### Ensure FirstOne Application Starts

Source: https://github.com/jeremyjh/dialyxir/blob/master/test/fixtures/umbrella/apps/first_one/README.md

Include this in your `mix.exs` file to ensure the FirstOne application is started before your own.

```elixir
def application do
  [applications: [:first_one]]
end
```

--------------------------------

### Ensure SecondOne Starts in Application

Source: https://github.com/jeremyjh/dialyxir/blob/master/test/fixtures/umbrella/apps/second_one/README.md

Add `second_one` to the list of applications in your `mix.exs` file to ensure it starts before your main application.

```elixir
def application do
  [applications: [:second_one]]
end
```

--------------------------------

### Install Dependencies and Compile Project

Source: https://github.com/jeremyjh/dialyxir/blob/master/README.md

After adding Dialyxir to your dependencies, run this command to fetch and compile all project dependencies.

```console
mix do deps.get, deps.compile
```

--------------------------------

### Install Dialyzer PLT and Compile Dependencies

Source: https://github.com/jeremyjh/dialyxir/wiki/Phoenix-Dialyxir-Quickstart

After updating `mix.exs`, run this command to fetch dependencies, compile them, and build the Dialyzer Program Logic Table (PLT).

```Shell
mix do deps.get, deps.compile, dialyzer --plt
```

--------------------------------

### Example Dialyzer Ignore File Content

Source: https://github.com/jeremyjh/dialyxir/blob/master/README.md

Content for a Dialyzer ignore file, specifying string matches for warnings to be suppressed. This example targets specific guard test failures.

```text
Guard test is_binary(_@5::#{'__exception__':='true', '__struct__':=_, _=>_}) can never succeed
Guard test is_atom(_@6::#{'__exception__':='true', '__struct__':=_, _=>_}) can never succeed
```

--------------------------------

### Ignore File using `ignore_file` formatter

Source: https://github.com/jeremyjh/dialyxir/blob/master/README.md

This example demonstrates the output of the `mix dialyzer --format ignore_file` command, which groups warnings by file and warning type for simpler ignore entries.

```elixir
# .dialyzer_ignore.exs
[
  # {file, warning_type}
  {"lib/something.ex", :no_return},
]
```

--------------------------------

### Explain Dialyzer Warnings

Source: https://github.com/jeremyjh/dialyxir/blob/master/README.md

Use the `dialyzer.explain` task to get information about specific Dialyzer warnings. For instance, to learn about the `unmatched_return` warning, run `mix dialyzer.explain unmatched_return`.

```console
mix dialyzer.explain unmatched_return
```

--------------------------------

### Ignore File using `ignore_file_strict` formatter

Source: https://github.com/jeremyjh/dialyxir/blob/master/README.md

This example shows the output of the `mix dialyzer --format ignore_file_strict` command, providing more granular ignore entries that include the specific warning description.

```elixir
# .dialyzer_ignore.exs
[
  # {file, warning_description}
  {"lib/something.ex", "Function init/1 has no local return."},
  {"lib/something.ex", "Function refresh/0 has no local return."},
  {"lib/something.ex", "Function create/2 has no local return."},
  {"lib/something.ex", "Function update/2 has no local return."},
  {"lib/something.ex", "Function delete/1 has no local return."},
]
```

--------------------------------

### Elixir Term Format Ignore File Example

Source: https://github.com/jeremyjh/dialyxir/blob/master/README.md

This snippet shows the various formats accepted in an Elixir term ignore file (`.dialyzer_ignore.exs`). It includes examples for ignoring warnings by short description, warning type, file, or using regex.

```elixir
# .dialyzer_ignore.exs
[
  # {short_description}
  {':0:unknown_function Function :erl_types.t_is_opaque/1/1 does not exist.'},
  # {short_description, warning_type}
  {':0:unknown_function Function :erl_types.t_to_string/1 does not exist.', :unknown_function},
  # {short_description, warning_type, line}
  {':0:unknown_function Function :erl_types.t_to_string/1 does not exist.', :unknown_function, 0},
  # {file, warning_type, line}
  {"lib/dialyxir/pretty_print.ex", :no_return, 100},
  # {file, warning_description}
  {"lib/dialyxir/warning_helpers.ex", "Function :erl_types.t_to_string/1 does not exist."},
  # {file, warning_type}
  {"lib/dialyxir/warning_helpers.ex", :no_return},
  # {file}
  {"lib/dialyxir/warnings/app_call.ex"},
  # regex
  ~r/my_file\.ex.*my_function.*no local return/
]
```

