A commit is a save point

You will learn

What a commit keeps, why editing afterwards cannot change it, and when to make one.

Try it

In the widget, read the value of the file at the three moments and find the one where the agent's edit is undone; then in the spec frame find RESTORED and say what would change if it were set to EDITED.

specs/vibecoding/commit.t27

// SPDX-License-Identifier: Apache-2.0
; specs/vibecoding/commit.t27 -- lesson "A commit is a save point" of the course "Vibecoding from zero with t27"
; A commit keeps your files exactly as they were at that moment. Edit later as much as you like:
; the saved copy does not change, and you can go back to it. Here a file is one number.
; ASCII only, English only.

module vibecoding_commit;

; The file when you committed, and the file after an agent changed it.
pub const SAVED : u8 = 10;
pub const EDITED : u8 = 99;

; What going back brings you: the saved copy, whatever the file says now.
pub const RESTORED : u8 = 10;

; Each commit adds one save point to the history; nothing is overwritten.
pub const COMMITS_BEFORE : u8 = 2;
pub const COMMITS_AFTER : u8 = 3;

test going_back_returns_the_saved_copy {
    assert RESTORED == SAVED;
}

test editing_does_not_touch_the_save {
    assert SAVED == 10;
    assert EDITED != SAVED;
}

test a_commit_adds_one_save_point {
    assert COMMITS_AFTER == COMMITS_BEFORE + 1;
}

; Negative control: plant the bug "going back reads the edit" (RESTORED = 99) and
; two tests turn red; with the line as written they stay green.
test negative_control_a_restore_is_not_the_edit {
    assert RESTORED != EDITED;
}

Open the lesson's spec in the player ↗

All lessons

• Module 1 · What vibecoding is

  You describe, an agent writes, you run it and check. What a program is, and five myths put to a test.

  1. 01 Describe, run, check
  2. 02 A program is steps in order
  3. 03 Five myths, each put to a test

• Module 2 · Your desk

  An editor with an agent beside it, ten terminal commands, and reading an error message.

  1. 04 An editor with an agent beside it
  2. 05 Ten terminal commands
  3. 06 Shortcuts, and reading an error

• Module 3 · Save points with git

  A commit is a save point, a branch is a safe try, and a key is a pair of which one stays private.

  1. 07 A commit is a save point
  2. 08 A branch is a safe try
  3. 09 A key is a pair

• Module 4 · Prompting

  The parts of a prompt, an example in place of an adjective, and one small step at a time.

  1. 10 The parts of a prompt
  2. 11 An example beats an adjective
  3. 12 One small step per prompt

• Module 5 · The working loop

  Four phases from idea to ship, the loop of ask, run, read and fix, and what to do when it is stuck.

  1. 13 Four phases: idea, build, test, ship
  2. 14 Ask, run, read, fix
  3. 15 When you are stuck

• Module 6 · A test as the judge

  A test says yes or no, a planted bug shows the test works, and a diff is read before it is accepted.

  1. 16 A test says yes or no
  2. 17 Plant a bug and watch it fail
  3. 18 Read the diff before you accept it

• Module 7 · The parts of an agent

  What an agent answers with, what it can do with tools, and what it keeps between messages.

  1. 19 The mind: an answer with a shape
  2. 20 The hands: tools an agent can call
  3. 21 Memory: what an agent keeps

• Module 8 · A first bot

  A bot is a message loop, a bot comes from a spec, and a secret stays out of the repository and the prompt.

  1. 22 A bot is a message loop
  2. 23 From a spec to a bot
  3. 24 Secrets stay out of the repository and the prompt

• Module 9 · Your own project

  A spec for your own idea, one thing measured after it runs, and an honest plan for the next month.

  1. 25 A spec for your own idea
  2. 26 Build it, then measure one thing
  3. 27 An honest plan for the next month