1 is the base complexity of a function
+1 for each 'if', 'for', 'case', '&&' or '||'

$ go install github.com/fzipp/gocyclo/cmd/gocyclo@latest

Calculate cyclomatic complexities of Go functions.
Usage:
    gocyclo [flags] <Go file or directory> ...

Flags:
    -over N               show functions with complexity > N only and
                          return exit code 1 if the set is non-empty
    -top N                show the top N most complex functions only
    -avg, -avg-short      show the average complexity over all functions;
                          the short option prints the value without a label
    -ignore REGEX         exclude files matching the given regular expression

The output fields for each line are:
<complexity> <package> <function> <file:line:column>

$ gocyclo .
$ gocyclo main.go
$ gocyclo -top 10 src/
$ gocyclo -over 25 docker
$ gocyclo -avg .
$ gocyclo -top 20 -ignore "_test|Godeps|vendor/" .
$ gocyclo -over 3 -avg gocyclo/

9 gocyclo (*complexityVisitor).Visit complexity.go:30:1
8 main main cmd/gocyclo/main.go:53:1
7 gocyclo (*fileAnalyzer).analyzeDecl analyze.go:96:1
4 gocyclo Analyze analyze.go:24:1
4 gocyclo parseDirectives directives.go:27:1
4 gocyclo (Stats).SortAndFilter stats.go:52:1
Average: 2.72

//gocyclo:ignore
func f1() {
	// ...
}
    
//gocyclo:ignore
var f2 = func() {
	// ...
}