Legacy, partial list of backward-incompatible changes.
Full, authorative list of incompatible changes is GitHub issues with “incompatible-change” label
General Starlark
Starlark Rules
cfg = "data"Objc
External repositories
Java
Misc
C++
We are removing the + operator on dictionaries. This includes the += form where the left-hand side is a dictionary. This is done to improve compatibility with Python. A possible workaround is to use the .update method instead.
--incompatible_disallow_dict_plustruePreviously, the load statement could appear anywhere in a .bzl file so long as it was at the top level. With this change, for .bzl files, load must appear at the beginning of the file, i.e. before any other non-load statement.
--incompatible_bzl_disallow_load_after_statementtrueWhen the flag is set to true, depset objects are not treated as iterable. This prohibits directly iterating over depsets in for loops, taking its size via len(), and passing it to many functions such as list, tuple, min, max, sorted, all, and any. It does not prohibit checking for emptiness by converting the depset to a boolean.
The goal of this change is to avoid accidental iteration on depset, which can be expensive. If you really need to iterate over a depset, you can call the .to_list() method to obtain a flattened list of its contents.
deps = depset() [x.path for x in deps] # deprecated [x.path for x in deps.to_list()] # recommended sorted(deps) # deprecated sorted(deps.to_list()) # recommended
--incompatible_depset_is_not_iterablefalseTo merge two sets, the following examples used to be supported, but are now deprecated:
depset1 + depset2 # deprecated depset1 | depset2 # deprecated depset1.union(depset2) # deprecated
The recommended solution is to use the depset constructor:
depset(transitive = [depset1, depset2])
See the depset documentation for more information.
--incompatible_depset_unionfalseWhen the flag is set to true, string objects are not treated as iterable. This affects for loops and many functions, e.g. list, tuple, min, max, sorted, all, and any. String iteration has been a source of errors and confusion, such as this error:
def my_macro(name, srcs): for src in srcs: # do something with src # equivalent to: my_macro("hello", ["f", "o", "o", ".", "c", "c"]) my_macro( name = "hello", srcs = "foo.cc", )
String indexing and len are still allowed. If you need to iterate over a string, you may explicitly use:
my_string = "hello world" for i in range(len(my_string)): char = my_string[i] # do something with char
--incompatible_string_is_not_iterabletrueThe current package name should be retrieved by calling package_name() in BUILD files or native.package_name() in .bzl files. The old way of referring to the magic PACKAGE_NAME variable bends the language since it is neither a parameter, local variable, nor global variable.
Likewise, the magic REPOSITORY_NAME variable is replaced by repository_name() and native.repository_name(). Both deprecations use the same flag.
--incompatible_package_name_is_a_functiontrueThe FileType function is going away. The main use-case was as an argument to the rule function. It's no longer needed, you can simply pass a list of strings to restrict the file types the rule accepts.
--incompatible_disallow_filetypetrueThis change removes the old methods for registering actions within rules, and requires that you use the new methods instead. The deprecated methods and their replacements are as follows.
ctx.new_file(...) --> ctx.actions.declare_file(...)ctx.experimental_new_directory(...) --> ctx.actions.declare_directory(...)ctx.action(...) --> either ctx.actions.run(...) or ctx.actions.run_shell(...)ctx.file_action(...) --> ctx.actions.write(...)ctx.empty_action(...) --> ctx.actions.do_nothing(...)ctx.template_action(...) --> ctx.actions.expand_template(...)--incompatible_new_actions_apifalseThe Args object returned by ctx.actions.args() has dedicated methods for appending the contents of a list or depset to the command line. Previously these use cases were lumped into its add() method, resulting in a more cluttered API.
With this flag, add() only works for scalar values, and its deprecated parameters are disabled. To add many arguments at once you must use add_all() or add_joined() instead.
--incompatible_disallow_old_style_args_addtrueThis flag disables certain deprecated resource fields on ObjcProvider.
--incompatible_objc_provider_resourcesfalseThis flag disables the output_group field on the Target Starlark type. Use OutputGroupInfo instead.
