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add blog post for 5.0 release #263

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Jan 19, 2022
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add blog post for 5.0 release #263

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c506cb5
add blog post for 5.0 release
Wyverald Jan 19, 2022
c969e9e
fix formatting
Wyverald Jan 19, 2022
b25a37f
remove duplicate contributor
Wyverald Jan 19, 2022
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address review comments
Wyverald Jan 19, 2022
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4 changes: 4 additions & 0 deletions _config.yml
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Expand Up @@ -192,3 +192,7 @@ authors:
ulfjack:
- Ulf Adams
- https://github.com/ulfjack

wyv:
- Xudong Yang
- https://github.com/Wyverald
148 changes: 148 additions & 0 deletions _posts/2022-01-19-bazel-5.0.md
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@@ -0,0 +1,148 @@
---
layout: posts
title: "Bazel 5.0"
authors:
- wyv
---

Bazel 5.0 is a major release and Bazel’s [second LTS release](https://blog.bazel.build/2020/11/10/long-term-support-release.html). It contains new features and backwards incompatible changes from 4.x, the previous LTS release.

## Highlights

* `--experimental_enable_bzlmod` enables the new external dependency subsystem, [Bzlmod](https://docs.bazel.build/versions/5.0.0/bzlmod.html).
* The minimum required JDK to run Bazel itself is now OpenJDK 11. Note that compiling binaries using JDK 8 and lower is still supported.
* Java rules now use toolchain resolution. ([#7849](https://github.com/bazelbuild/bazel/issues/7849))
* Starlark now permits `def` statements to be nested (closures) and supports lambda expressions (anonymous functions).

## General

* `//visibility:legacy_public` has been removed.
* The `--all_incompatible_changes` flag is now a no-op.
* Specifying a target pattern underneath a directory specified by `.bazelignore` will now emit a warning, not an error.
* The `test` and `coverage` commands no longer return 3 when a test action fails because of a system error. Instead, the exit code reflects the type of system error.
* Bazel will no longer create a `bazel-out` symlink if `--symlink_prefix` is specified: the directory pointed to via the `bazel-out` symlink is accessible via `${symlink_prefix}-out`.
* Removed flag `--experimental_no_product_name_out_symlink`; it is effectively always true.
* Removed `--action_graph` from the `dump` command.
* Removed `--{experimental_,}json_trace_compression`; its value is determined by the profile name.
* Removed `--experimental_profile_cpu_usage`; it is effectively always true.
* `--legacy_dynamic_scheduler` is now a no-op.
* Flipped `--trim_test_configuration` to true. ([#6842](https://github.com/bazelbuild/bazel/issues/6842))
* When using `--allow_analysis_failures` (for example, via bazel-skylib's `analysistest` with `expect_failure = True`), analysis-time failures in aspect implementation functions will now be propagated and saved in `AnalysisFailureInfo`, just like analysis-time failures in rules.
* Added `--experimental_reuse_sandbox_directories` to reuse already-created non-worker sandboxes with cleanup.
* Renamed `--experimental_run_validations` to `--run_validations` and flipped its default to true.
* Removed `--experimental_forward_instrumented_files_info_by_default`, now that this behavior is the default.
* When using MemoryProfiler with multiple GCs via the `--memory_profile_stable_heap_parameters` flag, we do a more precise calculation of heap used at the end of the build. This will generally result in lower values.
* Added support to length-delimited protos as undeclared output annotations.
* Added experimental flag `--experimental_dynamic_skip_first_build` to skip local execution in dynamic execution until there has been a successful build. This allows doing a first clean build from remote only, filling the cache.

## Android

* The minimum Android build tools version for the Android rules is now 30.0.0.
* The Android rules' `--use_singlejar_apkbuilder` is now a no-op. SingleJar will always be used to build APKs.
* `--apk_signing_method` now accepts the value `v4`.
* Proguard configs generated from aapt2 link step now exclude path location comments for better determinism.
* Removed obsolete `--incompatible_prohibit_aapt1`.

