We previously avoided generating a duplicate with another automatically
generated identifier; now we also avoid duplicates with explicit
identifiers that occur before the header for which an identifier
is being generated. (Collisions are still possible for identifiers
that occur after the header.)
T.P.Shared: `makeSections` is also modified so it doesn't give
bad results when the enclosing Div has a different identifier
from the header, as may now happen.
This change only affects the case where `--file-scope` is used
and more than one file is specified on the command line.
In this case, identifiers will be prefixed with a string
derived from the file path, to disambiguate them. For example,
an identifier `foo` in `contents/file1.txt` will become
`contents__file1.txt__foo`. Links will be adjusted accordingly:
if `file2.txt` links to `file1.txt#foo`, then the link will
be changed to point to `#file1.txt__foo`. Similarly, a link
to `file1.txt` will point to `#file1.txt`. A Div with an
identifier derived from the file path will be added around
each file's content, so that links to files will still work.
Closes#6384.
[API change]: Text.Pandoc.Shared exports `textToIdentifier`.
John MacFarlane