Incompatible change: java_output.source_jars will return a Depset instead of a list

[hvadehra]

The type returned by the source_jars field of JavaInfo.java_outputs is being changed from a list to a Depset. This is required to efficiently de-duplicate java_output provider instances in Starlark, since having a list field makes a provider mutable/non-hashable. Not de-duplicating would run into #17170

Migration

If there is a need to support old and new Bazel versions, one can update usages from:

source_jars = java_output.source_jars

to

source_jars = java_output.source_jars
if hasattr(source_jars, "to_list"):
    source_jars = source_jars.to_list()

Alternatively, for a more ergonomic solution, the appropriate check could be added to https://github.com/bazel-contrib/bazel_features

To temporarily preserve the old behavior, one can use the build flag --incompatible_depset_for_java_output_source_jars=false. Note this flag will become a no-op after the next Bazel LTS release (7.0).