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Document the file structure of the project
Also customize styling of headers so that the smaller ones are a little larger.
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‎docs/contributors/architecture/structure.md

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# Structure
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To help you in your contributing journey,
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this page offers insight into how the SuperDiff codebase is laid out.
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Note that this page does not mention every single file:
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some files which are unimportant,
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such as those which only serve to require other files,
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have been omitted.
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## Implementation files
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All implementation files in the project are located in `lib/`,
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and most are located in `lib/super_diff/`.
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In `lib/super_diff` there are 7 notable directories,
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which create 4 layers:
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```mermaid
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flowchart BT
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subgraph rails
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active_record
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active_support
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end
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basic --> core
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rspec --> basic
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active_record --> basic
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active_support --> basic
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active_record --> core
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active_support --> core
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rspec --> core
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equality_matchers --> core
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equality_matchers --> basic
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core --> csi
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rspec --> csi
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```
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Following is a breakdown of each directory.
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### Top level (`lib/`)
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- **`super_diff.rb`:**
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In addition to loading the whole library,
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this file contains helpers which are so useful that they can be called anywhere.
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### `SuperDiff::Core` (`lib/super_diff/core/`)
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The Core module provides building blocks, utilities, and other primitives
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that are used throughout the library.
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This directory can be grouped into the following themes:
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#### Initialization
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- **`configuration.rb`:**
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Stores settings for SuperDiff
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which can be used to control the behavior of various features.
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#### Differ
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- **`abstract_differ.rb`:**
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The superclass for all differ classes.
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- **`differ_dispatcher.rb`:**
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Finds the differ class that best matches a combination of "expected" and "actual" values,
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then uses it to run the diff between them.
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- **`no_differ_available_error.rb`:**
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The error produced when the DifferDispatcher fails to find a matching class.
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#### Operation tree
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- **`abstract_operation_tree_builder.rb`:**
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The superclass for all operation tree builder classes,
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defined elsewhere in SuperDiff or by users.
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- **`abstract_operation_tree.rb`:**
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The superclass for all operation tree classes,
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defined elsewhere in SuperDiff or by users.
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- **`abstract_operation_tree_flattener.rb`:**
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The superclass for all operation tree flattener classes,
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defined elsewhere in SuperDiff or by users.
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- **`binary_operation.rb`:**
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A node in an operation tree which represents a comparison between two values.
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- **`no_operation_tree_available_error.rb`:**
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The error produced when the OperationTreeFinder fails to find a matching class.
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- **`no_operation_tree_builder_available_error.rb`:**
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The error produced when the OperationTreeBuilderDispatcher fails to find a matching class.
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- **`operation_tree_builder_dispatcher.rb`:**
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Finds the operation tree builder class
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that best matches a combination of "expected" and "actual" values,
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then uses it to build the operation tree representing the difference between them.
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- **`operation_tree_finder.rb`:**
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Finds the operation tree matching a value.
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- **`unary_operation.rb`:**
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A node in an operation tree which represents an operation to a value.
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#### Lines
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- **`line.rb`:**
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A deconstructed, mutable version of a line in the final diff output.
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- **`tiered_lines_elider.rb`:**
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Collapses unchanged sections of a diff,
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represented by lines which are indented hierarchically.
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- **`tiered_lines_formatter.rb`:**
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Takes a collection of diff line objects and produces a diff string.
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#### Object inspection
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- **`inspection_tree_nodes/`:**
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Classes which represent directives that can be given
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when constructing an inspection tree.
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Different directives format the resulting text different ways
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or even hide text if it does not match a certain condition.
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- **`abstract_inspection_tree_builder.rb`:**
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The superclass for all inspection tree builder classes,
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defined elsewhere in SuperDiff or by users.
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- **`inspection_tree.rb`:**
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A domain-specific language used to format the contents of an object.
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The result can either be a single-line string,
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useful for descriptions and failure messages,
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or a series of Line objects,
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useful for inserting into diffs.
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- **`inspection_tree_builder_dispatcher.rb`:**
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Finds the inspection tree builder class that best matches a value,
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then uses it to build the inspection tree.
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- **`no_inspection_tree_builder_available_error.rb`:**
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The error produced when the InspectionTreeBuilderDispatcher fails to find a matching class.
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- **`prefix_for_next_inspection_tree_node.rb`:**
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A special token used to represent
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the result of the prefix passed to the `as_prefix_when_rendering_to_lines` directive.
