Description
Youʼre helping to develop an operating system and command set that as part of its
acceptance test is supposed to be used by a large government agency. The
agency has lots of requirements, some sensible and some persnickety, and one of
these requirements is that applications must use characters properly from
the Unicode character set. In particular, applications must use the Unicode
character “`” (grave accent, U+0060) only as a spacing accent character.
Unfortunately, one of your applications, GNU Diffutils, regularly uses “`” as a
quoting character in diagnostics. For example, the command “diff . -” outputs the
diagnostic “diff: cannot compare `-‘ to a directory”, and this misuse of “`” violates
your customerʼs requirements.
You need to change Diffutils so that it outputs “diff:
cannot compare ‘-‘ to a directory” instead, using an apostrophe (U+0027) for both
opening and closing quote. You donʼt want to use fancier quoting characters such
as “‘” and “ʼ” (left and right single quotation marks, U+2018and U+2019) because
they are not ASCII characters and another customer requirement is that the
programs must work in ASCII-only environments.
The good news is that the Diffutils maintainers have run into a similar problem, and
have a patch called “maint: quote ‘like this’ or “like this”, not `like this’” that does
what you want. The bad news is that your customer has specified Diffutils version
3.0, and the patch that you want is not in version 3.0.
Also, your customer is
conservative and wants a minimal patch so that itʼs easy to audit, whereas the
Diffutils maintainersʼ patch also affects commentary and documentation which
your customer doesnʼt need or want changed.
Laboratory: Managing a backported change
As usual, keep a log in the file lab9.txt of what you do in the lab so that you can
reproduce the results later. This should not merely be a transcript of what you
typed: it should be more like a true lab notebook, in which you briefly note down
g.
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gp.
gg.
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gj.
what you did and what happened.
Get a copy of the Diffutils repository, in Git format, from the file ~eggert/src/
gnu/diffutils on the SEASnet GNU/Linux servers, or from its main Savannah
repository.
Get a log of changes to Diffutilsʼ master branch using the “git log” command,
and put it into the file git-log.txt.
Generate a list of tags used for Diffutils using the “git tag” command, and
put it into the file git-tags.txt
Find the commit entitled “maint: quote ‘like this’ or “like this”, not `like this’”,
and generate a patch for that commit, putting it into the file quote-patch.txt.
Check out version 3.0 of Diffutils from your repository.
Use the patch command to apply quote-patch.txt to version 3.0. In some
cases it will not be able to figure out what file to patch; skip past those by
typing RETURN. Record any problems you had in applying the patch.
Use the git status command to get an overview of what happened.
Learn how to use the Emacs functions vc-diff (C-x v =) and vc-revert (C-x v
u). When you’re in the *vc-diff* buffer generated by vc-diff, use describemode (C-h m) to find out the Emacs functions that you can use there, and in
particular learn how to use the diff-apply-hunk (C-c C-a) and diff-gotosource (C-c C-c) functions.
Use Emacs to revert all the changes to files other than .c files, since you
want only changes to .c files.
Also,and don’t forget this part, undo all the
changes to .c files other than changes to character string constants, as the
character-string changes are the only changes that you want; this may
require editing some files by hand.
Use Emacs to examine the files src/*.c.rej carefully, and copy rejected
patches into the corresponding .cfiles as needed.
Remove all untracked files that git status warns you about, since you donʼt
plan on adding any files in your patch.
When youʼre done with the above, git status should report a half-dozen
modified files, and git diff should output a patch that is three or four hundred
lines long. Put that patch into a file quote-3.0-patch.txt.
Build the resulting modified version of Diffutils, using the commands
described in the file README-hacking, skipping the part about CVS; CVS is
obsolescent.
(If you are building on lnxsrv07 or lnxsrv09 or any other host
that is using version 2.16 or later of the GNU C Library, you will need to apply
an additional patch after running ./bootstrap and before running ./configure,
because glibc 2.16 removed the obsolete and dangerous gets function
declared by a Diffutils header.) Verify that Diffutils does the right thing with
the “diff . -” scenario, as well as with “diff –help”.
Do a sanity test using the modified version of Diffutils that you just built, by
using the just-built diff to compare the source code of Diffutils 3.0 to the
source code of your modified version. Put the former source code into a
gj.
gk.
g.
h.
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gp.
directory diffutils-3.0 and the latter source code into a directory diffutils-3.0-
patch, and run your implementation of diff with the command “D/diff -pru
diffutils-3.0 diffutils-3.0-patch >quote-3.0-test.txt”, where the D is the
directory containing your diff implementation.
Use diff to compare the contents of quote-3.0-test.txt and quote-3.0-
patch.txt. Are the files identical? If not, are the differences innocuous?
Homework: Verifying and publishing a backported change
Youʼre happy with the code that you wrote in your lab, but now youʼd like to
publish this patch, in a form similar to that presented in the original patch, so that
others can use it.
Maintain a file hw9.txt that logs the actions you do in solving the homework.
This is like your lab notebook lab9.txt, except itʼs for the homework instead
of the lab.
Check out version 3.0 of Diffutils from your repository, into a new branch
named “quote”.
Install your change into this new branch, by running the patch command with
your patch quote-3.0-patch.txt as input.
Learn how to use the Emacs function add-change-log-entry-otherwindow (C-x 4 a).
Use this Emacs function to compose an appropriate ChangeLog entry for
your patch, by adapting the change log from the original patch.
Commit your changes to the new branch, using the ChangeLog entry as the
commit message.
Use the command “git format-patch” to generate a file formatted-patch.txt.
This patch should work without having to fix things by hand afterwards.
Your teaching assistant will assign you a partner, who will also generate a
patch.
Verify that your partner’s patch works, by checking out version 3.0
again into a new temporary branch partner, applying the patch with the
command “git am”, and building the resulting system, checking that it works
with “make check”.
Verify that your ChangeLog entry works, by running the command “make
distdir” and inspecting the resulting diffutils*/ChangeLog file.
There is a copy of the GNU Emacs git repository’s master branch on SEASnet
in the directory~eggert/src/gnu/emacs. Run the command gitk on it, and find
the newest merge that is not newer than 2015-01-25. Take a screenshot gitkscreenshot.png of your view of the mergepoint, and in an ASCII text file gitkdescription.txt briefly describe the roles of subwindows that you see in the
screenshot.
Submit
Submit a compressed tarball hw9.tgz containing the following files.
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The files lab9.txt, git-log.txt, git-tags.txt, quote-patch.txt, and quote-3.0-
patch.txt as described in the lab.
The files hw9.txt formatted-patch.txt, gitk-screenshot.png, and gitkdescription.txt as described in the homework.
All .txt files should be ASCII text files, with no carriage returns.
You can create the tarball with the command:
tar czf hw9.tgz lab9.txt git-log.txt git-tags.txt \
quote-patch.txt quote-3.0-patch.txt hw9.txt formatted-patch.txt \
gitk-screenshot.png gitk-description.txt
© 2005, 2007–2015, 2017 Paul Eggert. See copying rules.
$Id: assign9.html,v 1.28 2017/01/25 00H24H31 eggert Exp $
