Bazel is still in Beta and new releases may include backward incompatible changes. As we make changes and polish the extension mechanism, old features may be removed and new features that are not backward compatible may be added.
Backward incompatible changes are introduced gradually:
true. You can still use the flag to disable the change.
To check if your code will be compatible with future releases you can:
--all_incompatible_changes. This flag enables all backward incompatible changes, and so you can ensure your code is compatible with upcoming changes.
The following are the backward incompatible changes that are implemented and guarded behind flags in the current release:
We are removing the
+ operator on dictionaries. This includes the
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.
load statement could appear anywhere in a
.bzl file so long
as it was at the top level. With this change, for
appear at the beginning of the file, i.e. before any other non-
When the flag is set to true,
depset objects are not treated as iterable. If
you need an iterable, call the
.to_list() method. This affects
for loops and
many functions, e.g.
The goal of this change is to avoid accidental iteration on
depset, which can
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
To 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 documentation for more information.
When the flag is set to true,
string objects are not treated as iterable. This
for loops and many functions, e.g.
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
Integer division operator is now
// instead of
/. This aligns with
Python 3 and it highlights the fact it is a floor division.
x = 7 / 2 # deprecated x = 7 // 2 # x is 3
The 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.
This 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.
The 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
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
When set, glob tracking is disabled. This is a legacy feature that we expect has no user-visible impact.