fix wd_test

Author: anonrig

.bazelrc

@@ -421,16 +421,18 @@ build:coverage --test_env=BAZEL_USE_LLVM_NATIVE_COVERAGE=1
 # GCOV is used by rules_cc to merge raw profile data (.profraw) into indexed profile data (.profdata)
 build:coverage --action_env=GCOV=llvm-profdata
 build:coverage --test_env=GCOV=llvm-profdata
-# COVERAGE_GCOV_PATH is passed through from the environment. Users must set this to the absolute path
-# of llvm-profdata (used by collect_cc_coverage.sh for merging .profraw files).
-# Example: export COVERAGE_GCOV_PATH=$(which llvm-profdata)
-build:coverage --action_env=COVERAGE_GCOV_PATH
-build:coverage --test_env=COVERAGE_GCOV_PATH
+# COVERAGE_GCOV_PATH is used by collect_cc_coverage.sh for merging .profraw files.
+# Set to absolute path of llvm-profdata (resolving symlinks for sandbox compatibility).
+build:coverage --action_env=COVERAGE_GCOV_PATH=/usr/lib/llvm-20/bin/llvm-profdata
+build:coverage --test_env=COVERAGE_GCOV_PATH=/usr/lib/llvm-20/bin/llvm-profdata
 # BAZEL_LLVM_COV is used by rules_cc to generate coverage reports from profile data
 build:coverage --action_env=BAZEL_LLVM_COV=llvm-cov
 build:coverage --test_env=BAZEL_LLVM_COV=llvm-cov
 # LLVM_COV is used by collect_cc_coverage.sh for generating LCOV output
 build:coverage --test_env=LLVM_COV=llvm-cov
+# GENERATE_LLVM_LCOV=1 tells collect_cc_coverage.sh to use llvm-cov export to generate LCOV format
+# instead of just outputting raw profdata. LLVM_COV specifies the llvm-cov binary to use.
+build:coverage --test_env=GENERATE_LLVM_LCOV=1
 build:coverage --experimental_use_llvm_covmap
 build:coverage --experimental_generate_llvm_lcov
 # Ensure that we fetch coverage data from remote cache

build/wd_test.bzl

@@ -234,16 +234,28 @@ def _wd_test_impl(ctx):
         if default_runfiles:
             runfiles = runfiles.merge(default_runfiles)
 
+    # Create runtime_objects_list.txt for LLVM coverage.
+    # This file tells collect_cc_coverage.sh where to find the instrumented binary
+    # so llvm-cov can export coverage data in LCOV format.
+    runtime_objects_list = ctx.actions.declare_file(ctx.label.name + "runtime_objects_list.txt")
+    workerd_file = ctx.file.workerd
+    ctx.actions.write(
+        output = runtime_objects_list,
+        content = workerd_file.path + "\n",
+        is_executable = False,
+    )
+
     # IMPORTANT: The workerd binary must be listed in dependency_attributes
     # to ensure its transitive dependencies (all the C++ source files) are
     # included in the coverage instrumentation. Without this, coverage data
     # won't be collected for the actual workerd implementation code.
+    # The runtime_objects_list.txt and workerd binary are included in metadata_files
+    # so that collect_cc_coverage.sh can find them for LLVM LCOV generation.
     instrumented_files_info = coverage_common.instrumented_files_info(
         ctx,
         source_attributes = ["src", "data"],
         dependency_attributes = ["workerd", "sidecar", "sidecar_supervisor"],
-        # Include all file types that might contain testable code
-        extensions = ["cc", "c++", "cpp", "cxx", "c", "h", "hh", "hpp", "hxx", "inc", "js", "ts", "mjs", "wd-test", "capnp"],
+        metadata_files = [runtime_objects_list, workerd_file],
     )
     environment = dict(ctx.attr.env)
     if ctx.attr.python_snapshot_test:
@@ -282,11 +294,14 @@ _wd_test = rule(
         ),
         # Source file
         "src": attr.label(allow_single_file = True),
-        # The workerd executable is used to run all tests
+        # The workerd executable is used to run all tests.
+        # Using cfg = "target" instead of "exec" ensures workerd is built with coverage
+        # instrumentation when running `bazel coverage`. With cfg = "exec", the binary
+        # would be built in exec configuration which doesn't include coverage flags.
         "workerd": attr.label(
             allow_single_file = True,
             executable = True,
-            cfg = "exec",
+            cfg = "target",
             default = "//src/workerd/server:workerd_cross",
         ),
         # A list of files that this test requires to be present in order to run.