Weeder

Weeder has moved!

Weeder 2.0 is being developed at https://github.com/ocharles/weeder on different foundations. This repo is for historical reference only.

Most projects accumulate code over time. Weeder detects unused Haskell exports, allowing dead code to be removed (pulling up the weeds). Weeder piggy-backs off files generated by

stack

• Install

  weeder

  by running

  stack install weeder --resolver=nightly

  .
• Ensure your project has a

  stack.yaml

  file. If you don't normally build with

  stack

  then run

  stack init

  to generate one.
• Make sure you have

  ghc-options: {"$locals": -ddump-to-file -ddump-hi}

  in your

  stack.yaml

  .
• Run

  weeder . --build

  , which builds your project with

  stack

  and reports any weeds.

What does Weeder detect?

Weeder detects a bunch of weeds, including:

• You export a function

  helper

  from module

  Foo.Bar

  , but nothing else in your package uses

  helper

  , and

  Foo.Bar

  is not an

  exposed-module

  . Therefore, the export of

  helper

  is a weed. Note that

  helper

  itself may or may not be a weed - once it is no longer exported

  -fwarn-unused-binds

  will tell you if it is entirely redundant.
• Your package

  depends

  on another package but doesn't use anything from it - the dependency should usually be deleted. This functionality is quite like packunused, but implemented quite differently.
• Your package has entries in the

  other-modules

  field that are either unused (and thus should be deleted), or are missing (and thus should be added). The

  stack

  tool warns about the latter already.
• A source file is used between two different sections in a

  .cabal

  file - e.g. in both the library and the executable. Usually it's better to arrange for the executable to depend on the library, but sometimes that would unnecessarily pollute the interface. Useful to be aware of, and sometimes worth fixing, but not always.
• A file has not been compiled despite being mentioned in the

  .cabal

  file. This situation can be because the file is unused, or the

  stack

  compilation was incomplete. I recommend compiling both benchmarks and tests to avoid this warning where possible - running

  weeder . --build

  will use a suitable command line.

Beware of conditional compilation (e.g.

CPP

flag

I recommend fixing the warnings relating to

other-modules

What else should I use?

Weeder detects dead exports, which can be deleted. To get the most code deleted from removing an export, use:

• GHC with

  -fwarn-unused-binds -fwarn-unused-imports

  , which finds unused definitions and unused imports in a module.
• HLint, looking for "Redundant extension" hints, which finds unused extensions.
• Unused, which works at the level of

  ctags

  information, so can be used if you don't want to use

  stack

  , can't compile your code, or want to detect unused code between projects.

Ignoring weeds

If you want your package to be detected as "weed free", but it has some weeds you know about but don't consider important, you can add a

.weeder.yaml

stack.yaml

weeder . --yaml > .weeder.yaml

You may wish to generalise/simplify the

.weeder.yaml

.weeder.yaml

ghcid

- message: Module reused between components
- message:
  - name: Weeds exported
  - identifier: withWaiterPoll

This configuration declares that I am not interested in the message about modules being reused between components (that's the way

ghcid

withWaiterPoll

Running with Continuous Integration

Before running Weeder on your continuous integration (CI) server, you should first ensure there are no existing weeds. One way to achieve that is to ignore existing hints by running

weeder . --yaml > .weeder.yaml

.weeder.yaml

On the CI you should then run

weeder .

weeder . --build

For the CI systems Travis, Appveyor and Azure Pipelines add the line:

curl -sSL https://raw.github.com/ndmitchell/weeder/master/misc/run.sh | sh -s .

The arguments after

-s

weeder

.

What about Cabal users?

Weeder requires the textual

.hi

.hi

What about false positives?

Weeder strives to avoid incorrectly warning about something that is required, if you find such an instance please report it on the issue tracker. Unfortunately there are some cases where there are still false positives, as GHC doesn't put enough information in the

.hi

Data.Coerce If you use

Data.Coerce.coerce

coerce

- message: Unused import

.weeder.yaml

Declaration QuasiQuotes If you use a declaration-level quasi-quote then weeder won't see the use of the quoting function, potentially leading to an unused import warning, and marking the quoting function as a weed. The only solution is to ignore the entries with a

.weeder.yaml

Stack extra-deps Packages marked extra-deps in your

stack.yaml

stack

.weeder.yaml

Linking to C functions If a library provides C functions, and these are used directly from another library/executable, the library providing these functions may be marked as a redundant

build-depends