Matt Payne

This commit **refactors** the error handling for missing argument separators in the `buck2 run` command, moving the `soft_error` from the client to the daemon. Previously, the client-side `soft_error` in **`buck2_client`** was not being logged correctly due to the absence of an `EventDispatcher` and `trace_id`. To address this, a new `run_args_missing_separator` boolean field is added to the **`buck2_cli_proto`** `BuildRequest` message. The client now communicates this state to the daemon, allowing the **`buck2_server_commands`** to issue the `soft_error` with proper logging context, significantly improving **debugging** and observability for this specific error condition.

This commit introduces a **deprecation soft error** for the **`buck2 run` command**, warning users when arguments are passed to the target binary without the `--` separator. This **feature enhancement** aims to standardize argument passing, aligning `buck2 run` with `buck2 test`, `buck2 install`, and `buck2 bxl`. Users will now see a warning guiding them to use `buck2 run //target -- my_arg`, though the command still succeeds unless `BUCK2_HARD_ERROR` is set. The change primarily affects the `buck2_client`'s `app/buck2_client/src/commands/run.rs` module and is validated by new tests in `tests/core/run/test_run.py`.

This commit performs **maintenance** by **removing the deprecated command-line flag** `--exit-when-different-state` from the system. It **refactors** the **client context initialization** within `app/buck2_client_ctx` to eliminate the handling logic for this flag, which was superseded by `--exit-when=differentstate`. Correspondingly, **test cases** in `tests/core/daemon/test_concurrency.py` are updated to use the current flag, ensuring consistency. This cleanup simplifies the codebase by removing an unused and redundant option.

This commit performs **maintenance** on the **concurrency end-to-end test suite** to resolve **test flakiness**. It specifically increases the sleep duration within the `test_exit_when_not_idle_after_command_exits` function in `tests/core/daemon/test_concurrency.py` from 0.5 to 2 seconds. This adjustment provides more time for the test's operations to complete, preventing premature timeouts that previously caused unreliable test results. The change improves the stability and reliability of the **daemon concurrency tests**, ensuring more accurate reporting of actual regressions.

This commit **fixes a bug** in the **Buck daemon's concurrency handling** related to the `--exit-when=notidle` flag. Previously, this flag could incorrectly prevent new commands from executing even when the daemon was idle, if the new command's state differed from a previous one. The `enter` method in `app/buck2_server_ctx/src/concurrency.rs` is updated to correctly check for active commands early, ensuring the flag only triggers when the daemon is genuinely busy. New test cases in `tests/core/daemon/test_concurrency.py` validate this corrected behavior, improving the reliability of daemon interaction by preventing false "daemon busy" errors.

This commit introduces a **new `--exit-when` flag** to Buck, significantly enhancing **concurrency management** for daemon commands. This **feature enhancement** replaces and expands upon the deprecated `--exit-when-different-state` flag, allowing users to specify granular conditions for a command to fail if another is already active. The flag offers options like `=differentstate` to fail if another command with a different state is running, and `=notidle` to fail if the daemon is not idle, which is crucial for background processes to defer to user-initiated commands. This change impacts the **Buck client and server contexts**, the **daemon's concurrency logic** (`buck2_server_ctx/src/concurrency.rs`), and improves the overall **user experience** by preventing resource contention.

This commit **fixes** a **bug** in Buck2's `representative_config_flags` logic, which was incorrectly including arguments intended for underlying binaries (passed after `--`) as Buck2 configuration modifiers for commands like `run` and `test`. The **argument parsing** within the **Buck2 client context** (`app/buck2_client_ctx/src/common.rs`) is now updated to **disregard anything after a bare `--`** when identifying these flags. This ensures that only actual Buck2 configuration modifiers are considered, significantly **improving the accuracy of build analysis** and configuration tracking. The fix is validated by **updated and new tests** in `tests/core/log/test_representative_config_flags.py`, preventing misinterpretation of user input and making post-hoc build comparisons more reliable.

This commit **disables default logging** of information from the **FBCC C++ compilation component** to Scuba. It modifies the `prelude/cxx/dist_lto/tools/dist_lto_opt_gnu.py` tool to **explicitly remove the `--log-fbcc` flag** during argument parsing, preventing unnecessary data collection by default. This **maintenance change** reduces logging overhead for Buck `build`, `run`, and `test` commands. Users can still opt-in to FBCC logging by setting the `-c cxx.log_fbcc=True` configuration flag, providing control over telemetry while improving default efficiency.

This commit **expands parser support for `genrule()`**, allowing it to be used as a `default_global` rule in addition to its existing native rule support. This **new capability** broadens the applicability of `genrule()` within the build system. Additionally, it includes a **maintenance refactoring** in the `prelude/toolchains/android/tools/build_rules/utils.bzl` file. Specifically, the `is_oss_build` function is updated to call `read_config` directly instead of `native.read_config`, which was causing errors in the `autodeps` system. This resolves a blocking issue for `autodeps` users and improves the robustness of build rule utilities.

This commit **refactors** the `prelude/rules_impl.bzl` file by converting all **relative `load` paths to absolute paths**. This **maintenance** change primarily affects the **build rules implementation**, standardizing how other `.bzl` files are imported. The change improves **build system consistency** and addresses compatibility issues with certain tooling that struggles with relative imports, ensuring more robust and predictable behavior.