What is the appropriate way to write and distribute an addon that works with both blender 2.80 and 2.79?

Question

I have written a python addon which is compatible with both 2.79 and 2.80. When setting the "blender" key in bl_info to the appropriate version, the code works otherwise unmodified in both versions, without warnings.

Now I want to distribute this code as a zipped addon. I'd prefer not having to create two separate zips for exactly the same code.

However:

• If I set the bl_info "blender" key to (2, 79, 0), then blender 2.80 refuses to load it
• If I set it to (2, 80, 0), then blender 2.79 displays a warning cautioning the user that the module isn't intended for this blender version, and that it is likely to malfunction (although the module then happily runs without problems anyway). This is going to scare and confuse users of 2.79, see for example MHX2 import in 2.79 and 2.80?
• If I use a variable and try to calculate the appropriate blender version outside the bl_info block, then the zipped addon won't install at all, eventhough the same code runs just fine when the addon is manually extracted in either version's addons directory. It seems the install-addon-from-zip code manually cuts out the bl_info block and parses it out of context, causing it to fail when encountering a variable set outside the block.

So my question is: Is there a way to create and distribute a single addon zip file that works without warnings in both blender 2.79 and 2.80?

EDIT:

The code I used in option 3 (calculating a variable to determine the appropriate blender version is this:

import bpy
appver = (2, 80, 0)

if bpy.app.version < appver:
    appver = (2, 79, 0)

bl_info = {
    ...
    "blender": appver,
    ...
    }

(which, as said, works fine when the addon is already unzipped, but crashes when trying to install from zip file)

The stack trace I get is this:

Traceback (most recent call last):
  File "/home/joepal/system/blender-2.80-d40bffa17f6-linux-glibc224-x86_64/2.80/scripts/modules/addon_utils.py", line 137, in fake_module
    mod.bl_info = ast.literal_eval(body.value)
  File "/home/joepal/system/blender-2.80-d40bffa17f6-linux-glibc224-x86_64/2.80/python/lib/python3.7/ast.py", line 91, in literal_eval
    return _convert(node_or_string)
  File "/home/joepal/system/blender-2.80-d40bffa17f6-linux-glibc224-x86_64/2.80/python/lib/python3.7/ast.py", line 79, in _convert
    map(_convert, node.values)))
  File "/home/joepal/system/blender-2.80-d40bffa17f6-linux-glibc224-x86_64/2.80/python/lib/python3.7/ast.py", line 90, in _convert
    return _convert_signed_num(node)
  File "/home/joepal/system/blender-2.80-d40bffa17f6-linux-glibc224-x86_64/2.80/python/lib/python3.7/ast.py", line 63, in _convert_signed_num
    return _convert_num(node)
  File "/home/joepal/system/blender-2.80-d40bffa17f6-linux-glibc224-x86_64/2.80/python/lib/python3.7/ast.py", line 55, in _convert_num
    raise ValueError('malformed node or string: ' + repr(node))
ValueError: malformed node or string: <_ast.Name object at 0x7fb74bd55780>
Traceback (most recent call last):
  File "/home/joepal/system/blender-2.80-d40bffa17f6-linux-glibc224-x86_64/2.80/scripts/startup/bl_operators/wm.py", line 2042, in execute
    addons_new = {mod.__name__ for mod in addon_utils.modules()} - addons_old
  File "/home/joepal/system/blender-2.80-d40bffa17f6-linux-glibc224-x86_64/2.80/scripts/modules/addon_utils.py", line 208, in modules
    modules_refresh(module_cache)
  File "/home/joepal/system/blender-2.80-d40bffa17f6-linux-glibc224-x86_64/2.80/scripts/modules/addon_utils.py", line 195, in modules_refresh
    force_support=force_support,
  File "/home/joepal/system/blender-2.80-d40bffa17f6-linux-glibc224-x86_64/2.80/scripts/modules/addon_utils.py", line 137, in fake_module
    mod.bl_info = ast.literal_eval(body.value)
  File "/home/joepal/system/blender-2.80-d40bffa17f6-linux-glibc224-x86_64/2.80/python/lib/python3.7/ast.py", line 91, in literal_eval
    return _convert(node_or_string)
  File "/home/joepal/system/blender-2.80-d40bffa17f6-linux-glibc224-x86_64/2.80/python/lib/python3.7/ast.py", line 79, in _convert
    map(_convert, node.values)))
  File "/home/joepal/system/blender-2.80-d40bffa17f6-linux-glibc224-x86_64/2.80/python/lib/python3.7/ast.py", line 90, in _convert
    return _convert_signed_num(node)
  File "/home/joepal/system/blender-2.80-d40bffa17f6-linux-glibc224-x86_64/2.80/python/lib/python3.7/ast.py", line 63, in _convert_signed_num
    return _convert_num(node)
  File "/home/joepal/system/blender-2.80-d40bffa17f6-linux-glibc224-x86_64/2.80/python/lib/python3.7/ast.py", line 55, in _convert_num
    raise ValueError('malformed node or string: ' + repr(node))
ValueError: malformed node or string: <_ast.Name object at 0x7fb74bd55780>

Answer 1

You can't put variables inside bl_info, because the fake module literally reads the addon file as plain text and will read your literal variable, not the content of your evaluated variable.