## Apple / Xcode

* `--apple_sdk` has been deleted. It is a no-op.
* The `--incompatible_disable_native_apple_binary_rule` flag has been added which disables the native `apple_binary` rule. Users who need to use `apple_binary` directly (if they cannot use one of the more specific Apple rules) should load it from [`rules_apple`](https://github.com/bazelbuild/rules_apple).
* Allowing the LIPO operations to be conditional in the `linkMultiArchBinary` API for Apple binaries. Single architecture slices are now returned through AppleBinaryOutput and the Starlark API.
* If `--experimental_prefer_mutual_xcode` is passed, Bazel will choose the local default (instead of the newest mutually available version) if it's available both locally and remotely.

## Build Event Protocol

* In the build event stream, `BuildMetrics.TargetMetrics.targets_loaded` is no longer populated. Its value was always mostly meaningless. `BuildMetrics.TargetMetrics.targets_configured` and `BuildMetrics.ActionSummary.actions_created` now include configured aspect data.
* `--bep_publish_used_heap_size_post_build` is removed. Use `--memory_profile=/dev/null` instead; the `used_heap_size_post_build` field in BEP is now populated when the `--memory_profile` flag is set.
* Added `--bes_header` flag to pass extra headers to the BES server.
* BEP now includes test suite expansions.
* BEP now includes all files from successful actions in requested output groups. Previously, an output group's files were excluded if any file in the output group was not produced due to a failing action. Users can expect BEP output to be larger for failed builds.
* In BEP, `TargetComplete.output_group` has a new field `incomplete` indicating that the `file_sets` field is missing one or more declared artifacts whose generating actions failed.
* When `--experimental_bep_target_summary` is enabled, BEP contains a new event, `TargetSummary`. For each top-level configured target, this event aggregates the results for building the configured target, tests run for that configured target (if any), and building all top-level aspects applied to that configured target. This flag will eventually default to enabled.

## C++ / Objective-C

* The Starlark method `generate_dsym` in `objc` fragment has been deleted. Please use the equivalent `apple_generate_dsym` in `cpp` fragment instead.
* Removed `--incompatible_objc_compile_info_migration`. ([#10854](https://github.com/bazelbuild/bazel/issues/10854))
* Removed `--incompatible_objc_provider_remove_compile_info`. ([#11359](https://github.com/bazelbuild/bazel/issues/11359))
* Made gcov optional in `cc_toolchain` tools.
* Added a new flag, `--incompatible_enable_cc_test_feature` which switches from the use of build variables to the feature of the same name.

## Configurability

* Added `--incompatible_enforce_config_setting_visibility` to make `config_setting` honor the `visibility` attribute (defaulting to `//visibility:public`) ([#12932](https://github.com/bazelbuild/bazel/issues/12932))
* The flag `--toolchain_resolution_debug` now takes a regex argument, which is used to check which toolchain types or targets should have debug info printed. You may use `.*` as an argument to keep the current behavior of debugging every toolchain type / target.

## Coverage

* All (instead of just C++) source files are now filtered for coverage output according to `--instrumentation_filter` and `--instrument_test_targets`.
* `genrule.srcs` is now considered a source attribute for coverage.
* Forward coverage-instrumented files from non-tool dependencies by default.
* `label_keyed_string_dict` attributes are now considered when gathering instrumented files for coverage.
* Java branch coverage now applies Jacoco’s coverage filters. ([#12696](https://github.com/bazelbuild/bazel/issues/12696))

