commit 20e0f1ce93e5c82cf1681e57fe670bd778beb113
author Benjamin Peterson <benjamin@python.org> Mon Nov 16 08:13:26 2020 -0800
committer Copybara-Service <copybara-worker@google.com> Mon Nov 16 08:14:48 2020 -0800
tree 6ed945f8685db55149445153b2a6592fda578f18
parent e1c62299ad7fd36c7b0ff570b807558c4065ee8c

Restore target cycle errors to their former grandeur.

In recent years, a frustrating error for Bazel users is the one caused by putting a reverse dependency rather than a package group into a target's visibility attribute. Such a mistake generally resulted in an error like this:
```
BUILD:7:10: in filegroup rule //pkg1:actual_target: cycle in dependency graph:
    //pkg1:actual_target
    //pkg1:dep_with_visibility
.-> //pkg1:actual_target
|   //pkg1:dep_with_visibility
`-- //pkg1:actual_target
This cycle occurred because of a configuration option
```
This was confusing primarily because users don't think of visibility as causing a dependency—see, for instance, https://github.com/bazelbuild/bazel/issues/11945. Additionally, the "This cycle occurred because of a configuration option" hint was not usually accurate or helpful.

That the visibility mistake will be reported as a cycle is a fundamental property of how analysis is mapped onto Skyframe today, but a better hint was certainly possible. In fact, deep within Bazel's bowels there was already code to produce a better message, but it became mostly dormant during the analysis-loading interleaving work of 2017.

This CL removes the "This cycle occurred because of a configuration option" hint completely and restores the old visibility hint when appropriate. The primary code change is to combine ConfiguredTargetCycleReporter and TransitiveTargetCycleReporter to form TargetCycleReporter.

Now, a visibility cycle looks like this:
```
BUILD:2:10: in filegroup rule //pkg1:actual_target: cycle in dependency graph:
    //pkg1:actual_target
    //pkg1:dep_with_visibility
.-> //pkg1:actual_target
|   //pkg1:dep_with_visibility
`-- //pkg1:actual_target
The cycle is caused by a visibility edge from //pkg1:dep_with_visibility to the non-package_group target //pkg1:actual_target. Note that visibility labels are supposed to be package_group targets, which prevents cycles of this form.
```

I humbly include this change in the https://github.com/bazelbuild/bazel/issues/11984 program.

Closes #12272.

PiperOrigin-RevId: 342638902