Claudio Ortolina
90f125d126
usage_rules 1.0.2 => 1.1.0 Fixes a bug that would cause skipping of included subrules.
867 lines
37 KiB
Markdown
867 lines
37 KiB
Markdown
# Project architecture
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[Project architecture](architecture.md)
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<!-- usage-rules-start -->
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<!-- usage_rules-start -->
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## usage_rules usage
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_A config-driven dev tool for Elixir projects to manage AGENTS.md files and agent skills from dependencies_
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## Using Usage Rules
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Many packages have usage rules, which you should *thoroughly* consult before taking any
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action. These usage rules contain guidelines and rules *directly from the package authors*.
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They are your best source of knowledge for making decisions.
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## Modules & functions in the current app and dependencies
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When looking for docs for modules & functions that are dependencies of the current project,
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or for Elixir itself, use `mix usage_rules.docs`
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```
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# Search a whole module
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mix usage_rules.docs Enum
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# Search a specific function
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mix usage_rules.docs Enum.zip
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# Search a specific function & arity
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mix usage_rules.docs Enum.zip/1
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```
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## Searching Documentation
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You should also consult the documentation of any tools you are using, early and often. The best
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way to accomplish this is to use the `usage_rules.search_docs` mix task. Once you have
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found what you are looking for, use the links in the search results to get more detail. For example:
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```
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# Search docs for all packages in the current application, including Elixir
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mix usage_rules.search_docs Enum.zip
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# Search docs for specific packages
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mix usage_rules.search_docs Req.get -p req
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# Search docs for multi-word queries
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mix usage_rules.search_docs "making requests" -p req
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# Search only in titles (useful for finding specific functions/modules)
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mix usage_rules.search_docs "Enum.zip" --query-by title
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```
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<!-- usage_rules-end -->
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<!-- usage_rules:elixir-start -->
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## usage_rules:elixir usage
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# Elixir Core Usage Rules
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## Pattern Matching
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- Use pattern matching over conditional logic when possible
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- Prefer to match on function heads instead of using `if`/`else` or `case` in function bodies
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- `%{}` matches ANY map, not just empty maps. Use `map_size(map) == 0` guard to check for truly empty maps
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## Error Handling
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- Use `{:ok, result}` and `{:error, reason}` tuples for operations that can fail
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- Avoid raising exceptions for control flow
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- Use `with` for chaining operations that return `{:ok, _}` or `{:error, _}`
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## Common Mistakes to Avoid
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- Elixir has no `return` statement, nor early returns. The last expression in a block is always returned.
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- Don't use `Enum` functions on large collections when `Stream` is more appropriate
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- Avoid nested `case` statements - refactor to a single `case`, `with` or separate functions
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- Don't use `String.to_atom/1` on user input (memory leak risk)
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- Lists and enumerables cannot be indexed with brackets. Use pattern matching or `Enum` functions
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- Prefer `Enum` functions like `Enum.reduce` over recursion
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- When recursion is necessary, prefer to use pattern matching in function heads for base case detection
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- Using the process dictionary is typically a sign of unidiomatic code
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- Only use macros if explicitly requested
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- There are many useful standard library functions, prefer to use them where possible
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## Function Design
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- Use guard clauses: `when is_binary(name) and byte_size(name) > 0`
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- Prefer multiple function clauses over complex conditional logic
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- Name functions descriptively: `calculate_total_price/2` not `calc/2`
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- Predicate function names should not start with `is` and should end in a question mark.
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- Names like `is_thing` should be reserved for guards
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## Data Structures
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- Use structs over maps when the shape is known: `defstruct [:name, :age]`
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- Prefer keyword lists for options: `[timeout: 5000, retries: 3]`
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- Use maps for dynamic key-value data
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- Prefer to prepend to lists `[new | list]` not `list ++ [new]`
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## Mix Tasks
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- Use `mix help` to list available mix tasks
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- Use `mix help task_name` to get docs for an individual task
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- Read the docs and options fully before using tasks
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## Testing
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- Run tests in a specific file with `mix test test/my_test.exs` and a specific test with the line number `mix test path/to/test.exs:123`
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- Limit the number of failed tests with `mix test --max-failures n`
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- Use `@tag` to tag specific tests, and `mix test --only tag` to run only those tests
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- Use `assert_raise` for testing expected exceptions: `assert_raise ArgumentError, fn -> invalid_function() end`
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- Use `mix help test` to for full documentation on running tests
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## Debugging
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- Use `dbg/1` to print values while debugging. This will display the formatted value and other relevant information in the console.
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<!-- usage_rules:elixir-end -->
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<!-- usage_rules-start -->
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## usage_rules usage
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_A config-driven dev tool for Elixir projects to manage AGENTS.md files and agent skills from dependencies_
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## Using Usage Rules
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Many packages have usage rules, which you should *thoroughly* consult before taking any
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action. These usage rules contain guidelines and rules *directly from the package authors*.
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They are your best source of knowledge for making decisions.
