scripts: make-index-json: rework for old Python versions

The current code uses functions and features only found in newer
versions of Python, so rework to allow use on systems only supporting
older Python.  Tested on Python 3.8 (released Oct 2019), but should
work on 3.7 also.

Suggested-by: Chen Minqiang <ptpt52@gmail.com>
Signed-off-by: Eric Fahlgren <ericfahlgren@gmail.com>

scripts/make-index-json.py

@@ -14,6 +14,12 @@ import email.parser
 import json
 
 
+def removesuffix(src, suffix):
+    # For compatibility with Python < 3.9.
+    suffix_length = len(suffix)
+    return src[:-suffix_length] if suffix_length and src.endswith(suffix) else src
+
+
 def parse_args():
     from argparse import ArgumentParser
 
@@ -42,7 +48,7 @@ def parse_apk(text: str) -> dict:
         for tag in package.get("tags", []):
             if tag.startswith("openwrt:abiversion="):
                 package_abi: str = tag.split("=")[-1]
-                package_name = package_name.removesuffix(package_abi)
+                package_name = removesuffix(package_name, package_abi)
                 break
 
         packages[package_name] = package["version"]
@@ -58,8 +64,9 @@ def parse_opkg(text: str) -> dict:
     for chunk in chunks:
         package: dict = parser.parsestr(chunk, headersonly=True)
         package_name: str = package["Package"]
-        if package_abi := package.get("ABIVersion"):
-            package_name = package_name.removesuffix(package_abi)
+        package_abi = package.get("ABIVersion")
+        if package_abi:
+            package_name = removesuffix(package_name, package_abi)
 
         packages[package_name] = package["Version"]