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Improved documentation.

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Removed the Cookbook link for now, since it's empty.
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Avery Pennarun 2018-11-20 09:50:37 -05:00
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3
Documentation/Contributing.md
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@ -35,6 +35,9 @@ The best things you can do for redo are:
in default redo build rules for common program types would probably be
very popular.
- Convince your favourite OS distro to build and include (up to date!) redo
packages.
- Tell your friends!

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Documentation/Cookbook.md
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@ -1 +0,0 @@
Not written yet! Sorry.

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Documentation/FAQImpl.md
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@ -1,22 +1,14 @@
# Hey, does redo even *run* on Windows?
# Does redo even run on Windows?
FIXME:
Probably under cygwin. But it hasn't been tested, so no.
redo works fine in [Windows Services for Linux (WSL)](https://docs.microsoft.com/en-us/windows/wsl/initialize-distro)
on Windows 10. You might consider that to be "real" Windows, or not. If
you use it, it runs more or less like it does on Linux. WSL is considerably
slower than native Linux, so there is definitely room for speed improvements.
If I were going to port redo to Windows in a "native" way,
I might grab the source code to a posix shell (like the
one in MSYS) and link it directly into redo.
`make` also doesn't *really* run on Windows (unless you use
MSYS or Cygwin or something like that). There are versions
of make that do - like Microsoft's version - but their
syntax is horrifically different from one vendor to
another, so you might as well just be writing for a
vendor-specific tool.
At least redo is simple enough that, theoretically, one
day, I can imagine it being cross platform.
One interesting project that has appeared recently is
busybox-w32 (https://github.com/pclouds/busybox-w32). It's
a port of busybox to win32 that includes a mostly POSIX
@ -28,11 +20,67 @@ all of this needs more experimentation.
# Can a *.do file itself be generated as part of the build process?
Not currently. There's nothing fundamentally preventing us from allowing
it. However, it seems easier to reason about your build process if you
*aren't* auto-generating your build scripts on the fly.
Yes and no. Kind of. Redo doesn't stop you from doing this, and it will
use a .do file if you generate one. However, you have to do the steps in
the right order if you want this to work. For example, this should work
fine:
This might change someday.
redo-ifchange default.o.do
redo-ifchange foo.o
You've told redo to generate `default.o.do` (presumably using a
script like default.do.do), and *then* you've told redo to generate `foo.o`.
When it considers how to build `foo.o`, it will look for a .do file, and
thus find `default.o.do`, so it'll run it. Great.
Some people would like us to go a step further, and *automatically* look for
rules that will help produce default.o.do. That is, you might want to just
write this:
redo-ifchange foo.o bar.o
and then expect that, implicitly, redo will know it needs to look for
`default.o.do`, and if `default.o.do` doesn't exist yet, it should look for
`default.do.do`, and so on.
The problem with this idea is... where does it end? If there's no
`default.o.do`, so we look for a `default.do.do`, what if that doesn't exist
either? Perhaps there's a `default.do.do.do` for generating `default.do.do`
files? And so on. You have to draw the line somewhere.
# What can I do instead of auto-generating *.do files?
When people ask about auto-generating .do files, they usually mean one of
two things:
1. They want to create a new directory and auto-populate it with .do files
copied from somewhere.
- This can be solved in various ways. For example, you might make a
trivial toplevel `default.do` file in the new directory; this will
match all possible targets. You can then use the sh "source" operator
(.) and `redo-whichdo` to pull the "real" rules from elsewhere. An
example of [.do file delegation can be found in the wvstreams
project](https://github.com/apenwarr/wvstreams/blob/master/delegate.od).
2. They want to generate, eg. `default.o.do` based on auto-detected compiler
settings, in order to support different brands of compilers, or different
architectures, etc.
- The trick here is not to generate `default.o.do`, but rather to
generate another script instead. For example, you could have a
`compile.do` that generates a script called `compile`. `default.o.do`
would simply be hard coded to something like `./compile $2 $3`. The
wvstreams project also has [an example of
compile.do](https://github.com/apenwarr/wvstreams/blob/master/compile.do).
- The advantage of separating out into separate default.o.do and compile
scripts is that you can put all your system-dependent conditionals
into compile.do, so they run only once and choose the "right" compile
command. Then, for each file, you can simply run that command. If
This kind of micro-optimization doesn't appeal to you, then there's no
shame in just putting all the logic directly into `default.o.do`.