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This prefix needs to be handled specially in the inspection tree rendering logic.
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- **`prelude_for_next_inspection_tree_node.rb`:**
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A special token used to represent
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the result of the prelude passed to the `as_prelude_when_rendering_to_lines` directive.
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This prelude needs to be handled specially in the inspection tree rendering logic.
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- **`tiered_lines.rb`:**
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Represents the final output of an inspection tree,
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broken up by lines which are indented hierarchically.
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#### Utilities
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- **`colorized_document_extensions.rb`:**
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Extends the ColorizedDocument DSL
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so that text can be colored
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using names that are not abstract
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but rather related to SuperDiff concepts.
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- **`gem_version.rb`:**
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A wrapper around Gem::Version
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which simplifies the interface
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so that operators can be used to compare versions.
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- **`helpers.rb`:**
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Utility methods which can be mixed in various places to do various things.
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- **`implementation_checks.rb`:**
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Provides a way to define an unimplemented method.
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Such a method will raise an error when called
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unless it is overridden in a superclass.
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- **`recursion_guard.rb`:**
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A set of globally accessible methods
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which is used to track repeated encounters of objects
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as a data structure is descended into
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and prevent cyclical or infinite recursion.
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### Feature modules
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There are 4 directories in `lib/super_diff/` which are collectively known as _feature modules_.
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Using the primitives from the Core module,
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they implement building blocks
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to instruct SuperDiff on how to diff many kinds of objects.
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As such, you may see one or more of the following directories:
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- `*/differs/`
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- `*/inspection_tree_builders/`
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- `*/operation_tree_builders/`
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- `*/operation_tree_flatteners/`
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- `*/operation_trees/`
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With that in mind, here is a list of feature modules.
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#### `SuperDiff::Basic` (`lib/super_diff/basic`)
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This module is so named
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because it provides functionality that begins to make SuperDiff useful for users
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by adding support for objects that are built into Ruby.
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#### `SuperDiff::ActiveSupport` (`lib/super_diff/active_support`)
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This module makes use of the building blocks in the Basic module
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to instruct SuperDiff how to diff ActiveSupport-specific objects,
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such as HashWithIndifferentAccess.
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#### `SuperDiff::ActiveRecord` (`lib/super_diff/active_record`)
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This module makes use of the building blocks in the Basic module
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to instruct SuperDiff how to diff ActiveRecord-specific objects,
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such as models and relation objects.
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#### `SuperDiff::RSpec` (`lib/super_diff/rspec`)
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This module is the largest one
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and makes use of the building blocks defined by the Basic module
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to provide support for expectation and argument matchers in diffs.
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It also patches sections of RSpec to replace its differ with SuperDiff's
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and to change failure messages so that they fit better with SuperDiff's philosophy.
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There are a few files and directories of note here:
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- **`matcher_text_builders/`:**
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These classes are used to craft descriptions and failure messages for RSpec matchers.
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- **`differ.rb`:**
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This class stands in for RSpec::Differ
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and conditionally diffs an expected and actual value
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that has been passed to a matcher.
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- **`matcher_text_template.rb`:**
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This class is used by matcher text builders
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to progressively build up a string by concatenating tokens together.
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It is similar to an inspection tree
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in that some parts of the string can be rendered differently
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depending on whether we've chosen to display the message
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in a single line or across multiple lines.
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Some tokens can also be colored differently as well.
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- **`monkey_patches.rb`:**
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The metaphorical skeleton closet,
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this file does the dirty and outright sinful work
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of overriding various private APIs of the whole RSpec suite of gems
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in order to integrate SuperDiff fully into the test framework.
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### Equality matchers (`lib/super_diff/equality_matchers/`)
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This directory offers a way to try out SuperDiff
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without integrating it into a test framework.
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The classes here are merely thin wrappers around building blocks in the Basic module.
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### CSI (`lib/super_diff/csi/`)
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This directory contains a small library, private to the codebase,
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which provides a DSL for colorizing text in the running terminal emulator
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with the use of CSI escape sequences.
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## Tests
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Tests are located in `spec/`.
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They are divided into two kinds:
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- **Unit tests**, located in `spec/unit/`,
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holds tests for individual classes and methods.
