cabal build fails with warning, return code 0 when failing to build dependency documentation

[robx]

Describe the bug

When calling cabal build on a project with:

• a dependency some-lib with malformatted haddock comments
• a cabal.project that asks for documentation to be built for all packages

the command fails pretty unclearly with a "Warning" and zero exit code.

To Reproduce
(I had a pretty messy concrete example, this is breaking it down to what
I believe is a minimal case, but I haven't actually verified this live.)

$ cd /src/some-lib
$ cabal v2-haddock
...
cabal: Failed to build documentation for some-lib-0.1
$ cd /src/main-proj
$ cat cabal.project.local
package *
  documentation: true
$ cabal v2-build
In order, the following will be built (use -v for more details):
 - some-lib-0.1 (lib:some-lib) (requires build)
 - main-proj-0.1 (lib) (first run)
Starting     some-lib-0.1 (all, legacy fallback)
Building     some-lib-0.1 (all, legacy fallback)
Haddock      some-lib-0.1 (all, legacy fallback)
Warning: Failed to build documentation for some-lib-0.1 (which is required by main-proj-0.1).
$ echo $?
0

Expected behavior

cabal build should fail explicitly with an error. I.e., output Error: instead of Warning: , and exit with a non-zero code.

System information

• Operating system: macos
• cabal version 3.4.0.0
• ghc 8.10.2

[Mikolaj]

This seems similar to #5974 (but you are getting exit code 0, not 1) and other issues mentioned there.

[ulysses4ever]

Since #5974 has been solved, I wonder if this is too. Although, the error code party is a bit worrying to me: think this may be be a different issue. Someone need to check!

[ulysses4ever]

I fail to repro it because no matter what I try Haddock succeeds with warnings rather than fail. Any ideas for things that would hard-fail Haddock are welcome.

[ulysses4ever]

Ok, I got a reproducer: https://github.com/ulysses4ever/cabal-t7517 The bug is still here, on today's master.