# How does redo store dependencies?
@ -42,11 +90,19 @@ named `.redo`. That directory contains a sqlite3 database
with dependency information.
The format of the `.redo` directory is undocumented because
it may change at any time. Maybe it will turn out that we
it may change at any time. It will likely turn out that we
can do something simpler than sqlite3. If you really need to make a
tool that pokes around in there, please ask on the mailing
list if we can standardize something for you.
Unfortunately, the design of having a *single* .redo directory at the
toplevel of a project has proven problematic: what exactly is the "top
level" of a "project"? If your project is a subdirectory of another project
that then switches to redo, should the .redo directory move up a level in
the hierarchy when that happens? And so on. Eventually, we will
probably migrate to a system where there is one .redo directory per target
directory. This avoids all kinds of problems with symlinks, directory
renames nested projects, and so on.
# Isn't using sqlite3 overkill? And un-djb-ish?
@ -66,18 +122,18 @@ it! Or if you want to be really horrified:
root root 1995612 2009-02-03 13:54 /usr/lib/libmysqlclient.so.15.0.0
The mysql *client* library is two megs, and it doesn't even
have a database server in it! People who think SQL
have a database in it! People who think SQL
databases are automatically bloated and gross have not yet
actually experienced the joys of sqlite. SQL has a
well-deserved bad reputation, but sqlite is another story
entirely. It's excellent, and much simpler and better
written than you'd expect.
But still, I'm pretty sure it's not very "djbish" to use a
Still, it's not very "djbish" to use a
general-purpose database, especially one that has a *SQL
parser* in it. (One of the great things about redo's
design is that it doesn't ever need to parse anything, so
a SQL parser is a bit embarrassing.)
embedding a whole SQL parser is a bit embarrassing.)
I'm pretty sure djb never would have done it that way.
However, I don't think we can reach the performance we want
@ -85,20 +141,15 @@ with dependency/build/lock information stored in plain text
files; among other things, that results in too much
fstat/open activity, which is slow in general, and even
slower if you want to run on Windows. That leads us to a
binary database, and if the binary database isn't sqlite or
libdb or something, that means we have to implement our own
data structures. Which is probably what djb would do, of
course, but I'm just not convinced that I can do a better
(or even a smaller) job of it than the sqlite guys did.
binary database. And example of the kind of structure we need is the [one
used by ninja](https://github.com/ninja-build/ninja/blob/master/src/deps_log.h#L29)
which is very simple, fast, and efficient.
Most of the state database stuff has been isolated in
state.py. If you're feeling brave, you can try to
implement your own better state database, with or without
sqlite.
It is almost certainly possible to do it much more nicely
than I have, so if you do, please send it in!
# What hash algorithm does redo-stamp use?
@ -181,6 +232,10 @@ were really annoying, and I definitely felt it. Adding
redo-stamp and redo-always work the way they do made the
pain disappear, so I stopped changing things.
A longer and even more detailed explanation of timestamp vs checksum-based
build dependencies can be found in
[mtime comparison considered harmful](https://apenwarr.ca/log/20181113).
# Why doesn't redo by default print the commands as they are run?
@ -244,7 +299,6 @@ choose to run only that step in verbose mode:
+ ./sleep 1.1
redo t/c.c.c.b.b (done)
If you're using an autobuilder or something that logs build results for
future examination, you should probably set it to always run redo with
the -x option.

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Documentation/GettingStarted.md
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@ -6,7 +6,7 @@ Optional, but recommended, is the
`ps` output prettier.
In modern versions of Debian, sqlite3 is already part of the python2.7 package.
You can install the requirements like this:
You can install the prerequisites like this:
```sh
sudo apt-get install python2.7 python-setproctitle
```
@ -34,3 +34,19 @@ your home directory:
```sh
PREFIX=$HOME ./redo install
```
# Distro packages
## MacOS
redo is available from the [Homebrew](https://brew.sh/) project:
brew install redo
## Linux
Various linux distributions include redo under different names. Most of the
packages are unfortunately obsolete and don't contain the most recent bug
fixes. At this time (late 2018), we recommend using the latest tagged
version [from github](https://github.com/apenwarr/redo).

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Documentation/index.md
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@ -1,49 +1,35 @@
# redo: a recursive, general-purpose build system
`redo` is a competitor to the long-lived, but sadly imperfect, `make`
program. There are many such competitors, because many people over the
years have been dissatisfied with make's limitations. However, of all the
replacements I've seen, only redo captures the essential simplicity and
flexibility of make, while avoiding its flaws. To my great surprise, it
manages to do this while being simultaneously simpler than make, more
flexible than make, and more powerful than make.
program. Unlike other such competitors, redo captures the essential
simplicity and flexibility of make, while avoiding its flaws. It manages to
do this while being simultaneously simpler than make, more flexible than
make, and more powerful than make, and without sacrificing performance - a
rare combination of features.
