go-sprintf-bomb

Optimize Sprintfs away!

About

It's a linter that tries to replace fmt.Sprintf calls with more efficient string concatenation. (Work in progress.)

Example

Before applied fixes:

import (
    "errors"
    "fmt"
)

func main() {
    name := "John"
    age := 3
    pi := wrappedFloat64(3.14)
    err := errors.New("some error")

    _ = fmt.Sprintf("%s is %d years old. Pi is %f. And some error: %s", name, age, pi, err)
}

type wrappedFloat64 float64

After applied fixes:

import (
    "errors"
    // updated import:
    "strconv"
)

func main() {
    name := "John"
    age := 3
    pi := wrappedFloat64(3.14)
    err := errors.New("some error")

    // replaced fmt.Sprintf with string-concatenation and required transformations:
    _ = name + " is " + strconv.Itoa(age) + " years old. Pi is " + strconv.FormatFloat(/*added cast:*/ float64(pi), 'f', -1, 64) + ". And some error: " + err.Error()
}

type wrappedFloat64 float64

More examples of possible transformations can be found in the analyzer/testdata/src/default/p.go.golden file.

Installation

go install github.com/m-ocean-it/go-sprintf-bomb@latest

Run

Dry-run:

go-sprintf-bomb ./...

Apply all fixes:

go-sprintf-bomb --fix ./...

Be careful! Applying the fixes would mofidy your files. Be sure to commit/copy them before doing so.

(You've been warned. After all, it's a bomb...)

Features

• Updates imports as needed.
• Does not care about the shape and size of the format-string. The formatting placeholders (%s, %d, %f, etc.) can be at any position in the string and in any amount.
• Knows about the errors.error and fmt.Stringer interfaces and considers them when processing the %s formatting directive. Assumes the precedence of those interfaces in the same way the fmt library does.

Issues

• The longer the string and the more placeholders are used in a Sprintf-call, the less significant the optimization would be. It might be useful to add some heuristics to the linter to avoid actually harming the performance.

TODO

• Make behavior-changing transformations (.Error(), .String(). etc.) optional.
• Format bools with %t and %v directives.
• Format (u)ints with %v directive?
• Add tests for comparing the resulting strings to using fmt.Sprintf. The strings must be the same.
• Support complex float-formatting (i.e. consider more directives than just the plain %f).