docs: reorder readme content

2026-09-09 16:22:45 +02:00
1 changed files with 198 additions and 184 deletions
--- a/README.md
+++ b/README.md
@@ -3,119 +3,26 @@
 A wrapper around `docker compose` for our dockerized Django projects, so the
 same commands work in every repository.
 It reads `docker compose config` to work out which service runs Django and
 which one is the database, so nothing here takes a service name or a `-f`.
 Everything it does, it does by running `docker`, `git` and the Postgres tools.
 ## Installing
-You will need Rust installed. Clone repo and run:
+You will need Rust installed. Clone the repo and run:
 ```bash
 cargo install --path .
 ```
 ## What it makes of a project
 `ahab status` prints the services it picked, the containers behind them, the
 credentials it would use and what the store holds, reporting whatever it cannot
 work out rather than stopping at the first thing:
 ```
 $ ahab status
 services: db, django
 django: django (built from the project)
 	container: 0a8b19e27634
 postgres: db (postgres:18-alpine)
 	container: 189d4d395d62
 	user:      myproject
 	database:  myproject_db
 store: /home/you/.local/share/ahab/git.aflabs.org/urnik/afurnik
 	linked:    2
 	`ahab link check` lists what a sandbox can still read
 ```
 ## Seeing what it runs
 `-v` prints each Docker command as it runs, `--dry-run` prints the ones it would
 run without running them, and `-q` prints only what was asked for, dropping the
 progress along the way (Compose's own progress included). All work before or
 after the subcommand.
 ```bash
 ahab -v django migrate
 ahab --dry-run postgres import ./dump
 ahab -q postgres dump ./dump
 ```
 Nothing is written under `--dry-run`, filesystem included: `link add` and
 `django make-command` say what they would do and leave the tree alone.
 ## Exit codes
 - `0` — It ran and had nothing to report
 - `1` — It could not finish
 - `2` — The arguments were wrong
 - `4` — It ran fine and found something worth reporting, i.e.
  `link check --exit-code` with anything outside the store
 ## Shell completion
 `ahab completions <shell>` writes a completion script to stdout, for Bash,
 Elvish, Fish, PowerShell or Zsh:
 ```bash
 ahab completions zsh > ~/.local/share/zsh/completions/_ahab
 eval "$(ahab completions zsh)"      # or one line in .zshrc, never goes stale
 ```
 Completions are also generated during the build. They land in
 `target/*/build/*/out/` by default, and `SHELL_COMPLETIONS_DIR_<SHELL>`
 installs a single shell's file straight into place:
 ```bash
 SHELL_COMPLETIONS_DIR_ZSH=~/.local/share/zsh/completions \
 SHELL_COMPLETIONS_DIR_FISH=~/.config/fish/completions \
  cargo install --path .
 ```
 `SHELL_COMPLETIONS_DIR` writes every shell into one directory instead.
 ## The compose file
 `ahab` does not pass `-f`. Docker Compose finds the file itself, so set
 Docker's own `COMPOSE_FILE` when it is not in the working directory, including
 its `base.yaml:override.yaml` form. A project's `.env` is a good place for it,
 since Docker reads that too:
 ```
 COMPOSE_FILE=docker/docker-compose.yaml
 ```
 ## Service detection
 `ahab` finds the services it needs in `docker compose config`, so they can be
 named anything:
 - **postgres**: The service whose image is a Postgres flavour, matching
  `postg`, `timescale`, `pgvector` or `citus`
 - **django**: The service that both builds an image and sets
  `DJANGO_SETTINGS_MODULE`. Where more than one does — a worker beside the web
  service, say — the one publishing ports wins
 If nothing matches, or two candidates cannot be told apart, `ahab` says so and
 lists the services it looked at rather than guessing. Two services that both
 build and set the settings module are ambiguous unless exactly one of them
 publishes ports.
 `POSTGRES_USER` and `POSTGRES_DB` are read off the detected Postgres service, so
 `dropdb`, `createdb`, `pg_restore` and `pg_dump` use the role and database the
 project declares, falling back to `db` when it declares neither. Both have to
 be names: `ahab` hands them to those tools as a role and a database, and libpq
 reads a database name holding an `=` or a URL as a whole connection string,
 which would send a dump to whatever server it names. A value that could be read
 as something other than a name is refused rather than passed on.