Although I wrote redo and I would love to take credit for it, the magical
simplicity and flexibility comes because I copied verbatim a design by
Daniel J. Bernstein (creator of qmail and djbdns, among many other useful
things). He posted some very terse notes on his web site at one point
(there is no date) with the unassuming title, "[Rebuilding target files when
source files have changed](http://cr.yp.to/redo.html)." Those notes are
enough information to understand how the system is supposed to work;
unfortunately there's no code to go with it. I get the impression that the
hypothetical "djb redo" is incomplete and Bernstein doesn't yet consider it
ready for the real world.
I was led to that particular page by random chance from a link on [The djb
way](http://thedjbway.b0llix.net/future.html), by Wayne Marshall.
The original design for redo comes from Daniel J. Bernstein (creator of
qmail and djbdns, among many other useful things). He posted some
terse notes on his web site at one point (there is no date) with the
unassuming title, "[Rebuilding target files when source files have
changed](http://cr.yp.to/redo.html)." Those notes are enough information to
understand how the system is supposed to work; unfortunately there's no code
to go with it. I wrote this implementation of redo from scratch, based on
that design.
After I found out about djb redo, I searched the Internet for any sign that
other people had discovered what I had: a hidden, unimplemented gem of
brilliant code design. I found only one interesting link: Alan Grosskurth,
whose [Master's thesis at the University of Waterloo](http://grosskurth.ca/papers/mmath-thesis.pdf)
was about top-down software rebuilding, that is, djb redo. He wrote his
own (admittedly slow) implementation in about 250 lines of shell script.
If you've ever thought about rewriting GNU make from scratch, the idea of
doing it in 250 lines of shell script probably didn't occur to you. redo is
so simple that it's actually possible. For testing, I actually wrote an
even more minimal version, which always rebuilds everything instead of
checking dependencies, in 210 lines of shell (about 4 kbytes).
The design is simply that good.
own (admittedly slow) implementation in about 250 lines of shell script,
which gives an idea for how straightforward the system is.
My implementation of redo is called `redo` for the same reason that there
are 75 different versions of `make` that are all called `make`. It's somehow
easier that way. Hopefully it will turn out to be compatible with the other
implementations, should there be any.
easier that way.
My extremely minimal implementation, called `do`, is in the `minimal/`
directory of this repository.
I also provide an extremely minimal pure-POSIX-sh implementation, called
`do`, in the `minimal/` directory of this repository.
(Want to discuss redo? See the bottom of this file for
information about our mailing list.)
@ -51,18 +37,19 @@ information about our mailing list.)
# What's so special about redo?
The theory behind redo is almost magical: it can do everything `make` can
do, only the implementation is vastly simpler, the syntax is cleaner, and you
can do even more flexible things without resorting to ugly hacks. Also, you
get all the speed of non-recursive `make` (only check dependencies once per
run) combined with all the cleanliness of recursive `make` (you don't have
code from one module stomping on code from another module).
The theory behind redo sounds too good to be true: it can do everything
`make` can do, but the implementation is vastly simpler, the syntax is
cleaner, and you have even more flexibility without resorting to ugly hacks.
Also, you get all the speed of non-recursive `make` (only check dependencies
once per run) combined with all the cleanliness of recursive `make` (you
don't have code from one module stomping on code from another module).
(Disclaimer: my current implementation is not as fast as `make` for some
things, because it's written in python. Eventually I'll rewrite it an C and
it'll be very, very fast.)
The easiest way to show it is with an example.
The easiest way to show it is to jump into an example. Here's one for
compiling a C++ program.
Create a file called default.o.do:
@ -128,34 +115,43 @@ run the *current script* over again."
Dependencies are tracked in a persistent `.redo` database so that redo can
check them later. If a file needs to be rebuilt, it re-executes the
`whatever.do` script and regenerates the dependencies. If a file doesn't
need to be rebuilt, redo can calculate that just using its persistent
need to be rebuilt, redo figures that out just using its persistent
`.redo` database, without re-running the script. And it can do that check
just once right at the start of your project build.
just once right at the start of your project build, which is really fast.
