core: Preserve true line endings in @go.printf

Closes #146. Works by adding the ASCII Unit Separator character after
every newline character and using it as the delimiter for `read`. This
way output that shouldn't end with a newline won't.

Seems to add about 0.003-0.005s to the time on average as measured by:

  time COLUMNS=<N> ./go help builtins

regardless of the value of `<N>` used to set `COLUMNS`. Also measurably
faster than the alternate methods of:

- counting the total number of characters printed and only emitting a
  newline if the number of `result` characters hasn't been reached
- counting the number of lines and only emitting a newline if the
  current line number is less than or equal to the length of
  `${result//[^$'\n']}`

Also includes an update to `libexec/get.d/file` to fix a test broken by
this new behavior, as it previously depended upon the old behavior to
add a newline by default.

Author: mbland

go-core.bash

@@ -154,19 +154,18 @@ declare _GO_INJECT_MODULE_PATH="$_GO_INJECT_MODULE_PATH"
   local result
   local line
   local prefix
-  local IFS=
 
   if [[ "$#" -eq 0 ]]; then
     format="${format//\%/%%}"
   fi
   printf -v result -- "$format" "$@"
   result="${result//$'\r\n'/$'\n'}"
 
-  # If `result` ends with a newline, chomp it, since the loop will add one.
-  while read -r line; do
+  # Use the ASCII Unit Separator as a delimiter to preserve true line endings.
+  while IFS= read -r -d $'\x1f' line; do
     while [[ "${#line}" -gt "$COLUMNS" ]]; do
       prefix="${line:0:$COLUMNS}"
-      prefix="${prefix% *}"
+      prefix="${prefix%[[:space:]]*}"
       line="${line#$prefix}"
 
       if [[ "$prefix" =~ [[:space:]]+$ ]]; then
@@ -177,8 +176,8 @@ declare _GO_INJECT_MODULE_PATH="$_GO_INJECT_MODULE_PATH"
       fi
       printf '%s\n' "$prefix"
     done
-    printf '%s\n' "$line"
-  done <<<"${result%$'\n'}"
+    printf '%s' "$line"
+  done <<<"${result//$'\n'/$'\n\x1f'}"$'\x1f'
 }
 
 # Prints the stack trace at the point of the call.

libexec/get.d/file

@@ -96,7 +96,7 @@ _@go.get_file_download_command() {
     if [[ -n "$dl_cmd" ]]; then
       @go.printf 'Download program not supported: %s\n' "$dl_cmd" >&2
     fi
-    @go.printf 'Please install curl or wget before running "%s".' \
+    @go.printf 'Please install curl or wget before running "%s".\n' \
       "${_GO_CMD_NAME[*]}" >&2
     return 1
     ;;
@@ -144,7 +144,7 @@ _@go.get_file_impl() {
   if ! "${__go_get_file_download_cmd[@]}" "$url" 2>"$errfile"; then
     errmsg="$(< "$errfile")"
     printf '%s\n' "$errmsg" >&2
-    @go.printf 'Failed to download using %s: %s' \
+    @go.printf 'Failed to download using %s: %s\n' \
       "${__go_get_file_download_cmd[0]}" "$url" >&2
 
     if [[ "${__go_get_file_download_cmd[0]}" != 'curl' ]]; then

tests/core/printf.bats

@@ -49,3 +49,11 @@ teardown() {
   COLUMNS=15 run "$TEST_GO_SCRIPT"
   assert_success $'123456789012345\n67890\n1234567890'
 }
+
+@test "$SUITE: don't add newline if format doesn't include one" {
+  @go.create_test_go_script "@go.printf '%s' 'foo'" \
+    "@go.printf '%s' 'bar'" \
+    "@go.printf '%s' 'baz'"
+  run "$TEST_GO_SCRIPT"
+  assert_success 'foobarbaz'
+}