 ## Django
 Each of these runs `docker compose run --rm` against the Django service, so it
 goes through the image's own entrypoint:
 ```bash
-ahab django run <cmd>                # in a fresh container, through the entrypoint
+ahab django run <cmd>                # anything, in a fresh container
-ahab django bash                     # shell in a fresh container
+ahab django bash                     # a shell in a fresh container
 ahab django manage <args>            # manage.py
 ahab django makemigrations
 ahab django migrate <args>
@@ -123,9 +30,10 @@ ahab django shell
 ahab django make-command <app> <name>
 ```
-There is no `ahab django test`: which runner a project uses is the project's
+There is no `ahab django test`. Which runner a project uses is the project's
-choice, and `manage.py test` exits 0 having collected nothing when the tests are
+choice, and `manage.py test` exits 0 having collected nothing when the tests
-written for pytest, so a wrong guess reads as a pass. Name the runner instead:
+are written for pytest, so a wrong guess reads as a pass. Name the runner
 instead:
 ```bash
 ahab django run pytest -x tests/
@@ -144,41 +52,45 @@ ahab postgres import <path>          # drop, create, then restore
 ahab postgres psql <args>             # psql in the database container
 ```
-A dump is written `0600` and under a name of its own until it is complete, then
+Dumps are written `0600`, under a name of their own until they are complete and
-renamed over the target: a cluster dump carries every role's password hash, and
+then renamed over the target. A cluster dump carries every role's password
-the default `0644` would hand it to anyone else with an account on the machine.
+hash, so the default `0644` would hand it to anyone else with an account.
-`psql` passes its arguments through and only asks Docker for a terminal when it
+Arguments reach `psql` untouched, and Docker is only asked for a terminal when
-has one to hand over, so both of these work:
+there is one to hand over, so both of these work:
 ```bash
 ahab postgres psql                          # interactive
 ahab postgres psql -tAc 'select count(*) from auth_user' | wc -l
 ```
-The format of a dump being imported is read from the file rather than its name.
+### What an import makes of a dump
 A custom format dump starts with `PGDMP` and a tar one with `toc.dat`, both of
 which go to `pg_restore`, as does a directory produced by `pg_dump -Fd`.
 Anything else is treated as SQL and fed to `psql` with `ON_ERROR_STOP` and
 `--single-transaction`, so a bad file rolls back instead of half applying.
 A whole cluster dump from `pg_dumpall` is recognised by its header and handled
 differently again: it creates its own databases and carries role statements, so
 the database is dropped but not recreated, the dump goes to `psql` connected to
 `postgres`, and it runs without `ON_ERROR_STOP` because roles that already exist
 report errors that are expected. Any error it does not expect is reported and
 fails the import, since `psql` without `ON_ERROR_STOP` exits 0 having applied
 only part of the dump. Gzipped dumps are decompressed on the way in, whichever
 of the three they hold. A cluster that has never held the database yet is a
 valid target either way, so importing into a fresh one works.
-`import` stops the project before it starts, so an import that fails leaves it
+The shape is read from the file rather than from its name:
-stopped and says so: `docker compose up` brings it back.
+
 - a `PGDMP` or `toc.dat` header — an archive, restored with `pg_restore`, as is
  a directory produced by `pg_dump -Fd`
 - a `pg_dumpall` header — a whole cluster, which creates its own databases and
  carries role statements, so the database is dropped but not recreated and the
  dump goes to `psql` connected to `postgres`
 - gzip magic — decompressed on the way in, whichever of the three is inside
 - anything else — SQL, fed to `psql` with `ON_ERROR_STOP` and
  `--single-transaction`, so a bad file rolls back instead of half applying
 A cluster restore is the one that runs without `ON_ERROR_STOP`, because roles
 that already exist report errors which are expected. Any other error fails the
 import, since psql would otherwise exit 0 having applied part of the dump.
