abuild: test for duplicates when doing checksum

fixes https://gitlab.alpinelinux.org/alpine/abuild/-/issues/10013

abuild.in

@@ -2260,7 +2260,11 @@ checksum() {
 	[ -z "$source" ] && return 0
 	fetch
 	for s in $source; do
-		files="$files $(filename_from_uri $s)"
+		local name="$(filename_from_uri $s)"
+		case " $files " in
+		*" $name "*) die "duplicate found in \$source: $name";;
+		esac
+		files="$files $name"
 	done
 
 	msg "Updating the sha512sums in APKBUILD..."

tests/abuild.bats

@@ -97,3 +97,17 @@ teardown() {
 	sha512sum -c sums
 }
 
+@test "abuild: test duplicates in checksum generation" {
+	mkdir -p "$tmpdir"/foo "$tmpdir"/foo/dir1 "$tmpdir"/foo/dir2
+	cat >> "$tmpdir"/foo/APKBUILD <<-EOF
+		pkgname="foo"
+		pkgver="1.0"
+		source="dir1/testfile dir2/testfile"
+	EOF
+	echo "first" > "$tmpdir"/foo/dir1/testfile
+	echo "second" > "$tmpdir"/foo/dir2/testfile
+	cd "$tmpdir"/foo
+	run $ABUILD checksum
+	[ $status -ne 0 ]
+}
+