Initial haskell_binary implementation.

BUILD

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+load("@io_tweag_rules_haskell//haskell:haskell.bzl",
+    "haskell_library",
+    "haskell_binary",
+)

haskell/haskell.bzl

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+HASKELL_FILETYPE = FileType([".hs"])
+
+# TODO
+haskell_library = 1
+
+_haskell_common_attrs = {
+    "srcs": attr.label_list(allow_files = HASKELL_FILETYPE),
+    "deps": attr.label_list(),
+}
+
+def _haskell_binary_impl(ctx):
+    haskell_binary = ctx.outputs.executable
+
+    compile_inputs = ctx.files.srcs
+
+    ctx.actions.run(
+        inputs = compile_inputs,
+        outputs = [haskell_binary],
+        mnemonic = "Ghc",
+        executable = "ghc",
+        arguments = [
+            "-o",
+            haskell_binary.path,
+        ] + [
+            src.path for src in compile_inputs
+        ],
+        use_default_shell_env = True,
+        progress_message = ("Compiling Haskell binary %s (%d files)"
+                            % (ctx.label.name, len(ctx.files.srcs))))
+
+    return struct(haskell_srcs = ctx.files.srcs,
+                  haskell_deps = ctx.attr.deps)
+
+haskell_binary = rule(
+    _haskell_binary_impl,
+    attrs = _haskell_common_attrs,
+    executable = True,
+)

tests/BUILD

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+package(default_testonly = 1)
+
+load("//haskell:haskell.bzl",
+    "haskell_library",
+    "haskell_binary",
+)
+
+haskell_binary(
+    name = "hello",
+    srcs = ["hello.hs"],
+    # main_is = "hello.hs",
+)
+
+[sh_test(
+    name = "Run" + binary,
+    srcs = ["test_binary.sh"],
+    args = ["$(location %s)" % binary],
+    data = [":%s" % binary],
+) for binary in [
+    "hello",
+]]

tests/hello.hs

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+module Main where
+
+main = do
+    putStrLn "hello"

tests/test_binary.sh

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+#!/bin/sh
+
+echo "Executing: " $@
+$@