hexops / valast

Convert Go values to their AST

valast - convert Go values to their AST

Valast converts Go values at runtime into their go/ast equivalent, e.g.:

x := &foo.Bar{
    a: "hello world!",
    B: 1.234,
}
fmt.Println(valast.String(x))

Prints string:

&foo.Bar{a: "hello world!", B: 1.234}

What is this useful for?

This can be useful for debugging and testing, you may think of it as a more comprehensive and configurable version of the fmt package's %+v and %#v formatting directives. It is similar to e.g. repr in Python.

Features

• Produces Go code via a go/ast, defers formatting to the best-in-class Go formatter gofumpt.
• Fully handles unexported fields, types, and values (optional.)
• Strong emphasis on being used for producing valid Go code that can be copy & pasted directly into e.g. tests.
• Extensively tested, over 88 tests and handling numerous edge cases (such as pointers to unaddressable literal values like &"foo" properly, and even finding bugs in alternative packages').

Alternatives comparison

The following are alternatives to Valast, making note of the differences we found that let us to create Valast:

• github.com/davecgh/go-spew
  • may be inactive
  • Produces Go-like output, but not Go syntax.
• github.com/shurcooL/go-goon (based on go-spew)
  • Produces valid Go syntax, but not via a go/ast.
  • Produces less idiomatic/terse results)
  • Was deprecated in favor of valast.
• github.com/alecthomas/repr
  • Produces Go syntax, but not always valid code (e.g. can emit illegal &23, whereas Valast will emit a valid expression valast.Addr(23).(int)), not via a go/ast.
  • Does not handle unexported fields/types/values.

You may also wish to look at autogold and go-cmp, which aim to solve the "compare Go values in a test" problem.