Broken repository name handling for build_settings and label_flag

[moroten]

Description of the problem:

When using a label_flag that is defined in the main repository, it must be referred to as //:my_label_flag on the command line and in transitions. Using @my_repo//:my_label_flag will not work but will also not render any error message.

If the same repository is used as an external, using by @my_repo//:my_label_flag is a must in the transitions as //:my_label_flag always points to the main repository.

Basically, the functionality is there, but the repository name handling is broken.

Expected behaviour

Transitions should not allow build_setting names without @, either @//... or @my_repo//... should be used. Using //... should render an error suggesting @my_repo//... or @//..., apart from when using the built in //command_line_option:....

Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

cat <<EOF > WORKSPACE
local_repository(
    name = "sub",
    path = "sub",
)
EOF

mkdir sub
cat <<EOF > sub/WORKSPACE
workspace(name = "sub")
EOF

cat <<EOF > sub/BUILD.bazel
load(":rules.bzl", "rule_with_transition")
package(default_visibility = ["//visibility:public"])
label_flag(
    name = "the_label_flag",
    build_setting_default = ":bad_filegroup",
)
filegroup(name = "bad_filegroup", srcs = [])
filegroup(name = "good_filegroup", srcs = [])

rule_with_transition(
    name = "output_target",
    srcs = [":the_label_flag"],
)
EOF

cat <<EOF > sub/rules.bzl
def _my_transition_impl(settings, attr):
    print(settings)
    return {
        '@sub//:the_label_flag': Label("@sub//:good_filegroup"),
    }

my_transition = transition(
    implementation = _my_transition_impl,
    inputs = ["@sub//:the_label_flag"],
    outputs = ["@sub//:the_label_flag"],
)

def _rule_impl(ctx):
    print(ctx.attr.srcs)

rule_with_transition = rule(
    implementation = _rule_impl,
    # cfg = my_transition,
    attrs = {
        "srcs": attr.label_list(allow_files = True, cfg = my_transition),
        "_whitelist_function_transition": attr.label(default = "@bazel_tools//tools/whitelists/function_transition_whitelist"),
    },
)
EOF

Now run

$ bazel build @sub//:output_target
DEBUG: .../external/sub/rules.bzl:2:5: {"@sub//:the_label_flag": Label("@sub//:bad_filegroup")}
DEBUG: .../external/sub/rules.bzl:14:5: [<alias target @sub//:the_label_flag of @sub//:good_filegroup>]  <---- CORRECT

$ bazel build @sub//:output_target --@sub//:the_label_flag=@sub//:good_filegroup
DEBUG: .../external/sub/rules.bzl:2:5: {"@sub//:the_label_flag": Label("@sub//:good_filegroup")}  <--- CORRECT
DEBUG: .../external/sub/rules.bzl:14:5: [<alias target @sub//:the_label_flag of @sub//:good_filegroup>]  <--- Still CORRECT

$ (cd sub && bazel build output_target)
DEBUG: ./sub/rules.bzl:2:5: {"@sub//:the_label_flag": Label("@sub//:bad_filegroup")}
DEBUG: ./sub/rules.bzl:14:5: [<alias target //:the_label_flag of //:bad_filegroup>]  <--- WRONG

$ (cd sub && bazel build output_target --//:the_label_flag=:good_filegroup)
DEBUG: ./sub/rules.bzl:2:5: {"@sub//:the_label_flag": Label("//:bad_filegroup")}  <--- WRONG
DEBUG: ./sub/rules.bzl:14:5: [<alias target //:the_label_flag of //:good_filegroup>]  <--- CORRECT

$ (cd sub && bazel build output_target --@sub//:the_label_flag=:good_filegroup)
DEBUG: ./sub/rules.bzl:2:5: {"@sub//:the_label_flag": Label("//:good_filegroup")}  <--- CORRECT
DEBUG: ./sub/rules.bzl:14:5: [<alias target //:the_label_flag of //:bad_filegroup>]  <--- WRONG

Remove @sub from sub/rules.bzl and you will get

$ bazel build @sub//:output_target
ERROR: Analysis of target '@sub//:output_target' failed; build aborted: no such package '': BUILD file not found in any of the following directories. Add a BUILD file to a directory to mark it as a package.
^--- This error is because ./BUILD.bazel does not exist to define @//:the_label_flag.

