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Related-to: #issue-number-here (partially)

A continuation of: #7756 since the author seems to have left the chat

More informative error messages when scripts are misspecified.

Main difference is that the error message has been updated with more information, and the no-context information ("too many/too few values to unpacked") is removed.

The previously proposed error message was still a bit too cryptic, so I added separate cases for "too many colons" vs "colons absent" because they are different problems - with no colons, one might be trying to specify a whole python module because their script runs module-level code. I added a hint in that case to just wrap it in a main function with a suggestion of how to change pyproject.toml. The other case is just a warning that there are too many colons and shows what the current value is.

So for "no colons" with a pyproject.toml like:

[tool.poetry.scripts]
foo = "bar.bin.foo"
baz = "bar.bin.baz"

The error message is:

Bad script (baz): script needs to specify a function within a module like: module(.submodule):function
Instead got: bar.bin.baz
Hint: If the script depends on module-level code, try wrapping it in a main() function and modifying your script like:
baz = "bar.bin.baz:main"

and for a "too many colons" with a pyproject.toml like:

[tool.poetry.scripts]
foo = "foo::bar"
fux = "fuz.foo:bar:fux"

the error message is:

Bad script (foo): script needs to specify a function within a module like: module(.submodule):function
Instead got: foo::bar
Too many ":" found!

I also removed script specifiers like "foo.bar:baz.bin" because they were misleading about what the test handled.

It seems like the ultimate thing that needs to happen here is to add regex to the JSON schema file so that editors alert people before the time they try and install a package - https://github.com/python-poetry/poetry-core/blob/main/src/poetry/core/json/schemas/poetry-schema.json - but that's not for me today ;)

• Added tests for changed code.
• Updated documentation for changed code.