Cake3

Cake3 is a EDSL for building Makefiles, written in Haskell. With cake3, developer can write their build logic in Haskell, obtain clean and safe Makefile and distribute it among the non-Haskell-aware users. Currenly, GNU Make is the only backend supported.

The Goals

Make is a build tool which was created more than 20 yesrs ago. It has a number of versions and dialects. Basic Makefiles are really easy to write and understand. Unfortunately, it is hard to write real-world scale set of rules correctly due to tricky syntax and lots of pitfails. As of today, Make has automatic, declarative and imperative variables, builtin rules, pattern-rules, double-colon rules, C-style ifdefs (which doesn't work well with declarative variables) and lots of other strange things. Nevertheless, it is still widely used as a de-facto standard tool which everyone has access to.

The goals of Cake3 are to help the developer to:

• Stop overusing Make by writing complex logic in make-language
• Still have a correct Makefile which could be distributed among the users
• Take a bit of Haskell practice :)

Installation

From Hackage:

$ cabal install cake3

From the Github:

1. Install Haskell Platform

2. Install dependencies

   $ cabal install haskell-src-meta monadloc QuasiText
   

3. Build the thirdcake from Github

   $ git clone http://github.com/grwlf/cake3
   $ cd cake3
   $ cabal configure && cabal install
   

Usage

1. Create the Cakefile.hs in the root dir of your project

   $ cake3 init

2. Edit Cakefile.hs, fill it with rules or other logic you need

   $ vim Cakefile.hs

3. Debug your generator with

   $ cake3 ghci Prelude> :lo Cakefile.hs

4. Build the Makefile with cake3

   $ cake3

5. Run GNU make as usual

How does it work

Cake3 allows user to write Cakefile.hs in plain Haskell to define rules, targets and other stuff as usual. After that, cake3 compiles it into ./Cakegen application which builds your Makefile (ghc is required for that). GNU Make knows how to do the rest.

Example

Here is the example of simple Cakefile.hs:

module Cakefile where

import Development.Cake3
import Cakefile_P

main = writeMake "Makefile" $ do

  selfUpdate

  cs <- filterDirectoryContentsRecursive [".c"]

  d <- rule $ do
    shell [cmd|gcc -M $cs -MF @(file "depend.mk")|]

  os <- forM cs $ \c -> do
    rule $ do
      shell [cmd| gcc -c $(extvar "CFLAGS") -o @(c.="o") $c |]

  elf <- rule $ do
    shell [cmd| gcc -o @(file "main.elf") $os |]

  rule $ do
    phony "clean"
    unsafeShell [cmd|rm $elf $os $d|]

  rule $ do
    phony "all"
    depend elf

  includeMakefile d

• Cakefile_P is an autogenerated module. It defines file :: String -> File function plus some others.
• Main building blocks - rule functions - build Makefile rules one-to-one. The prerequisites are computed based on it's actions.
• All actions live in Action monad (A Monad). shell is the most important operation of this monad.
• Quasy-quotation is used to simplify the shell code. [cmd|..|] takes a string as an argument. It's syntax includes:
  • $name untiquotes hasell expressions name of type File, Variable plus few others. They define a prerequisites of a rule
  • @name untiquotes hasell expressions name of type File. They define rule's targets
  • complex expressions are also supported with $(foo bar) and @(bar baz).
  • $$ and @@ expands to $ and @
• Rules appears in the Makefile in the reversed order. Normally, you want 'all' rule to be at the bottom.

Features and limitations

Thirdcake follows Autoconf's path in a sence that it builds the program may do some checks and tests and generates the Makefile. In the same time, the idea of this EDSL is to move as much logic as possible in the final Makefile, to drop the cake3 dependency at the build time.

Of cause, it is possible up to some degree. For example, Cake3 doe not provide a way to scan the project tree with Make's wildcards. But it is possible and may be implemented in future.

Still, some common patterns are supported so I hope that users would call resulting Makefiles safe and robust enough for, say, package maintainers.

Features

• Allows spaces inside the filenames.

  Everyone knows that Makefiles don't like spaces in filenames. Cake3 carefully inserts '\ ' to make make happy.

