Rehabilitating pkglint

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# Rehabilitating pkglint

## Amitai Schlair, The NetBSD Project

### pkgsrcCon Berlin 2013/03/23
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.left-column[
## Why pkglint?
]
.right-column[

### [PR pkg/46570 infelicities in pkglint](http://gnats.netbsd.org/46570)

"A good start would be rewriting it not in perl."
]
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.left-column[
## Why pkglint?
]
.right-column[

### [PR pkg/46570 infelicities in pkglint](http://gnats.netbsd.org/46570)

"A good start would be rewriting it not in perl."

### [Things You Should Never Do, Part I](http://www.joelonsoftware.com/articles/fog0000000069.html)

"When you throw away code and start from scratch, you are throwing
away all that knowledge. All those collected bug fixes. Years of
programming work."
]
---
.left-column[
## Why pkglint?
]
.right-column[

### [PR pkg/46570 infelicities in pkglint](http://gnats.netbsd.org/46570)

"A good start would be rewriting it not in perl."

### [Things You Should Never Do, Part I](http://www.joelonsoftware.com/articles/fog0000000069.html)

"When you throw away code and start from scratch, you are throwing
away all that knowledge. All those collected bug fixes. Years of
programming work."

"It's important to remember that when you start from scratch there
is absolutely no reason to believe that you are going to do a better
job than you did the first time."
]
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.left-column[
## (How pkglint?)
]
.right-column[

### Local `git`

$ echo .git >> ~/.cvsignore
    $ echo CVS >> ~/.gitignore_global
    $ cd $PKGSRCDIR/pkgtools/pkglint
    $ git init
    $ git add .
    $ git commit -am 'Add pkglint to git for offline hacking.'
    $ git checkout -b rehab
    
    $ cd $PKGSRCDIR/pkgtools/pkglint
    $ git checkout master
    $ cvs update
    $ git commit -am 'Track upstream changes from pkgsrc CVS.'
    $ git checkout rehab
    $ git rebase master
    $ vi files/pkglint.t files/pkglint.pl && make test && make clean
    $ git commit -am 'More cool stuff on my branch.'
]
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.left-column[
## Why me?
]
.right-column[

### I've been writing a lot of Perl lately

### I know a way to revive legacy code
]
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.left-column[
## TDD
]
.right-column[

### Test-Driven Development

* Misnomer!
* Design technique (happens to result in automated tests)
* Programmer documentation (happens to be executable)

TDD leads to code that _looks like_ it was written by someone
careful, skillful, and tasteful.
]
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.left-column[
## "TED"
]
.right-column[

### "Test-Eventually Development"

* We didn't write pkglint test-first
* Design suffered
* Programmer documentation suffered

Whether or not we decide to rewrite pkglint, first we have to
understand and document its current behavior.

Never too late to test first. Just a bit more difficult.
]
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.left-column[
## Retrofit
]
.right-column[

### In `pkgsrc-current`

* Convert to ["modulino"](http://www.drdobbs.com/scripts-as-modules/184416165)
* Add a [test script](http://cvsweb.netbsd.org/bsdweb.cgi/pkgsrc/pkgtools/pkglint/files/pkglint.t)
* Hook it up to `make test` (just barely)
* Write a few tests (very simple)
* Prove that they fail when they should

Approved-by: `wiz`
]
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.left-column[
## Retrofit
]
.right-column[

### In my `git`

* Add ["characterization tests"](https://en.wikipedia.org/wiki/Characterization_test) over a few mature packages
* Extract some Perl classes to separate files
* Fix `make test` (no custom settings needed)
* Deepen an existing test to prepare for [refactoring](https://en.wikipedia.org/wiki/Refactoring)
* Change huge `if/elsif/else` block to dispatch table
* Fix a bug (!) found during refactoring

Planning to merge to `pkgsrc`. In the meantime, see
[GitHub](https://github.com/schmonz/pkglint/tree/rehab).
]
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# A bit of the old code-reading
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.left-column[
## Why does this matter?
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.right-column[

### pkglint isn't such a big deal

### `pkgsrc/mk` is
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.left-column[
## Why does this matter?
]
.right-column[

### pkglint isn't such a big deal

### But `pkgsrc/mk` is

Gradually...

* Cover infrastructure code with automated tests
* Gain shared understanding of complex internals
* Freely and safely change them for the better
* Keep what makes `pkgsrc` special
* Push `pkgsrc` forward
]
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.left-column[
## "A bit more difficult"
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.right-column[

### "Never too late to test first"

* Tangle of implementation languages
* Tangle of dependencies
* Progress won't be fast
* The alternative is worse
* We'll have to work together
* We'll have to be patient and persistent
]
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# FIN