vulkan: return default string for undefined enum

Instead of a unreachable.

This would avoid an assert on debug builds that uses vkfoo_to_str to
print structure types. This will become more common as some tests will
start to use VK_STRUCTURE_TYPE_MAX_ENUM to mark structures from
unsupported extensions more often.

v2 (Jason):
   * Include enum name on the default message
   * Handle MAX_ENUM as a special case

v3 (Jason):
   * vk_ObjectType_to_ObjectName don't need to use ${enum.name}

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14525>
(cherry picked from commit 821c66e50c)

.pick_status.json

@@ -4549,7 +4549,7 @@
         "description": "vulkan: return default string for undefined enum",
         "nominated": false,
         "nomination_type": null,
-        "resolution": 4,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": null
     },

src/vulkan/util/gen_enum_to_str.py

@@ -78,8 +78,9 @@ C_TEMPLATE = Template(textwrap.dedent(u"""\
         case ${v}:
             return "${enum.values[v]}";
     % endfor
+        case ${enum.max_enum_name}: return "${enum.max_enum_name}";
         default:
-            unreachable("Undefined enum value.");
+            return "Unknown ${enum.name} value.";
         }
     }
 
@@ -116,7 +117,7 @@ C_TEMPLATE = Template(textwrap.dedent(u"""\
             return "${object_types[0].enum_to_name[object_type]}";
     % endfor
         default:
-            unreachable("Undefined enum value.");
+            return "Unknown VkObjectType value.";
         }
     }
     """))
@@ -246,12 +247,24 @@ class VkExtension(object):
 def CamelCase_to_SHOUT_CASE(s):
    return (s[:1] + re.sub(r'(?<![A-Z])([A-Z])', r'_\1', s[1:])).upper()
 
+def compute_max_enum_name(s):
+    max_enum_name = CamelCase_to_SHOUT_CASE(s)
+    last_prefix = max_enum_name.rsplit('_', 1)[-1]
+    # Those special prefixes need to be always at the end
+    if last_prefix in ['AMD', 'EXT', 'INTEL', 'KHR', 'NV'] :
+        max_enum_name = "_".join(max_enum_name.split('_')[:-1])
+        max_enum_name = max_enum_name + "_MAX_ENUM_" + last_prefix
+    else:
+        max_enum_name = max_enum_name + "_MAX_ENUM"
+
+    return max_enum_name
 
 class VkEnum(object):
     """Simple struct-like class representing a single Vulkan Enum."""
 
     def __init__(self, name, bitwidth=32, values=None):
         self.name = name
+        self.max_enum_name = compute_max_enum_name(name)
         self.bitwidth = bitwidth
         self.extension = None
         # Maps numbers to names