Revert "Load environment variables as a resolver (#480)"

This reverts commit 3cedc44821.

Fixes #497, #498

resolver.go

@@ -2,9 +2,7 @@ package kong
 
 import (
 	"encoding/json"
-	"fmt"
 	"io"
-	"os"
 	"strings"
 )
 
@@ -68,69 +66,3 @@ func snakeCase(name string) string {
 	name = strings.Join(strings.Split(strings.Title(name), "-"), "")
 	return strings.ToLower(name[:1]) + name[1:]
 }
-
-// EnvResolver provides a resolver for environment variables tags
-func EnvResolver() Resolver {
-	// Resolvers are typically only invoked for flags, as shown here:
-	// https://github.com/alecthomas/kong/blob/v1.6.0/context.go#L567
-	// However, environment variable annotations can also apply to arguments,
-	// as demonstrated in this test:
-	// https://github.com/alecthomas/kong/blob/v1.6.0/kong_test.go#L1226-L1244
-	// To handle this, we ensure that arguments are resolved as well.
-	// Since the resolution only needs to happen once, we use this boolean
-	// to track whether the resolution process has already been performed.
-	argsResolved := false
-	return ResolverFunc(func(context *Context, parent *Path, flag *Flag) (interface{}, error) {
-		if !argsResolved {
-			if err := resolveArgs(context.Path); err != nil {
-				return nil, err
-			}
-			// once resolved we do not want to run this anymore
-			argsResolved = true
-		}
-		for _, env := range flag.Tag.Envs {
-			envar, ok := os.LookupEnv(env)
-			// Parse the first non-empty ENV in the list
-			if ok {
-				return envar, nil
-			}
-		}
-		return nil, nil
-	})
-}
-
-func resolveArgs(paths []*Path) error {
-	for _, path := range paths {
-		if path.Command == nil {
-			continue
-		}
-		for _, positional := range path.Command.Positional {
-			if positional.Tag == nil {
-				continue
-			}
-			if err := visitValue(positional); err != nil {
-				return err
-			}
-		}
-		if path.Command.Argument != nil {
-			if err := visitValue(path.Command.Argument); err != nil {
-				return err
-			}
-		}
-	}
-	return nil
-}
-
-func visitValue(value *Value) error {
-	for _, env := range value.Tag.Envs {
-		envar, ok := os.LookupEnv(env)
-		if !ok {
-			continue
-		}
-		token := Token{Type: FlagValueToken, Value: envar}
-		if err := value.Parse(ScanFromTokens(token), value.Target); err != nil {
-			return fmt.Errorf("%s (from envar %s=%q)", err, env, envar)
-		}
-	}
-	return nil
-}