support/download/check-hash: accept hash files without terminating \n

Lots of people are using broken text editors that 1. do not naturally
terminate text files with a final \n as is customary in UNIX text files,
and 2. do not respect our .editorconfig settings, which explicitly
require adding that final newline. See this nice summary of what a text
file is (with references to applicable standards):

    https://stackoverflow.com/questions/12916352/shell-script-read-missing-last-line/12916758#12916758

So, it is not surprising that read does not read the last "line" of a
file, when said "line" does not end with a newline, because it is thus
not really a line.

Even though we do mandate actual text files, let's be a little bit lax
in this respect, because people may write packages, and their hash
files, in a br2-external tree, and they may not have our .editorconfig
in the directory heierarchy (e.g. if buildroot is a submodule of their
br2-external tree, or whatever).

mapfile does not suffer from this limitation, though, and correctly
reads all lines from a file, even the final line-that-is-not-a-line.

mapfile was introduced in bash 4.0, released on 2009-01-20, more than
15 years ago. Debian squeeze, released in 2011 already had bash 4.1.
Those are really ancient. So, it means we can indeed expect bash
version 4.0 or later; which means mapfile is available.

"It should be fine!"

Fixes: #15976

Reported-by: masonwardle@gmail.com
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Arnout Vandecappelle <arnout@mind.be>
(cherry picked from commit ac2e6b3927)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

support/download/check-hash

@@ -78,8 +78,10 @@ nb_checks=0
 for h_file in "${h_files[@]}"; do
     [ -f "${h_file}" ] || continue
     : $((nb_h_files++))
-    # shellcheck disable=SC2094  # we're really reading it only once
-    while read -r t h f; do
+    # mapfile reads all lines, even the last one if it is missing a \n
+    mapfile -t hash_lines <"${h_file}"
+    for hash_line in "${hash_lines[@]}"; do
+        read -r t h f <<<"${hash_line}"
         case "${t}" in
             ''|'#'*)
                 # Skip comments and empty lines
@@ -87,13 +89,12 @@ for h_file in "${h_files[@]}"; do
                 ;;
             *)
                 if [ "${f}" = "${base}" ]; then
-                    # shellcheck disable=SC2094  # we're only printing the h_file filename
                     check_one_hash "${t}" "${h}" "${file}" "${h_file}"
                     : $((nb_checks++))
                 fi
                 ;;
         esac
-    done <"${h_file}"
+    done
 done
 
 # shellcheck disable=SC2086  # nb_h_files is a non-empty int