Overview

Dialyzer is a static analysis tool for Erlang and Elixir that identifies software discrepancies such as type errors, unreachable code, and unnecessary tests.

Configuration Files

dialyzer.ignore-warnings

# Ignore specific warnings
lib/my_module.ex:42:pattern_match_cov

.dialyzer_ignore.exs

[
  {"lib/generated_code.ex", :no_return},
  {~r/lib\/legacy\/.*/, :unknown_function}
]

mix.exs Configuration

def project do
  [
    app: :my_app,
    dialyzer: [
      plt_add_apps: [:mix, :ex_unit],
      plt_core_path: "priv/plts",
      plt_file: {:no_warn, "priv/plts/dialyzer.plt"},
      flags: [:error_handling, :underspecs, :unmatched_returns],
      ignore_warnings: ".dialyzer_ignore.exs",
      list_unused_filters: true
    ]
  ]
end

Common Configuration Options

PLT Management

• plt_add_apps: Additional applications to include in PLT
• plt_core_path: Directory for core PLT files
• plt_file: Custom PLT file location
• plt_add_deps: Include dependencies (:app_tree, :apps_direct, :transitive)

Analysis Flags

• :error_handling - Check error handling
• :underspecs - Warn on under-specified functions
• :unmatched_returns - Warn on unmatched return values
• :unknown - Warn on unknown functions/types
• :overspecs - Warn on over-specified functions

Filter Options

• ignore_warnings: File with warning patterns to ignore
• list_unused_filters: Show unused ignore patterns

Best Practices

1. Incremental PLT Building: Use project-specific PLTs to speed up analysis
2. Gradual Adoption: Start with subset of checks, expand over time
3. CI Integration: Run Dialyzer in continuous integration
4. Type Specs: Add comprehensive @spec annotations
5. Warning Management: Document intentional ignores

Common Patterns

Conditional Analysis

if Mix.env() in [:dev, :test] do
  {:dialyxir, "~> 1.4", only: [:dev, :test], runtime: false}
end

Custom Check Script

#!/bin/bash
mix dialyzer --format github

GitHub Actions Integration

- name: Run Dialyzer
  run: mix dialyzer --format github