Fix folder spec for plugin filename regex

[andrewhand]

Fixed bug where API would not except plugin filenames as a directory and added test to support.

[jkglasbrenner]

Here's a Python test file that contains the regex that seems to handle most cases, as well as tests to run.

EDIT: I added a couple of additional tests in invalid_paths that verify that attempting to use a relative path will fail.

import re

python_filepath_pattern = r'^(?!.*/_)(?!_/)([a-zA-Z][a-zA-Z0-9_]*/)*[a-zA-Z_][a-zA-Z0-9_]*(?<!_)\.py$'

def validate_python_filepath(filepath):
    return re.match(python_filepath_pattern, filepath) is not None

# Valid paths (for reference)
valid_paths = [
    r'hello.py',
    r'hello_world.py',
    r'hello_world/main.py',
    r'package/sub_package/module.py',
    r'a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p.py',  # Many nested directories
    r'_underscore_start.py',
]

# Invalid paths (expanded)
invalid_paths = [
    r'hello world.py',        # Space in filename
    r'3ight/hello.py',        # Directory starting with a number
    r'hello_world//main.py',  # Double slash
    r'module.py.txt',         # Wrong extension
    r'/absolute/path.py',     # Absolute path
    r'.py',                   # Just the extension
    r'hello.py/',             # Ends with a slash
    r'/hello.py',             # Starts with a slash
    r'hello..py',             # Double dot in extension
    r'hello.py.py',           # Double .py extension
    r'hello_.py',             # Ends with underscore before extension
    r'_/hello.py',            # Single underscore directory name
    r'hello/_.py',            # Single underscore filename
    r'hello/_file.py',        # Underscore start in nested file
    r'HELLO.PY',              # Uppercase extension (assuming case-sensitive)
    r'hello.pY',              # Mixed case extension
    r'hello/world/.py',       # Hidden file in nested directory
    r'hello/.world/file.py',  # Hidden directory
    r' hello.py',             # Leading space
    r'hello.py ',             # Trailing space
    r'\thello.py',            # Tab character
    r'hello\world.py',       # Backslash instead of forward slash
    r'hello:world.py',        # Invalid character (colon)
    r'hello@world.py',        # Invalid character (at sign)
    r'hello/world.py/extra',  # Extra content after .py
    r'',                      # Empty string
    r'hello/',                # Directory without file
    r'hello.py/world.py',     # .py in middle of path
    r'1/2/3/4.py',            # All numeric directory names
    r'../sample.py',          # No relative paths
    r'..sample.py',           # No prefix with dots
]

# Test all paths
for path in valid_paths + invalid_paths:
    result = 'Valid' if validate_python_filepath(path) else 'Invalid'
    print(f"{path}: {result}")

Here's the output when you run the above:

hello.py: Valid
hello_world.py: Valid
hello_world/main.py: Valid
package/sub_package/module.py: Valid
a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p.py: Valid
_underscore_start.py: Valid
hello world.py: Invalid
3ight/hello.py: Invalid
hello_world//main.py: Invalid
module.py.txt: Invalid
/absolute/path.py: Invalid
.py: Invalid
hello.py/: Invalid
/hello.py: Invalid
hello..py: Invalid
hello.py.py: Invalid
hello_.py: Invalid
_/hello.py: Invalid
hello/_.py: Invalid
hello/_file.py: Invalid
HELLO.PY: Invalid
hello.pY: Invalid
hello/world/.py: Invalid
hello/.world/file.py: Invalid
 hello.py: Invalid
hello.py : Invalid
\thello.py: Invalid
hello\world.py: Invalid
hello:world.py: Invalid
hello@world.py: Invalid
hello/world.py/extra: Invalid
: Invalid
hello/: Invalid
hello.py/world.py: Invalid
1/2/3/4.py: Invalid
../sample.py: Invalid
..sample.py: Invalid