--------------------------------

### Dialyzer PLT Generation with Cache

Source: https://github.com/jeremyjh/dialyxir/blob/master/docs/gitlab_ci.md

This job generates the Dialyzer Program Logic (PLT) file. It depends on the `build-dev` job and uses a cache policy that pulls the existing PLT cache at the start and pushes any updated cache after completion. This is useful for Dialyzer's initial setup.

```yaml
dialyzer-plt:
  stage: check-elixir-types
  needs:
    - build-dev
  cache:
    - key:
        files:
          - .tool-versions
          - mix.lock
      paths:
        - priv/plts
      # Pull cache at start, push updated cache after completion
      policy: pull-push
  script:
    - mix dialyzer --plt
```

--------------------------------

### Configure Dialyzer to Ignore Warnings File in Mix Project

Source: https://github.com/jeremyjh/dialyxir/blob/master/README.md

Specify a file path in the Mix project configuration for Dialyzer to read ignore warnings from. This example points to 'dialyzer.ignore-warnings'.

```elixir
def project do
  [
    app: :my_app,
    version: "0.0.1",
    deps: deps,
    dialyzer: [ignore_warnings: "dialyzer.ignore-warnings"]
  ]
end
```

--------------------------------

### Configure Dialyzer Paths and Flags in Mix Project

Source: https://github.com/jeremyjh/dialyxir/blob/master/README.md

Set additional paths for Dialyzer to search for BEAM files and configure warning flags. This example includes :mnesia for PLT, specific flags, and custom paths.

```elixir
def project do
  [
    app: :my_app,
    version: "0.0.1",
    deps: deps,
    dialyzer: [
      plt_add_apps: [:mnesia],
      flags: [:unmatched_returns, :error_handling, :no_opaque],
      paths: ["_build/dev/lib/my_app/ebin", "_build/dev/lib/foo/ebin"]
    ]
  ]
end
```

--------------------------------

### Run Dialyzer with Specific Warning Flags

Source: https://github.com/jeremyjh/dialyxir/blob/master/README.md

Pass warning flags directly to Dialyzer by appending them to the `mix dialyzer` command. For example, to check for unmatched return values, use `--unmatched_returns`.

```console
mix dialyzer --unmatched_returns
```

--------------------------------

### Configure Dialyzer Flags in Mix Project

Source: https://github.com/jeremyjh/dialyxir/blob/master/README.md

Specify Dialyzer warning flags directly in the Mix project configuration. This example shows how to include flags like '-Wunmatched_returns', :error_handling, and :underspecs.

```elixir
def project do
  [
    app: :my_app,
    version: "0.0.1",
    deps: deps,
    dialyzer: [flags: ["-Wunmatched_returns", :error_handling, :underspecs]]
  ]
end
```

--------------------------------

### Ignore Specific Function Warnings with @dialyzer

Source: https://github.com/jeremyjh/dialyxir/blob/master/README.md

Use the @dialyzer module attribute to suppress warnings for specific functions. This example disables warnings for the 'rollback/1' function.

```elixir
defmodule Myapp.Repo do
  use Ecto.Repo, otp_app: :myapp
  @dialyzer {:nowarn_function, rollback: 1}
end
```

--------------------------------

### Add FirstOne Dependency

Source: https://github.com/jeremyjh/dialyxir/blob/master/test/fixtures/umbrella/apps/first_one/README.md

Add this to your `mix.exs` file to include FirstOne as a project dependency.

```elixir
def deps do
  [{:first_one, "~> 0.1.0"}]
end
```

--------------------------------

### Set Up Elixir Environment in GitHub Actions

Source: https://github.com/jeremyjh/dialyxir/blob/master/docs/github_actions.md

Configures the Erlang/OTP and Elixir versions for the build environment. Specify the desired OTP and Elixir versions using the `otp-version` and `elixir-version` inputs.

```yaml
  - name: Set up Elixir
    id: beam
    uses: erlef/setup-beam@v1
    with:
      otp-version: "24.1" # Define the OTP version
      elixir-version: "1.12.3" # Define the Elixir version
```

--------------------------------

### Run Dialyzer Analysis

Source: https://github.com/jeremyjh/dialyxir/blob/master/README.md

Execute this command from the root of your Mix project to initiate Dialyzer analysis. Dialyxir will automatically create or update the necessary PLT file and compile your project if needed.

```console
mix dialyzer
```

