Refactor ghc_bindist.bzl for use with haskell_toolchains extension

This helps the haskell_toolchains module extensions to declare all of its toolchains in one BUILD file.

haskell/ghc_bindist.bzl

@@ -274,8 +274,8 @@ _ghc_bindist = repository_rule(
  },
 )
 
-def _ghc_bindist_toolchain_impl(ctx):
- os, _, arch = ctx.attr.target.partition("_")
+def ghc_bindist_toolchain_declaration(target, bindist_name, toolchain_name):
+ os, _, arch = target.partition("_")
  os_constraint = {
  "darwin": "osx",
  "linux": "linux",
@@ -290,21 +290,29 @@ def _ghc_bindist_toolchain_impl(ctx):
  "@platforms//cpu:{}".format(cpu_constraint),
  ]
  target_constraints = exec_constraints
- ctx.file(
- "BUILD",
- executable = False,
- content = """
+ return """
 toolchain(
- name = "toolchain",
+ name = "{toolchain_name}",
  toolchain_type = "@rules_haskell//haskell:toolchain",
  toolchain = "@{bindist_name}//:toolchain-impl",
  exec_compatible_with = {exec_constraints},
  target_compatible_with = {target_constraints},
 )
- """.format(
+""".format(
+ toolchain_name = toolchain_name,
+ bindist_name = bindist_name,
+ exec_constraints = exec_constraints,
+ target_constraints = target_constraints,
+ )
+
+def _ghc_bindist_toolchain_impl(ctx):
+ ctx.file(
+ "BUILD",
+ executable = False,
+ content = ghc_bindist_toolchain_declaration(
+ target = ctx.attr.target,
  bindist_name = ctx.attr.bindist_name,
- exec_constraints = exec_constraints,
- target_constraints = target_constraints,
+ toolchain_name = "toolchain",
  ),
  )
 
@@ -342,6 +350,21 @@ _windows_cc_toolchain = repository_rule(
  },
 )
 
+# Toolchains declarations for bindists used by the `haskell_toolchains` module
+# extension to register all the haskell toolchains in the same BUILD file
+def ghc_bindists_toolchain_declarations(version):
+ version = version or _GHC_DEFAULT_VERSION
+ if not GHC_BINDIST.get(version):
+ fail("Binary distribution of GHC {} not available.".format(version))
+ return [
+ ghc_bindist_toolchain_declaration(
+ target = target,
+ bindist_name = "rules_haskell_ghc_{}".format(target),
+ toolchain_name = "rules_haskell_ghc_{}".format(target),
+ )
+ for target in GHC_BINDIST[version]
+ ]
+
 def ghc_bindist(
  name,
  version,