Simplify script by assuming find supports -print0

`find -print0` is not POSIX, but supported systems include:

- GNU/Linux systems, using GNU findutils
- Other Linux-based systems using BusyBox find (e.g. Alpine Linux)
- BSD systems, including macOS (all versions, since 10)

Since this is a Bash script, and even the old versions of Bash on
macOS systems support `read -d ''` to read null-byte-delimited
input, assuming `find -print0` is supported everywhere needed, this
is highly likely to work everywhere needed. It allows filenames to
be safely read even if they contain weird characters including
newlines, as can happen accidentally (hopefully not intentionally).

It would be nicer to loop through the result of a recursive glob
(globstar, **), but Bash only supports that starting in version 4,
which no version of macOS ships (or is likely to ship).

The benefit of this approach, compared to the `find -exec` way used
before, is that the code is simpler, no longer needs to call itself
as a subprocess through find, and no longer needs a help to clarify
a mode that is not meant to be used from the outside. (It may also
be slightly faster.)

This makes some behavioral changes, in areas where the design had
been driven by the implementation rather than the other way around:

- We stop on the first failure.

- Because of that, there is no need to restate what files could not
  be generated (it is at most one, and the failure should show it).

- As noted above, this script can no longer be invoked to process
  an individual file (which as not a design goal), and it therefore
  no longer accepts any command-line arguments (they are ignored).

This also fixes a misspelling the big first_line_ends_crlf comment.

Author: EliahKagan

etc/copy-packetline.sh

@@ -2,15 +2,6 @@
 
 set -euC -o pipefail
 
-function usage() {
-  local name
-
-  name="$(basename -- "$0")"
-  printf '%s [--all]         regenerate gix-packetline-blocking source\n' "$name"
-  printf '%s --file {path}   regenerate a single file (avoid; prefer --all)\n' "$name"
-  printf '%s --help          print this message\n' "$name"
-}
-
 function fail () {
   printf '%s: error: %s\n' "$0" "$1" >&2
   exit 1
@@ -62,47 +53,12 @@ function check_target () {
   fi
 }
 
-function indent () {
-  sed 's/^/    /'
-}
-
-function generate_all () {
-  local failures
-
-  chdir_toplevel
-
-  if ! test -d gix-packetline/src; then
-    fail 'no source directory: gix-packetline/src'
-  fi
-  if ! test -d gix-packetline-blocking; then
-    fail 'no target parent directory: gix-packetline-blocking'
-  fi
-
-  check_target
-
-  rm -rf gix-packetline-blocking/src  # No trailing /. It may be a symlink.
-  if test -e gix-packetline-blocking/src; then
-    fail 'unable to remove target'
-  fi
-
-  failures="$(
-    find gix-packetline/src/ \
-    -exec etc/copy-packetline.sh --file {} \; \
-    -o -print
-  )"
-
-  # If we get here, traversal succeeded, but perhaps some generations failed.
-  if test -n "$failures"; then
-    fail $'failed to generate from:\n'"$(indent <<<"$failures")"
-  fi
-}
-
 function first_line_ends_crlf () {
   # This is tricky to check portably. In Cygwin-like environments including
   # MSYS2 and Git Bash, most text processing tools, including awk, sed, and
   # grep, automatically ignore \r before \n. Some ignore \r everywhere. Some
   # can be told to keep \r, but in non-portable ways that may affect other
-  # implementations. Bash ignores \r in some places even without "-o icncr",
+  # implementations. Bash ignores \r in some places even without "-o igncr",
   # and ignores \r even more with it, including in all text from command
   # substitution. Simple checks may be non-portable to other OSes. Fortunately,
   # tools that treat input as binary data are exempt (even cat, but "-v" is
@@ -118,6 +74,7 @@ function first_line_ends_crlf () {
 
 function make_header () {
   local source endline
+
   source="$1"
   endline="$2"
 
@@ -142,14 +99,10 @@ function copy_with_header () {
 }
 
 function generate_one () {
-  local source shared target
+  local source target
 
   source="$1"
-  shared="${source#gix-packetline/src/}"
-  if test "$source" = "$shared"; then
-    fail "source path seems to be outside gix-packetline/src/: $source"
-  fi
-  target="gix-packetline-blocking/src/$shared"
+  target="gix-packetline-blocking/src/${source#gix-packetline/src/}"
 
   if test -d "$source"; then
     mkdir -p -- "$target"
@@ -166,12 +119,28 @@ function generate_one () {
   fi
 }
 
-if { test "$#" -eq 1 && test "$1" = '--all'; } || test "$#" -eq 0; then
-  generate_all
-elif test "$#" -eq 2 && test "$1" = '--file'; then
-  generate_one "$2"
-elif test "$#" -eq 1 && test "$1" = '--help'; then
-  usage
-else
-  fail 'unrecognized syntax, try passing only --help for usage'
-fi
+function generate_all () {
+  local source
+
+  chdir_toplevel
+
+  if ! test -d gix-packetline/src; then
+    fail 'no source directory: gix-packetline/src'
+  fi
+  if ! test -d gix-packetline-blocking; then
+    fail 'no target parent directory: gix-packetline-blocking'
+  fi
+
+  check_target
+
+  rm -rf gix-packetline-blocking/src  # No trailing "/" as it may be a symlink.
+  if test -e gix-packetline-blocking/src; then
+    fail 'unable to remove target'
+  fi
+
+  find gix-packetline/src/ -print0 | while IFS= read -r -d '' source; do
+    generate_one "$source"
+  done
+}
+
+generate_all