Saturday, March 18, 2017

Followup on Bash long options

A followup on Bash long options.

The top-level option parsing while-loop I discussed works fine for regular options. Sometimes you need special parsing for subcommand options. A hypothetical example might be:

$ my-script --toplevel-thing my-subcommand --something-wonderful option-arg

Here the --toplevel-thing option is for my-script, and --something-wonderful option and its option-arg is for my-subcommand. Regular getopts parsing will try to handle all options for the top level, failing to distinguish subcommand options as separate. Further, getopts in a function does not behave quite as expected.

One solution is simple and hearkens back to the pre-getopts days. For the top level:

while (( 0 < $# ))
do
    case $1 in
        --toplevel-thing ) _toplevel_thing=true ; shift ;;
        -* ) usage >&2 ; exit 2 ;;
        * ) break ;;
    esac
done

Using a while-loop with explicit breaks avoids looking too far along the command line, and wrongly consuming options meant for subcommands. Rechecking $# each time through the loop breaks gracefully. Similarly, for subcommands expressed in a function:

function my-subcommand {
    while (( 0 < $# ))
    do
        case $1 in
            --something-special ) local option_arg="$2" ; shift 2 ;;
            * ) usage >&2 ; exit 2 ;;
        esac
    done
    # Rest of my-subcommand, using `option_arg` if provided

This uses the same pattern as the top level so you avoid needing to remember to handle top level one way, and subcommand another.

An example script using this pattern.

Monday, March 13, 2017

Frequent commits

Pair posting with guest Sarah Krueger!

A source control pattern for TDD

At work we recently revisited our commit practices. One issue spotted: we didn't commit often enough. To address we adopted the source control pattern in this post. There are lots of benefits; the one that mattered to me most: No more throwing the baby out with the bathwater, that is, no more two hour coding sessions only to start again and lose the good with the bad.

So we worked out this command-line pattern using single unit-of-work commits (without git rebase -i!):

# TDD cycle: edit code, run tests, rather-rinse-repeat until green
$ git pull --rebase --autostash && run tests && git commit -a --amend --no-edit
# Simple unit-of-work commit, push, begin TDD cycle again
$ git commit --amend && git push && git commit --allow-empty -m WIP

What is this?

  1. Start with a pull. This ensures you are always current, and find conflicts as soon as possible.
  2. Run your full tests. This depends on your project, for example, mvn verify or rake. If some tests are slow, split them out, and add a full test run before pushing.
  3. Amend your work to the current commit. This gives you a safe fallback known to pass tests. Worst case you might lose some recent work, but not hours worth. (Hint: run tests often.)
  4. When ready to push, update the commit message to the final message for public push.
  5. Push. Share. Make the world better.
  6. Restart the TDD cycle with an empty commit using a message that makes sense to you, for example "WIP" (work in progress); the message should be obvious not to push. Key: the TDD cycle command line only amends commits, so you need a first, empty commit to amend against.

Why?

They key feature of this source control pattern is: Always commit after reaching green on tests; never commit without testing. When tests fail, the commit fails (the && is short-circuit logical and).

In the math sense, this pattern makes testing and committing one-to-one and onto. Since TDD requires frequent running of tests, this means frequent commits when those tests pass. To avoid a long series of tiny commits when pushing, amend to collect a unit of work.

Bootstrapping

The TDD cycle depends on an initial, empty commit. The first time using this source control pattern:

# Do this after the most recent commit, before any edits
$ git commit --allow-empty -m WIP

Adding files

This pattern, though very useful, does not address new files. You do need to run git add with new files to include them in the commit. Automatically adding new files can be dangerous if gitignore isn't set up right.

It depends on your style

The exact command line depends on your style. You could include a script to run before tests, or before commit (though the latter might be better done with a git pre-commit hook). You might prefer merge pulls instead of rebase pulls. If your editor runs from the command line you might toss $EDITOR at the front of the TDD cycle.

The command lines assume git, but this source control pattern works with any system that supports similar functionality.

