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* Test that licenses are valid. * Move license script from flutter/buildroot to flutter/engine
81 lines
3.9 KiB
Plaintext
81 lines
3.9 KiB
Plaintext
This license collection script is, fundamentally, one giant pile of
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special cases. As such, while there is an attempt to model the rules
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that apply to licenses and apply some sort of order to the process,
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the code is less than clear. This file attempts to provide an overview.
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main.dart is the core of the operation. It first walks the entire
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directory tree starting from the root of the repository (which is to
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be specified on the command line as the only argument), creating an
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in-memory representation of the project (make sure to run this only
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after you've run gclient sync, so that all dependencies are on disk).
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This is the step that is labeled "Preparing data structures".
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Then, it walks this in-memory representation, attempting to assign to
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each file one or more licenses. This is the step labeled "Collecting
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licenses", which takes a long time.
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Finally, it prints out these licenses.
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The in-memory representation is a tree of RepositoryEntry objects.
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There's three important types of these objects: RepositoryDirectory
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objects, which represent directories; RepositoryLicensedFile, which
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represents source files and resources that might end up in the binary,
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and RepositoryLicenseFile, which represents license files that do not
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themselves end up in the binary other than as a side-effect of this
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script.
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RepositoryDirectory objects contain three lists, the list of
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RepositoryDirectory subdirectories, the list of RepositoryLicensedFile
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children, and the list of RepositoryLicenseFile children.
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RepositoryDirectory objects are the objects that crawl the filesystem.
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While the script is pretty conservative (including probably more
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licenses than strictly necessary), it tries to avoid including
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material that isn't actually used. To do this, RepositoryDirectory
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objects only crawl directories and files for which shouldRecurse
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returns true. For example, shouldRecurse returns false for ".git"
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files.
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Some directories and files require special handling, and have specific
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subclasses of the above classes. To create the appropriate objects,
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RepositoryDirectory calls createSubdirectory and createFile to create
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the nodes of the tree.
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The low-level handling of files is done by classes in filesystem.dart.
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This code supports transparently crawling into archives (e.g. .jar
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files), as well as handling UTF-8 vs latin1. It contains much magic
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and hard-coded file names and so on to handle distinguishing binary
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files from text files, and so forth.
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This code uses the cache described in cache.dart to try to avoid
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having to repeatedly reopen the same file many times in a row.
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In the case of a binary file, the license is found by crawling around
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the directory structure looking for a "default" license file. In the
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case of text files, though, it's often the case that the file itself
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mentions the license and therefore the file itself is inspected
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looking for copyright or license text. This scanning is done by
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determineLicensesFor() in licenses.dart.
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This function uses patterns that are themselves in patterns.dart. In
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this file we find all manner of long complicated and somewhat crazy
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regular expressions. This is where you see quite how absurd this work
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can actually be. It is left as an exercise to the reader to look for
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the implications of many of the regular expressions; as one example,
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though, consider the case of the pattern that matches the AFL/LGPL
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dual license statement: there is one file in which the ZIP code for
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the Free Software Foundation is off by one, for no clear reason,
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leading to the pattern ending with "MA 0211[01]-1307, USA".
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The license.dart file also contains the License object, the currently
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simplistic normalizer (_reformat) for license text (which mostly just
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removes comment syntax), the code that attempts to determine what
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copyrights apply to which licenses, and the code that attempts to
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identify the licenses themselves (at a high level), to make sure that
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appropriate clauses are followed (e.g. including the copyright with a
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BSD notice).
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