 Importing into a cluster that has never held the database works either way.
 Containers are stopped before an import starts, so one that fails leaves the
 project stopped and says so.
 ## Link
-`ahab link` moves untracked paths out of the repository into an out-of-repo
+A sandbox that mounts the repository can read anything untracked sitting in it
-store and symlinks them back, so a sandbox that mounts the repository sees a
+— a `.env`, a dump, a key. Those paths can be moved out to a store of ahab's
-dangling symlink instead of the contents, while the host resolves it as before.
+own and symlinked back, so the host resolves the link as before while the
 sandbox is left with a symlink into somewhere it was never given.
 ```bash
 ahab link add .env secrets/         # move out, leave symlinks behind
@@ -190,12 +102,12 @@ ahab link check --porcelain         # `<code> <path>`, for scripts
 ahab link check --exit-code         # exit 4 when anything is outside the store
 ```
-`restore` is the inverse of `add`: the file moves out of the store and back to
+Restoring is the inverse of adding: the file comes back to where it was and the
-where it was, and the store keeps nothing. A second checkout linking the same
+store keeps nothing. A second checkout linking the same path is left with a
-path is left with a dangling symlink, since there is only ever one stored copy.
+dangling symlink, there being only ever one stored copy.
-`list` says what state each stored path is in, which `check` cannot see because
+Every stored path is in one of three states, which `list` reads from the store
-it asks Git about the repository rather than reading the store:
+rather than from git:
 ```
 $ ahab link list
@@ -205,39 +117,141 @@ store: /home/you/.local/share/ahab/git.aflabs.org/urnik/afurnik
 	missing:   secrets/token
 ```
-`missing` is a path whose symlink is gone, `shadowed` one that a real file took
+- `linked` — the symlink is there and points at the store, which is the point
-back; either way the stored copy is the one nobody reads.
+- `shadowed` — a real file took the path back, so nothing reads the stored copy
 - `missing` — the symlink is gone, and nothing reads the stored copy either
-`restore --all` moves back the linked ones and says how many it left, since
+Only a linked path can be moved back, so `restore --all` says how many it left
-there is nothing to undo for a path whose symlink is gone.
+alone.
-`-z` is the porcelain format for scripts that must survive any filename: entries
+Two things adding will not do:
 end with a NUL, and the two paths of a symlink leading elsewhere are separated
 by one as well, the way `git status -z` reports a rename.
-`check` looks at tracked paths too, since Git tracks symlinks and one can lead
+- **a tracked path**, which git would restore into the repository anyway. Where
-out of the repository without appearing in any untracked listing. `add` cannot
+  one is a symlink leading out, `check` reports it under the code `T>`, and
-externalize a tracked path, so all `check` can do is report it, under the code
+  saying so is all it can do
-`T>`.
+- **a symlink already leading out of the repository**, because moving the link
  would move the pointer and leave the contents where they are. The store would
  then hold a way back out, while `check` saw a link into the store and called
  the repository clean
-A symlink already leading out of the repository is not something `add` will
+For scripts there is `--porcelain`, and `-z` for filenames that need it:
-take: moving the link would move the pointer and leave the contents where they
+entries end with a NUL, and the two paths of a symlink leading elsewhere are
-are, so the store would hold a way back out while `check`, seeing a link into
+separated by one as well, the way `git status -z` reports a rename.
 the store, called the repository clean.
 The store lives under
 `${XDG_DATA_HOME:-$HOME/.local/share}/ahab/<host>/<owner>/<repo>/`, derived
 from the Git `origin` remote, or `_local/<checkout>` when there is no remote to
-name it after. Its directories are created `0700`: it exists to hold what
+name it after. Two details of that:
 should not be readable from the repository, and on a shared machine the default
 `0755` would leave that to whoever else has an account. A store path derived
 from a remote, or a checkout name, that needed characters replacing carries a
 short fingerprint of the original, so two of them cannot land on one directory.
-## Configuration
+- its directories are created `0700`, since it holds what should not be
  readable from the repository and `0755` would leave that to whoever else has
  an account on the machine
 - a remote or checkout name that needed characters replacing carries a short
  fingerprint of the original, so two of them cannot land on one directory
-Currently `ahab` respects the following environment variables.
