Packages included in an Extra

[BeRT2me]

• Poetry version: Poetry (version 1.5.1)
• Python version: Python: 3.10.10
• OS version and name: macOS 13.5
• pyproject.toml:

[tool.poetry.dependencies]
package =  {version = "^1.4.49", optional = false}

[tool.poetry.extras]
extra = ["package"]

• [x] I am on the latest stable Poetry version, installed using a recommended method.
• [x] I have searched the issues of this repo and believe that this is not a duplicate.
• [x] I have consulted the FAQ and blog for any relevant entries or release notes.
• [x] If an exception occurs when executing a command, I executed it again in debug mode (-vvv option) and have included the output below.

Issue

If I run poetry install, package installs as expected.

However,

• If I add this project to another project poetry add <path_to_project>, then package doesn't install. (It should!)
• If I publish the project and then do pip install my_project, then package doesn't install. (It should!)
  • But if I do pip install my_project[extra] then package does install.

Summary:

package =  {version = "^1.4.49", optional = false}

Should not have the same result as:

package =  {version = "^1.4.49", optional = true}

When it comes to installing a project externally. Just because it's included in one of the extras... especially when it installs as expected within a project.