How to identify package licenses
The information about what licenses apply to a project typically can be found in a few places:
License files: The source code may contain a specific file containing just the license text (most often named LICENSE or COPYING, but many other conventions and variant practices exist). These license files are usually, but not always, in the root directory of the source tree. There may be more than one such file, in which case, hopefully, there is information elsewhere in the source tree that explains the applicability of the different licenses. License files may also be present in non-root directories in the source tree, such as in cases where the files in one part of the source tree are licensed under a license that is different from the rest of the source tree.
Source files: License notices referencing a particular license, or even the full text of relatively short licenses, are often found in source files. License notices may include: standard license notices suggested by the license itself (e.g., GPL, Apache-2.0); short concise statements (e.g., "This file is under the MIT license" or "SPDX-License-Identifier: MIT"); statements that simply refer to the license file that require finding that file (e.g., "See COPYING"); or unclear or ambiguous statements that require further investigation (e.g., "This file is licensed the same as Ruby").
Information about applicable license terms may be present in descriptive form, such as a statement in a README, the project webpage, metadata intended for a downstream packaging system or package repository, or in a file dedicated to explaining the license terms.
Unfortunately, it is rather common for this sort of information to be inconsistent with or contradict other license information elsewhere. While it’s difficult to give general guidance on this situation, you generally cannot ignore license information that is "closer" to the code (for example, a license notice in a source file) even if it might seem to be contradicted by license information "further" from the code (for example, a license statement in a top-level README or on a project website).
As a project evolves, it is not uncommon for license information in the project repository to become outdated. This is less likely to be the case for license files and source file license notices. But we have been finding this to be a problem for relatively old and complex projects that have recorded some information about third-party licensing in so-called "notice files" or other files containing informal license information. The file will say that a particular license applies to something in the repository, but close examination may reveal that the material the license applied to has been deleted from the repository. We have been using the term "phantom license" to refer to this phenomenon.
Because such phantom licenses don’t actually apply to anything being packaged, you do not need to ensure that they are allowed for Fedora and you do not need to include them in the SPDX expression in the license tag. Of course, you should only conclude that something is a phantom license if it is clear that what it was formerly applicable to is no longer present in the repository. If you find a phantom license, we encourage you to report it to the upstream project.
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