• Rebuilds a rule when variable changes.

  Consider following antipattern:

  # You often write rules like this, don't you?
  out : in
       foo $(FLAGS) -o $@ $^
  

  Unfortunately, changes in FLAGS don't lead to rebuilding of out. Hardly-trackable bugs may appear if one part of a project was built with one set of optimisation flags and another part was build with another set by mistake.

  Thirdcake implements the makevar checksum pattern from StackOverflow to detect changes in variables and rebuild targets when nessesary.

  rule $ do
    shell [cmd|foo $(extvar "FLAGS") -o @out $in |]
  

  will rebuild out on FLAGS change

• Supports rules with more than one target.

  It is not that simple to write a rule which has more than one target. Really,

  out1 out2 : in1 in2
      foo in1 in2 -o out1 -o out2
  

  is not corret. Read this Automake article if you are surprised. Thirdcake implements .INTERMEDIATE pattern to deal with this problem so rule like this

  rule $ do
    shell [cmd|foo $in1 $in2 -o @out1 -o @out2 |]
  

  will always notice inputs changes and rebuild both outputs

• Supports global prebuild\postbuild actions

  Common human-made Makefile with prebuild commands would support them for one rule, typically, "all". Other targets often stay uncovered. Cake3 makes sure that actions are executed for any target you call.

• Lets user organize build hierarchy.

  Say, we have a project A with subproject L. L has it's own Makefile and we want to re-use it from our global A/Makefile. Make provides only two ways of doing that. We could either include L/Makefile or call $(MAKE) -C L. First solution is a pain because merging two Makefiles together is generally a hard work. Second approach is OK, but only if we don't need to pass additional paramters or depend on a specific rule from L.

  Thirdcake's approach in this case is a compromise: since it employs Haskell's module system, it is possible to write:

  -- Project/lib/CakeLib.hs
  import CakeLib_P.hs
  librule = do
    rule $ do
      shell [cmd|build a lib|]
  
  -- Project/Cakefile.hs
  import Cakefile_P.hs
  import CakeLib.hs 
  -- ^ note the absence of lib folder here. cake3 will copy all Cake*hs to
  --   the temp dir, then build them there.
  
  all = do
    lib <- librule
    rule $ do
      shell [cmd|build an app with $lib |]
  

  A/Cakefile.hs and do whatever you want to. Resulting makefiles will always be monolitic.

Limitations

Make syntax

• Make is not able to detect directory content chages. For example, user has to rerun the ./Cakegen if they add/remove a source file. I plan to automate this kind of checks. so it is on my TODO list.
• ifdef/endif instructions is not supported generally. User has to move this logic in Haskell for now. Also on my TODO list
• Cake3 doesn't check the contents of Makefile variables. It is user's responsibility to keep them safe.
• Variables as targets is not supported. Implement this logic in Haskell for now.

General

• Resulting Makefile is actually a GNUMakefile. GNU extensions (shell function and others) are needed to make various tricks to work. Also, posix environment with coreututils package is required. So, Linux, Probably Mac, Probably Windows+Cygwin.
• All Cakefiles across the project tree should have unique names in order to be copied. Duplicates are found, the first one is used

Random implementation details

1. User writes a cakefile (./Cake*.hs) describing the rules. Refer to Example/GHC/Cakefile.hs. Note, that different cakefiles should have different names even if they are in different directories due to GHC import restrictions. This way user can import one cakefile from another, as if they were in the same directory. Actually, cake3 copies all cakefiles into one temporary directory and compiles them there. Note that cake3 calls ghc having several common haskell extentions enabled.

2. Cake3 copies all Cake*.hs files from your project tree into temporary dir and compiles them with GHC (or calls GHCi). Before that, it creates a ./Cake*_P.hs pathfile containing information about paths. The most important is files function which translates relative filename into "." </> path_to_subproject </> filename.

3. Cake3 uses relative paths only for the final Makefile.

4. Cake3 uses it's own representation of files (File). Many filepath functions (takeDirectory, takeBaseName, dropExtensions, </>, etc) are defined for them. See System.FilePath.Wrapper.hs. FileLike typeclass makes it possible to use them with plain FilePath as well.