Stale Struct Types Lead to Dialyzer Warnings

[aj-foster]

Hello 👋🏼 This could be ElixirLS or dialyzer related. Any help is appreciated. 🙂

Environment

• Elixir & Erlang versions (elixir --version):
  • Project: 1.12.3 (compiled with Erlang/OTP 24)
  • ElixirLS compiled with Elixir 1.12.3 and erlang 24
• Elixir Language Server version: v0.9.0
• Operating system: macOS 12.4
• Editor or IDE name (e.g. Emacs/VSCode): VSCode
• Editor Plugin/LSP Client name and version: ElixirLS for VSCode, v0.9.0 (with custom compiled ElixirLS)

Current behavior

Dialyzer occasionally ignores changes to a struct type %__MODULE__{...} when dialyzing other modules. For example, if I add a new field to struct type %A{}, and then access that field in another module B, dialyzer warns that the new field "cannot exist in a map of type...".

ElixirLS logs when saving the new field to struct %A{}

MIX_ENV: test
MIX_TARGET: host
Compiling 39 files (.ex)
[Info  - 10:29:59 AM] Compile took 3196 milliseconds
[Info  - 10:29:59 AM] [ElixirLS WorkspaceSymbols] Updating index...
MIX_ENV: test
MIX_TARGET: host
[Info  - 10:30:00 AM] Compile took 895 milliseconds
[Info  - 10:30:00 AM] [ElixirLS Dialyzer] Checking for stale beam files
[Info  - 10:30:00 AM] [ElixirLS WorkspaceSymbols] 5 modules need reindexing
[Info  - 10:30:00 AM] [ElixirLS WorkspaceSymbols] 0 callbacks added to index
[Info  - 10:30:00 AM] [ElixirLS WorkspaceSymbols] 5 modules added to index
[Info  - 10:30:00 AM] [ElixirLS WorkspaceSymbols] 6 types added to index
[Info  - 10:30:00 AM] [ElixirLS WorkspaceSymbols] 91 functions added to index
[Info  - 10:30:00 AM] [ElixirLS Dialyzer] Found 72 changed files in 248 milliseconds
[Info  - 10:30:01 AM] [ElixirLS Dialyzer] Analyzing 21 modules: [...unrelated modules omitted..., B, A]
[Info  - 10:30:02 AM] [ElixirLS Dialyzer] Analysis finished in 1439 milliseconds
[Info  - 10:30:02 AM] Dialyzer analysis is up to date
[Info  - 10:30:03 AM] [ElixirLS Dialyzer] Writing manifest...
[Info  - 10:30:04 AM] [ElixirLS Dialyzer] Done writing manifest in 2058 milliseconds.

ElixirLS logs when saving module B, which accesses the new field of type %A{}

MIX_ENV: test
MIX_TARGET: host
Compiling 38 files (.ex)
[Info  - 10:30:19 AM] Compile took 3210 milliseconds
[Info  - 10:30:19 AM] [ElixirLS Dialyzer] Checking for stale beam files
[Info  - 10:30:19 AM] [ElixirLS WorkspaceSymbols] Updating index...
[Info  - 10:30:20 AM] [ElixirLS WorkspaceSymbols] 1 modules need reindexing
[Info  - 10:30:20 AM] [ElixirLS WorkspaceSymbols] 0 callbacks added to index
[Info  - 10:30:20 AM] [ElixirLS WorkspaceSymbols] 0 types added to index
[Info  - 10:30:20 AM] [ElixirLS WorkspaceSymbols] 1 modules added to index
[Info  - 10:30:20 AM] [ElixirLS WorkspaceSymbols] 57 functions added to index
[Info  - 10:30:20 AM] [ElixirLS Dialyzer] Found 41 changed files in 345 milliseconds
[Info  - 10:30:20 AM] [ElixirLS Dialyzer] Analyzing 20 modules: [...unrelated modules omitted..., B]
[Info  - 10:30:21 AM] [ElixirLS Dialyzer] Analysis finished in 1461 milliseconds
[Info  - 10:30:22 AM] Dialyzer analysis is up to date
[Info  - 10:30:23 AM] [ElixirLS Dialyzer] Writing manifest...
[Info  - 10:30:24 AM] [ElixirLS Dialyzer] Done writing manifest in 1986 milliseconds.

Dialyzer warning

A key of type 
          'test' cannot exist in a map of type 
          #{'__meta__' := _,
            '__struct__' := 'A',
            ...all fields except "test"...
          }

(No seemingly relevant console messages in the VSCode devtools. Only the usual "starting client" message.)