+## What ahab makes of your project
- `AHAB_LINK_ROOT`: Where `ahab link` keeps its store — the same as `--store`,
+Running `ahab status` prints the services it picked, the containers behind
-  which takes precedence, and defaults to `${XDG_DATA_HOME:-$HOME/.local/share}/ahab`.
+them, the credentials it would use and what the store holds. It reports
-  `ahab status` reads it too, so it reports the store the link commands use
+whatever it cannot work out rather than stopping at the first thing:
 ```
 $ ahab status
 services: db, django
 django: django (built from the project)
 	container: 0a8b19e27634
 postgres: db (postgres:18-alpine)
 	container: 189d4d395d62
 	user:      myproject
 	database:  myproject_db
 store: /home/you/.local/share/ahab/git.aflabs.org/urnik/afurnik
 	linked:    2
 	`ahab link check` lists what a sandbox can still read
 ```
 ## Seeing what it runs
 - `-v` — print each Docker command as it runs
 - `--dry-run` — print the commands it would run, without running them
 - `-q` — print only what was asked for, dropping the progress along the way,
  Compose's own included
 All three work before or after the subcommand:
 ```bash
 ahab -v django migrate
 ahab --dry-run postgres import ./dump
 ahab -q postgres dump ./dump
 ```
 Nothing is written under `--dry-run`, the filesystem included: `link add` and
 `django make-command` say what they would do and leave the tree alone.
 ## Service detection
 Services can be named anything, since ahab looks at what they are rather than
 what they are called:
 - **postgres** — the service whose image is a Postgres flavour, matching
  `postg`, `timescale`, `pgvector` or `citus`
 - **django** — the service that both builds an image and sets
  `DJANGO_SETTINGS_MODULE`. Where more than one does, a worker beside the web
  service say, the one publishing ports wins
 If nothing matches, or two candidates cannot be told apart, ahab says so and
 lists the services it looked at rather than guessing.
 The role and database come from `POSTGRES_USER` and `POSTGRES_DB` on the
 detected service, falling back to `db` when neither is set. Both have to be
 names: libpq reads a database name holding an `=` or a URL as a whole
 connection string, which would send a dump to whatever server that names, so a
 value which could be read as anything but a name is refused.
 ## The compose file
 Compose finds its own file and ahab does not pass `-f`, so set Docker's own
 `COMPOSE_FILE` when the file is not in the working directory, including its
 `base.yaml:override.yaml` form. A project's `.env` is a good place for it,
 since Docker reads that too:
 ```
 COMPOSE_FILE=docker/docker-compose.yaml
 ```
 ## Shell completion
 Completion scripts are written to stdout, for Bash, Elvish, Fish, PowerShell
 or Zsh:
 ```bash
 ahab completions zsh > ~/.local/share/zsh/completions/_ahab
 eval "$(ahab completions zsh)"      # or one line in .zshrc, never goes stale
 ```
 They are generated during the build as well, landing in
 `target/*/build/*/out/`. To install a single shell's file straight into place:
 ```bash
 SHELL_COMPLETIONS_DIR_ZSH=~/.local/share/zsh/completions \
 SHELL_COMPLETIONS_DIR_FISH=~/.config/fish/completions \
  cargo install --path .
 ```
 Set `SHELL_COMPLETIONS_DIR` to write every shell into one directory instead.
 Either way the path has to be absolute, since a build script runs from wherever
 cargo happens to be building.
 ## Exit codes
 - `0` — it ran and had nothing to report
 - `1` — it could not finish
 - `2` — the arguments were wrong
 - `4` — it ran fine and found something worth reporting, which today means
  `link check --exit-code` with anything outside the store
 ## Environment variables
 - `AHAB_LINK_ROOT` — where `ahab link` keeps its store, the same as `--store`,
  which takes precedence. Defaults to
  `${XDG_DATA_HOME:-$HOME/.local/share}/ahab`. Read by `ahab status` too, so it
  reports the store the link commands actually use