## Java

* Removed `javac_jar` from JavaToolchainInfo.
* Flipped `--incompatible_disallow_resource_jars` to `true`, disabling `resouce_jars` attribute on `java_library`. ([#13221](https://github.com/bazelbuild/bazel/issues/13221))
* Flipped `--incompatible_java_common_parameters` to `true`, removing `host_javabase` parameter from `java_common.compile`. ([#12373](https://github.com/bazelbuild/bazel/issues/12373))
* Flipped `--incompatible_use_toolchain_resolution_for_java_rules` to `true`. Flags `--javabase` and `--java_toolchain` are now no-op. ([#7849](https://github.com/bazelbuild/bazel/issues/7849))
* Only native libraries supported by C++ targets in `deps` and `runtime_deps` are collected. No longer collecting `.so` files ([#13043](https://github.com/bazelbuild/bazel/issues/13043)) or libraries in the `data` attribute. ([#13550](https://github.com/bazelbuild/bazel/issues/13550))
* `JavaToolchainInfo.jvm_opt` returns a `depset` instead of a list.
* Added a `_direct_source_jars` output group to Java related targets.
* Added an `enable_annotation_processing` option to `java_common.compile`, which can be used to disable any annotation processors passed to `plugins` or in `exported_plugins` of `deps`.
* Removed `java_lite_proto_library.strict_deps` attribute.
* Bazel now uses the Starlark implementations of `java_library` and `java_plugin` instead of their native counterparts.
* `java_plugins` can now only be used in the `plugins` and `exported_plugins` attributes. ([#14012](https://github.com/bazelbuild/bazel/issues/14012))
* Javac workers now support cancellation.
* Javac workers now cache the bootclasspath classes.

## Packaging

* `pkg_deb` is no longer part of `@bazel_tools//build_defs/pkg:pkg.bzl`. Use [https://github.com/bazelbuild/rules_pkg/tree/main/pkg](https://github.com/bazelbuild/rules_pkg/tree/main/pkg) instead.
* Dropped fragile xz support from built in `pkg_tar`. Users requiring xz compression should switch to `[bazelbuild/rules_pkg](https://github.com/bazelbuild/rules_pkg)`.

## Persistent Workers

* Multiplex persistent workers can now use the JSON protocol [(#7998](https://github.com/bazelbuild/bazel/issues/7998)).
* Updated worker protocol to allow request cancellation, and added `--experimental_worker_cancellation` flag to turn on cancellation for workers that implement it ([#614](https://github.com/bazelbuild/bazel/issues/614)).

## Python

* The `--incompatible_load_python_rules_from_bzl` flag is now a no-op.
* Relax restriction for "-" in the package name for Python sources. Now `py_binary` and `py_test` targets can have a main source file with "-" in the path.

## Remote Execution

* Disk cache can now be used in remote execution. ([#13852](https://github.com/bazelbuild/bazel/pull/13852))
* Merkle tree calculation can be cached with `--experimental_remote_merkle_tree_cache`. The cache size is unlimited by default but can be controlled by `--experimental_remote_merkle_tree_cache_size`. ([#13879](https://github.com/bazelbuild/bazel/pull/13879))
* File uploads are scheduled into background if `--experimental_remote_cache_async` is set. ([#13655](https://github.com/bazelbuild/bazel/pull/13655))
* `--remote_max_connections` applies to gRPC connections as well. ([#14202](https://github.com/bazelbuild/bazel/pull/14202))
* Remote metadata is saved into action cache if `--exprimental_action_cache_store_output_metadata` is set. ([#13604](https://github.com/bazelbuild/bazel/pull/13604))
* Data transfers between Bazel and remote server are compressed via zstd if `--experimental_remote_cache_compression` is set. ([#14041](https://github.com/bazelbuild/bazel/pull/14041))
* Added support for tag `no-remote-cache-upload`. ([#14338](https://github.com/bazelbuild/bazel/pull/14338))
* Bug fixes and UX improvements.

## Query

* Query `output=xml/proto/location` for source files will now show the location of line 1 of the source file (as the new default) instead of its location in the BUILD file.
* Query `--order_output=auto` will now sort lexicographically. However, when `somepath` is used as a top level function (e.g. `query 'somepath(a, b)'`), it will continue to output in dependency order. If you do not want the lexicographical output ordering, specify another `--order_output` value (`no`, `deps` or `full`) based on what ordering you require.
* cquery `--noimplicit_deps` now correctly filters out resolved `cc_toolchain`s.