For example, replace:
dep_bin = ctx.attr.dep.output_group.bin
with:
dep_bin = ctx.attr.dep[OutputGroupInfo].bin
--incompatible_no_target_output_groupfalseThis flag disables the default parameter on attr.output and attr.output_list. Use Starlark macros to specify defaults for these attributes instead.
For example, replace:
my_rule = rule( ... attrs = {"out" : attr.output(default = "foo.txt")} ...
with:
# myrule.bzl my_rule = rule( ... attrs = {"out" : attr.output()} ... # mymacro.bzl load(":myrule.bzl", _my_rule = "my_rule") def my_rule(name): _my_rule( name = name, output = "%s_out.txt" % name )
The previous default parameter of these attribute types was severely bug-prone, as two targets of the same rule would be unable to exist in the same package under default behavior. (Two targets both generating foo.txt in the same package would conflict.)
--incompatible_no_output_attr_defaultfalseWhen set, the native git_repository and new_git_repository rules are disabled. The Starlark versions
load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository", "new_git_repository")
should be used instead. These are drop-in replacements of the corresponding native rules, however with the additional requirement that all label arguments be provided as a fully qualified label (usually starting with @//), for example: build_file = "@//third_party:repo.BUILD".
--incompatible_remove_native_git_repositorytrueWhen set, the native http_archive and all related rules are disabled. The Starlark version
load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
should be used instead. This is a drop-in replacement, however with the additional requirement that all label arguments be provided as fully qualified labels (usually starting with @//). The Starlark http_archive is also a drop-in replacement for the native new_http_archive (with the same proviso). http.bzl also provides http_jar and http_file (the latter only supports the urls parameter, not url).
--incompatible_remove_native_http_archivetrueWhen set, the native maven_jar rule is disabled. The Starlark version
load("@bazel_tools//tools/build_defs/repo:java.bzl", "java_import_external")
or the convenience wrapper
load("@bazel_tools//tools/build_defs/repo:jvm.bzl", "jvm_maven_import_external")
should be used instead. These rules are more reliable and offer additional functionality over the native maven_jar rule. In addition to downloading the jars, they allow defining the jar's dependencies. They also enable downloading src-jars.
Given a WORKSPACE file that looks like the following:
maven_jar( name = "truth", artifact = "com.google.truth:truth:0.30", sha1 = "9d591b5a66eda81f0b88cf1c748ab8853d99b18b", )
It will need to look like this after updating:
load("@bazel_tools//tools/build_defs/repo:jvm.bzl", "jvm_maven_import_external") jvm_maven_import_external( name = "truth", artifact = "com.google.truth:truth:0.30", artifact_sha256 = "59721f0805e223d84b90677887d9ff567dc534d7c502ca903c0c2b17f05c116a", server_urls = ["http://central.maven.org/maven2"], licenses = ["notice"], # Apache 2.0 )
Notably
licenses attribute is mandatoryserver_urls attribute is mandatory. If your maven_jar rule did not specify a url then you should use the default server (“http://central.maven.org/maven2”). If your rule did specify a url then keep using that one.Documentation for the rule is here.
--incompatible_remove_native_maven_jarfalseWhen set, java_common.create_provider and certain arguments to JavaInfo are deprecated. The deprecated arguments are: actions, sources, source_jars, use_ijar, java_toolchain, and host_javabase.
