Added linting article

_posts/2024-05-22-linting.md

@@ -0,0 +1,141 @@
+---
+title: Linting code for LLMs with tree-sitter
+excerpt: Aider now lints code after every LLM edit and automatically fixes errors, using tree-sitter and AST-aware code context.
+---
+
+# Linting code for LLMs with tree-sitter
+
+Aider now lints your code after every LLM edit, and offers to automatically fix
+any linting errors.
+You can also use aider's lint-and-fix functionality on your source files any time
+you like, to speedily resolve issues with code written by humans.
+
+Aider shows linting errors to the LLM in a novel format,
+using the abstract syntax tree (AST) to display relevant code context for each
+error.
+This increases the ability of the LLM to understand the problem and
+make the correct changes to resolve it.
+
+Aider ships with basic linters built with tree-sitter that support
+[most popular programming languages](https://github.com/paul-gauthier/grep-ast/blob/main/grep_ast/parsers.py).
+These built in linters will detect syntax errors and other fatal problems with the code.
+
+You can also configure aider to use your preferred linters.
+This allows aider to check for a larger class of problems, keep the code style
+aligned with the rest of your team, etc.
+
+## Linting and fixing your code
+
+Aider now lints each source file after it applies the edits
+suggested by an LLM.
+If problems are found, aider will ask if you'd like it to
+attempt to fix the errors.
+If so, aider will send the LLM a report of the lint errors
+and request changes to fix them. This process may iterate a few times
+as the LLM works to fully resolve all the issues.
+
+You can also lint and fix files any time, on demand from within the aider chat or via the
+command line:
+
+- The in-chat `/lint` command will lint and fix all the files which have
+been added to the chat by default. Or you can name any files
+in your git repo as arguments.
+- From the command line, you can run `aider --lint` to lint and fix
+all the dirty files in the repo.
+Or you can specify specific filenames on the command line.
+
+
+## An LLM-friendly lint report
+
+Most linting tools produce terse and cryptic output,
+which is one reason many engineers appreciate IDEs that highlight
+linting errors.
+LLM's don't have the luxury of using an IDE, so aider sends
+the linting errors in an LLM friendly format.
+
+Here's an example of raw output of the `flake8` python linter:
+
+```
+app.py:23:36: F821 undefined name 'num'
+app.py:41:16: F541 f-string is missing placeholders
+```
+
+This sort of output depends on the user to reference line numbers to find and fix
+each reported error.
+LLMs are quite bad at working with source code line numbers, often
+making off-by-one errors and other mistakes even when provided with
+a fully numbered code listing.
+
+Aider augments the raw linter by
+displaying and
+highlighting the lines that have errors within their
+containing functions, methods, classes.
+To do this, aider uses tree-sitter to obtain the code's AST and analyzes it
+in light of the linting errors.
+LLMs are more effective at editing code that's provided
+with context like this.
+
+```
+app.py:23:36: F821 undefined name 'num'
+app.py:41:16: F541 f-string is missing placeholders
+
+app.py:
+...⋮...
+  6│class LongNum:
+  7│    def __init__(self, num):
+  8│        """
+  9│        Initialize the number.
+ 10│        """
+...⋮...
+ 19│    def __str__(self):
+ 20│        """
+ 21│        Render the number as a string.
+ 22│        """
+ 23█        return str(num)
+ 24│
+ 25│
+ 26│@app.route('/subtract/<int:x>/<int:y>')
+...⋮...
+ 38│@app.route('/divide/<int:x>/<int:y>')
+ 39│def divide(x, y):
+ 40│    if y == 0:
+ 41█        return f"Error: Cannot divide by zero"
+ 42│    else:
+ 43│        result = x / y
+ 44│        return str(result)
+ 45│
+...⋮...
+```
+
+## Basic linters for most popular languages
+
+Aider comes batteries-included with built in linters for
+[most popular programming languages](https://github.com/paul-gauthier/grep-ast/blob/main/grep_ast/parsers.py).
+This provides wide support for linting without requiring
+users to manually install a linter and configure it to work with aider.
+
+Aider's built in language-agnostic linter uses tree-sitter to parse
+the AST of each file.
+When tree-sitter encounters a syntax error or other fatal issue
+parsing a source file, it inserts an AST node with type `ERROR`.
+Aider simply uses these `ERROR` nodes to identify all the lines
+with syntax or other types of fatal error, and displays
+them in the LLM friendly format described above.
+
+## Configuring your preferred linters
+
+You can optionally configure aider to use
+your preferred linters with the `--lint-cmd` switch.
+
+```
+# To lint javascript with jslint
+aider --lint-cmd javascript:jslint
+
+# To lint python with flake8 using some specific args:
+aider --lint-cmd "python:flake8 --select=E9,F821,F823..."
+```
+
+You can provide multiple `--lint-cmd` switches
+to set linters for various languages.
+You can also durably set linters in your `.aider.conf.yml` file.
+