Report caching does not appear to be working

[Wheest]

I'm finding that repeated runs using clang-tidy is not caching the report. This means that even with unchanged source files, clang-tidy is running on everything for several minutes.

I'm trying to figure out if this is expected behavior, or if I have a config error somewhere.

I'm using the tool with a hermetic clang toolchain, with the following bazelrc:

# Enable the clang-tidy aspect
build:clang-tidy --aspects @bazel_clang_tidy//clang_tidy:clang_tidy.bzl%clang_tidy_aspect
build:clang-tidy --output_groups=report

# Override the .clang-tidy config file target
build:clang-tidy --@bazel_clang_tidy//:clang_tidy_config=//:clang_tidy_config

# Use hermetic clang-tidy binary
build:clang-tidy --@bazel_clang_tidy//:clang_tidy_executable=@llvm-project//clang-tools-extra/clang-tidy:clang-tidy

# Provide builtin headers (resource dir)
build:clang-tidy --@bazel_clang_tidy//:clang_tidy_resource_dir=@llvm-project//clang:builtin_headers_gen

In my project, bazel build cache is used when I run:

bazel build //lib/... \
                  --config=clang-tidy

However, it always run the full clang-tidy checks again on every source file, even if I haven't changed any of the files.

INFO: Invocation ID: 41278bac-7ea8-4f69-ada2-b2490977cc13
INFO: Analyzed 7 targets (0 packages loaded, 0 targets configured).
[85 / 95] 10 actions running
    Run clang-tidy on lib/writer.cpp; 260s disk-cache, darwin-sandbox
    Run clang-tidy on lib/writer.hpp; 260s disk-cache, darwin-sandbox
    Run clang-tidy on lib/tests/writer_tests.cpp; 260s disk-cache, darwin-sandbox
...

There are some outputs inside my bazel-bin, but I'm unsure if those are relevant to the caching:

find . -name '*clang_tidy*'

./lib/tests/bazel_clang_tidy_lib
./lib/bazel_clang_tidy_lib

[erenon]

This is not the expected behavior. Try --explain=why, maybe it says why the target was rebuilt.

[Wheest]

Ah, I'm seeing:

WARNING: Build options --@@+_repo_rules2+bazel_clang_tidy//:clang_tidy_config, --@@+_repo_rules2+bazel_clang_tidy//:clang_tidy_executable, and --@@+_repo_rules2+bazel_clang_tidy//:clang_tidy_resource_dir have changed, discarding analysis cache (this can be expensive, see https://bazel.build/advanced/performance/iteration-speed).

and then checking the explain file, there is a bunch of:

Build options: --java_runtime_version=remotejdk_11 --credential_helper='storage.googleapis.com=%workspace%/build_tools/credential-helper' --experimental_repository_cache_hardlinks --copt='-fdiagnostics-color=always' --test_output=errors --disk_cache='~/.cache/proj/bazel' --experimental_disk_cache_gc_max_size=100G --experimental_downloader_config=build_tools/bazel_downloader.cfg --enable_platform_specific_config --action_env='BAZEL_USE_CPP_ONLY_TOOLCHAIN=1' --apple_platform_type=macos --macos_minimum_os=15.0 --macos_sdk_version=15.0 --incompatible_strict_action_env --config=clang-tidy --aspects=@bazel_clang_tidy//clang_tidy:clang_tidy.bzl%clang_tidy_aspect --output_groups=report --explain=why
Executing action 'BazelWorkspaceStatusAction stable-status.txt': unconditional execution is requested.
Executing action 'Writing repo mapping manifest for @@+llvm_project_overlay+llvm-project//mlir:mlir-tblgen [for tool]': action command has changed (try --verbose_explanations for more info).
Executing action 'Writing repo mapping manifest for @@+llvm_project_overlay+llvm-project//llvm:llvm-min-tblgen [for tool]': action command has changed (try --verbose_explanations for more info).
Executing action 'Writing repo mapping manifest for @@+llvm_project_overlay+llvm-project//llvm:llvm-tblgen [for tool]': action command has changed (try --verbose_explanations for more info).
Executing action 'Compiling clang-tools-extra/clang-tidy/misc/ConfusableTable/BuildConfusableTable.cpp [for tool]': One of the files has changed.
...