Story Details

This blog post details how to implement custom syntax highlighting in Emacs using tree-sitter. The author demonstrates creating a minor mode for highlighting TODO items and FIXMEs in comments within C++ code. This involves defining specific queries that target the comment nodes in the tree-sitter parse tree and then associating faces (colors and styles) with the captured nodes. The example provides a practical illustration of leveraging tree-sitter's structured code understanding to achieve more precise and context-aware highlighting than traditional regular expression-based approaches. The post also briefly covers how to incorporate these queries into a theme for broader application and includes a troubleshooting tip for ensuring tree-sitter highlighting is active.

Amit Patel's blog post, "Emacs Tree-sitter Custom Highlighting," explores leveraging the power of tree-sitter, a parsing library, for granular and context-aware syntax highlighting within Emacs. He begins by highlighting the limitations of traditional regular expression-based highlighting, noting its struggles with complex language constructs and the potential for slowdowns due to backtracking. Tree-sitter, in contrast, parses the code into an abstract syntax tree, allowing for more precise and efficient highlighting based on the actual structure of the code.

Patel meticulously details the process of setting up tree-sitter in Emacs, including the installation of necessary packages and configuration steps. He then delves into the core of the post: customizing highlighting rules. He explains how to define custom "queries" using tree-sitter's query language. These queries effectively target specific nodes in the parsed syntax tree, enabling the application of distinct highlighting styles. He provides concrete examples demonstrating how to highlight function calls, variable declarations, and even specific keywords within different contexts.

He emphasizes the flexibility and expressiveness of tree-sitter queries, showcasing how they can match patterns based not just on node types but also on their relationships within the tree, enabling highly specific highlighting scenarios. He illustrates this with an example of highlighting the self parameter in Python methods. Patel also covers handling language-specific configurations and ensuring smooth integration with existing Emacs themes.

Furthermore, Patel explores more advanced usage, such as highlighting based on capture groups within queries and dynamically updating the highlighting as the code is modified. He acknowledges the initial complexity of learning the tree-sitter query language but argues that its power and precision justify the effort. He concludes by expressing his enthusiasm for the potential of tree-sitter to significantly enhance the code editing experience in Emacs. He encourages readers to explore the possibilities and contribute to the growing ecosystem of tree-sitter grammars and highlighting configurations.