toast

ToAST

ToAST is a thin wrapper for the Go standard library ast package that provides a simple interface for working with Go types.

This package only supports parsing of type definitions. It was originally intended to be used for generating type definitions for other languages -- particularly CUE, a typesafe superset of JSON.

Types

Each go/ast type specification maps to one of four structs:

• PlainType: Basic types, type aliases, and pointers
• ArrayType: Array and slice types
• MapType: Maps
• StructType: Structs, which may contain fields that are themselves one of the four types.

There is also partial support for an EnumType, which is expressed by convention in Go as a type declaration with a group of constants of the same type.

Transforms

When parsing a file, ToAST can apply a number of transformations on matching objects:

• ExcludeImport excludes specific imports
• ModifyImport mutates specific imports
• ExcludeTypeDecl excludes specific type declarations
• ExcludeType excludes specific type declarations and references
• ModifyType mutates specific types
• ExcludeField excludes specific fields in a StructType
• ModifyField mutates specific fields in a StructType
• CopyIntoStruct copies fields from one or more named StructTypes into a target StructType, replacing the field at of a given name
• PromoteToEnumType converts a PlainType into an EnumType
• GenFieldTransform takes a StructType and a Field and returns some Transform that can be matched on subsequent nodes in the file
• GenEnumTypeTransform takes a string and go/ast.ValueSpec and returns a PromoteToEnumType transform that can be matched on a PlainType in the file

Usage

First, load an *ast.File. For example:

import "go/parser"

filePath := "path/to/file.go"
astFile, err := parser.ParseFile(token.NewFileSet(), filePath, nil, parser.ParseComments)
if err != nil {
	panic(err)
}

Then create a *toast.File:

file := toast.NewFile(astFile,
  WithTransform(&toast.ExcludeImport{
    Match: func(i Import) bool {
      return i.Name == "foo"
    }
  }),
  WithTransform(&toast.ExcludeType{
    Match: func(t Type) bool {
      return t.Name == "bar"
    }
  }),
  ...
)