Do not create empty libraries

Author: avdv

haskell/cabal.bzl

@@ -604,7 +604,6 @@ def _haskell_cabal_library_impl(ctx):
             transitive = [dep_info.deps_hs_libraries],
             order = "topological",
         ),
-        empty_hs_libraries = dep_info.empty_hs_libraries,
         interface_dirs = depset([interfaces_dir], transitive = [dep_info.interface_dirs]),
         deps_interface_dirs = dep_info.deps_interface_dirs,
         compile_flags = [],
@@ -892,7 +891,6 @@ def _haskell_cabal_binary_impl(ctx):
         import_dirs = sets.make(),
         hs_libraries = dep_info.hs_libraries,
         deps_hs_libraries = dep_info.deps_hs_libraries,
-        empty_hs_libraries = dep_info.empty_hs_libraries,
         interface_dirs = dep_info.interface_dirs,
         deps_interface_dirs = dep_info.deps_interface_dirs,
         compile_flags = [],

haskell/experimental/private/module.bzl

@@ -354,7 +354,6 @@ def _build_haskell_module(
                     dep_info.hs_libraries,
                     dep_info.deps_hs_libraries,
                     narrowed_deps_info.deps_hs_libraries,
-                    narrowed_deps_info.empty_hs_libraries,
                     object_inputs,
                 ]
                 # libraries and object inputs are only needed if the module uses TH

haskell/private/actions/package.bzl

@@ -64,7 +64,7 @@ def package(
       exposed_modules: List of exposed modules.
       other_modules: List of hidden modules.
       my_pkg_id: Package id object for this package.
-      has_hs_library: Whether hs-libraries should be non-null.
+      has_hs_library: Whether hs-libraries should be created.
 	  empty_libs_dir: Directory name where the empty library should be.
           If empty, this is assumed to be a package description
 		  for a real library. See Note [Empty Libraries] in haskell_impl.bzl.
@@ -91,9 +91,7 @@ def package(
 
     pkgroot_lib_path = paths.join("${pkgroot}", empty_libs_dir)
 
-    # Create a file from which ghc-pkg will create the actual package
-    # from.
-    write_package_conf(hs, conf_file, {
+    config = {
         "name": my_pkg_id.package_name,
         "version": my_pkg_id.version,
         "id": pkg_id.to_string(my_pkg_id),
@@ -103,12 +101,20 @@ def package(
         "import-dirs": [import_dir],
         "library-dirs": [pkgroot_lib_path] + extra_lib_dirs,
         "dynamic-library-dirs": [pkgroot_lib_path] + extra_dynamic_lib_dirs,
-        "hs-libraries": [pkg_id.library_name(hs, my_pkg_id)] if has_hs_library else [],
         "extra-libraries": extra_libs,
         "depends": hs.package_ids,
         # TODO[AH] Add haskell_module modules
         "exposed-modules": exposed_modules,
-    })
+    }
+
+    if has_hs_library:
+        config.update({
+            "hs-libraries": [pkg_id.library_name(hs, my_pkg_id)],
+        })
+
+    # Create a file from which ghc-pkg will create the actual package
+    # from.
+    write_package_conf(hs, conf_file, config)
 
     cache_file = ghc_pkg_recache(hs, posix, conf_file)
 

haskell/private/dependencies.bzl

@@ -37,11 +37,6 @@ def gather_dep_info(name, deps):
         for dep in deps
         if HaskellInfo in dep
     ])
-    empty_hs_libraries = depset(transitive = [
-        dep[HaskellInfo].empty_hs_libraries
-        for dep in deps
-        if HaskellInfo in dep
-    ])
     interface_dirs = depset(transitive = [
         dep[HaskellInfo].interface_dirs
         for dep in deps
@@ -87,7 +82,6 @@ def gather_dep_info(name, deps):
         version_macros = sets.make(),
         hs_libraries = hs_libraries,
         deps_hs_libraries = deps_hs_libraries,
-        empty_hs_libraries = empty_hs_libraries,
         interface_dirs = interface_dirs,
         deps_interface_dirs = deps_interface_dirs,
         source_files = source_files,
@@ -110,7 +104,6 @@ def gather_dep_info(name, deps):
                 version_macros = set.mutable_union(acc.version_macros, binfo.version_macros),
                 hs_libraries = depset(transitive = [acc.hs_libraries, binfo.hs_libraries]),
                 deps_hs_libraries = depset(transitive = [acc.deps_hs_libraries, binfo.deps_hs_libraries]),
-                empty_hs_libraries = depset(transitive = [acc.empty_hs_libraries, binfo.empty_hs_libraries]),
                 interface_dirs = acc.interface_dirs,
                 deps_interface_dirs = acc.deps_interface_dirs,
                 import_dirs = import_dirs,
@@ -135,7 +128,6 @@ def gather_dep_info(name, deps):
                 compile_flags = acc.compile_flags,
                 hs_libraries = acc.hs_libraries,
                 deps_hs_libraries = acc.deps_hs_libraries,
-                empty_hs_libraries = acc.empty_hs_libraries,
                 extra_source_files = acc.extra_source_files,
                 interface_dirs = acc.interface_dirs,
                 deps_interface_dirs = acc.deps_interface_dirs,

haskell/private/haskell_impl.bzl

@@ -53,18 +53,18 @@ load("//haskell/experimental/private:module.bzl", "build_haskell_modules", "get_
 
