: produce message with successful return for help command" {
+  create_test_command_script 'foo' '# Does foo stuff'
+  create_test_command_script 'bar' '# Does bar stuff'
+  create_test_command_script 'baz' '# Does baz stuff'
   run "$TEST_GO_SCRIPT" help
+
   assert_success
   assert_line_equals 0 "Usage: $TEST_GO_SCRIPT <command> [arguments...]"
+  assert_output_matches '  foo  Does foo stuff'
+  assert_output_matches '  bar  Does bar stuff'
+  assert_output_matches '  baz  Does baz stuff'
+}
+
+@test "$SUITE: produce usage message when error retrieving command summaries" {
+  run "$TEST_GO_SCRIPT" help
+
+  assert_failure
+  assert_line_equals 0 "Usage: $TEST_GO_SCRIPT <command> [arguments...]"
+
+  local expected_err="<No commands found in or error retrieving summaries "
+  expected_err+="from: $TEST_GO_SCRIPTS_DIR>"
+  assert_output_matches "$expected_err"
 }
 
 @test "$SUITE: accept -h, -help, and --help as synonyms" {
+  # Create a command to ensure a sucessful exit status.
+  create_test_command_script 'foo' '# Does foo stuff'
   run "$TEST_GO_SCRIPT" help
   assert_success