cabal: Add ignore_setup flag to cabal_args

It can occur that a module has a source file named "Setup.hs" that isn't
a cabal setup module. The current setup finder will find such a module
and then setup will break. Add a flag to cabal_args to indicate that any
such module should be ignored.

Author: iteratee

haskell/cabal.bzl

@@ -103,13 +103,14 @@ def _find_cabal(srcs):
         fail("A .cabal file was not found in the srcs attribute.")
     return cabal
 
-def _find_setup(hs, cabal, srcs):
+def _find_setup(hs, cabal, srcs, ignore_setup=False):
     """Check that a Setup script exists. If not, create a default one."""
     setup = None
-    for f in srcs:
-        if f.basename in ["Setup.hs", "Setup.lhs"]:
-            if not setup or f.dirname < setup.dirname:
-                setup = f
+    if not ignore_setup:
+        for f in srcs:
+            if f.basename in ["Setup.hs", "Setup.lhs"]:
+                if not setup or f.dirname < setup.dirname:
+                    setup = f
     if not setup:
         setup = hs.actions.declare_file("Setup.hs", sibling = cabal)
         hs.actions.write(
@@ -424,8 +425,10 @@ def _shorten_library_symlink(dynamic_library):
 
 def _haskell_cabal_args_impl(ctx):
     is_empty = ctx.attr.is_empty
+    ignore_setup = ctx.attr.ignore_setup
     cabal_args = HaskellCabalArgs(
       is_empty = is_empty,
+      ignore_setup = ignore_setup
     )
     return [cabal_args]
 
@@ -437,6 +440,10 @@ haskell_cabal_args = rule(
             doc = """True if this (sub) library is empty, with only re-exports, and no source files of its own.
             It is necessary to set this, otherwise bazel will complain about missing "*libHS.a" files.""",
         ),
+        "ignore_setup": attr.bool(
+            default = False,
+            doc = """True if this package has a "Setup.hs" that is not a cabal "Setup.hs". """,
+        ),
     },
     provides = [HaskellCabalArgs],
 )
@@ -452,8 +459,10 @@ def _haskell_cabal_library_impl(ctx):
     )
 
     is_empty = False
+    ignore_setup = False
     if ctx.attr.cabal_args:
         is_empty = ctx.attr.cabal_args[HaskellCabalArgs].is_empty
+        ignore_setup = ctx.attr.cabal_args[HaskellCabalArgs].ignore_setup
 
     # All C and Haskell library dependencies.
     cc_info = cc_common.merge_cc_infos(
@@ -482,7 +491,7 @@ def _haskell_cabal_library_impl(ctx):
         fail("ERROR: `compiler_flags` attribute was removed. Use `cabalopts` with `--ghc-option` instead.")
 
     cabal = _find_cabal(ctx.files.srcs)
-    setup = _find_setup(hs, cabal, ctx.files.srcs)
+    setup = _find_setup(hs, cabal, ctx.files.srcs, ignore_setup)
     package_database = hs.actions.declare_file(
         "_install/{}.conf.d/package.cache".format(package_id),
         sibling = cabal,
@@ -823,6 +832,10 @@ def _haskell_cabal_binary_impl(ctx):
         override_cc_toolchain = hs.tools_config.maybe_exec_cc_toolchain,
     )
 
+    ignore_setup = False
+    if ctx.attr.cabal_args:
+        ignore_setup = ctx.attr.cabal_args[HaskellCabalArgs].ignore_setup
+
     # All C and Haskell library dependencies.
     cc_info = cc_common.merge_cc_infos(
         cc_infos = [dep[CcInfo] for dep in ctx.attr.deps if CcInfo in dep],
@@ -844,7 +857,7 @@ def _haskell_cabal_binary_impl(ctx):
         fail("ERROR: `compiler_flags` attribute was removed. Use `cabalopts` with `--ghc-option` instead.")
 
     cabal = _find_cabal(ctx.files.srcs)
-    setup = _find_setup(hs, cabal, ctx.files.srcs)
+    setup = _find_setup(hs, cabal, ctx.files.srcs, ignore_setup)
     package_database = hs.actions.declare_file(
         "_install/{}.conf.d/package.cache".format(hs.label.name),
         sibling = cabal,
@@ -984,6 +997,10 @@ haskell_cabal_binary = rule(
         "flags": attr.string_list(
             doc = "List of Cabal flags, will be passed to `Setup.hs configure --flags=...`.",
         ),
+        "cabal_args": attr.label(
+            doc = """A haskell_cabal_args target with cabal specific settings for this package.""",
+            providers = [[HaskellCabalArgs]],
+        ),
         "_cabal_wrapper": attr.label(
             executable = True,
             cfg = "exec",

haskell/providers.bzl

@@ -38,6 +38,7 @@ HaskellCabalArgs = provider(
     doc = "Settings for a haskell_cabal_library",
     fields = {
         "is_empty": "True if this (sub) library is empty, with only re-exports, and no source files of its own.",
+        "ignore_setup": "True if this package contains a \"Setup.hs\" that isn't a cabal Setup module.",
     },
 )