How to concantenate select objects to a list in bazel - bazel

Question

I have a bazel target with attribute that must be a list.
However, I need selectively add elements to the list based on the outcome of a select.
glob_tests(
# some stuff
exclude = [
"a.foo",
] + if_A([
"x.foo",
]) + if_B([
"y.foo",
]),
)
In the above code snippet, the functions if_A and if_B return select objects.
But when I run this as is, I get an error stating that a sequence object was expected but a select object was encountered instead.
How can I convert the select objects to sequence objects?

Answer 1

(I assume glob_test is a macro that calls the builtin function glob.) globs are evaluated when a BUILD file is loaded, which is before any configuration is known. This means glob cannot take any select objects as inputs because the knowledge to turn select objects into lists is not present.
The way to solve this is to lift the select calls above the globs like this
some_test(
name = "some_test",
srcs = select({
"//cond1": glob(["t*", "s*"], exclude=["thing"]),
"//cond2": glob(["t*", "s*"], exclude=["something else"]),
}),
)
instead of
some_test(
name = "some_test",
srcs = glob(
["t*", "s*"],
exclude=select({
"//cond1": ["thing"],
"//cond2": ["something else"],
}),
),
)