Don't use hash for cdylib (#1066)

Author: ddeville

rust/private/rust.bzl

@@ -61,14 +61,14 @@ def _assert_correct_dep_mapping(ctx):
                 ),
             )
 
-def _determine_lib_name(name, crate_type, toolchain, lib_hash = ""):
+def _determine_lib_name(name, crate_type, toolchain, lib_hash = None):
     """See https://github.com/bazelbuild/rules_rust/issues/405
 
     Args:
         name (str): The name of the current target
         crate_type (str): The `crate_type`
         toolchain (rust_toolchain): The current `rust_toolchain`
-        lib_hash (str, optional): The hashed crate root path. Defaults to "".
+        lib_hash (str, optional): The hashed crate root path
 
     Returns:
         str: A unique library name
@@ -97,10 +97,10 @@ def _determine_lib_name(name, crate_type, toolchain, lib_hash = ""):
     if toolchain.target_arch == "wasm32" and crate_type == "cdylib":
         prefix = ""
 
-    return "{prefix}{name}-{lib_hash}{extension}".format(
+    return "{prefix}{name}{lib_hash}{extension}".format(
         prefix = prefix,
         name = name,
-        lib_hash = lib_hash,
+        lib_hash = "-" + lib_hash if lib_hash else "",
         extension = extension,
     )
 
@@ -243,8 +243,15 @@ def _rust_library_common(ctx, crate_type):
 
     toolchain = find_toolchain(ctx)
 
-    # Determine unique hash for this rlib
-    output_hash = determine_output_hash(crate_root)
+    # Determine unique hash for this rlib.
+    # Note that we don't include a hash for `cdylib` since they are meant to be consumed externally and having a
+    # deterministic name is important since it ends up embedded in the executable. This is problematic when one needs
+    # to include the library with a specific filename into a larger application.
+    # (see https://github.com/bazelbuild/rules_rust/issues/405#issuecomment-993089889 for more details)
+    if crate_type != "cdylib":
+        output_hash = determine_output_hash(crate_root)
+    else:
+        output_hash = None
 
     crate_name = crate_name_from_attr(ctx.attr)
     rust_lib_name = _determine_lib_name(

test/unit/cdylib_name/BUILD.bazel

@@ -0,0 +1,4 @@
+load(":cdylib_name_analysis_test.bzl", "cdylib_name_analysis_test_suite")
+
+############################ UNIT TESTS #############################
+cdylib_name_analysis_test_suite(name = "cdylib_name_analysis_test_suite")

test/unit/cdylib_name/cdylib_name_analysis_test.bzl

@@ -0,0 +1,48 @@
+"""Analysis tests for the name we assign to cdylib libraries."""
+
+load("@bazel_skylib//lib:unittest.bzl", "analysistest", "asserts")
+load("//rust:defs.bzl", "rust_shared_library")
+
+def _cdylib_name_test_impl(ctx):
+    env = analysistest.begin(ctx)
+    target = analysistest.target_under_test(env)
+
+    # We're expecting the `.dylib`/`.so` to be the only file on Unix and Windows to
+    # contain a pair of `.dll` and `.lib` files.
+    files = target[DefaultInfo].files.to_list()
+    if len(files) == 1:
+        asserts.true(env, files[0].extension in ("so", "dylib"))
+        if files[0].extension == "so":
+            asserts.equals(env, files[0].basename, "libsomething.so")
+        elif files[0].extension == "dylib":
+            asserts.equals(env, files[0].basename, "libsomething.dylib")
+    elif len(files) == 2:
+        expected_filenames = ["something.dll", "something.dll.lib"]
+        for file in files:
+            asserts.true(env, file.basename in expected_filenames)
+            expected_filenames.remove(file.basename)
+
+    return analysistest.end(env)
+
+cdylib_name_test = analysistest.make(_cdylib_name_test_impl)
+
+def cdylib_name_analysis_test_suite(name):
+    """Analysis tests for the name we assign to cdylib libraries.
+
+    Args:
+        name: the test suite name
+    """
+    rust_shared_library(
+        name = "something",
+        srcs = ["lib.rs"],
+    )
+
+    cdylib_name_test(
+        name = "cdylib_name_test",
+        target_under_test = ":something",
+    )
+
+    native.test_suite(
+        name = name,
+        tests = [":cdylib_name_test"],
+    )

test/unit/cdylib_name/lib.rs

@@ -0,0 +1,4 @@
+#[no_mangle]
+pub extern "C" fn say_hello() {
+    println!("Hello");
+}