Example migration from create_provider:
# Before provider = java_common.create_provider( ctx.actions, compile_time_jars = [output_jar], use_ijar = True, java_toolchain = ctx.attr._java_toolchain, transitive_compile_time_jars = transitive_compile_time, transitive_runtime_jars = transitive_runtime_jars, ) # After compile_jar = java_common.run_ijar( ctx.actions, jar = output_jar, target_label = ctx.label, java_toolchain = ctx.attr._java_toolchain, ) provider = JavaInfo( output_jar = output_jar, compile_jar = compile_jar, deps = deps, runtime_deps = runtime_deps, )
Example migration from deprecated JavaInfo arguments:
# Before provider = JavaInfo( output_jar = my_jar, use_ijar = True, sources = my_sources, deps = my_compile_deps, runtime_deps = my_runtime_deps, actions = ctx.actions, java_toolchain = my_java_toolchain, host_javabase = my_host_javabase, ) # After my_ijar = java_common.run_ijar( ctx.actions, jar = my_jar, target_label = ctx.label, java_toolchain, my_java_toolchain, ) my_source_jar = java_common.pack_sources( ctx.actions, sources = my_sources, java_toolchain = my_java_toolchain, host_javabase = my_host_javabase, ) provider = JavaInfo( output_jar = my_jar, compile_jar = my_ijar, source_jar = my_source_jar, deps = my_compile_deps, runtime_deps = my_runtime_deps, )
A tool is an input coming from an attribute of type label where the attribute has been marked executable = True. In order for an action to run a tool, it needs access to its runfiles.
Under the old API, tools are passed to ctx.actions.run() and ctx.actions.run_shell() via their inputs parameter. Bazel scans this argument (which may be a large depset) to find all the inputs that are tools, and adds their runfiles automatically.
In the new API, tools are instead passed to a dedicated tools parameter. The inputs are not scanned. If a tool is accidentally put in inputs instead of tools, the action will fail during the execution phase with an error due to missing runfiles. This may be somewhat cryptic.
To support a gradual transition, all actions with a tools argument are opted into the new API, while all actions without a tools argument still follow the old one. In the future (when this flag is removed), all actions will use the new API unconditionally.
This flag turns on a safety check that is useful for migrating existing code. The safety check applies to all actions that do not have a tools argument. It scans the inputs looking for tools, and if it finds any, it raises an error during the analysis phase that clearly identifies the offending tools.
In the rare case that your action requires a tool as input, but does not actually run the tool and therefore does not need its runfiles, the safety check will fail even though the action would have succeeded. In this case, you can bypass the check by adding a (possibly empty) tools argument to your action. Note that once an action has been modified to take a tools argument, you will no longer get helpful analysis-time errors for any remaining tools that should have been migrated from inputs.
--incompatible_no_support_tools_in_action_inputsfalsePreviously, directories created by ctx.actions.declare_directory expanded to the path of the directory when added to an Args object.
With this flag enabled, directories are instead replaced by the full file contents of that directory when passed to args.add_all() or args.add_joined(). (Directories may not be passed to args.add().)
If you want the old behavior on a case-by-case basis (perhaps your tool can handle directories on the command line), you can pass expand_directories=False to the args.add_all() or args.add_joined() call.
d = ctx.action.declare_directory("dir")
# ... Some action runs and produces ["dir/file1", "dir/file2"] ...
f = ctx.action.declare_file("file")
args = ctx.action.args()
args.add_all([d, f])
# -> Used to expand to ["dir", "file"]
# Now expands to ["dir/file1", "dir/file2", "file"]
--incompatible_expand_directoriesfalseWhen the flag is set, use a saner way to resolve variables. The previous behavior was buggy in a number of subtle ways. See the proposal for background and examples.
The proposal is not fully implemented yet.
--incompatible_static_name_resolutiontrueWhen the flag is set, load can only import symbols that were explicitly defined in the target file, using either = or def.
When the flag is unset (legacy behavior), load may also import symbols that come from other load statements.
In other words, the x below is exported only if the flag is unset:
load(":file.bzl", "x") y = 1
--incompatible_no_transitive_loadstrue0.19.0If false, Bazel constructs an in-memory //tools/defaults package based on the command line options. If true, //tools/defaults:* is resolved from file system as a regular package.
--incompatible_disable_tools_defaults_packagefalse//tools/default was initially created as virtual in-memory package. It generates content dynamically based on current configuration. There is no need of having //tools/defaults any more as LateBoundAlias can do dynamic configuration-based label resolving. Also, having //tools/default makes negative impact on performance, and introduces unnecessary code complexity.
