Declare a GHC plugin.

Example:

haskell_library(
    name = "plugin-lib",
    srcs = ["Plugin.hs"],
)

ghc_plugin(
    name = "plugin",
    module = "Plugin",
    deps = [":plugin-lib"],
)

haskell_binary(
    name = "some-binary",
    srcs = ["Main.hs"],
    plugins = [":plugin"],

Plugins to use during compilation by GHC are given by the plugins attribute to Haskell rules. Plugins are haskell libraries with some extra metadata, like the name of the module that acts as the entrypoint for the plugin and plugin options.

See https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/extending_ghc.html#writing-compiler-plugins for more information.

A unique name for this target.

Plugin options.

Plugin dependencies. These are compile-time dependencies only.

Plugin entrypoint.

Tools needed by the plugin when it used.

Create API documentation.

Builds API documentation (using Haddock) for the given Haskell libraries. It will automatically build documentation for any transitive dependencies to allow for cross-package documentation linking.

Examples

haskell_library(
  name = "my-lib",
  ...
)

haskell_doc(
  name = "my-lib-doc",
  deps = [":my-lib"],
)

A unique name for this target.

List of Haskell libraries to generate documentation for.

Whether to include documentation of transitive dependencies in index.

A unique name for this target.

Build a REPL for multiple targets.

Examples

haskell_repl(
    name = "repl",
    deps = [
        "//lib:some_lib",
        "//exe:some_exe",
    ],
    experimental_from_source = [
        "//lib/...",
        "//exe/...",
        "//common/...",
    ],
    experimental_from_binary = [
        "//lib/vendored/...",
    ],
)

Collects all transitive Haskell dependencies from deps. Those that match experimental_from_binary or are defined in an external workspace will be loaded as binary packages. Those that match experimental_from_source and are defined in the local workspace will be loaded by source.

You can call the REPL like this:

$ bazel run //:repl

IDE Support (Experimental)

haskell_repl targets provide the hie_bios output group to optionally generate GHCi flags for hie-bios's bios cradle. You can use this for IDE support with ghcide.

Given a haskell_repl target //:repl an example .hie-bios script could look as follows. Please refer to the hie-bios documentation for further information.

#!/usr/bin/env bash
set -euo pipefail
bazel build //:repl --output_groups=hie_bios
cat bazel-bin/repl@hie-bios >"$HIE_BIOS_OUTPUT"

A unique name for this target.

Whether to collect the data runfiles from the dependencies in srcs, data and deps attributes.

See Bazel documentation. Only available when collect_data = True.

List of Haskell targets to load into the REPL

Black-list of targets to not load by source but as packages.

Wild-card targets such as //... or //:all are allowed.

The black-list takes precedence over the white-list.

Note, this attribute will change depending on the outcome of https://github.com/bazelbuild/bazel/issues/7763.

White-list of targets to load by source.

Wild-card targets such as //... or //:all are allowed.

The black-list takes precedence over the white-list.

Note, this attribute will change depending on the outcome of https://github.com/bazelbuild/bazel/issues/7763.

Arbitrary extra arguments to pass to GHCi. This extends compiler_flags and repl_ghci_args from the toolchain. Subject to Make variable substitution.

Arbitrary extra commands to execute in GHCi.

Import packages that are prebuilt outside of Bazel.

Examples

haskell_toolchain_library(
    name = "base_pkg",
    package = "base",
)

haskell_library(
    name = "hello-lib",
    srcs = ["Lib.hs"],
    deps = [
        ":base_pkg",
        "//hello-sublib:lib",
    ],
)

Use this rule to make dependencies that are prebuilt (supplied as part of the compiler toolchain) available as targets.

A unique name for this target.

The name of a GHC package not built by Bazel. Defaults to the name of the rule.

Build an executable from Haskell source.

Every haskell_binary target also defines an optional REPL target that is not built by default, but can be built on request. The name of the REPL target is the same as the name of binary with "@repl" added at the end. For example, the target above also defines main@repl.

You can call the REPL like this (requires Bazel 0.15 or later):

$ bazel run //:hello@repl

Examples

haskell_binary(
    name = "hello",
    srcs = ["Main.hs", "Other.hs"],
    deps = ["//lib:some_lib"]
)

A unique name for this rule.

DEPRECATED. Attribute has no effect.

Haskell source files.

Extra (non-Haskell) source files that will be needed at compile time (e.g. by Template Haskell).

List of other Haskell libraries to be linked to this target.

See Bazel documentation.,

Flags to pass to Haskell compiler. Subject to Make variable substitution.

Arbitrary extra arguments to pass to GHCi. This extends compiler_flags and repl_ghci_args from the toolchain. Subject to Make variable substitution.,

Arbitrary extra arguments to pass to runghc. This extends compiler_flags and repl_ghci_args from the toolchain. Subject to Make variable substitution.

Compiler plugins to use during compilation.

Extra tools needed at compile-time, like preprocessors.

Experimental. Worker binary employed by Bazel's persistent worker mode. See use-cases documentation.

