fix(arcup): accept checksum files without a trailing newline

verify_checksum_file() decided emptiness from the exit status of
`read -r expected_checksum expected_name < "$checksum_path"`. `read`
returns non-zero when it reaches EOF before a newline, even though it has
already populated the variables. A .sha256 whose single line lacks a
trailing newline is valid, but arcup rejected it with
"Checksum file is empty", aborting a correct install.

Decide emptiness from the parsed hash instead of read's exit status.
A genuinely empty file still yields an empty hash and is still rejected.

Adds regression tests covering the no-trailing-newline and empty cases.

Author: osr21

arcup/arcup

@@ -656,7 +656,12 @@ verify_checksum_file() {
     local archive_name="$3"
     local expected_checksum expected_name actual_checksum
 
-    if ! read -r expected_checksum expected_name < "$checksum_path"; then
+    # `read` returns non-zero when it hits EOF before a newline, even though it
+    # still populates the variables. A checksum file whose single line has no
+    # trailing newline is valid, so decide emptiness from the parsed hash rather
+    # than from read's exit status.
+    read -r expected_checksum expected_name < "$checksum_path" || true
+    if [[ -z "$expected_checksum" ]]; then
         error "Checksum file is empty: $checksum_path"
     fi
 

arcup/test_arcup.sh

@@ -119,6 +119,15 @@ test_checksum_validation() {
 
     printf '%s  other-asset.tar.gz\n' "$checksum" > "$checksum_file"
     expect_fail "checksum filename mismatch fails" verify_checksum_file "$archive" "$checksum_file" "$archive_name"
+
+    # A checksum file whose only line has no trailing newline is still valid.
+    printf '%s  %s' "$checksum" "$archive_name" > "$checksum_file"
+    verify_checksum_file "$archive" "$checksum_file" "$archive_name"
+    pass "checksum file without trailing newline passes"
+
+    # A genuinely empty checksum file must still be rejected.
+    : > "$checksum_file"
+    expect_fail "empty checksum file fails" verify_checksum_file "$archive" "$checksum_file" "$archive_name"
 }
 
 test_download_error_lists_assets() {