go/src/cmd/go/internal/load/godebug.go

var ErrNotGoDebug …

func ParseGoDebug(text string) (key, value string, err error) { … }

// defaultGODEBUG returns the default GODEBUG setting for the main package p.
// When building a test binary, directives, testDirectives, and xtestDirectives
// list additional directives from the package under test.
func defaultGODEBUG(p *Package, directives, testDirectives, xtestDirectives []build.Directive) string { … }

func godebugForGoVersion(v string) map[string]string { … }