Heavily abbreviated LSP trace when saving module A

[Trace - 10:42:56 AM] Sending request 'textDocument/formatting - (268)'.
Params: {
    "textDocument": {
        "uri": "file:///path/to/a.ex"
    },
    "options": {
        "tabSize": 2,
        "insertSpaces": true
    }
}
[Trace - 10:42:56 AM] Received response 'textDocument/formatting - (268)' in 10ms.
Result: []
[Trace - 10:42:56 AM] Sending notification 'textDocument/didSave'.
Params: {
"textDocument": {
"uri": "file:///path/to/a.ex",
"version": 92
},
"text": ...
}
[omitting traces for emitting log messages shown in the copies above]
[Trace - 10:42:56 AM] Sending notification 'workspace/didChangeWatchedFiles'.
Params: {
"changes": [
{
"uri": "file:///path/to/a.ex",
"type": 2
},
{
"uri": "file:///path/to/a.ex",
"type": 2
}
]
}
[Trace - 10:42:59 AM] Sending notification 'workspace/didChangeWatchedFiles'.
Params: {
"changes": [
{
"uri": "file:///path/to/b.ex",
"type": 2
},
...other files that reference A...
Note: every file appears twice.
]
}
[Trace - 10:43:00 AM] Received notification 'textDocument/publishDiagnostics'.
...for every file in the project that currently has a dialyzer warning, including module B...
[Info  - 10:43:01 AM] [ElixirLS Dialyzer] Checking for stale beam files
[Trace - 10:43:01 AM] Received notification 'textDocument/publishDiagnostics'.
...for every file in the project that currently has a dialyzer warning, including module B...
[Info  - 10:43:02 AM] [ElixirLS Dialyzer] Analysis finished in 1385 milliseconds
[Trace - 10:43:02 AM] Received notification 'textDocument/publishDiagnostics'.
...for every file in the project that currently has a dialyzer warning, including module B...
...
[Info  - 10:43:03 AM] Dialyzer analysis is up to date
[Info  - 10:43:04 AM] [ElixirLS Dialyzer] Writing manifest...
[Info  - 10:43:05 AM] [ElixirLS Dialyzer] Done writing manifest in 1961 milliseconds.

Heavily abbreviated LSP trace when saving module B

[Trace - 10:59:54 AM] Sending request 'textDocument/formatting - (315)'.
Params: {
    "textDocument": {
        "uri": "file:///path/to/b.ex"
    },
    "options": {
        "tabSize": 2,
        "insertSpaces": true
    }
}
[Trace - 10:59:54 AM] Received response 'textDocument/formatting - (315)' in 71ms.
Result: []
[Trace - 10:59:54 AM] Sending notification 'textDocument/didSave'.
Params: {
"textDocument": {
"uri": "file:///path/to/b.ex",
"version": 43
},
"text": ...
}
[omitting traces for emitting log messages shown in the copies above]
MIX_TARGET: host
[Trace - 10:59:54 AM] Sending notification 'workspace/didChangeWatchedFiles'.
Params: {
"changes": [
{
"uri": "file:///path/to/b.ex",
"type": 2
},
{
"uri": "file:///path/to/b.ex",
"type": 2
}
]
}
[Trace - 10:59:57 AM] Received notification 'textDocument/publishDiagnostics'.
...for every file in the project that currently has a dialyzer warning, including module B...
Note: no new warning, yet.
[Info  - 10:59:58 AM] [ElixirLS Dialyzer] Found 41 changed files in 366 milliseconds
...
[Info  - 11:00:00 AM] [ElixirLS Dialyzer] Analysis finished in 1470 milliseconds
[Trace - 11:00:00 AM] Received notification 'textDocument/publishDiagnostics'.
...for every file in the project that currently has a dialyzer warning, including module B...
Note: includes new warning.
[Info  - 11:00:00 AM] Dialyzer analysis is up to date
[Info  - 11:00:01 AM] [ElixirLS Dialyzer] Writing manifest...
[Info  - 11:00:02 AM] [ElixirLS Dialyzer] Done writing manifest in 2093 milliseconds.

Steps to reproduce:

Anecdotally, I only encounter this issue in larger projects, at least the size of a Phoenix app with a few schemas (which unfortunately I cannot make public).

• Create a module A with use Ecto.Schema and some number of fields defined.
• Create a module B with a function that references %A{}, perhaps pattern matching a value.
• Allow dialyzer to write out a manifest.
• In A add a new field to the schema.
• In B, attempt to use the new field, e.g. %A{a | new_field: "value"}
• Observe dialyzer warning for the usage of the new field.

Other Notes

• I usually have a canonical type t :: %__MODULE__{} defined when this occurs.
• Manually deleting the BEAM file for module A in .elixir_ls/build and .elixir_ls/dialyzer_tmp, and then reloading the window, does nothing. The BEAM file is not regenerated until another change is made to A.
• Deleting .elixir_ls and reloading, as you might imagine, fixes the issue.
• I've experienced this issue over a wide range of Elixir/OTP versions (both the versions running the project, and the versions used to compile ElixirLS).

Expected behavior

Dialyzer should recognize the change to type %A{}.

[lukaszsamson]

OTP 26 is going to improve incremental dialyzer

[lukaszsamson]

This should help https://github.com/elixir-lsp/elixir-ls/issues/742. Otherwise we can't really fix that

[lukaszsamson]

This issue will be resolved on OTP 26+ in the upcoming 0.21 release. This release switches dialyzer backend to builtin OTP incremental mode. Incremental dialyzer mode is much better at tracking dependencies. I tested it and the scenario no longer results in persisting warnings. Unfortunately it is much slower