--------------------------------

### List All Known Dialyzer Warnings

Source: https://github.com/jeremyjh/dialyxir/blob/master/README.md

If invoked without arguments, `mix dialyzer.explain` will list all the warnings that Dialyxir is aware of.

```console
mix dialyzer.explain
```

--------------------------------

### Add SecondOne Dependency to Mix.exs

Source: https://github.com/jeremyjh/dialyxir/blob/master/test/fixtures/umbrella/apps/second_one/README.md

Add this to your `mix.exs` file to include `second_one` as a project dependency.

```elixir
def deps do
  [{:second_one, "~> 0.1.0"}]
end
```

--------------------------------

### Add Runtime Dependencies to Applications List

Source: https://github.com/jeremyjh/dialyxir/wiki/Upgrading-to-0.4

If your project has runtime dependencies on Elixir libraries like `:eex`, ensure they are included in your `applications` list in `mix.exs` to avoid warnings.

```elixir
def application do
  [applications: [:logger, :eex, :public_key]]
end
```

--------------------------------

### Run Dialyzer Analysis in GitHub Actions

Source: https://github.com/jeremyjh/dialyxir/blob/master/docs/github_actions.md

Executes Dialyzer analysis on the project. It's recommended to use both `--format github` for PR annotations and `--format dialyxir` for detailed logs in the GitHub Actions output.

```yaml
  - name: Run dialyzer
    # Two formats are included for ease of debugging and it is lightly recommended to use both, see https://github.com/jeremyjh/dialyxir/issues/530 for reasoning
    # --format github is helpful to print the warnings in a way that GitHub understands and can place on the /files page of a PR
    # --format dialyxir allows the raw GitHub actions logs to be useful because they have the full warning printed
    run: mix dialyzer --format github --format dialyxir
```

--------------------------------

### Configure Dialyxir PLT Dependencies

Source: https://github.com/jeremyjh/dialyxir/blob/master/README.md

Customize PLT dependency inclusion and exclusion. Use `:apps_direct` for direct OTP dependencies, `:plt_add_apps` to add specific applications, and `:plt_ignore_apps` to exclude unwanted dependencies. This is useful for managing memory issues with large dependency trees.

```elixir
def project do
  [
    app: :my_app,
    version: "0.0.1",
    deps: deps,
    dialyzer: [
      plt_add_deps: :apps_direct,
      plt_add_apps: [:wx],
      plt_ignore_apps: [:mnesia]
    ]
  ]
end
```

--------------------------------

### Checkout Source Code in GitHub Actions

Source: https://github.com/jeremyjh/dialyxir/blob/master/docs/github_actions.md

This step checks out the source code from the repository into the GitHub Actions runner.

```yaml
steps:
  - name: Check out source
    uses: actions/checkout@v2
```

--------------------------------

### Configure Dialyzer in mix.exs

Source: https://github.com/jeremyjh/dialyxir/wiki/Phoenix-Dialyxir-Quickstart

Configure Dialyzer options within the `project` function in `mix.exs`. `plt_add_deps: :transitive` helps Dialyzer build a more comprehensive program. 

```Elixir
dialyzer: [plt_add_deps: :transitive]
```

--------------------------------

### Add Dev-Only Dependencies to PLT

Source: https://github.com/jeremyjh/dialyxir/wiki/Upgrading-to-0.4

For development-only runtime dependencies such as `:phoenix_live_reload`, use `plt_add_apps:` in your `mix.exs` project configuration to include them in the PLT without adding them to the main `:applications` list.

```elixir
def project do
 [ app: :my_app,
  version: "0.0.1",
  deps: deps,
  dialyzer: [plt_add_apps: [:phoenix_live_reload]]
 ]
end
```

--------------------------------

### CircleCI Configuration for Elixir Build with Dialyzer

Source: https://github.com/jeremyjh/dialyxir/blob/master/docs/circleci.md

This configuration sets up a CircleCI build job for an Elixir project. It utilizes Docker for the build environment and includes steps for caching Dialyzer's PLT files to speed up analysis. The caching strategy is based on the Elixir/Erlang versions and the project's mix.lock file hash.

```yaml
version: 2

jobs:
  build:
    docker:
      - image: cimg/elixir:1.14

    steps:
      - checkout

      # Compile steps omitted for simplicity

      # Cache key based on Erlang/Elixir version and the mix.lock hash
      - run:
          name: "Save Elixir and Erlang version for PLT caching"
          command: echo "$ELIXIR_VERSION $ERLANG_VERSION" > .elixir_otp_version

      - restore_cache:
          name: "Restore PLT cache"
          keys:
            - plt-{{ arch }}-{{ checksum ".elixir_otp_version" }}-{{ checksum "mix.lock" }}

      - run:
          name: "Create PLTs"
          command: mix dialyzer --plt

      - save_cache:
          name: "Save PLT cache"
          key: plt-{{ arch }}-{{ checksum ".elixir_otp_version" }}-{{ checksum "mix.lock" }}
          paths: "priv/plts"

      - run:
          name: "Run dialyzer"
          command: mix dialyzer

