go-codegenutil

Basic code generation utilities for Go metaprogrammers.

The codegenutil package provides primitives for representing Go identifiers as (import path, name) pairs--the *codegenutil.Symbol type--as well as a codegenutil.Package type that represents a unique name for a Go package.

The unusedimport package provides the import pruning features of the goimports command in library form and can be used without depending on the other packages in this library.

The codetemplate package provides an alternative to the "text/template" package for writing Go code templates. It is based on a 2022 fork of the "text/template" package and uses the same parser. Such templates can use *codegenutil.Symbol values directly as well as a "header" function to insert the package statement and imports blocks. codetemplate will ensure an import exists for each identifier from other package, and it will format the symbol according to the local name of the generated import statement.

Example

import (
    "github.com/meta-programming/go-codegenutil"
    "github.com/meta-programming/go-codegenutil/codetemplate"
)

func example() {
    // Parse the template.
    template, err := codetemplate.Parse(`// Package mypkg does neat things.
{{header}}

import "automaticallyremoved"

var result1 = {{.maxFn1}}(1, 2)
var result2 = {{.maxFn2}}(1, 2)

func main() {
    fmt.Printf("%f and %f\n", result1, result2)
    fmt.Printf("The people's choice: %f\n", {{.peoplesChoice}})
}
`)
    if err != nil {
        fmt.Printf("error parsing template: %v", err)
        return
    }

    // Execute the template with whatever data you'd like, and use symbols directly.
    filePackage := codegenutil.AssumedPackageName("abc.xyz/mypkg")
    code := &strings.Builder{}
    if err := template.Execute(codegenutil.NewFileImports(filePackage), code, map[string]*codegenutil.Symbol{
        "maxFn1":        codegenutil.Sym("math", "Max"),
        "maxFn2":        codegenutil.Sym("alternative/math", "Max"),
        "peoplesChoice": filePackage.Symbol("result2"),
    }); err != nil {
        fmt.Printf("error executing template: %v", err)
        return
    }

    fmt.Print(code.String())
}

Outputs:

// Package mypkg does neat things.
package mypkg

import (
	"math"

	math2 "alternative/math"
)

var result1 = math.Max(1, 2)
var result2 = math2.Max(1, 2)

func main() {
	fmt.Printf("%f and %f\n", result1, result2)
	fmt.Printf("The people's choice: %f\n", result2)
}