$ bazel build @sub//:output_target --@sub//:the_label_flag=@sub//:good_filegroup
ERROR: Analysis of target '@sub//:output_target' failed; build aborted: no such package '': BUILD file not found in any of the following directories. Add a BUILD file to a directory to m
ark it as a package.
^--- This error is because ./BUILD.bazel does not exist to define @//:the_label_flag.

$ (cd sub && bazel build output_target)
DEBUG: ./sub/rules.bzl:2:5: {"//:the_label_flag": Label("//:bad_filegroup")}
DEBUG: ./sub/rules.bzl:14:5: [<alias target //:the_label_flag of //:good_filegroup>]  <--- CORRECT

$ (cd sub && bazel build output_target --//:the_label_flag=:good_filegroup)
DEBUG: ./sub/rules.bzl:2:5: {"//:the_label_flag": Label("//:good_filegroup")}  <--- CORRECT
DEBUG: ./sub/rules.bzl:14:5: [<alias target //:the_label_flag of //:good_filegroup>]  <--- CORRECT

$ (cd sub && bazel build output_target --@sub//:the_label_flag=:good_filegroup)
DEBUG: ./sub/rules.bzl:2:5: {"//:the_label_flag": Label("//:bad_filegroup")}  <--- WRONG
DEBUG: ./sub/rules.bzl:14:5: [<alias target //:the_label_flag of //:good_filegroup>]  <--- CORRECT

What operating system are you running Bazel on?

Linux

What's the output of bazel info release?

release 2.0.0

Have you found anything relevant by searching the web?

Nothing found when searching for label_flag on GitHub issues: https://github.com/bazelbuild/bazel/issues?utf8=%E2%9C%93&q=is%3Aissue+label_flag

Relates to bazel-dicsuss platforms, build_settings, transitions and features.

The example above is loosely based on https://github.com/bazelbuild/bazel/blob/master/src/test/shell/integration/starlark_configurations_test.sh.

[gregestren]

I'm a bit weak on repositories but I can at least triage.

[moroten]

I can confirm that the problem is not just for label_flag, it also applies to string_flag. With the code below, use the same command lines but with e.g. --@sub//:the_setting=good instead.

cat <<EOF > WORKSPACE
local_repository(
    name = "sub",
    path = "sub",
)
EOF

mkdir sub
cat <<EOF > sub/WORKSPACE
workspace(name = "sub")
EOF

cat <<EOF > sub/BUILD.bazel
load(":rules.bzl", "rule_with_transition", "string_flag")
package(default_visibility = ["//visibility:public"])
string_flag(
    name = "the_setting",
    build_setting_default = "bad",
)

rule_with_transition(
    name = "output_target",
    string_value = ":the_setting",
)
EOF

cat <<EOF > sub/rules.bzl
BuildSettingInfo = provider(
    fields = {"value": "The value."}
)

def _impl(ctx):
    return BuildSettingInfo(value = ctx.build_setting_value)

string_flag = rule(
    implementation = _impl,
    build_setting = config.string(flag = True),
)

def _my_transition_impl(settings, attr):
    print(settings)
    return {
        "@sub//:the_setting": "good",
    }

my_transition = transition(
    implementation = _my_transition_impl,
    inputs = ["@sub//:the_setting"],
    outputs = ["@sub//:the_setting"],
)

def _rule_impl(ctx):
    print(ctx.attr.string_value[BuildSettingInfo])

rule_with_transition = rule(
    implementation = _rule_impl,
    cfg = my_transition,
    attrs = {
        "string_value": attr.label(),
        "_whitelist_function_transition": attr.label(default = "@bazel_tools//tools/whitelists/function_transition_whitelist"),
    },
)
EOF

[gregestren]

I'm having trouble prioritizing this at the moment. I'm going to refer to @juliexxia for better triage, and check if she has context that I don't.

@juliexxia I don't understand the intersection of SBC and repositories very well. Feel free to own this or assign to someone else, but also feel free to assign back to me if there's no better obvious owner.

I also appreciate input from anyone on the right impact priority.

[gregestren]

Let's consolidate these bugs into #11128.

When that one is fixed, it if doesn't address this we can re-open this.

[juliexxia]

Wanted to express thanks for the detail of this issue report. Helped immensely with writing appropriate tests when writing this fix. Should be all fixed now, thanks for your patience.