Fine-grained commits

An example of style choice. If you prefer fine-grained commits to unit-of-work single commits (depending on your taste or project; they're both good practice):

# TDD cycle: edit code, run tests, rather-rinse-repeat until green
$ git pull --rebase --autostash && run tests && git commit -a
# Fine-grained commits, push, begin TDD cycle again
$ git push

Improving your life

No matter your exact command line, it can be made friendlier for you. Yes, shell history can story your long chain of commands. What if they vary slightly between programmers sharing a project, or what if there is a common standard approach? Extend git. Let's call our example subcommand "tdd". Save this in a file named git-tdd in your $PATH:

#!/bin/sh
set -e
case $1 in
    test ) git pull --rebase --autostash && run tests && git commit -a --amend --no-edit ;;
    accept ) git commit --amend && git push && git commit --allow-empty -m WIP ;;
esac

Now your command line becomes:

$ git tdd test  # Repeat until unit of work is ready
$ git tdd accept

The source is in GitHub.

Updated:

An editing error left out the Why? section when initially posted.

Remember to autostash.

Saturday, March 11, 2017

Two BDD styles in Kotlin

Experimenting with BDD syntax in Kotlin, I tried these two styles:

fun main(args: Array<String>) {
    println(So
            GIVEN "an apple"
            WHEN "it falls"
            THEN "Newton thinks")
}

data class BDD constructor(
        val GIVEN: String, val WHEN: String, val THEN: String) {
    companion object {
        val So = So()
    }

    class So {
        infix fun GIVEN(GIVEN: String) = Given(GIVEN)
        data class Given(private val GIVEN: String) {
            infix fun WHEN(WHEN: String) = When(GIVEN, WHEN)
            data class When(private val GIVEN: String, private val WHEN: String) {
                infix fun THEN(THEN: String) = BDD(GIVEN, WHEN, THEN)
            }
        }
    }
}

And:

fun main(args: Array<String>) {
    println(GIVEN `an apple`
            WHEN `it falls`
            THEN `Newton thinks`
            QED)
}

infix fun Given.`an apple`(WHEN: When) = When()
infix fun When.`it falls`(THEN: Then) = Then(GIVEN)
infix fun Then.`Newton thinks`(QED: Qed) = BDD(GIVEN, WHEN)

inline fun whoami() = Throwable().stackTrace[1].methodName

data class BDD(val GIVEN: String, val WHEN: String, val THEN: String = whoami()) {
    companion object {
        val GIVEN = Given()
        val WHEN = When()
        val THEN = Then("")
        val QED = Qed()
    }

    class Given
    class When(val GIVEN: String = whoami())
    class Then(val GIVEN: String, val WHEN: String = whoami())
    class Qed
}

Comparing main() methods, which is easier to read or use? I haven't tried implementing, just have looked at testing code style. Note that I'm using the infix feature of Kotlin to have my BDD "GIVEN/WHEN/THEN" as punctuation free as I'm able.

In the one case—using strings to describe cases—, an implementation would be more similar to Spec or Cucumber, which usually uses pattern matching to associate text with implementation. In the other case—using functions to describe cases—, an implementation goes directly into the function definition. In either case, Kotlin only supports binary infix functions, not unary (of course, you say, that's what "infix" means!), so I need either an initial starting token (So in the strings case) or an ending one (QED in the functions case).

I'm curious how implementation sorts out.

(Code here.)

UPDATE:

I have working code now that runs these BDD sentences but remain unclear which of the two styles (strings vs functions) would be easier to work with:

fun main(args: Array<String>) {
    var apple: Apple? = null
    upon("an apple") {
        apple = Apple(Newton(thinking = false))
    }
    upon("it falls") {
        apple?.falls()
    }
    upon("Newton thinks") {
        assert(apple?.physicist?.thinking ?: false) {
            "Newton is sleeping"
        }
    }

    println(So
            GIVEN "an apple"
            WHEN "it falls"
            THEN "Newton thinks")
}

Vs:

fun main(args: Array<String>) {
    println(GIVEN `an apple`
            WHEN `it falls`
            THEN `Newton thinks`
            QED)
}

var apple: Apple? = null

infix fun Given.`an apple`(WHEN: When) = upon(this) {
    apple = Apple(Newton(thinking = false))
}

infix fun When.`it falls`(THEN: Then) = upon(this) {
    apple?.falls()
}

infix fun Then.`Newton thinks`(QED: Qed) = upon(this) {
    assert(apple?.physicist?.thinking ?: false) {
        "Newton is sleeping"
    }
}

The strings style is certainly more familiar. However, mistakes in registering matches of "GIVEN/WHEN/THEN" clauses appear at runtime and do not provide much help.

The functions style is more obtuse. However, mistakes cause compile-time errors that are easier to understand, and your code editor can navigate between declaration and usage.