handle signed integers

lib/private/string.bzl

@@ -567,8 +567,10 @@ def hex(number):
     Returns:
         hexdecimal representation of the number argument 
     """
-    r = number
+
     hex_string = ""
+    is_signed = number < 0
+    r = number * -1 if is_signed else number
     for _ in range(1000000):
         if r > 0:
             rem = r % 16
@@ -577,6 +579,8 @@ def hex(number):
         else:
             break
 
-    hex_string = hex_string if hex_string else "0"
-    return "{}0x{}".format("-" if number < 0 else "", hex_string)
+    if not hex_string:
+        hex_string = "0"
+
+    return "{}0x{}".format("-" if is_signed else "", hex_string)
 

lib/tests/string_tests.bzl

@@ -45,8 +45,12 @@ def _hex_test_impl(ctx):
     asserts.equals(env, hex(1111), "0x457")
     asserts.equals(env, hex(97), "0x61")
     asserts.equals(env, hex(1000000000000), "0xe8d4a51000")
-    asserts.equals(env, hex(0), "0x0")
     asserts.equals(env, hex(1), "0x1")
+    # https://en.wikipedia.org/wiki/Signed_zero
+    asserts.equals(env, hex(0), "0x0")
+    asserts.equals(env, hex(-0), "0x0")
+    asserts.equals(env, hex(-1234), "-0x4d2")
+    asserts.equals(env, hex(-99999999), "-0x5f5e0ff")
 
     return unittest.end(env)