Code Metrics

Plugin shows complexity information

This plugin implements live calculation of the Cognitive Complexity metric, which was proposed by G. Ann Campbell in Cognitive Complexity - A new way of measuring understandability (c) SonarSource S.A. 2016-2021, Switzerland.

Abstract: Cyclomatic Complexity was initially formulated as a measurement of the "testability and maintainability" of the control flow of a module. While it excels at measuring the former, its underlying mathematical model is unsatisfactory at producing a value that measures the latter. This white paper describes a new metric that breaks from the use of mathematical models to evaluate code in order to remedy Cyclomatic Complexity’s shortcomings and produce a measurement that more accurately reflects the relative difficulty of understanding, and therefore of maintaining methods, classes, and applications.

Table of Contents

• Code Metrics
  • 💾 Installation
  • 🔍 Method 1. with straight.el and use-package:
  • 🔍 Method 2. Manual
  • 🖥 Usage
  • 📚 Use it as a library
  • 🔨 Supported languages
  • 📝 Customization
  • ⚪ Analysis on new nodes
    • ❔ Example
  • 🔍 Writing new analysis functions
  • 🔗 References
  • 🛠️ Contribute
  • 🔬 Development
  • ❓ How to add an analysis rules?
    • 🔍 Where can I look for tree-sitter node?
  • ⚜️ License

💾 Installation

🔍 Method 1. with straight.el and use-package:

(use-package codemetrics
  :straight (codemetrics :type git :host github :repo "jcs-elpa/codemetrics"))

🔍 Method 2. Manual

git clone https://github.com/jcs-elpa/codemetrics /path/to/lib

then in Emacs:

(add-to-list 'load-path "/path/to/lib")
(require 'codemetrics)

or

(use-package codemetrics
  :load-path "/path/to/lib")

🖥 Usage

The simplest way to start using this package:

(codemetrics-mode 1)

📚 Use it as a library

These are functions you can use to analyze:

All these functions return the score data indicating the complexity.

🔨 Supported languages

⚠️ Please sort these two lists alphabetically!

These languages are fairly complete:

• Bash
• C / C++ / C#
• Elisp
• Go
• Java / JavaScript / JSX / Julia
• Kotlin
• Lua
• PHP / Python
• Ruby / Rust
• Swift
• TypeScript / TSX

These languages are in development:

• Agda
• Elm
• Elixir
• OCaml
• Scala (upstream, kinda buggy)

📝 Customization

Although codemetrics aims to have good analysis rules out of the box for all supported definitions, people will indubitably have their own preferences or desired functionality. The following section outlines how to add your own analysis definitions and analysis functions to make codemetrics work for you. If there are any improvements you find for existing or new languages, please do raise a PR so that others may benefit from better analysis in the future!

⚪ Analysis on new nodes

Code-Metrics defines all its analysis definitions in the variable codemetrics-rules which is an alist with the key of the alist being the mode and the value being another alist of analysis definitions.

;; Example of codemetrics-rules' structure
'((c-mode      . c-analysis-definitions)  ; <language>-analysis-definitions is structured as shown below
  (csharp-mode . csharp-analysis-definitions)
  (go-mode     . go-analysis-definitions)
  (scala-mode  . scala-analysis-definitions)
  ...)

;; Examle of a analysis definition alist
(setq csharp-analysis-definitions
    (if_statement   . (1 t))
    ("&&"           . codemetrics-rules--logical-operators))

So you can select whatever node that you want to analyze on it.

To find what node you'll want to analyze, refer to the tree-sitter documentation about viewing nodes. tree-sitter-debug and tree-sitter-query-builder are both very useful for this.

❔ Example

Let's look at a quick example of adding a new analysis definition. Let's say you want to add analysis to go-mode's if_statement. The analysis definition that is needed will be '(if_statement . (1 t)). To add this to the codemetrics-rules, you can do something like the following.

(push '(if_statement . (1 t)) (alist-get 'go-mode codemetrics-rules))

Now the new analysis definition should be usable by codemetrics!

🔍 Writing new analysis functions

For more complex analysis, you can write your own analysis rules!

• node - (optional) the targeted tree-sitter node, in this example, if_statement will be the targeting node.
• depth - (optional) current depth of from the root tree.
• nested - (optional) current nested level apply from current complexity algorithm.

Then the function needs to return an integer represent the score and a boolean represent increment of the nested level in the form (score-to-add . nested?). This can be useful if you want to add extra conditional logic onto your analysis.

As an example of an analysis function, take a look at the definition of the basic codemetrics-rules--class-declaration.

(defun codemetrics-rules--class-declaration (_node depth _nested)
  "..."
  (codemetrics-with-complexity
    (if (< 1 depth)  ; if class inside class,
        '(1 nil)     ; we score 1, but don't increase nested level
      '(0 nil))
    '(1 nil)))

🔗 References

• codemetrics
• resharper-cognitivecomplexity
• gocognit

🛠️ Contribute

If you would like to contribute to this project, you may either clone and make pull requests to this repository. Or you can clone the project and establish your own branch of this tool. Any methods are welcome!

🔬 Development

To run the test locally, you will need the following tools:

• Eask
• Make (optional)

Install all dependencies and development dependencies:

$ eask install-deps --dev

To test the package's installation:

$ eask package
$ eask install

To test compilation:

$ eask compile

🪧 The following steps are optional, but we recommend you follow these lint results!

The built-in checkdoc linter:

$ eask lint checkdoc

The standard package linter:

$ eask lint package

📝 P.S. For more information, find the Eask manual at https://emacs-eask.github.io/.

❓ How to add an analysis rules?

When adding a new analysis rules, add the analysis definition function to codemetrics.el itself near where the other rules functions live and then add the parser to codemetrics-rules.el file. Finally, if you are adding support for a new language, remember to add it to the codemetrics-rules variable.

When creating a new parser, name it codemetrics-rules-<language>.

When creating a new analysis function, name it codemetrics-rules-<language>-<feature> or something similar.

🔍 Where can I look for tree-sitter node?

Here are some techniques for finding your desired nodes in tree-sitter.

To look for the correct node you have three options:

• look at the tree-sitter-[lang]/grammar.js implementation. In the above example, if_statement node is defined in the tree-sitter-c-sharp's grammar.js file
• open a file of your language choice in emacs and M-x tree-sitter-debug-mode. This will display the whole s-expr representing your file
• (message "%S" (tsc-node-to-sexp)) in your function to display what your function is seeing

⚠️ Warning

Make sure you look into the correct repository. Repositories are managed under tree-sitter-langs's using git submodule. Some tree-sitter module aren't using the latest version!

⚜️ License

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see https://www.gnu.org/licenses/.

See LICENSE for details.