```

--------------------------------

### Create PLTs if Cache Not Found

Source: https://github.com/jeremyjh/dialyxir/blob/master/docs/github_actions.md

This step conditionally creates the Dialyzer PLTs using `mix dialyzer --plt` only if the cache was not found in the previous step. This ensures PLTs are available for analysis.

```yaml
  - name: Create PLTs
    if: steps.plt_cache.outputs.cache-hit != 'true'
    run: mix dialyzer --plt
```

--------------------------------

### Configure Dialyxir to Disable Umbrella Project Detection

Source: https://github.com/jeremyjh/dialyxir/blob/master/README.md

This Elixir configuration demonstrates how to set the `no_umbrella` flag to `true` in `mix.exs` to treat a project as non-umbrella, even if a lockfile exists in a parent folder.

```elixir
dialyzer: [
  no_umbrella: true
]
```

--------------------------------

### Configure Dialyzer PLT File Path in mix.exs

Source: https://github.com/jeremyjh/dialyxir/blob/master/README.md

Specify a custom path for the project-level PLT file within the `mix.exs` configuration. This is useful for managing PLT files in CI environments.

```elixir
def project do
  [
    ...
    dialyzer: [
      # Put the project-level PLT in the priv/ directory (instead of the default _build/ location)
      plt_file: {:no_warn, "priv/plts/project.plt"}

      # The above is equivalent to:
      # plt_local_path: "priv/plts/project.plt"

      # You could also put the core Erlang/Elixir PLT into the priv/ directory like so:
      # plt_core_path: "priv/plts/core.plt"
    ]
  ]
end
```

--------------------------------

### Configure Dialyxir to List Unused Filters

Source: https://github.com/jeremyjh/dialyxir/blob/master/README.md

This Elixir configuration shows how to enable the listing of unused filters by setting the `:list_unused_filters` option to `true` in `mix.exs`. This can also be set via the command line.

```elixir
dialyzer: [
  ignore_warnings: "ignore_test.exs",
  list_unused_filters: true
]
```

--------------------------------

### Elixir Build Job with Dependency Caching

Source: https://github.com/jeremyjh/dialyxir/blob/master/docs/gitlab_ci.md

This job compiles Elixir dependencies and the project itself. It uses a cache strategy based on `.tool-versions` and `mix.lock` files to store and retrieve `deps/` and `_build/dev` directories, speeding up subsequent builds.

```yaml
build-dev:
  stage: compile
  cache:
    - key:
        files:
          - .tool-versions
          - mix.lock
      paths:
        - deps/
        - _build/dev
      policy: pull-push
  script:
    - mix do deps.get, compile
```

--------------------------------

### Ignore PLT Files in .gitignore

Source: https://github.com/jeremyjh/dialyxir/blob/master/README.md

Add patterns to your `.gitignore` file to prevent Dialyzer's PLT files and their hashes from being committed to version control.

```shell
# .gitignore
/priv/plts/*.plt
/priv/plts/*.plt.hash
```

--------------------------------

### Silence Ecto.Repo rollback warning

Source: https://github.com/jeremyjh/dialyxir/wiki/Phoenix-Dialyxir-Quickstart

Add the `@dialyzer` attribute to suppress the 'Function rollback/1 has no local return' warning emitted by Ecto.Repo.

```Elixir
defmodule Myapp.Repo do
  use Ecto.Repo, otp_app: :myapp
  @dialyzer {:nowarn_function, rollback: 1}
end
```

--------------------------------

### Silence Phoenix.View pattern match warning

Source: https://github.com/jeremyjh/dialyxir/wiki/Phoenix-Dialyxir-Quickstart

Add the `@dialyzer` attribute to the `Phoenix.View` module to prevent warnings about patterns that can never match, like `{'safe', _@2}` not matching a `binary()`.

```Elixir
defmodule Myapp.PageView do
  use Chat.Web, :view
  @dialyzer :no_match
end
```

