goshift

A toolkit for go codemods

Overview

goshift is a command-line tool that performs user-defined AST transformations on a directory of Go source code files. The tool will traverse the directory structure recursively, applying the specified transformation functions to all matching files. The output will be a single patch file containing all the changes made by the AST transformations.

Features

• Apply one or more AST transformations to Go source code files in a directory.
• Traverse directories recursively, processing all nested Go files.
• Support file matching using glob patterns to include or exclude specific files and folders.
• Generate a single patch file containing all changes made by the transformations.

Usage

goshift [options] <source_directory> <output_patch_file>

Options

• -t, --transform: Path to a Go source code file containing one or more AST transformation functions. This option can be specified multiple times to include multiple transformation functions.
• -g, --glob: A glob pattern to filter the files and folders to be processed. By default, all .go files in the specified directory and its subdirectories will be processed.

Transformation Functions

The AST transformation functions should be written in Go and have the following signature:

func Transform(node ast.Node) (ast.Node, error)

The Transform function takes an ast.Node as input, representing the current node in the AST being processed. The function should return a modified ast.Node or an error if the transformation cannot be applied.

Examples

Apply a single transformation to all Go files in the ./src directory and output the changes to changes.patch:

goshift -t transform_function.go ./src changes.patch

Apply multiple transformations to Go files in the ./src directory, but only process files inside the ./src/models and ./src/controllers folders:

goshift -t transform_function1.go -t transform_function2.go -g "./src/{models,controllers}/**/*.go" ./src changes.patch

Implementation

The Go AST Transformer tool can be implemented using the following steps:

1. Parse the command-line arguments, including the source directory, output patch file, transformation function files, and file matching glob pattern.
2. Load and compile the transformation function(s) using the plugin package, which allows loading Go functions from source code files at runtime.
3. Traverse the source directory recursively, processing all files that match the specified glob pattern.
   • For each matching file, use the go/parser package to parse the file into an AST.
   • Apply the transformation function(s) to the AST using the ast.Inspect function.
   • Use the go/format package to convert the modified AST back to Go source code.
   • Generate a diff between the original and transformed source code using a library like github.com/sergi/go-diff/diffmatchpatch.
   • Append the diff to the output patch file.
4. Save the output patch file to the specified location.

Dependencies

• The Go standard library packages: go/parser, go/token, go/ast, go/format
• github.com/sergi/go-diff: A library to generate diffs between text files.
• The plugin package from the Go standard library for loading transformation functions from source code files. Note that this package is only supported on certain platforms (e.g., Linux and macOS).