Function returning something useful for passing directly into `class_addProperty` when copying properties from one class to another.

property_copyAttributeList.m

#import <objc/runtime.h>

// Lifted from https://github.com/numist/Debugger/blob/master/debugger.h
#define BailWithBlockUnless(exp,block) \
    do { \
        if (!(exp)) { \
            return block(); \
        } \
    } while(0)

// Like the other class_copy* functions, the caller must free the return value of this function with free()
objc_property_attribute_t *nn_property_copyAttributeList(objc_property_t property, unsigned int *outCount)
{
    void *(^failure)(void) = ^{
        if (outCount) {
            *outCount = 0;
        }
        return NULL;
    };

    // For more information about the property type string, see the Declared Properties section of the Objective-C Runtime Programming Guide
    const char *constAttributes = property_getAttributes(property);
    BailWithBlockUnless(constAttributes, failure);
    
    /**
     *  ┏━━━━━━━━━━━━━━━━┓
     *  ┃nameptr         ┃
     *  ┃valueptr        ┃
     *  ┠────────────────┨
     *  ┃nameptr         ┃
     *  ┃valueptr        ┃
     *  ┠────────────────┨
     *  ┃nameptr         ┃
     *  ┃valueptr        ┃
     *  ┠────────────────┨
     *  ┃...             ┃
     *  ┠────────────────┨
     *  ┃NULL            ┃
     *  ┃NULL            ┃
     *  ┠────────────────┨
     *  ┃N0Valueue0N0Valu┃
     *  ┃e0N0Valueueueue0┃
     *  ┃...             ┃
     *  ┗━━━━━━━━━━━━━━━━┛
     */

    // Get the number of attributes
    size_t attributeCount = strlen(constAttributes) ? 1 : 0;
    for (unsigned i = 0; constAttributes[i] != '\0'; i++) {
        if (constAttributes[i] == ',') {
            attributeCount++;
        }
    }

    // Calculate and allocate the attribute list to be returned to the caller
    size_t attributeListSize = (attributeCount + 1) * sizeof(objc_property_attribute_t); // The list of attributes, plus an extra attribute containing NULL for its name and value.
    size_t attributeStringsSize = (strlen(constAttributes) + attributeCount + 1) * sizeof(char); // The attribute names and values, plus the extra necessary NUL terminators.
    objc_property_attribute_t *attributeList = calloc(attributeListSize + attributeStringsSize, 1);
    BailWithBlockUnless(attributeList, failure);

    // Initialize the attribute string area.
    char *attributeStrings = (char *)attributeList + attributeListSize;
    strcpy(attributeStrings, constAttributes);

    char *name;
    char *next = attributeStrings;
    unsigned attributeIndex = 0;
    while ((name = strsep(&next, ",")) != NULL) {
        // Attribute pairs must contain a name!
        if (*name == '\0') {
            free(attributeList);
            return failure();
        }
        
        // NUL-terminating the name requires first moving the rest of the string which requires some extra housekeeping because of strsep.
        char *value = name + 1;
        int remainingBufferLength = (int)attributeStringsSize - (int)(value - attributeStrings);
        if (remainingBufferLength > 1) {
            memmove(value + 1, value, remainingBufferLength - 1);
            // Update next pointer for strsep
            if (next) next++;
        }
        
        // Add NUL termination to name and update value pointer.
        *(name + 1) = '\0';
        value++;
        
        attributeList[attributeIndex].name = name;
        attributeList[attributeIndex].value = value;
        attributeIndex++;
    }

    if (outCount) {
        *outCount = attributeCount;
    }
    
    return attributeList;
}

I just realized, other than the use of blocks, there's nothing innately Objective-C about this function. Success?