## Starlark / Build Language

* Starlark now permits `def` statements to be nested (closures) and supports lambda expressions (anonymous functions). Recursion is still not permitted.
* `Args.add_all` and `Args.add_joined` can now accept closures in `map_each` if explicitly enabled via the `allow_closure` parameter. Beware that closures may retain large data structures into the execution phase.
* dict.setdefault(key, ...) now fails if dict is frozen, even if it already contains key. This is an incompatible API change. ([#12642](https://github.com/bazelbuild/bazel/pull/12642))
* The deprecated `relative_to_caller_repository` parameter has been removed from the `Label` constructor.
* The undocumented `ctx.expand` feature no longer exists.
* Add `runfiles.merge_all()` for merging a sequence of runfiles objects.
* `runfiles.merge()` and `merge_all()` now respect `--nested_set_depth_limit`. If you hit the depth limit because you were calling `merge()` in a loop, use `merge_all()` on a sequence of runfiles objects instead.
* `native.existing_rule` now returns select values in a form that is accepted by rule instantiation. This is a breaking API change, though the fallout is expected to be small.
* Added `--incompatible_existing_rules_immutable_view` flag to make the `native.existing_rule` and `native.existing_rules` functions more efficient by returning immutable, lightweight dict-like view objects instead of mutable dicts.
* Flipped `--incompatible_disable_depset_items` ([#9017](https://github.com/bazelbuild/bazel/issues/9017)). The flag is now a no-op.

## Acknowledgments

This release contains contributions from many people at Google, as well as Adam Liddell, Alex Eagle, Andrew Katson, Anthony Pratti, Artem V. Navrotskiy, Austin Schuh, Benedek Thaler, Benjamin Lee, Benjamin Peterson, Brandon Jacklyn, Brentley Jones, bromano, Cameron Mulhern, Christopher Sauer, Cristian Hancila, Dan Bamikiya, Daniel McCarney, Daniel Wagner-Hall, Danny Wolf, Dave Nicponski, David Cummings, David Ostrovsky, Delwin9999, Denys Kurylenko, Dmitry Ivankov, dorranh, ecngtng, Ed Schouten, Eitan Adler, Elliotte Rusty Harold, Eric Cousineau, Ethan Steinberg, Fabian Meumertzheim, FaBrand, Felix Ehrenpfort, Finn Ball, frazze-jobb, Fredrik Medley, Garrett Holmstrom, Gautam Korlam, George Gensure, goodspark, Grzegorz Lukasik, hvadehra, Ikko Ashimine, Jesse Chan, Joe Lencioni, Johannes Abt, John Laxson, Jonathan Schear, Justus Tumacder, Keith Smiley, kekxv, Kevin Hogeland, Lauri Peltonen, Liu Liu, László Csomor, Marc Zych, Mark Karpov, Masoud Koleini, Mathieu Olivari, Matt Mackay, Mauricio Galindo, Max Liu, Menny Even Danan, Michael Chinen, Nathaniel Brough, Nick Korostelev, Niek Peeters, Nikolay Shelukhin, odisseus, Oleh Stolyar, Olek Wojnar, Olle Lundberg, Omar Zuniga, Paul Gschwendtner, Peter Kasting, Philipp Schrader, Pras Velagapudi, Qais Patankar, Rabi Shanker Guha, Rai, Ron Braunstein, Ryan Beasley, samhowes, Samuel Giddins, Sebastian Olsson, Sergey Tyurin, Steve Siano, steve-the-bayesian, Stiopa Koltsov, tatiana, Tetsuo Kiso, Thi Doãn, Thomas Carmet, ThomasCJY, Timothe Peignier, Timothy Klim, Tobi, Torgil Svensson, Trustin Lee, Ulf Adams, Ulrik Falklof, Uri Baghin, Vaidas Pilkauskas, Vertexwahn, wisechengyi, Wren Turkal, Xavier Bonaventura, Yannic Bonenberger, Yury Evtikhov, Yuval Kaplan, zqzzq.