--------------------------------

### Add Dialyxir to mix.exs dependencies

Source: https://github.com/jeremyjh/dialyxir/wiki/Phoenix-Dialyxir-Quickstart

Add Dialyxir to your project's development dependencies in `mix.exs`. This ensures it's only compiled and available in development environments.

```Elixir
{:dialyxir, "~> 0.5.0", only: [:dev], runtime: false}
```

--------------------------------

### Silence Phoenix.Router call warning

Source: https://github.com/jeremyjh/dialyxir/wiki/Phoenix-Dialyxir-Quickstart

In newer Phoenix projects (e.g., Elixir 1.8.1, Phoenix 1.4.0), a warning about `Function call/2 has no local return` in `Phoenix.Router` may appear. This snippet shows how to suppress it.

```Elixir
lib/phoenix/router.ex:2: Function call/2 has no local return
```

--------------------------------

### Silence Phoenix.Presence function warnings

Source: https://github.com/jeremyjh/dialyxir/wiki/Phoenix-Dialyxir-Quickstart

For projects using `Phoenix.Presence`, add this `@dialyzer` attribute to each presence module to suppress warnings about functions like `init`, `track`, and `update` not having local returns.

```Elixir
@dialyzer [
  {:nowarn_function, 'init': 1},
  {:nowarn_function, 'track': 3},
  {:nowarn_function, 'track': 4},
  {:nowarn_function, 'update': 3},
  {:nowarn_function, 'update': 4},
  ]
```

--------------------------------

### Dialyzer Type Checking with Cache Policy

Source: https://github.com/jeremyjh/dialyxir/blob/master/docs/gitlab_ci.md

This job performs the actual Dialyzer type check. It depends on the `dialyzer-plt` job and uses a cache policy that only pulls the PLT cache. It does not push any updates, as the PLT file is assumed to be generated and sufficient for the check.

```yaml
dialyzer-check:
  stage: check-elixir-types
  needs:
    - dialyzer-plt
  cache:
    - key:
        files:
          - .tool-versions
          - mix.lock
      paths:
        - priv/plts
      # Pull cache at start, don't push cache after completion
      policy: pull
  script:
    - mix dialyzer --format short
```

--------------------------------

### Save PLT Cache in GitHub Actions

Source: https://github.com/jeremyjh/dialyxir/blob/master/docs/github_actions.md

Saves the newly created PLT cache to the GitHub Actions cache. This step is separated from the restore step to ensure the cache is saved even if the Dialyzer analysis fails. It uses the same cache key as the restore step.

```yaml
  - name: Save PLT cache
    id: plt_cache_save
    uses: actions/cache/save@v3
    if: steps.plt_cache.outputs.cache-hit != 'true'
    with:
      key:
        plt-${{ runner.os }}-${{ steps.beam.outputs.otp-version }}-${{ steps.beam.outputs.elixir-version }}-${{ hashFiles('**/mix.lock') }}
      path:
        priv/plts
```

--------------------------------

### Restore PLT Cache in GitHub Actions

Source: https://github.com/jeremyjh/dialyxir/blob/master/docs/github_actions.md

Restores the compiled Dialyzer PLT (Persistent Lookaside Table) cache using the GitHub Actions cache mechanism. The cache key is generated based on the runner OS, Erlang/Elixir versions, and the `mix.lock` file hash. This speeds up subsequent runs by avoiding recompilation.

```yaml
  - name: Restore PLT cache
    id: plt_cache
    uses: actions/cache/restore@v3
    with:
      key: |
        plt-${{ runner.os }}-${{ steps.beam.outputs.otp-version }}-${{ steps.beam.outputs.elixir-version }}-${{ hashFiles('**/mix.lock') }}
      restore-keys: |
        plt-${{ runner.os }}-${{ steps.beam.outputs.otp-version }}-${{ steps.beam.outputs.elixir-version }}-
      path:
        priv/plts
```

--------------------------------

### Silence Gettext macro warnings

Source: https://github.com/jeremyjh/dialyxir/wiki/Phoenix-Dialyxir-Quickstart

Use the `@dialyzer` attribute to suppress warnings related to Gettext macros, such as type mismatches in `dgettext` and `dngettext` functions. This is particularly useful for older Elixir versions with known bugs.

```Elixir
@dialyzer [{:nowarn_function, 'MACRO-dgettext': 3},
           {:nowarn_function, 'MACRO-dgettext': 4},
           {:nowarn_function, 'MACRO-dngettext': 5},
           {:nowarn_function, 'MACRO-dngettext': 6},
          ]
```

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