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||
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## Modules & functions in the current app and dependencies
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||
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When looking for docs for modules & functions that are dependencies of the current project,
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or for Elixir itself, use `mix usage_rules.docs`
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```
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# Search a whole module
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mix usage_rules.docs Enum
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# Search a specific function
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mix usage_rules.docs Enum.zip
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# Search a specific function & arity
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mix usage_rules.docs Enum.zip/1
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```
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## Searching Documentation
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You should also consult the documentation of any tools you are using, early and often. The best
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way to accomplish this is to use the `usage_rules.search_docs` mix task. Once you have
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found what you are looking for, use the links in the search results to get more detail. For example:
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```
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# Search docs for all packages in the current application, including Elixir
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mix usage_rules.search_docs Enum.zip
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# Search docs for specific packages
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mix usage_rules.search_docs Req.get -p req
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# Search docs for multi-word queries
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mix usage_rules.search_docs "making requests" -p req
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# Search only in titles (useful for finding specific functions/modules)
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mix usage_rules.search_docs "Enum.zip" --query-by title
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```
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<!-- usage_rules-end -->
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<!-- usage_rules:otp-start -->
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## usage_rules:otp usage
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# OTP Usage Rules
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## GenServer Best Practices
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- Keep state simple and serializable
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- Handle all expected messages explicitly
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- Use `handle_continue/2` for post-init work
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- Implement proper cleanup in `terminate/2` when necessary
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## Process Communication
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- Use `GenServer.call/3` for synchronous requests expecting replies
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- Use `GenServer.cast/2` for fire-and-forget messages.
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- When in doubt, use `call` over `cast`, to ensure back-pressure
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- Set appropriate timeouts for `call/3` operations
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## Fault Tolerance
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- Set up processes such that they can handle crashing and being restarted by supervisors
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- Use `:max_restarts` and `:max_seconds` to prevent restart loops
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## Task and Async
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- Use `Task.Supervisor` for better fault tolerance
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- Handle task failures with `Task.yield/2` or `Task.shutdown/2`
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- Set appropriate task timeouts
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- Use `Task.async_stream/3` for concurrent enumeration with back-pressure
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<!-- usage_rules:otp-end -->
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<!-- phoenix:ecto-start -->
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## phoenix:ecto usage
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## Ecto Guidelines
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- **Always** preload Ecto associations in queries when they'll be accessed in templates, ie a message that needs to reference the `message.user.email`
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- Remember `import Ecto.Query` and other supporting modules when you write `seeds.exs`
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- `Ecto.Schema` fields always use the `:string` type, even for `:text`, columns, ie: `field :name, :string`
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- `Ecto.Changeset.validate_number/2` **DOES NOT SUPPORT the `:allow_nil` option**. By default, Ecto validations only run if a change for the given field exists and the change value is not nil, so such as option is never needed
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- You **must** use `Ecto.Changeset.get_field(changeset, :field)` to access changeset fields
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- Fields which are set programatically, such as `user_id`, must not be listed in `cast` calls or similar for security purposes. Instead they must be explicitly set when creating the struct
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- **Always** invoke `mix ecto.gen.migration migration_name_using_underscores` when generating migration files, so the correct timestamp and conventions are applied
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<!-- phoenix:ecto-end -->
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<!-- phoenix:elixir-start -->
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## phoenix:elixir usage
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## Elixir guidelines
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- Elixir lists **do not support index based access via the access syntax**
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**Never do this (invalid)**:
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i = 0
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mylist = ["blue", "green"]
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mylist[i]
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Instead, **always** use `Enum.at`, pattern matching, or `List` for index based list access, ie:
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i = 0
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mylist = ["blue", "green"]
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Enum.at(mylist, i)
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- Elixir variables are immutable, but can be rebound, so for block expressions like `if`, `case`, `cond`, etc
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you *must* bind the result of the expression to a variable if you want to use it and you CANNOT rebind the result inside the expression, ie:
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# INVALID: we are rebinding inside the `if` and the result never gets assigned
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if connected?(socket) do
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socket = assign(socket, :val, val)
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end
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# VALID: we rebind the result of the `if` to a new variable
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socket =
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if connected?(socket) do
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assign(socket, :val, val)
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end
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- **Never** nest multiple modules in the same file as it can cause cyclic dependencies and compilation errors