All references to //tools/defaults:* targets should be removed or replaced to corresponding target in @bazel_tools//tools/jdk: and @bazel_tools//tools/cpp: packages.
Targets in //tools/default will not exist any more. If you have any references inside your BUILD or *.bzl files to any of its, then bazel will fail to resolve.
Please replace all occurrences:
//tools/defaults:jdk@bazel_tools//tools/jdk:current_java_runtime@bazel_tools//tools/jdk:current_host_java_runtime//tools/defaults:java_toolchain@bazel_tools//tools/jdk:current_java_toolchain//tools/defaults:crosstool@bazel_tools//tools/cpp:current_cc_toolchain@bazel_tools//tools/cpp:current_cc_host_toolchainlibc_top, then @bazel_tools//tools/cpp:current_libc_topThese targets will not be supported any more:
//tools/defaults:coverage_report_generator//tools/defaults:coverage_supportIf true, Bazel will stop retrieving the value of compiler from the cpp configuration when --compiler is not specified. This will cause a config_setting that have values = {"compiler": "x"} to not work properly when --compiler is not specified at command line.
The former behavior can be achieved by changing the config_setting to use flag_values = {"@bazel_tools//tools/cpp:compiler": "x"} instead:
# Before config_setting( name = "cpu_x_compiler_y", values = { "cpu": "x", "compiler": "y", }, ) # After config_setting( name = "cpu_x_compiler_y", values = { "cpu": "x", }, flag_values = { "@bazel_tools//tools/cpp:compiler": "y", }, )
--incompatible_disable_late_bound_option_defaultsfalse0.18.0If true, Bazel will no longer accept depsets in user_compile_flags for create_compile_variables, and in user_link_flags for create_link_variables. Use plain lists instead.
--incompatible_disable_depset_in_cc_user_flagsfalse0.18.0Currently Bazel selects the cc_toolchain to use from the toolchains dictionary attribute of cc_toolchain_suite. The key it uses is constructed the following way:
--compiler option is specified, the key is --cpu|--compiler. Bazel errors out if the entry doesn't exist.--compiler option was not specified on command line, Bazel checks if an entry with the key --cpu exists, and uses it if it does. If such an entry doesn‘t exist, it loops through the default_toolchain list in the CROSSTOOL file, selects the first one that matches the --cpu option, finds the CToolchain whose identifier matches the default_toolchain.toolchain_identifier field, and then uses the key CToolchain.targetCpu|Ctoolchain.compiler. It errors out if the entry doesn’t exist.We're making selection of the cc_toolchain label independent of the CROSSTOOL file: when the flag is set to True, Bazel will no longer loop through the default_toolchain list in order to construct a key for selecting a cc_toolchain label from cc_toolchain_suite.toolchains, but throw an error instead.
In order to not be affected by this change, one should add entries in the cc_toolchain_suite.toolchains for the potential values of --cpu:
# Before cc_toolchain_suite( toolchains = { "cpu1|compiler1": ":cc_toolchain_label1", "cpu2|compiler2": ":cc_tolchain_label2", } ) # After cc_toolchain_suite( toolchains = { "cpu1|compiler1": ":cc_toolchain_label1", "cpu2|compiler2": ":cc_toolchain_label2", "cpu1": ":cc_toolchain_label3", "cpu2": ":cc_tolchain_label4", } )
Before, it could happen that the same cc_toolchain is used with multiple CToolchains from the CROSSTOOL through default_toolchains. This is no longer allowed, each cc_toolchain must point to at most one CToolchain by:
cc_toolchain.toolchain_identifier equal to CToolchain.toolchain_identifiercompiler) specifying cc_toolchain.cpu and cc_toolchain.compiler fields that match CToolchain.target_cpu and CToolchain.compiler respectively.--cpu and --compiler options.Using cc_toolchain.toolchain_identifier will save you one migration in the future.
