Rust: Enable LTO for the extractor

misc/bazel/rust.bzl

@@ -1,17 +1,44 @@
 load("@rules_rust//rust:defs.bzl", "rust_binary")
 load("@semmle_code//buildutils-internal:glibc_symbols_check.bzl", "glibc_symbols_check")
 load("@semmle_code//buildutils-internal:lipo.bzl", "universal_binary")
+load("//misc/bazel:transitions.bzl", "forward_binary_from_transition", "get_transition_attrs")
+
+def _full_lto_transition_impl(_settings, _attr):
+    return {"@rules_rust//rust/settings:lto": "fat"}
+
+_full_lto_transition = transition(
+    implementation = _full_lto_transition_impl,
+    inputs = [],
+    outputs = ["@rules_rust//rust/settings:lto"],
+)
+
+_full_lto_binary = rule(
+    implementation = forward_binary_from_transition,
+    attrs = get_transition_attrs(_full_lto_transition),
+)
 
 def codeql_rust_binary(
         name,
+        full_lto = False,
         target_compatible_with = None,
         visibility = None,
         symbols_test = True,
         **kwargs):
     rust_label_name = "single_arch/" + name
+    binary_dep = ":" + rust_label_name
+    if full_lto:
+        # rustc must consume the LLVM bitcode because the C++ linker may use an
+        # incompatible LLVM version.
+        kwargs["experimental_use_cc_common_link"] = 0
+        lto_label_name = "full_lto/" + name
+        _full_lto_binary(
+            name = lto_label_name,
+            dep = binary_dep,
+        )
+        binary_dep = ":" + lto_label_name
     universal_binary(
         name = name,
-        dep = ":" + rust_label_name,
+        dep = binary_dep,
         target_compatible_with = target_compatible_with,
         visibility = visibility,
     )

misc/bazel/transitions.bzl

@@ -0,0 +1,47 @@
+load("@bazel_skylib//lib:paths.bzl", "paths")
+
+def forward_binary_from_transition(ctx):
+    binary = ctx.attr.dep[0]
+    default_info = binary[DefaultInfo]
+    original_executable = default_info.files_to_run.executable
+    if not original_executable:
+        fail("Cannot transition a target that is not executable")
+
+    (_, extension) = paths.split_extension(original_executable.basename)
+    new_executable = ctx.actions.declare_file(ctx.label.name + extension)
+    inputs = [original_executable]
+    command = "cp %s %s" % (original_executable.path, new_executable.path)
+
+    providers = []
+    if OutputGroupInfo in binary:
+        pdb_file = getattr(binary[OutputGroupInfo], "pdb_file", None)
+        if pdb_file:
+            (pdb_file,) = pdb_file.to_list()
+            linked_pdb_file = ctx.actions.declare_file(ctx.label.name + ".pdb")
+            ctx.actions.symlink(target_file = pdb_file, output = linked_pdb_file)
+            inputs.append(linked_pdb_file)
+        providers.append(binary[OutputGroupInfo])
+
+    ctx.actions.run_shell(
+        inputs = inputs,
+        outputs = [new_executable],
+        command = command,
+    )
+    files = depset(direct = [new_executable])
+    runfiles = default_info.default_runfiles.merge(ctx.runfiles([new_executable]))
+    providers.append(
+        DefaultInfo(
+            files = files,
+            runfiles = runfiles,
+            executable = new_executable,
+        ),
+    )
+    return providers
+
+def get_transition_attrs(transition_rule):
+    return {
+        "_allowlist_function_transition": attr.label(
+            default = "@bazel_tools//tools/allowlists/function_transition_allowlist",
+        ),
+        "dep": attr.label(mandatory = True, cfg = transition_rule),
+    }

rust/extractor/BUILD.bazel

@@ -11,6 +11,7 @@ codeql_rust_binary(
         "src/qltest_cargo.mustache",
         "src/nightly-toolchain/rust-toolchain.toml",
     ],
+    full_lto = True,
     proc_macro_deps = all_crate_deps(
         proc_macro = True,
     ) + [