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- **Never** use map access syntax (`changeset[:field]`) on structs as they do not implement the Access behaviour by default. For regular structs, you **must** access the fields directly, such as `my_struct.field` or use higher level APIs that are available on the struct if they exist, `Ecto.Changeset.get_field/2` for changesets
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- Elixir's standard library has everything necessary for date and time manipulation. Familiarize yourself with the common `Time`, `Date`, `DateTime`, and `Calendar` interfaces by accessing their documentation as necessary. **Never** install additional dependencies unless asked or for date/time parsing (which you can use the `date_time_parser` package)
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- Don't use `String.to_atom/1` on user input (memory leak risk)
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- Predicate function names should not start with `is_` and should end in a question mark. Names like `is_thing` should be reserved for guards
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- Elixir's builtin OTP primitives like `DynamicSupervisor` and `Registry`, require names in the child spec, such as `{DynamicSupervisor, name: MyApp.MyDynamicSup}`, then you can use `DynamicSupervisor.start_child(MyApp.MyDynamicSup, child_spec)`
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- Use `Task.async_stream(collection, callback, options)` for concurrent enumeration with back-pressure. The majority of times you will want to pass `timeout: :infinity` as option
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## Mix guidelines
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- Read the docs and options before using tasks (by using `mix help task_name`)
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- To debug test failures, run tests in a specific file with `mix test test/my_test.exs` or run all previously failed tests with `mix test --failed`
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- `mix deps.clean --all` is **almost never needed**. **Avoid** using it unless you have good reason
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## Test guidelines
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- **Always use `start_supervised!/1`** to start processes in tests as it guarantees cleanup between tests
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- **Avoid** `Process.sleep/1` and `Process.alive?/1` in tests
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- Instead of sleeping to wait for a process to finish, **always** use `Process.monitor/1` and assert on the DOWN message:
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ref = Process.monitor(pid)
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assert_receive {:DOWN, ^ref, :process, ^pid, :normal}
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- Instead of sleeping to synchronize before the next call, **always** use `_ = :sys.get_state/1` to ensure the process has handled prior messages
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<!-- phoenix:elixir-end -->
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<!-- phoenix:html-start -->
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## phoenix:html usage
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## Phoenix HTML guidelines
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- Phoenix templates **always** use `~H` or .html.heex files (known as HEEx), **never** use `~E`
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- **Always** use the imported `Phoenix.Component.form/1` and `Phoenix.Component.inputs_for/1` function to build forms. **Never** use `Phoenix.HTML.form_for` or `Phoenix.HTML.inputs_for` as they are outdated
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- When building forms **always** use the already imported `Phoenix.Component.to_form/2` (`assign(socket, form: to_form(...))` and `<.form for={@form} id="msg-form">`), then access those forms in the template via `@form[:field]`
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- **Always** add unique DOM IDs to key elements (like forms, buttons, etc) when writing templates, these IDs can later be used in tests (`<.form for={@form} id="product-form">`)
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- For "app wide" template imports, you can import/alias into the `my_app_web.ex`'s `html_helpers` block, so they will be available to all LiveViews, LiveComponent's, and all modules that do `use MyAppWeb, :html` (replace "my_app" by the actual app name)
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- Elixir supports `if/else` but **does NOT support `if/else if` or `if/elsif`**. **Never use `else if` or `elseif` in Elixir**, **always** use `cond` or `case` for multiple conditionals.
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**Never do this (invalid)**:
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<%= if condition do %>
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...
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<% else if other_condition %>
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...
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<% end %>
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Instead **always** do this:
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<%= cond do %>
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<% condition -> %>
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...
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<% condition2 -> %>
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...
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<% true -> %>
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...
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<% end %>
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- HEEx require special tag annotation if you want to insert literal curly's like `{` or `}`. If you want to show a textual code snippet on the page in a `<pre>` or `<code>` block you *must* annotate the parent tag with `phx-no-curly-interpolation`:
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<code phx-no-curly-interpolation>
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let obj = {key: "val"}
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</code>
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Within `phx-no-curly-interpolation` annotated tags, you can use `{` and `}` without escaping them, and dynamic Elixir expressions can still be used with `<%= ... %>` syntax
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- HEEx class attrs support lists, but you must **always** use list `[...]` syntax. You can use the class list syntax to conditionally add classes, **always do this for multiple class values**:
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<a class={[
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"px-2 text-white",
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@some_flag && "py-5",
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if(@other_condition, do: "border-red-500", else: "border-blue-100"),
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...
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]}>Text</a>
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and **always** wrap `if`'s inside `{...}` expressions with parens, like done above (`if(@other_condition, do: "...", else: "...")`)
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and **never** do this, since it's invalid (note the missing `[` and `]`):
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<a class={
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"px-2 text-white",
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@some_flag && "py-5"
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}> ...
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=> Raises compile syntax error on invalid HEEx attr syntax
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- **Never** use `<% Enum.each %>` or non-for comprehensions for generating template content, instead **always** use `<%= for item <- @collection do %>`
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- HEEx HTML comments use `<%!-- comment --%>`. **Always** use the HEEx HTML comment syntax for template comments (`<%!-- comment --%>`)
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- HEEx allows interpolation via `{...}` and `<%= ... %>`, but the `<%= %>` **only** works within tag bodies. **Always** use the `{...}` syntax for interpolation within tag attributes, and for interpolation of values within tag bodies. **Always** interpolate block constructs (if, cond, case, for) within tag bodies using `<%= ... %>`.
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**Always** do this:
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<div id={@id}>
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{@my_assign}
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<%= if @some_block_condition do %>
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{@another_assign}
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<% end %>
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</div>
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and **Never** do this – the program will terminate with a syntax error:
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<%!-- THIS IS INVALID NEVER EVER DO THIS --%>
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<div id="<%= @invalid_interpolation %>">
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{if @invalid_block_construct do}
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{end}
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</div>
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<!-- phoenix:html-end -->
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<!-- phoenix:liveview-start -->
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## phoenix:liveview usage
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## Phoenix LiveView guidelines
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- **Never** use the deprecated `live_redirect` and `live_patch` functions, instead **always** use the `<.link navigate={href}>` and `<.link patch={href}>` in templates, and `push_navigate` and `push_patch` functions LiveViews
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- **Avoid LiveComponent's** unless you have a strong, specific need for them
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- LiveViews should be named like `AppWeb.WeatherLive`, with a `Live` suffix. When you go to add LiveView routes to the router, the default `:browser` scope is **already aliased** with the `AppWeb` module, so you can just do `live "/weather", WeatherLive`
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### LiveView streams
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- **Always** use LiveView streams for collections for assigning regular lists to avoid memory ballooning and runtime termination with the following operations:
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- basic append of N items - `stream(socket, :messages, [new_msg])`
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- resetting stream with new items - `stream(socket, :messages, [new_msg], reset: true)` (e.g. for filtering items)
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- prepend to stream - `stream(socket, :messages, [new_msg], at: -1)`
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- deleting items - `stream_delete(socket, :messages, msg)`
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- When using the `stream/3` interfaces in the LiveView, the LiveView template must 1) always set `phx-update="stream"` on the parent element, with a DOM id on the parent element like `id="messages"` and 2) consume the `@streams.stream_name` collection and use the id as the DOM id for each child. For a call like `stream(socket, :messages, [new_msg])` in the LiveView, the template would be:
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<div id="messages" phx-update="stream">
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<div :for={{id, msg} <- @streams.messages} id={id}>
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{msg.text}
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</div>
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</div>
|
||
|
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- LiveView streams are *not* enumerable, so you cannot use `Enum.filter/2` or `Enum.reject/2` on them. Instead, if you want to filter, prune, or refresh a list of items on the UI, you **must refetch the data and re-stream the entire stream collection, passing reset: true**:
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def handle_event("filter", %{"filter" => filter}, socket) do
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# re-fetch the messages based on the filter
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messages = list_messages(filter)
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{:noreply,
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socket
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|> assign(:messages_empty?, messages == [])
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# reset the stream with the new messages
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|> stream(:messages, messages, reset: true)}
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end
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- LiveView streams *do not support counting or empty states*. If you need to display a count, you must track it using a separate assign. For empty states, you can use Tailwind classes:
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|
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<div id="tasks" phx-update="stream">
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<div class="hidden only:block">No tasks yet</div>
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<div :for={{id, task} <- @stream.tasks} id={id}>
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{task.name}
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</div>
|
||
</div>
|
||
|
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The above only works if the empty state is the only HTML block alongside the stream for-comprehension.
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||
|
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- When updating an assign that should change content inside any streamed item(s), you MUST re-stream the items
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along with the updated assign:
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|
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def handle_event("edit_message", %{"message_id" => message_id}, socket) do
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message = Chat.get_message!(message_id)
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edit_form = to_form(Chat.change_message(message, %{content: message.content}))
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# re-insert message so @editing_message_id toggle logic takes effect for that stream item
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{:noreply,
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socket
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|> stream_insert(:messages, message)
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|> assign(:editing_message_id, String.to_integer(message_id))
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|> assign(:edit_form, edit_form)}
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end
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And in the template:
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<div id="messages" phx-update="stream">
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<div :for={{id, message} <- @streams.messages} id={id} class="flex group">
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{message.username}
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||
<%= if @editing_message_id == message.id do %>
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<%!-- Edit mode --%>
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||
<.form for={@edit_form} id="edit-form-#{message.id}" phx-submit="save_edit">
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...
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</.form>
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<% end %>
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</div>
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</div>
|
||
|
||
- **Never** use the deprecated `phx-update="append"` or `phx-update="prepend"` for collections
|
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|
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### LiveView JavaScript interop
|
||
|
||
- Remember anytime you use `phx-hook="MyHook"` and that JS hook manages its own DOM, you **must** also set the `phx-update="ignore"` attribute
|
||
- **Always** provide an unique DOM id alongside `phx-hook` otherwise a compiler error will be raised
|
||
|
||
LiveView hooks come in two flavors, 1) colocated js hooks for "inline" scripts defined inside HEEx,
|
||
and 2) external `phx-hook` annotations where JavaScript object literals are defined and passed to the `LiveSocket` constructor.
|
||
|
||
#### Inline colocated js hooks
|
||
|
||
**Never** write raw embedded `<script>` tags in heex as they are incompatible with LiveView.
|
||
Instead, **always use a colocated js hook script tag (`:type={Phoenix.LiveView.ColocatedHook}`)
|
||
when writing scripts inside the template**:
|
||
|
||
<input type="text" name="user[phone_number]" id="user-phone-number" phx-hook=".PhoneNumber" />
|
||
<script :type={Phoenix.LiveView.ColocatedHook} name=".PhoneNumber">
|
||
export default {
|
||
mounted() {
|
||
this.el.addEventListener("input", e => {
|
||
let match = this.el.value.replace(/\D/g, "").match(/^(\d{3})(\d{3})(\d{4})$/)
|
||
if(match) {
|
||
this.el.value = `${match[1]}-${match[2]}-${match[3]}`
|
||
}
|
||
})
|
||
}
|
||
}
|
||
</script>
|
||
|
||
- colocated hooks are automatically integrated into the app.js bundle
|
||
- colocated hooks names **MUST ALWAYS** start with a `.` prefix, i.e. `.PhoneNumber`
|
||
|
||
#### External phx-hook
|
||
|
||
External JS hooks (`<div id="myhook" phx-hook="MyHook">`) must be placed in `assets/js/` and passed to the
|
||
LiveSocket constructor:
|
||
|
||
const MyHook = {
|
||
mounted() { ... }
|
||
}
|
||
let liveSocket = new LiveSocket("/live", Socket, {
|
||
hooks: { MyHook }
|
||
});
|
||
|
||
#### Pushing events between client and server
|
||
|
||
Use LiveView's `push_event/3` when you need to push events/data to the client for a phx-hook to handle.
|
||
**Always** return or rebind the socket on `push_event/3` when pushing events:
|
||
|
||
# re-bind socket so we maintain event state to be pushed
|
||
socket = push_event(socket, "my_event", %{...})
|
||
|
||
# or return the modified socket directly:
|
||
def handle_event("some_event", _, socket) do
|
||
{:noreply, push_event(socket, "my_event", %{...})}
|
||
end
|
||
|
||
Pushed events can then be picked up in a JS hook with `this.handleEvent`:
|
||
|
||
mounted() {
|
||
this.handleEvent("my_event", data => console.log("from server:", data));
|
||
}
|
||
|
||
Clients can also push an event to the server and receive a reply with `this.pushEvent`:
|
||
|
||
mounted() {
|
||
this.el.addEventListener("click", e => {
|
||
this.pushEvent("my_event", { one: 1 }, reply => console.log("got reply from server:", reply));
|
||
})
|
||
}
|
||
|
||
Where the server handled it via:
|
||
|
||
def handle_event("my_event", %{"one" => 1}, socket) do
|
||
{:reply, %{two: 2}, socket}
|
||
end
|
||
|
||
### LiveView tests
|
||
|
||
- `Phoenix.LiveViewTest` module and `LazyHTML` (included) for making your assertions
|
||
- Form tests are driven by `Phoenix.LiveViewTest`'s `render_submit/2` and `render_change/2` functions
|
||
- Come up with a step-by-step test plan that splits major test cases into small, isolated files. You may start with simpler tests that verify content exists, gradually add interaction tests
|
||
- **Always reference the key element IDs you added in the LiveView templates in your tests** for `Phoenix.LiveViewTest` functions like `element/2`, `has_element/2`, selectors, etc
|
||
- **Never** tests again raw HTML, **always** use `element/2`, `has_element/2`, and similar: `assert has_element?(view, "#my-form")`
|
||
- Instead of relying on testing text content, which can change, favor testing for the presence of key elements
|
||
- Focus on testing outcomes rather than implementation details
|
||
- Be aware that `Phoenix.Component` functions like `<.form>` might produce different HTML than expected. Test against the output HTML structure, not your mental model of what you expect it to be
|
||
- When facing test failures with element selectors, add debug statements to print the actual HTML, but use `LazyHTML` selectors to limit the output, ie:
|
||
|
||
html = render(view)
|
||
document = LazyHTML.from_fragment(html)
|
||
matches = LazyHTML.filter(document, "your-complex-selector")
|
||
IO.inspect(matches, label: "Matches")
|
||
|
||
### Form handling
|
||
|
||
#### Creating a form from params
|
||
|
||
If you want to create a form based on `handle_event` params:
|
||
|
||
def handle_event("submitted", params, socket) do
|
||
{:noreply, assign(socket, form: to_form(params))}
|
||
end
|
||
|
||
When you pass a map to `to_form/1`, it assumes said map contains the form params, which are expected to have string keys.
|
||
|
||
You can also specify a name to nest the params:
|
||
|
||
def handle_event("submitted", %{"user" => user_params}, socket) do
|
||
{:noreply, assign(socket, form: to_form(user_params, as: :user))}
|
||
end
|
||
|
||
#### Creating a form from changesets
|
||
|
||
When using changesets, the underlying data, form params, and errors are retrieved from it. The `:as` option is automatically computed too. E.g. if you have a user schema:
|
||
|
||
defmodule MyApp.Users.User do
|
||
use Ecto.Schema
|
||
...
|
||
end
|
||
|
||
And then you create a changeset that you pass to `to_form`:
|
||
|
||
%MyApp.Users.User{}
|
||
|> Ecto.Changeset.change()
|
||
|> to_form()
|
||
|
||
Once the form is submitted, the params will be available under `%{"user" => user_params}`.
|
||
|
||
In the template, the form form assign can be passed to the `<.form>` function component:
|
||
|
||
<.form for={@form} id="todo-form" phx-change="validate" phx-submit="save">
|
||
<.input field={@form[:field]} type="text" />
|
||
</.form>
|
||
|
||
Always give the form an explicit, unique DOM ID, like `id="todo-form"`.
|
||
|
||
#### Avoiding form errors
|
||
|
||
**Always** use a form assigned via `to_form/2` in the LiveView, and the `<.input>` component in the template. In the template **always access forms this**:
|
||
|
||
<%!-- ALWAYS do this (valid) --%>
|
||
<.form for={@form} id="my-form">
|
||
<.input field={@form[:field]} type="text" />
|
||
</.form>
|
||
|
||
And **never** do this:
|
||
|
||
<%!-- NEVER do this (invalid) --%>
|
||
<.form for={@changeset} id="my-form">
|
||
<.input field={@changeset[:field]} type="text" />
|
||
</.form>
|
||
|
||
- You are FORBIDDEN from accessing the changeset in the template as it will cause errors
|
||
- **Never** use `<.form let={f} ...>` in the template, instead **always use `<.form for={@form} ...>`**, then drive all form references from the form assign as in `@form[:field]`. The UI should **always** be driven by a `to_form/2` assigned in the LiveView module that is derived from a changeset
|
||
|
||
<!-- phoenix:liveview-end -->
|
||
<!-- phoenix:phoenix-start -->
|
||
## phoenix:phoenix usage
|
||
## Phoenix guidelines
|
||
|
||
- Remember Phoenix router `scope` blocks include an optional alias which is prefixed for all routes within the scope. **Always** be mindful of this when creating routes within a scope to avoid duplicate module prefixes.
|
||
|
||
- You **never** need to create your own `alias` for route definitions! The `scope` provides the alias, ie:
|
||
|
||
scope "/admin", AppWeb.Admin do
|
||
pipe_through :browser
|
||
|
||
live "/users", UserLive, :index
|
||
end
|
||
|
||
the UserLive route would point to the `AppWeb.Admin.UserLive` module
|
||
|
||
- `Phoenix.View` no longer is needed or included with Phoenix, don't use it
|
||
|
||
<!-- phoenix:phoenix-end -->
|
||
<!-- usage_rules-start -->
|
||
## usage_rules usage
|
||
_A config-driven dev tool for Elixir projects to manage AGENTS.md files and agent skills from dependencies_
|
||
|
||
## Using Usage Rules
|
||
|
||
Many packages have usage rules, which you should *thoroughly* consult before taking any
|
||
action. These usage rules contain guidelines and rules *directly from the package authors*.
|
||
They are your best source of knowledge for making decisions.
|
||
|
||
## Modules & functions in the current app and dependencies
|
||
|
||
When looking for docs for modules & functions that are dependencies of the current project,
|
||
or for Elixir itself, use `mix usage_rules.docs`
|
||
|
||
```
|
||
# Search a whole module
|
||
mix usage_rules.docs Enum
|
||
|
||
# Search a specific function
|
||
mix usage_rules.docs Enum.zip
|
||
|
||
# Search a specific function & arity
|
||
mix usage_rules.docs Enum.zip/1
|
||
```
|
||
|
||
|
||
## Searching Documentation
|
||
|
||
You should also consult the documentation of any tools you are using, early and often. The best
|
||
way to accomplish this is to use the `usage_rules.search_docs` mix task. Once you have
|
||
found what you are looking for, use the links in the search results to get more detail. For example:
|
||
|
||
```
|
||
# Search docs for all packages in the current application, including Elixir
|
||
mix usage_rules.search_docs Enum.zip
|
||
|
||
# Search docs for specific packages
|
||
mix usage_rules.search_docs Req.get -p req
|
||
|
||
# Search docs for multi-word queries
|
||
mix usage_rules.search_docs "making requests" -p req
|
||
|
||
# Search only in titles (useful for finding specific functions/modules)
|
||
mix usage_rules.search_docs "Enum.zip" --query-by title
|
||
```
|
||
|
||
|
||
<!-- usage_rules-end -->
|
||
<!-- usage_rules:elixir-start -->
|
||
## usage_rules:elixir usage
|
||
# Elixir Core Usage Rules
|
||
|
||
## Pattern Matching
|
||
- Use pattern matching over conditional logic when possible
|
||
- Prefer to match on function heads instead of using `if`/`else` or `case` in function bodies
|
||
- `%{}` matches ANY map, not just empty maps. Use `map_size(map) == 0` guard to check for truly empty maps
|
||
|
||
## Error Handling
|
||
- Use `{:ok, result}` and `{:error, reason}` tuples for operations that can fail
|
||
- Avoid raising exceptions for control flow
|
||
- Use `with` for chaining operations that return `{:ok, _}` or `{:error, _}`
|
||
|
||
## Common Mistakes to Avoid
|
||
- Elixir has no `return` statement, nor early returns. The last expression in a block is always returned.
|
||
- Don't use `Enum` functions on large collections when `Stream` is more appropriate
|
||
- Avoid nested `case` statements - refactor to a single `case`, `with` or separate functions
|
||
- Don't use `String.to_atom/1` on user input (memory leak risk)
|
||
- Lists and enumerables cannot be indexed with brackets. Use pattern matching or `Enum` functions
|
||
- Prefer `Enum` functions like `Enum.reduce` over recursion
|
||
- When recursion is necessary, prefer to use pattern matching in function heads for base case detection
|
||
- Using the process dictionary is typically a sign of unidiomatic code
|
||
- Only use macros if explicitly requested
|
||
- There are many useful standard library functions, prefer to use them where possible
|
||
|
||
## Function Design
|
||
- Use guard clauses: `when is_binary(name) and byte_size(name) > 0`
|
||
- Prefer multiple function clauses over complex conditional logic
|
||
- Name functions descriptively: `calculate_total_price/2` not `calc/2`
|
||
- Predicate function names should not start with `is` and should end in a question mark.
|
||
- Names like `is_thing` should be reserved for guards
|
||
|
||
## Data Structures
|
||
- Use structs over maps when the shape is known: `defstruct [:name, :age]`
|
||
- Prefer keyword lists for options: `[timeout: 5000, retries: 3]`
|
||
- Use maps for dynamic key-value data
|
||
- Prefer to prepend to lists `[new | list]` not `list ++ [new]`
|
||
|
||
## Mix Tasks
|
||
|
||
- Use `mix help` to list available mix tasks
|
||
- Use `mix help task_name` to get docs for an individual task
|
||
- Read the docs and options fully before using tasks
|
||
|
||
## Testing
|
||
- Run tests in a specific file with `mix test test/my_test.exs` and a specific test with the line number `mix test path/to/test.exs:123`
|
||
- Limit the number of failed tests with `mix test --max-failures n`
|
||
- Use `@tag` to tag specific tests, and `mix test --only tag` to run only those tests
|
||
- Use `assert_raise` for testing expected exceptions: `assert_raise ArgumentError, fn -> invalid_function() end`
|
||
- Use `mix help test` to for full documentation on running tests
|
||
|
||
## Debugging
|
||
|
||
- Use `dbg/1` to print values while debugging. This will display the formatted value and other relevant information in the console.
|
||
|
||
<!-- usage_rules:elixir-end -->
|
||
<!-- usage_rules:otp-start -->
|
||
## usage_rules:otp usage
|
||
# OTP Usage Rules
|
||
|
||
## GenServer Best Practices
|
||
- Keep state simple and serializable
|
||
- Handle all expected messages explicitly
|
||
- Use `handle_continue/2` for post-init work
|
||
- Implement proper cleanup in `terminate/2` when necessary
|
||
|
||
## Process Communication
|
||
- Use `GenServer.call/3` for synchronous requests expecting replies
|
||
- Use `GenServer.cast/2` for fire-and-forget messages.
|
||
- When in doubt, use `call` over `cast`, to ensure back-pressure
|
||
- Set appropriate timeouts for `call/3` operations
|
||
|
||
## Fault Tolerance
|
||
- Set up processes such that they can handle crashing and being restarted by supervisors
|
||
- Use `:max_restarts` and `:max_seconds` to prevent restart loops
|
||
|
||
## Task and Async
|
||
- Use `Task.Supervisor` for better fault tolerance
|
||
- Handle task failures with `Task.yield/2` or `Task.shutdown/2`
|
||
- Set appropriate task timeouts
|
||
- Use `Task.async_stream/3` for concurrent enumeration with back-pressure
|
||
|
||
<!-- usage_rules:otp-end -->
|
||
<!-- usage_rules-start -->
|
||
## usage_rules usage
|
||
_A config-driven dev tool for Elixir projects to manage AGENTS.md files and agent skills from dependencies_
|
||
|
||
## Using Usage Rules
|
||
|
||
Many packages have usage rules, which you should *thoroughly* consult before taking any
|
||
action. These usage rules contain guidelines and rules *directly from the package authors*.
|
||
They are your best source of knowledge for making decisions.
|
||
|
||
## Modules & functions in the current app and dependencies
|
||
|
||
When looking for docs for modules & functions that are dependencies of the current project,
|
||
or for Elixir itself, use `mix usage_rules.docs`
|
||
|
||
```
|
||
# Search a whole module
|
||
mix usage_rules.docs Enum
|
||
|
||
# Search a specific function
|
||
mix usage_rules.docs Enum.zip
|
||
|
||
# Search a specific function & arity
|
||
mix usage_rules.docs Enum.zip/1
|
||
```
|
||
|
||
|
||
## Searching Documentation
|
||
|
||
You should also consult the documentation of any tools you are using, early and often. The best
|
||
way to accomplish this is to use the `usage_rules.search_docs` mix task. Once you have
|
||
found what you are looking for, use the links in the search results to get more detail. For example:
|
||
|
||
```
|
||
# Search docs for all packages in the current application, including Elixir
|
||
mix usage_rules.search_docs Enum.zip
|
||
|
||
# Search docs for specific packages
|
||
mix usage_rules.search_docs Req.get -p req
|
||
|
||
# Search docs for multi-word queries
|
||
mix usage_rules.search_docs "making requests" -p req
|
||
|
||
# Search only in titles (useful for finding specific functions/modules)
|
||
mix usage_rules.search_docs "Enum.zip" --query-by title
|
||
```
|
||
|
||
|
||
<!-- usage_rules-end -->
|
||
<!-- usage_rules:elixir-start -->
|
||
## usage_rules:elixir usage
|
||
# Elixir Core Usage Rules
|
||
|
||
## Pattern Matching
|
||
- Use pattern matching over conditional logic when possible
|
||
- Prefer to match on function heads instead of using `if`/`else` or `case` in function bodies
|
||
- `%{}` matches ANY map, not just empty maps. Use `map_size(map) == 0` guard to check for truly empty maps
|
||
|
||
## Error Handling
|
||
- Use `{:ok, result}` and `{:error, reason}` tuples for operations that can fail
|
||
- Avoid raising exceptions for control flow
|
||
- Use `with` for chaining operations that return `{:ok, _}` or `{:error, _}`
|
||
|
||
## Common Mistakes to Avoid
|
||
- Elixir has no `return` statement, nor early returns. The last expression in a block is always returned.