--incompatible_disable_cc_toolchain_label_from_crosstool_protofalse0.18.0Currently Bazel allows rule authors to access certain Make variables that are implicitly provided to every rule by the CppConfiguration. This causes every target to implicitly depend on CppConfiguration, which creates an undesirable number of extra, unused, dependencies.
We are removing the implicit provision of these Make variables, and requiring rules and targets that use these Make variables to explicitly depend on a C++ toolchain in order to access them.
The list of Make variables is:
In order to not be affected by this change, add a C++ toolchain to the toolchains attribute for targets, or to the_toolchains attribute for Starlark rules. The best choice for this value is the alias target @bazel_tools//tools/cpp:current_cc_toolchain, which will always resolve to the currently selected C++ toolchain.
Genrules will still have access to these Make variables for the time being because that information is plumbed not through CppConfiguration, but through an implicit dependency on the C++ toolchain. That will also be removed at some point in the future, so it's considered good practice to add an explicit dependency on the toolchain as demonstrated below.
For genrules and other targets using C++ Make Variables:
# Before genrule( cmd = "$(STRIP) file-to-be-stripped.o", ) # After genrule( cmd = "$(STRIP) file-to-be-stripped.o", toolchains = ["@bazel_tools//tools/cpp:current_cc_toolchain"], )
For Starlark rules using C++ Make Variables:
# Before def _impl(ctx): strip = ctx.var["STRIP"] ... my_rule = rule( implementation = _impl, attrs = { }, ) # After def _impl(ctx): strip = ctx.var["STRIP"] ... my_rule = rule( implementation = _impl, attrs = { "_toolchains": attr.label_list(default = [Label("@bazel_tools//tools/cpp:current_cc_toolchain")]), }, )
--incompatible_disable_cc_configuration_make_variablesfalse0.18.0You might want to migrate for this flag together with --incompatible_disable_legacy_flags_cc_toolchain_api in a single go. Migration instructions for --incompatible_disable_legacy_cpp_toolchain_skylark_api use an API that is already deprecated by --incompatible_disable_legacy_flags_cc_toolchain_api
This turns off legacy Starlark access to cc toolchain information via the ctx.fragments.cpp fragment. Instead of declaring dependency on the ctx.fragments.cpp using the fragments attribute declare a dependency on the @bazel_tools//tools/cpp:current_cc_toolchain via implicit attribute named _cc_toolchain (see example below). Use find_cpp_toolchain from @bazel_tools//tools/cpp:toolchain_utils.bzl to get the current C++ toolchain in the rule implementation.
# Before def _impl(ctx): ... ctx.fragments.cpp.compiler_options() foo = rule( implementation = _impl, fragments = ["cpp"], ... ) # After load("@bazel_tools//tools/cpp:toolchain_utils.bzl", "find_cpp_toolchain") def _impl(ctx): ... cc_toolchain = find_cpp_toolchain(ctx) cc_toolchain.compiler_options() foo = rule( implementation = _impl, attrs = { "_cc_toolchain": attr.label( default = Label("@bazel_tools//tools/cpp:current_cc_toolchain") ), }, )
List of all legacy fields and their corresponding cc_toolchain alternative:
ctx.fragments.cpp | cc_toolchain |
|---|---|
ar_executable | ar_executable() |
built_in_include_directories | built_in_include_directories |
c_options | c_options() |
compiler | compiler |
compiler_executable | compiler_executable() |
compiler_options(unused_arg) | compiler_options() |
cpu | cpu |
cxx_options(unused_arg) | cxx_options() |
dynamic_link_options(unused_arg, bool) | dynamic_link_options(bool) |
fully_static_link_options(unused_arg, True) | fully_static_link_options(True) |
ld_executable | ld_executable() |
link_options | link_options_do_not_use |
mostly_static_link_options(unused_arg, bool) | mostly_static_link_options(bool) |
nm_executable | nm_executable() |
objcopy_executable | objcopy_executable() |
