bazel: 'required_providers' for an aspect does not always work together with the 'aspects' requirement on rule attributes

Description of the bug:

I want to create an aspect which is only meaningful for C++ targets. To ensure my aspect is only invoked on such targets, I added required_providers = [CcInfo],.

This works as expected when invoke the aspect through the CLI. However, it fails if the aspect is invoked by a rule on a cc_binary target. Given the aspect documentation and considering that cc_binary does provide CcInfo, this seems like a bug to me.

Which category does this issue belong to?

C++/Objective-C Rules, Core

What’s the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

Given below example

• bazel build --aspects=//:aspect.bzl%my_aspect //:lib succeeds
• bazel build --aspects=//:aspect.bzl%my_aspect //:main succeeds
• bazel build //:my_aspect_rule_lib succeeds and yields as expected

  DEBUG: <some_path>/aspect.bzl:4:10: <target //:lib, keys:[CcInfo, InstrumentedFilesInfo, 
  OutputGroupInfo]>
  DEBUG: <some_path>/aspect.bzl:21:14: 1
  

• bazel build //:my_aspect_rule_main fails with

  ERROR: <some_path>/BUILD:18:15: in my_aspect_rule rule //:my_aspect_rule_main: 
  Traceback (most recent call last):
  	File "<some_path>/aspect.bzl", line 21, column 18, in _my_aspect_rule_impl
  		print(dep[FileCountInfo].count)
  Error: <target //:main> (rule 'cc_binary') doesn't contain declared provider 'FileCountInfo'
  

---

BUILD file

load("//:aspect.bzl", "my_aspect_rule")

cc_library(
    name = "lib",
    srcs = ["lib.h"],  # empty file, content irrelevant
)

cc_binary(
    name = "main",
    srcs = ["main.cpp"],  # simple main returning 0
)

my_aspect_rule(
    name = "my_aspect_rule_lib",
    deps = [":lib"],
)

my_aspect_rule(
    name = "my_aspect_rule_main",
    deps = [":main"],
)

aspect.bzl

FileCountInfo = provider(fields = {"count": "number of files"})

def _my_aspect_impl(target, ctx):
    print(target)

    count = 0
    for src in ctx.rule.attr.srcs:
        for f in src.files.to_list():
            count = count + 1

    return [FileCountInfo(count = count)]

my_aspect = aspect(
    implementation = _my_aspect_impl,
    required_providers = [CcInfo],
    attr_aspects = [],
)

def _my_aspect_rule_impl(ctx):
    for dep in ctx.attr.deps:
        print(dep[FileCountInfo].count)

my_aspect_rule = rule(
    implementation = _my_aspect_rule_impl,
    attrs = {"deps": attr.label_list(aspects = [my_aspect])},
)

Which operating system are you running Bazel on?

Linux Mint 21.1 Cinnamon

What is the output of bazel info release?

release 6.3.2

If bazel info release returns development version or (@non-git), tell us how you built Bazel.

What’s the output of git remote get-url origin; git rev-parse master; git rev-parse HEAD ?

Is this a regression? If yes, please try to identify the Bazel commit where the bug was introduced.

As far as I can tell this is no regression. Tested this with various Bazel versions in the range 5.1.0 to latest 7.0.0-pre.20230917.3 and all show the same behavior.

However, with Bazel 5.0.0 bazel build //:my_aspect_rule_lib fails as well (invoking the aspect via CLI remains working). This indicates between 5.0.0 and 5.1.0 something was changed/fixed, but cc_binary was forgotten.

Have you found anything relevant by searching the web?

No

Any other information, logs, or outputs that you want to share?

There is a workaround to this. One can add the following to the beginning of the aspect implementation to achieve the desired behavior.

if not CcInfo in target:
   return []