 # Note [Empty Libraries]
 #
-# GHC 8.10.x wants to load the shared libraries corresponding to packages needed
-# for running TemplateHaskell splices. It wants to do this even when all the
-# necessary object files are passed in the command line.
-#
-# In order to satisfy GHC, and yet avoid passing the linked library as input, we
-# create a ficticious package which points to an empty shared library. The
-# ficticious and the real package share the same interface files.
+# GHC wants to load the shared libraries given in `extra-libraries` or
+# `hs-libraries` fields of package config files corresponding to packages needed
+# for running TemplateHaskell splices.
 #
 # Avoiding to pass the real shared library as input is necessary when building
 # individual modules with haskell_module, otherwise building the module would
 # need to wait until all of the modules of library dependencies have been built.
 #
+# In order to achieve that, we create a fictitious package which does not refer
+# to a library file at all. The fictitious and the real package share the same
+# interface files.
+#
 # See Note [Narrowed Dependencies] for an overview of what this feature is
 # needed for.
 
@@ -395,41 +395,6 @@ def _haskell_binary_common_impl(ctx, is_test):
         )),
     ]
 
-def _create_empty_library(hs, cc, posix, my_pkg_id, with_shared, with_profiling, empty_libs_dir):
-    """See Note [Empty Libraries]"""
-    dep_info = gather_dep_info("haskell_module-empty_lib", [])
-    empty_c = hs.actions.declare_file("empty.c")
-    hs.actions.write(empty_c, "")
-
-    static_library = link_library_static(
-        hs,
-        cc,
-        posix,
-        dep_info,
-        depset([empty_c]),
-        my_pkg_id,
-        with_profiling = with_profiling,
-        libdir = empty_libs_dir,
-    )
-    libs = [static_library]
-
-    if with_shared:
-        dynamic_library = link_library_dynamic(
-            hs,
-            cc,
-            posix,
-            dep_info,
-            depset(),
-            depset([empty_c]),
-            my_pkg_id,
-            [],
-            None,
-            empty_libs_dir,
-        )
-        libs = [dynamic_library, static_library]
-
-    return libs
-
 def haskell_library_impl(ctx):
     hs = haskell_context(ctx)
     deps = ctx.attr.deps + ctx.attr.exports + ctx.attr.narrowed_deps
@@ -589,8 +554,8 @@ def haskell_library_impl(ctx):
         exposed_modules,
         other_modules,
         my_pkg_id,
-        non_empty,
-        empty_libs_dir,
+        has_hs_library = False,
+        empty_libs_dir = empty_libs_dir,
     )
 
     interface_dirs = depset(
@@ -607,8 +572,6 @@ def haskell_library_impl(ctx):
             generate_version_macros(ctx, package_name, version),
         ])
 
-    empty_libs = _create_empty_library(hs, cc, posix, my_pkg_id, with_shared, with_profiling, empty_libs_dir)
-
     export_infos = gather_dep_info(ctx.attr.name, ctx.attr.exports)
     hs_info = HaskellInfo(
         package_databases = depset([cache_file], transitive = [all_deps_info.package_databases]),
@@ -636,10 +599,6 @@ def haskell_library_impl(ctx):
         deps_hs_libraries = depset(
             transitive = [dep_info.hs_libraries, narrowed_deps_info.deps_hs_libraries],
         ),
-        empty_hs_libraries = depset(
-            direct = empty_libs,
-            transitive = [all_deps_info.empty_hs_libraries, export_infos.empty_hs_libraries],
-        ),
         interface_dirs = depset(transitive = [interface_dirs, export_infos.interface_dirs]),
         deps_interface_dirs = depset(transitive = [dep_info.interface_dirs, narrowed_deps_info.deps_interface_dirs]),
         compile_flags = c.compile_flags,
@@ -857,7 +816,6 @@ def haskell_import_impl(ctx):
         import_dirs = sets.make(),
         hs_libraries = depset(),
         deps_hs_libraries = depset(),
-        empty_hs_libraries = depset(),
         interface_dirs = depset(),
         deps_interface_dirs = depset(),
         compile_flags = [],

haskell/providers.bzl

@@ -13,7 +13,6 @@ HaskellInfo = provider(
         "extra_source_files": "Depset of non-Haskell source files.",
         "hs_libraries": "Depset of compiled Haskell libraries in all available GHC ways.",
         "deps_hs_libraries": "Depset of compiled Haskell libraries belonging to libraries in the deps field of the rule or in the deps field of any transitive dependency (libraries in narrowed_deps are included in transitive dependencies for this sake)",
-        "empty_hs_libraries": "Depset of compiled empty Haskell libraries in all available GHC ways.",
         "interface_dirs": "Depset of interface dirs belonging to the packages.",
         "deps_interface_dirs": "Depset of interface dirs belonging to libraries in the deps field of the rule or in the deps field of any transitive dependency (libraries in narrowed_deps are included in transitive dependencies for this sake)",
         "compile_flags": "Arguments that were used to compile the code.",