objdump_executable | objdump_executable() |
preprocessor_executable | preprocessor_executable() |
strip_executable | strip_executable() |
sysroot | sysroot |
target_gnu_system_name | target_gnu_system_name |
unfiltered_compiler_options(unused_arg) | unfiltered_compiler_options(unused_arg) |
If you use legacy Starlark API on ctx.host_fragment.cpp, let us know on the tracking bug for C++ migration to platforms about your use case. The current plan is that host fragments will be removed. To migrate, add an implicit rule attribute in the host configuration:
"_host_cc_toolchain": attr.label( cfg = "host", default = Label("//tools/cpp:current_cc_toolchain"), ),
Then in your rules access the provider using:
host_cc_toolchain = ctx.attr._host_cc_toolchain[cc_common.CcToolchainInfo]
--incompatible_disable_legacy_cpp_toolchain_skylark_apifalse0.18.0We have deprecated the cc_toolchain Starlark API returning legacy CROSSTOOL fields:
Use the new API from cc_common
# Before: load("@bazel_tools//tools/cpp:toolchain_utils.bzl", "find_cpp_toolchain") def _impl(ctx): cc_toolchain = find_cpp_toolchain(ctx) compiler_options = ( cc_toolchain.compiler_options() + cc_toolchain.unfiltered_compiler_options([]) + ["-w", "-Wno-error"] ) link_options = ( ["-shared", "-static-libgcc"] + cc_toolchain.mostly_static_link_options(True) + ["-Wl,-whole-archive"] + [l.path for l in libs] + ["-Wl,-no-whole-archive"] + cc_toolchain.link_options_do_not_use ) # After load("@bazel_tools//tools/cpp:toolchain_utils.bzl", "find_cpp_toolchain") load( "@bazel_tools//tools/build_defs/cc:action_names.bzl", "CPP_LINK_DYNAMIC_LIBRARY_ACTION_NAME", "C_COMPILE_ACTION_NAME", ) def _impl(ctx): cc_toolchain = find_cpp_toolchain(ctx) feature_configuration = cc_common.configure_features( cc_toolchain = cc_toolchain, requested_features = ctx.features, unsupported_features = ctx.disabled_features, ) compile_variables = cc_common.create_compile_variables( feature_configuration = feature_configuration, cc_toolchain = cc_toolchain, user_compile_flags = depset(["-w", "-Wno-error"]), ) compiler_options = cc_common.get_memory_inefficient_command_line( feature_configuration = feature_configuration, action_name = C_COMPILE_ACTION_NAME, variables = compile_variables, ) link_variables = cc_common.create_link_variables( feature_configuration = feature_configuration, cc_toolchain = cc_toolchain, is_linking_dynamic_library = True, user_link_flags = ["-static-libgcc"] + ["-Wl,-whole-archive"] + [lib.path for lib in libs] + ["-Wl,-no-whole-archive"], ) link_flags = cc_common.get_memory_inefficient_command_line( feature_configuration = feature_configuration, action_name = CPP_LINK_DYNAMIC_LIBRARY_ACTION_NAME, variables = link_variables, )
--incompatible_disable_legacy_flags_cc_toolchain_apifalse0.19.0cfg = "data"cfg = "data" is a no-op that incorrectly gives the impression dependencies under it are built in a distinct “data” mode:
my_rule = rule( ... "some_attr": attr.label_list( cfg = "data" # This line does nothing ) )
The original semantics were unclear and were removed in 0.16.0.
Because this syntax is non-functional and confusing, it's being removed outright (#6153). The functionality it implies will be provided by Starlark build configuration.
When --incompatible_disallow_data_transition=true, builds using this syntax fail with an error.
--incompatible_disallow_data_transitiontrue0.16.0Previously, the label argument to the load statement (the first argument) was checked to ensure that it referenced an existing package but it was not checked to ensure that it didn't cross a package boundary.
For example, in
load("//a:b/c.bzl", "doesntmatter")
if this flag is set to true, the above statement will be in error if //a/b is a package; in such a case, the correct way to reference c.bzl via a label would be //a/b:c.bzl.
--incompatible_disallow_load_labels_to_cross_package_boundariesfalse