rustc: correctly handle alwayslink staticlibs

In order to do this, we have to inline get_libs_for_static_executable so we
can interact with the LibraryToLink entity as we're categorizing staticlibs.

Fixes #325.

bindgen/bindgen.bzl

@@ -16,7 +16,7 @@
 load("//rust:rust.bzl", "rust_library")
 
 # buildifier: disable=bzl-visibility
-load("//rust/private:utils.bzl", "find_toolchain", "get_libs_for_static_executable")
+load("//rust/private:utils.bzl", "find_toolchain", "get_preferred_artifact")
 
 def rust_bindgen_library(
         name,
@@ -84,7 +84,8 @@ def _rust_bindgen_impl(ctx):
     output = ctx.outputs.out
 
     # libclang should only have 1 output file
-    libclang_dir = get_libs_for_static_executable(libclang).to_list()[0].dirname
+    linker_inputs = dep[CcInfo].linking_context.linker_inputs.to_list()
+    libclang_dir = depset([get_preferred_artifact(lib) for li in linker_inputs for lib in li.libraries]).to_list()[0].dirname
     include_directories = cc_lib[CcInfo].compilation_context.includes.to_list()
     quote_include_directories = cc_lib[CcInfo].compilation_context.quote_includes.to_list()
     system_include_directories = cc_lib[CcInfo].compilation_context.system_includes.to_list()

rust/private/rustc.bzl

@@ -23,7 +23,7 @@ load(
     "expand_locations",
     "find_cc_toolchain",
     "get_lib_name",
-    "get_libs_for_static_executable",
+    "get_preferred_artifact",
     "relativize",
     "rule_attrs",
 )
@@ -57,6 +57,7 @@ DepInfo = provider(
         "transitive_dylibs": "depset[File]",
         "transitive_libs": "List[File]: All transitive dependencies, not filtered by type.",
         "transitive_staticlibs": "depset[File]",
+        "transitive_staticlibs_alwayslink": "depset[File]",
     },
 )
 
@@ -151,6 +152,7 @@ def collect_deps(label, deps, proc_macro_deps, aliases, toolchain):
     transitive_crates = []
     transitive_dylibs = []
     transitive_staticlibs = []
+    transitive_staticlibs_alwayslink = []
     transitive_build_infos = []
     build_info = None
 
@@ -167,24 +169,29 @@ def collect_deps(label, deps, proc_macro_deps, aliases, toolchain):
             transitive_crates.append(depset([dep[rust_common.crate_info]], transitive = [dep[DepInfo].transitive_crates]))
             transitive_dylibs.append(dep[DepInfo].transitive_dylibs)
             transitive_staticlibs.append(dep[DepInfo].transitive_staticlibs)
+            transitive_staticlibs_alwayslink.append(dep[DepInfo].transitive_staticlibs_alwayslink)
             transitive_build_infos.append(dep[DepInfo].transitive_build_infos)
         elif CcInfo in dep:
             # This dependency is a cc_library
 
             # TODO: We could let the user choose how to link, instead of always preferring to link static libraries.
-            libs = get_libs_for_static_executable(dep)
-
-            transitive_dylibs.append(depset([
-                lib
-                for lib in libs.to_list()
-                # Dynamic libraries may have a version number nowhere, or before (macos) or after (linux) the extension.
-                if lib.basename.endswith(toolchain.dylib_ext) or lib.basename.split(".", 2)[1] == toolchain.dylib_ext[1:]
-            ]))
-            transitive_staticlibs.append(depset([
-                lib
-                for lib in libs.to_list()
-                if lib.basename.endswith(toolchain.staticlib_ext)
-            ]))
+            linker_inputs = dep[CcInfo].linking_context.linker_inputs.to_list()
+            for li in linker_inputs:
+                always = []
+                static = []
+                dylib = []
+                for lib in li.libraries:
+                    art = get_preferred_artifact(lib)
+                    if lib.alwayslink:
+                        always.append(lib.static_library or lib.pic_static_library)
+                        # Dynamic libraries may have a version number nowhere, or before (macos) or after (linux) the extension.
+                    elif art.basename.endswith(toolchain.dylib_ext) or art.basename.split(".", 2)[1] == toolchain.dylib_ext[1:]:
+                        dylib.append(art)
+                    elif art.basename.endswith(toolchain.staticlib_ext):
+                        static.append(art)
+                transitive_staticlibs_alwayslink.append(depset(always))
+                transitive_dylibs.append(depset(dylib))
+                transitive_staticlibs.append(depset(static))
         elif BuildInfo in dep:
             if build_info:
                 fail("Several deps are providing build information, only one is allowed in the dependencies", "deps")
@@ -196,7 +203,7 @@ def collect_deps(label, deps, proc_macro_deps, aliases, toolchain):
     transitive_crates_depset = depset(transitive = transitive_crates)
     transitive_libs = depset(
         [c.output for c in transitive_crates_depset.to_list()],
-        transitive = transitive_staticlibs + transitive_dylibs,
+        transitive = transitive_staticlibs + transitive_dylibs + transitive_staticlibs_alwayslink,
     )
 
     return (
@@ -208,6 +215,7 @@ def collect_deps(label, deps, proc_macro_deps, aliases, toolchain):
                 order = "topological",  # dylib link flag ordering matters.
             ),
             transitive_staticlibs = depset(transitive = transitive_staticlibs),
+            transitive_staticlibs_alwayslink = depset(transitive = transitive_staticlibs_alwayslink),
             transitive_libs = transitive_libs.to_list(),
             transitive_build_infos = depset(transitive = transitive_build_infos),
             dep_env = build_info.dep_env if build_info else None,
@@ -822,6 +830,20 @@ def _add_native_link_flags(args, dep_info, crate_type, cc_toolchain, feature_con
     args.add_all(dep_info.transitive_dylibs, map_each = get_lib_name, format_each = "-ldylib=%s")
     args.add_all(dep_info.transitive_staticlibs, map_each = get_lib_name, format_each = "-lstatic=%s")
 
+    # alwayslink=True libraries need special handling so the alwayslink args
+    # make it to the linker. Eventually we might be able to use a first-class
+    # rustc flag for this (https://github.com/rust-lang/cargo/issues/7586),
+    # but until then we have to do it this way.
+    for lib in dep_info.transitive_staticlibs_alwayslink.to_list():
+        args.add_all([
+            "-C",
+            "link-arg=-Wl,--whole-archive",
+            "-C",
+            ("link-arg=-l%s" % get_lib_name(lib)),
+            "-C",
+            "link-arg=-Wl,--no-whole-archive",
+        ])
+
     if crate_type in ["dylib", "cdylib"]:
         # For shared libraries we want to link C++ runtime library dynamically
         # (for example libstdc++.so or libc++.so).

rust/private/utils.bzl

@@ -118,19 +118,7 @@ def determine_output_hash(crate_root):
     """
     return repr(hash(crate_root.path))
 
-def get_libs_for_static_executable(dep):
-    """find the libraries used for linking a static executable.
-
-    Args:
-        dep (Target): A cc_library target.
-
-    Returns:
-        depset: A depset[File]
-    """
-    linker_inputs = dep[CcInfo].linking_context.linker_inputs.to_list()
-    return depset([_get_preferred_artifact(lib) for li in linker_inputs for lib in li.libraries])
-
-def _get_preferred_artifact(library_to_link):
+def get_preferred_artifact(library_to_link):
     """Get the first available library to link from a LibraryToLink object.
 
     Args: