MarkupAnalyzer Lint Rule

Description

MarkupAnalyzer is a customizable lint rule for the custom_lint package in Dart/Flutter. It allows you to prohibit specific types of string expressions in the parameters of Flutter widgets.

This rule enables you to control the usage of string expressions such as simple string literals, interpolations, binary expressions, and others based on your configuration.

Installation

  1. Add the package to your project's dependencies:

    Add the following to your project's pubspec.yaml under dev_dependencies:

    dev_dependencies:
  custom_lint: 
  markup_analyzer: ^latest_version

  2. Get the dependencies:

    flutter pub get

  3. Activate the plugin in analysis_options.yaml:

    Create or update the analysis_options.yaml file at the root of your project:

    analyzer:
  plugins:
    - custom_lint

custom_lint:
  rules:
    - markup_analyzer

Configuration

You can configure the MarkupAnalyzer rule via analysis_options.yaml by specifying which types of string expressions should be prohibited and the severity level of the error.

Example of a full configuration:

custom_lint:
  rules:
    markup_analyzer:
      simple: true
      prefixed_identifier: false
      interpolation: true
      binary: true
      adjacent: true
      method: false
      simple_identifier: false
      property: false
      function: false
      severity: error  # Possible values: error, warning, info

Configuration Parameters:

  • **simple**: Prohibits the use of simple string literals.

  • **prefixed_identifier**: Prohibits the use of prefixed identifiers (e.g., widget.title).

  • **interpolation**: Prohibits the use of string interpolation (e.g., 'Hello, $name').

  • **binary**: Prohibits the use of binary expressions with the + operator for string concatenation.

  • **adjacent**: Prohibits the use of adjacent string literals (e.g., 'Hello, ''world').

  • **method**: Prohibits method invocations that return a string (e.g., 'Hello'.toUpperCase()).

  • **simple_identifier**: Prohibits the use of simple identifiers (e.g., variables like title).

  • **property**: Prohibits accessing object properties that return a string (e.g., object.property).

  • **function**: Prohibits function invocations that return a string (e.g., getString()).

  • **severity**: The severity level of the error. Possible values: error, warning, info.

Usage

After setting up the plugin and configuring the rules, run the analyzer on your project:

dart run custom_lint

All rule violations will be displayed in the console and highlighted in your IDE if it supports custom_lint.

Examples

1. Simple String Literals (simple)

Configuration:

custom_lint:
rules:
  markup_analyzer:
    simple: true

// BAD
Text('Hello, world!'); // Simple string literal is prohibited.

// GOOD
final greeting = 'Hello, world!';
Text(greeting); // Using a variable instead of a literal.

2. Prefixed Identifiers (prefixed_identifier)

Configuration:

custom_lint:
rules:
  markup_analyzer:
    prefixed_identifier: true

// BAD
Text(widget.title); // Prefixed identifier is prohibited.

// GOOD
final title = widget.title;
Text(title); // Assign to a local variable first.

3. String Interpolation (interpolation)

Configuration:

custom_lint:
rules:
  markup_analyzer:
    interpolation: true

// BAD
Text('Hello, $name!'); // String interpolation is prohibited.

// GOOD
Text('Hello, ' + name + '!'); // Use string concatenation instead.

4. Binary Expressions (binary)

Configuration:

custom_lint:
rules:
  markup_analyzer:
    binary: true

// BAD
Text('Hello, ' + 'world!'); // Binary expression with '+' is prohibited.

// GOOD
Text('Hello, world!'); // Use a single string literal.

5. Adjacent Strings (adjacent)

Configuration:

custom_lint:
rules:
  markup_analyzer:
    adjacent: true

// BAD
Text(
'Hello, '
'world!'
); // Adjacent strings are prohibited.

// GOOD
Text('Hello, world!'); // Combine into a single string.

6. Method Invocations (method)

Configuration:

custom_lint:
rules:
  markup_analyzer:
    method: true

// BAD
Text('hello'.toUpperCase()); // Method invocation is prohibited.

// GOOD
final upperCaseHello = 'hello'.toUpperCase();
Text(upperCaseHello); // Use a variable that holds the result.

7. Simple Identifiers (simple_identifier)

Configuration:

custom_lint:
rules:
  markup_analyzer:
    simple_identifier: true

// BAD
Text(title); // Simple identifier is prohibited.

// GOOD
Text('Static Title'); // Use a static string literal.

8. Property Access (property)

Configuration:

custom_lint:
rules:
  markup_analyzer:
    property: true

// BAD
Text(user.name); // Property access is prohibited.

// GOOD
final userName = user.name;
Text(userName); // Assign the property to a variable first.

9. Function Invocations (function)

Configuration:

custom_lint:
rules:
  markup_analyzer:
    function: true

// BAD
Text(getGreeting()); // Function invocation is prohibited.

// GOOD
final greeting = getGreeting();
Text(greeting); // Use a variable containing the result.

If your configuration has simple: true, running the analyzer will produce an error:

Libraries

config
markup_analyzer