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- **Integration tests**, located in `spec/integration/`,
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construct tiny test suites which import SuperDiff
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and run them in isolated environments
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to ensure that SuperDiff works as designed
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in more real-world scenarios.
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The files in `spec/support/` (imported via `spec_helper.rb`)
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contain helpers, matchers, and tests
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that are shared among unit and integration tests,
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at their respective levels.
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Beyond this, [Zeus][zeus], a way to speed up integration tests,
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and is run and configured via these files:
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- `bin/start-dev`
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- `config/zeus_plan.rb`
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- `support/test_plan.rb`
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- `zeus.json`
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The [official Zeus docs](https://github.com/burke/zeus/blob/master/docs/ruby/modifying.md)
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is helpful for understanding how these files work together.
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[zeus]: https://github.com/burke/zeus
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## Ruby
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The following files are used to set up Ruby,
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specify dependencies and gem publishing settings,
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and run tasks:
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- **`.ruby-version`:**
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Specifies the Ruby version required for development.
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Used by tools like `rbenv` and `asdf.`
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- **`bin/setup`:**
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Ensures that Ruby, Node, Python, and anything else necessary for development
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is installed on your machine.
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- **`gemfiles/`:**
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Holds generated gemspecs and lockfiles for appraisals.
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- **`lib/super_diff/version.rb`:**
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Holds the current version of the gem,
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which is used by the gemspec.
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Updating the constant in this file changes the published version.
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- **`spec/support/current_bundle.rb`:**
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A support file used by common tasks
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which tracks the currently set appraisal or sets a default.
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- **`Appraisals`:**
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Specifies different gemfiles for different testing environments.
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- **`Gemfile`:**
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Specifies common development dependencies.
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- **`Rakefile`:**
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Contains tasks for running tests and publishing the gem.
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- **`super_diff.gemspec`:**
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Standard configuration file for the gem,
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containing the name, description, and production dependencies.
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## Linting
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The following files are used for linting and formatting the codebase:
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- **`.husky/`:**
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Contains Git hooks which are installed via `husky install`.
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- **`.yarn/`:**
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Holds the executable and plugins for [Yarn][yarn],
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a package manager for JavaScript.
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- **`.prettierignore`:**
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Excludes files from being formatted with [Prettier][prettier].
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- **`.prettierrc.json`:**
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Configures Prettier.
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- **`.nvmrc`:**
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Specifies the Node version required to run Prettier.
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Used by tools like NVM and `asdf`.
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- **`.yarnrc.yml`:**
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Configures Yarn.
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- **`package.json`:**
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Specifies JavaScript dependencies needed to run Prettier.
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[prettier]: https://prettier.io/
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[yarn]: https://yarnpkg.com/
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## Documentation
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The following files are used for documentation purposes:
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- **`docs/`:**
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Contains the documentation that you're reading now!
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- **`docs-support/`:**
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Other files which are used for documentation purposes,
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but are not included in any Markdown files.
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Currently only used to generate the screenshots in the README.
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- **`.python-version`:**
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Specifies the Python version to use for documentation generation.
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Used by tools like `pyenv` and `asdf`.
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- **`mkdocs.yml`:**
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The configuration file for [Mkdocs][mkdocs],
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which reads the Markdown files in `docs/` and generates an HTML version.
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- **`pyproject.toml`:**
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Specifies Python dependencies needed to run Mkdocs.
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- **`README.md`:**
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The "front of house" for this repository;
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summarizes the project's purpose and goals and how to use it.
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- **`CHANGELOG.md`:**
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Describes the changes that appeared in each release over time.
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- **`LICENSE`:**
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The full text of the license granted to users of this gem.
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[mkdocs]: https://www.mkdocs.org/
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## CI
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The following files are used for CI and other automated tasks on GitHub:
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- **`.github/workflows/`:**
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Describes tasks to run on GitHub when events occur,
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such as automatically running tests on pull requests.
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- **`scripts/collect-release-info.rb`:**
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A script which is used in one of the GitHub workflows
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to determine whether a commit refers to a new release
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and, if so, determine the release version.
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## Miscellaneous
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These files don't belong in a particular category:
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- **`.editorconfig`:**
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Keeps basic editor-specific configuration,
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such as how many spaces to use, line length, etc.
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- **`.gitattributes`:**
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Used by Git and GitHub
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to configure presentation of certain types of files in diffs.
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- **`.gitignore`:**
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Specifies files that shouldn't show up in the repository.

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