Dialyzer error: Old PLT file

Questions / Help
1

I’m working with a team that are running (relatively) old versions of Elixir and Erlang. Last month I added dialyzer, via dialyxir (can never spell that) to their build. Today we are running into an issue:

:dialyzer.run error: Old PLT file /apps/[redacted]/priv/plts/application.plt

The build is on Azure. The PLTs are cached using Azure Pipeline caching (here if you want to know but I wouldn’t if I could avoid it).

Dialyxir config is

  defp dialyzer do
    [
      plt_add_apps: [:mix, :ex_insights],
      plt_file: {:no_warn, "priv/plts/application.plt"},
      ignore_warnings: "dialyzer.ignore_warnings"
    ]
  end

The plts are excluded from source control.

Versions:

elixir 1.14.2-otp-25
erlang 25.3.2.6

I know I can fix the issue by invalidating the cache but I would like to understand how it happened in the first place. The only thing I’ve been able to find is this somewhat cryptic Erlang mailing list q&a. Old PLT file? .

The checking is going on here which looks like there is some discrepancy between an internally held hash in the PLT and the file contents.

Thoughts?

2

Here is the place in code where this error is raised: otp/lib/dialyzer/src/dialyzer_cplt.erl at 53ffb6a1363180ec67c36e3baa9745ee73e7b5a3 · erlang/otp · GitHub

I cannot figure out though what the code tries to accomplish, it seems there is some kind of file tracking involved.

Does this happen after invalidating the cache?

3

I did link to that in my question :wink:

I am about to invalidate the cache. It definitely doesn not happen locally.

[edit s/no/not/]

1 Like
4

NVM, my bad, I’ve noticed only the mail listing link.

My assumption is that the PLT format is somehow versioned and you upgraded dialyzer version along the way. I would say that if invalidating the cache fixes the situation, then this issue falls most probably on some weird initial setup.

5

Yeah, the link was pretty subtle. It looks like the PLT is an erlang record, stored as a binary term which contains a version and an MD5 hash and if hash does not agree with a recomputed hash then it is an old plt. I don’t get it. ¯\(°_o)/¯☕️

6

Still not solved, but I have not spent a ton of time trying to dig into the Erlang dialyzer code. Some more context though.

This is not a single plt file becoming somehow corrupt. Azure Pipelines being Azure Pipelines, caching is isolated to a specific branch. This error was occurring across multiple PR builds. Also the main build, which uses a different cache key, also got the error. Each PLT became old on the 7th of Jan.

As mentioned we’re using dialyxir . Briefly looking at the output it checks that the plt is up to date before running dialyzer with checking disabled .

So the output looks like

Checking PLT...
[(redacted the list of applications), ...]
PLT is up to date!
ignore_warnings: dialyzer.ignore_warnings

Starting Dialyzer
[
  check_plt: false,
  init_plt: '(redacted)/priv/plts/application.plt',
  files: [(redacted the list of files)],
  warnings: [:unknown]
]
:dialyzer.run error: Old PLT file (redacted)/priv/plts/application.plt

Also I have checked and at that time:

  • there was no change to any dependencies
  • no change to the dialyzer config
  • no change to Elixir and Erlang versions

Even if there were, I don’t see how it could have affected multiple pipelines given the cache isolation.

7

Did invalidating of cache help?

1 Like
8

Yes, thanks. Building and caching a new plt worked.

1 Like