Nevernester is a Go linter that finds nesting in golang functions. Many levels of nesting reduces readability and adds cognitive load.
To many levels of nesting makes it hard to understand what the code does. Here is a simple example with five levels of nesting being reduced to three:
func calculate(order *Order) int {
sum := 0
if order != nil {
if order.Header.IsValid {
for _, row := range order.Rows {
if row.IsValid {
sum = sum + row.Price
}
}
}
}
return sum
}Here the calculate function is easier to understand:
func calculate(order *Order) int {
sum := 0
if order == nil {
return sum
}
if order.Header.IsValid {
sum = getPrice(order.Rows)
}
return sum
}
func getPrice(rows []OrderRow) int {
sum := 0
for _, row := range rows {
if row.IsValid {
sum = sum + row.Price
}
}
return sum
}$go install github.com/raffepaffe/nevernester@latest
$nevernester ./...
The default level of nesting is 4. If you want another level, say 5, use the maxNesting option
$nevernester -max-nesting 5 ./...
If you want to skip checking tests or benchmarks use the skipTests and skipBenchmarks options
$nevernester -skip-tests=true -skip-benchmarks=true ./...
Linus Torvalds is pretty good developer and the coding style rules for the linux kernel states:
The answer to that is that if you need more than 3 levels of indentation, you're screwed anyway, and should fix your program.
Well, most of us are not as cool as Linus so nevernester has a default value of 4 levels. You can change that to whatever you want.
running nevernester on go 1.20.2 source with skip-tests, skip-benchmarks and max-nesting set to 6
$nevernester -skip-tests=true -skip-benchmarks=true -max-nesting 6 ./...
/usr/local/go/src/runtime/map.go:1152:1: calculated nesting for function evacuate is 7, max is 6
/usr/local/go/src/crypto/x509/parser.go:643:1: calculated nesting for function processExtensions is 7, max is 6
/usr/local/go/src/encoding/xml/xml.go:544:1: calculated nesting for function rawToken is 7, max is 6
/usr/local/go/src/regexp/syntax/parse.go:894:1: calculated nesting for function parse is 7, max is 6
/usr/local/go/src/go/parser/parser.go:1055:1: calculated nesting for function parseMethodSpec is 7, max is 6
/usr/local/go/src/image/draw/draw.go:956:1: calculated nesting for function drawPaletted is 7, max is 6
/usr/local/go/src/image/jpeg/scan.go:51:1: calculated nesting for function processSOS is 8, max is 6
/usr/local/go/src/database/sql/fakedb_test.go:881:1: calculated nesting for function QueryContext is 7, max is 6
/usr/local/go/src/go/parser/parser_test.go:360:1: calculated nesting for function getField is 9, max is 6
/usr/local/go/src/runtime/pprof/pprof_test.go:568:1: calculated nesting for function matchAndAvoidStacks is 7, max is 6
running nevernester on golangci-lint 1.52.1 source with skip-tests, skip-benchmarks with default nesting
$nevernester -skip-tests=true -skip-benchmarks=true ./...
golangci-lint/pkg/golinters/goanalysis/errors.go:22:1: calculated nesting for function buildIssuesFromIllTypedError is 5, max is 4
golangci-lint/pkg/golinters/goanalysis/runners.go:126:1: calculated nesting for function saveIssuesToCache is 5, max is 4
golangci-lint/pkg/golinters/gofmt_common.go:237:1: calculated nesting for function extractIssuesFromPatch is 5, max is 4
golangci-lint/pkg/golinters/nakedret.go:109:1: calculated nesting for function Visit is 5, max is 4
running nevernester on opentelemetry-go 1.15.0-rc.2 source with default settings
$nevernester ./...
opentelemetry-go/attribute/set_test.go:51:1: calculated nesting for function TestSetDedup is 5, max is 4
opentelemetry-go/exporters/otlp/internal/envconfig/envconfig_test.go:59:1: calculated nesting for function TestEnvConfig is 6, max is 4
The idea for this linter came after I watched this video discussing nesting in code.
Before I started to code I looked at other linters like cyclop, nilnil and wrapcheck.
Special thanks to Björn for helping out with testing.
Credit also goes to (in alphabetic order) Anders, Björn, Hampus and Oscar for helping me becoming a better Go developer.
As with most tools, this will likely miss some cases. If you come across a case which you think should be covered and isn't, please file an issue including a minimum reproducible example of the case.
This project is licensed under the MIT license. See the LICENSE file for more details.