Awesome
errwrap
Wrap and fix Go errors with the new %w
verb directive. This tool analyzes
fmt.Errorf()
calls and reports calls that contain a verb directive that is
different than the new %w
verb directive introduced in Go v1.13. It's also capable of rewriting calls to use the new %w
wrap verb directive.
Install
# minimum v1.16 is required
go install github.com/fatih/errwrap@latest
or download one of the pre-compiled binaries from the releases page and copy to the desired location.
Usage
By default, errwrap
prints the output of the analyzer to stdout. You can pass
a file, directory or a Go package:
$ errwrap foo.go # pass a file
$ errwrap ./... # recursively analyze all files
$ errwrap github.com/fatih/gomodifytags # or pass a package
When called it displays the error with the line and column:
gomodifytags@v1.0.1/main.go:200:16: call could wrap the error with error-wrapping directive %w
gomodifytags@v1.0.1/main.go:641:17: call could wrap the error with error-wrapping directive %w
gomodifytags@v1.0.1/main.go:749:15: call could wrap the error with error-wrapping directive %w
errwrap
is also able to rewrite your source code to replace any verb
directive used for an error
type with the %w
verb directive. Assume we have
the following source code:
$ cat demo.go
package main
import (
"errors"
"fmt"
)
func main() {
_ = foo()
}
func foo() error {
err := errors.New("bar!")
return fmt.Errorf("foo failed: %s: %s bar ...", "foo", err)
}
Calling errwrap
with the -fix
flag will rewrite the source code:
$ errwrap -fix main.go
main.go:14:9: call could wrap the error with error-wrapping directive %w
diff --git a/main.go b/main.go
index 41d1c42..6cb42b8 100644
--- a/main.go
+++ b/main.go
@@ -11,5 +11,5 @@ func main() {
func foo() error {
err := errors.New("bar!")
- return fmt.Errorf("failed for %s with error: %s", "foo", err)
+ return fmt.Errorf("failed for %s with error: %w", "foo", err)
}
Whether to Wrap or not?
Wrapping an error is not always the best approach. Wrapping exposes the underlying error and makes it part of your public API. This means clients who rely on them could see breaking changes if you change your underlying implementation or don't wrap anymore.
The blog post Working with Errors in Go
1.13 contains a section called
Whether to Wrap
that explains this in more detail
Credits
This tool is built on top of the excellent go/analysis
package that makes it
easy to write custom analyzers in Go. If you're interested in writing a tool,
check out my Using go/analysis to write a custom
linter
blog post.
Also part of the code that parses the verb directives is from the
go/analysis/passes/printf
analyzer. It's a simplified version and might
contain discrepancies.