|
||
- Don't use `Enum` functions on large collections when `Stream` is more appropriate
|
||
- Avoid nested `case` statements - refactor to a single `case`, `with` or separate functions
|
||
- Don't use `String.to_atom/1` on user input (memory leak risk)
|
||
- Lists and enumerables cannot be indexed with brackets. Use pattern matching or `Enum` functions
|
||
- Prefer `Enum` functions like `Enum.reduce` over recursion
|
||
- When recursion is necessary, prefer to use pattern matching in function heads for base case detection
|
||
- Using the process dictionary is typically a sign of unidiomatic code
|
||
- Only use macros if explicitly requested
|
||
- There are many useful standard library functions, prefer to use them where possible
|
||
|
||
## Function Design
|
||
- Use guard clauses: `when is_binary(name) and byte_size(name) > 0`
|
||
- Prefer multiple function clauses over complex conditional logic
|
||
- Name functions descriptively: `calculate_total_price/2` not `calc/2`
|
||
- Predicate function names should not start with `is` and should end in a question mark.
|
||
- Names like `is_thing` should be reserved for guards
|
||
|
||
## Data Structures
|
||
- Use structs over maps when the shape is known: `defstruct [:name, :age]`
|
||
- Prefer keyword lists for options: `[timeout: 5000, retries: 3]`
|
||
- Use maps for dynamic key-value data
|
||
- Prefer to prepend to lists `[new | list]` not `list ++ [new]`
|
||
|
||
## Mix Tasks
|
||
|
||
- Use `mix help` to list available mix tasks
|
||
- Use `mix help task_name` to get docs for an individual task
|
||
- Read the docs and options fully before using tasks
|
||
|
||
## Testing
|
||
- Run tests in a specific file with `mix test test/my_test.exs` and a specific test with the line number `mix test path/to/test.exs:123`
|
||
- Limit the number of failed tests with `mix test --max-failures n`
|
||
- Use `@tag` to tag specific tests, and `mix test --only tag` to run only those tests
|
||
- Use `assert_raise` for testing expected exceptions: `assert_raise ArgumentError, fn -> invalid_function() end`
|
||
- Use `mix help test` to for full documentation on running tests
|
||
|
||
## Debugging
|
||
|
||
- Use `dbg/1` to print values while debugging. This will display the formatted value and other relevant information in the console.
|
||
|
||
<!-- usage_rules:elixir-end -->
|
||
<!-- usage_rules:otp-start -->
|
||
## usage_rules:otp usage
|
||
# OTP Usage Rules
|
||
|
||
## GenServer Best Practices
|
||
- Keep state simple and serializable
|
||
- Handle all expected messages explicitly
|
||
- Use `handle_continue/2` for post-init work
|
||
- Implement proper cleanup in `terminate/2` when necessary
|
||
|
||
## Process Communication
|
||
- Use `GenServer.call/3` for synchronous requests expecting replies
|
||
- Use `GenServer.cast/2` for fire-and-forget messages.
|
||
- When in doubt, use `call` over `cast`, to ensure back-pressure
|
||
- Set appropriate timeouts for `call/3` operations
|
||
|
||
## Fault Tolerance
|
||
- Set up processes such that they can handle crashing and being restarted by supervisors
|
||
- Use `:max_restarts` and `:max_seconds` to prevent restart loops
|
||
|
||
## Task and Async
|
||
- Use `Task.Supervisor` for better fault tolerance
|
||
- Handle task failures with `Task.yield/2` or `Task.shutdown/2`
|
||
- Set appropriate task timeouts
|
||
- Use `Task.async_stream/3` for concurrent enumeration with back-pressure
|
||
|
||
<!-- usage_rules:otp-end -->
|
||
<!-- fluxon-start -->
|
||
## fluxon usage
|
||
_Fluxon UI Components_
|
||
|
||
@deps/fluxon/usage-rules.md
|
||
<!-- fluxon-end -->
|
||
<!-- usage-rules-end -->
|