But best of all, as you can see in `default.o.do`, you can declare a
dependency *after* building the program. In C, you get your best dependency
Best of all, as you can see in `default.o.do`, you can declare a dependency
*after* building the program. In C, you get your best dependency
information by trying to actually build, since that's how you find out which
headers you need. redo is based on the following simple insight:
you don't actually
care what the dependencies are *before* you build the target; if the target
doesn't exist, you obviously need to build it. Then, the build script
itself can provide the dependency information however it wants; unlike in
`make`, you don't need a special dependency syntax at all. You can even
declare some of your dependencies after building, which makes C-style
autodependencies much simpler.
headers you need. redo is based on this simple insight: you don't
actually care what the dependencies are *before* you build the target. If
the target doesn't exist, you obviously need to build it.
Once you're building it anyway, the build script itself can calculate the
dependency information however it wants; unlike in `make`, you don't need a
special dependency syntax at all. You can even declare some of your
dependencies after building, which makes C-style autodependencies much
simpler.
redo therefore is a unique combination of imperative and declarative
programming. The initial build is almost entirely imperative (running a
series of scripts). As part of that, the scripts declare dependencies a few
at a time, and redo assembles those into a larger data structure. Then, in
the future, it uses that pre-declared data structure to decide what work
needs to be redone.
(GNU make supports putting some of your dependencies in include files, and
auto-reloading those include files if they change. But this is very
confusing - the program flow through a Makefile is hard to trace already,
and even harder if it restarts randomly from the beginning when a file
changes. With redo, you can just read the script from top to bottom. A
`redo-ifchange` call is like calling a function, which you can also read
from top to bottom.)
and even harder when it restarts from the beginning because an include file
changes at runtime. With redo, you can just read each build script from top
to bottom. A `redo-ifchange` call is like calling a function, which you can
also read from top to bottom.)
# What projects use redo?
Here are a few open source examples:
Some larger proprietary projects are using it, but unfortunately they can't
easily be linked from this document. Here are a few open source examples:
* [Liberation Circuit](https://github.com/linleyh/liberation-circuit) is a
straightforward example of a C++ binary (a game) compiled with redo.
@ -177,11 +173,12 @@ Here are a few open source examples:
[`t/111-example/`](t/111-example) subdir of the redo project itself.
If you switch your program's build process to use redo, please let us know and
we can link to it here.
we can link to it here for some free publicity.
(Please don't use the code in the `t/` directory as serious examples of how
to use redo. Many of the tests are doing things in deliberately psychotic
ways in order to stress redo's code and find bugs.)
(Please don't use the integration testing code in the redo project's `t/`
directory as serious examples of how to use redo. Many of the tests are
doing things in intentionally psychotic ways in order to stress redo's code
and find bugs.)
# How does this redo compare to other redo implementations?
@ -190,11 +187,13 @@ djb never released his version, so other people have implemented their own
variants based on his [published specification](http://cr.yp.to/redo.html).
This version, sometimes called apenwarr/redo, is probably the most advanced
one, including support for parallel builds, advanced build logs, and helpful
debugging features. It's currently written in python for easier
one, including support for parallel builds,
[resilient timestamps](https://apenwarr.ca/log/20181113) and checksums,
[build log linearization](https://apenwarr.ca/log/20181106), and
helpful debugging features. It's currently written in python for easier
experimentation, but the plan is to eventually migrate it to plain C. (Some
people like to call this version "python-redo", but I don't like that name.
We shouldn't have to rename it just because we port the code to C.)
We shouldn't have to rename it when we later transliterate the code to C.)
Here are some other redo variants (thanks to Nils Dagsson Moskopp for many
of these links):
@ -241,4 +240,4 @@ redo semantics, and/or have few or no automated tests.
At the time of this writing, none of them except apenwarr/redo (ie. this
project) support parallel builds (`redo -j`). For large projects,
parallel builds are usually essential.
parallel builds are usually considered essential.

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mkdocs.yml
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@ -7,7 +7,6 @@ strict: true
pages:
- Introduction: index.md
- Getting Started: GettingStarted.md
- Cookbook.md
- FAQ:
- Basics: FAQBasics.md
- Semantics: FAQSemantics.md
@ -15,7 +14,8 @@ pages:
- Parallel Builds: FAQParallel.md
- Implementation Details: FAQImpl.md
- Contributing.md
- Command Reference (man pages):
- Reference:
- Manual Pages:
- redo: redo.md
- redo-ifchange: redo-ifchange.md
- redo-ifcreate: redo-ifcreate.md