Link dependencies statically wherever possible. Some system libraries may still be linked dynamically, as are libraries for which there is no static library. So the resulting executable will still be dynamically linked, hence only mostly static.

A function with type IO _, either the qualified name of a function from any module or the bare name of a function from a Main module. It is also possible to give the qualified name of any module exposing a main function.

Executable version. If this is specified, CPP version macros will be generated for this build.

Common rule attributes. See Bazel documentation.

Build a library from Haskell source.

Every haskell_library target also defines an optional REPL target that is not built by default, but can be built on request. It works the same way as for haskell_binary.

Examples

haskell_library(
    name = "hello-lib",
    srcs = glob(["src/**/*.hs"]),
    src_strip_prefix = "src",
    deps = [
        "//hello-sublib:lib",
    ],
    reexported_modules = {
        "//hello-sublib:lib": "Lib1 as HelloLib1, Lib2",
    },
)

A unique name for this rule.

DEPRECATED. Attribute has no effect.

Haskell source files.

Extra (non-Haskell) source files that will be needed at compile time (e.g. by Template Haskell).

List of other Haskell libraries to be linked to this target.

See Bazel documentation.,

Flags to pass to Haskell compiler. Subject to Make variable substitution.

Arbitrary extra arguments to pass to GHCi. This extends compiler_flags and repl_ghci_args from the toolchain. Subject to Make variable substitution.,

Arbitrary extra arguments to pass to runghc. This extends compiler_flags and repl_ghci_args from the toolchain. Subject to Make variable substitution.

Compiler plugins to use during compilation.

Extra tools needed at compile-time, like preprocessors.

Experimental. Worker binary employed by Bazel's persistent worker mode. See use-cases documentation.

Modules that should be unavailable for import by dependencies.

A dictionary mapping dependencies to module reexports that should be available for import by dependencies.

A list of other haskell libraries that will be transparently added as a dependency to every downstream rule

Create a static library, not both a static and a shared library.

Library name used in version macro generation. Only used if the version attribute is defined, see version attribute documentation. Optional, defaults to target name.

Library version. Not normally necessary unless to build a library originally defined as a Cabal package. If this is specified, CPP version macro will be generated.

Common rule attributes. See Bazel documentation.

Register GHC binary distributions for all platforms as toolchains.

Build a test suite.

Additionally, it accepts all common bazel test rule fields. This allows you to influence things like timeout and resource allocation for the test.

A unique name for this rule.

DEPRECATED. Attribute has no effect.

Haskell source files.

Extra (non-Haskell) source files that will be needed at compile time (e.g. by Template Haskell).

List of other Haskell libraries to be linked to this target.

See Bazel documentation.,

Flags to pass to Haskell compiler. Subject to Make variable substitution.

Arbitrary extra arguments to pass to GHCi. This extends compiler_flags and repl_ghci_args from the toolchain. Subject to Make variable substitution.,

Arbitrary extra arguments to pass to runghc. This extends compiler_flags and repl_ghci_args from the toolchain. Subject to Make variable substitution.

Compiler plugins to use during compilation.

Extra tools needed at compile-time, like preprocessors.

Experimental. Worker binary employed by Bazel's persistent worker mode. See use-cases documentation.

Link dependencies statically wherever possible. Some system libraries may still be linked dynamically, as are libraries for which there is no static library. So the resulting executable will still be dynamically linked, hence only mostly static.

A function with type IO _, either the qualified name of a function from any module or the bare name of a function from a Main module. It is also possible to give the qualified name of any module exposing a main function.

Executable version. If this is specified, CPP version macros will be generated for this build.

The expected percentage of expressions covered by testing.

The expected number of expressions which are not covered by testing.

Requires that the coverage metric is matched exactly, even doing better than expected is not allowed.

The format to output the coverage report in.

Supported values: "text", "html". Default: "text".

Report can be seen in the testlog XML file, or by setting --test_output=all when running bazel coverage.

The path patterns specifying which targets to analyze for test coverage metrics.

Wild-card targets such as //... or //:all are allowed. The paths must be relative to the workspace, which means they must start with "//".

Note, this attribute may leave experimental status depending on the outcome of https://github.com/bazelbuild/bazel/issues/7763.

Common rule attributes. See Bazel documentation.

Declare a compiler toolchain.

You need at least one of these declared somewhere in your BUILD files for the other rules to work. Once declared, you then need to register the toolchain using register_toolchains in your WORKSPACE file (see example below).

Examples

In a BUILD file:

haskell_toolchain(
    name = "ghc",
    version = "1.2.3",
    static_runtime = static_runtime,
    fully_static_link = fully_static_link,
    tools = ["@sys_ghc//:bin"],
    compiler_flags = ["-Wall"],
)

where @sys_ghc is an external repository defined in the WORKSPACE, e.g. using:

nixpkgs_package(
    name = 'sys_ghc',
    attribute_path = 'haskell.compiler.ghc822',
)

register_toolchains("//:ghc")