Create Haskell Bazel Target

Create Haskell Bazel Target

Instruction

1. When creating a binary use haskell_binary
2. When creating a test use haskell_test
3. When creating a library use haskell_library
4. Always want to include //:base for dependencies
5. Any other 3rd party package from hackage, need to use either @stackage or @stackage_alt depending on the packages needed

CRITICAL: Dependency Prefix Rules

Core GHC packages MUST use //: prefix (NOT @stackage//:)

Core GHC Packages (use //:package-name)

• //:base - Always required
• //:bytestring
• //:containers
• //:directory
• //:filepath
• //:text
• //:time
• //:array
• //:deepseq
• //:process
• //:mtl
• //:transformers

Third-Party Packages (use @stackage//:package-name)

• @stackage//:aeson
• @stackage//:yaml
• @stackage//:cmark
• @stackage//:QuickCheck
• @stackage//:hspec
• @stackage//:http-conduit
• @stackage//:vector
• @stackage//:random
• Any package not bundled with GHC

Common Error

Using @stackage//:base or @stackage//:text will cause visibility errors:

ERROR: target '@@rules_haskell~~stack_snapshot~stackage//:base' is not visible from target

Fix: Replace @stackage//:base with //:base (same for text, containers, etc.)

Custom Dependencies in non_module_deps.bzl

When configuring custom Hackage packages in non_module_deps.bzl, ensure glob patterns match the directory structure AFTER strip_prefix is applied:

WRONG:

http_archive(
    name = "libyaml",
    urls = ["https://hackage.haskell.org/​package/​libyaml-0.1.4/​libyaml-0.1.4.tar.gz"],
    strip_prefix = "libyaml-0.1.4",  # This strips the directory
    build_file_content = """
haskell_cabal_library(
    name = "libyaml",
    srcs = glob(["libyaml-0.1.4/​**/​*"]),  # ❌ WRONG - directory already stripped!
    ...
)
"""
)

CORRECT:

http_archive(
    name = "libyaml",
    urls = ["https://hackage.haskell.org/​package/​libyaml-0.1.4/​libyaml-0.1.4.tar.gz"],
    strip_prefix = "libyaml-0.1.4",  # This strips the directory
    build_file_content = """
haskell_cabal_library(
    name = "libyaml",
    srcs = glob(["**/​*"]),  # ✓ CORRECT - files are at root after strip
    ...
)
"""
)

Without strip_prefix:

http_archive(
    name = "yaml",
    urls = ["https://hackage.haskell.org/​package/​yaml-0.11.11.2/​yaml-0.11.11.2.tar.gz"],
    # No strip_prefix - directory preserved
    build_file_content = """
haskell_cabal_library(
    name = "yaml",
    srcs = glob(["yaml-0.11.11.2/​**/​*"]),  # ✓ CORRECT - directory exists
    ...
)
"""
)

Checklist

1. Check if it is already declared in the MODULE.bazel
2. Check if the target is build clean
3. When adding custom dependencies to non_module_deps.bzl, ensure glob patterns match the post-strip_prefix directory structure
4. When adding data as a bazel dependencies, the relative path needs to be from the repository root,

    haskell_test(
        name = "hackage-doc-cli-test",
        srcs = glob(["**/​*.hs"]),
        data = glob(["Fixtures/​**/​*"])
    )

source code

haskell/​app/​hackage-doc-cli/​test/​Fixtures/​aeson-package.json

Examples of Bazel Target

haskell_binary Example

# Neural network from scratch application
haskell_binary(
    name = "neural-network",
    srcs = [":Main.hs"],
    deps = [
        "//:base",                           # Core GHC package
        "//haskell/​libs/​neural-network",     # Local library
        "@stackage//:random",                # Third-party package
    ],
)

haskell_library Example

haskell_library(
    name = "neural-network",
    srcs = glob(["src/​**/​*.hs"]),
    src_strip_prefix = "src",
    ghcopts = ["-XRecordWildCards"],
    visibility = ["//visibility:public"],
    deps = [
        "//:base",                # Core GHC package
        "@stackage//:vector",     # Third-party package
        "@stackage//:random",     # Third-party package
    ],
)

haskell_test Example

haskell_test(
    name = "unit-tests",
    srcs = glob(["test/​**/​*.hs"]),
    src_strip_prefix = "test",
    deps = [
        ":my-library",            # Local library being tested
        "//:base",                # Core GHC package
        "//:text",                # Core GHC package
        "//:containers",          # Core GHC package
        "@stackage//:QuickCheck", # Third-party test framework
        "@stackage//:hspec",      # Third-party test framework
    ],
)

Library with Multiple Core Dependencies

haskell_library(
    name = "rpg-ruleset-core",
    srcs = glob(["src/​**/​*.hs"]),
    src_strip_prefix = "src",
    visibility = ["//visibility:public"],
    deps = [
        # Core GHC packages (use //:)
        "//:base",
        "//:bytestring",
        "//:containers",
        "//:directory",
        "//:filepath",
        "//:text",
        "//:time",

        # Third-party packages (use @stackage//:)
        "@stackage//:aeson",
        "@stackage//:cmark",
        "@stackage//:yaml",
    ],
)