From 3a832f83439002319ba860bfdf2cfe9eff2dc12e Mon Sep 17 00:00:00 2001
From: Alec Thomas <alec@swapoff.org>
Date: Fri, 21 Sep 2018 12:06:24 +1000
Subject: [PATCH] Treat envars as higher priority than resolvers.

---
 context.go       |  3 +++
 kong.go          | 24 ++++++++++++------------
 model.go         | 14 +++++++++++++-
 resolver.go      | 14 --------------
 resolver_test.go | 25 -------------------------
 5 files changed, 28 insertions(+), 52 deletions(-)

diff --git a/context.go b/context.go
index 78c4b0e..a502412 100644
--- a/context.go
+++ b/context.go
@@ -198,6 +198,9 @@ func (c *Context) FlagValue(flag *Flag) interface{} {
 			return v.Interface()
 		}
 	}
+	if flag.Target.IsValid() {
+		return flag.Target.Interface()
+	}
 	return flag.DefaultValue.Interface()
 }
 
diff --git a/kong.go b/kong.go
index 53c345d..b1c45c4 100644
--- a/kong.go
+++ b/kong.go
@@ -63,13 +63,12 @@ type Kong struct {
 // See the README (https://github.com/alecthomas/kong) for usage instructions.
 func New(grammar interface{}, options ...Option) (*Kong, error) {
 	k := &Kong{
-		Exit:      os.Exit,
-		Stdout:    os.Stdout,
-		Stderr:    os.Stderr,
-		registry:  NewRegistry().RegisterDefaults(),
-		resolvers: []ResolverFunc{Envars()},
-		vars:      Vars{},
-		bindings:  bindings{},
+		Exit:     os.Exit,
+		Stdout:   os.Stdout,
+		Stderr:   os.Stderr,
+		registry: NewRegistry().RegisterDefaults(),
+		vars:     Vars{},
+		bindings: bindings{},
 	}
 
 	options = append(options, Bind(k))
@@ -169,11 +168,12 @@ func (k *Kong) extraFlags() []*Flag {
 	value := reflect.ValueOf(&helpTarget).Elem()
 	helpFlag := &Flag{
 		Value: &Value{
-			Name:   "help",
-			Help:   "Show context-sensitive help.",
-			Target: value,
-			Tag:    &Tag{},
-			Mapper: k.registry.ForValue(value),
+			Name:         "help",
+			Help:         "Show context-sensitive help.",
+			Target:       value,
+			Tag:          &Tag{},
+			Mapper:       k.registry.ForValue(value),
+			DefaultValue: reflect.ValueOf(false),
 		},
 	}
 	helpFlag.Flag = helpFlag
diff --git a/model.go b/model.go
index 50c1df9..5b90741 100644
--- a/model.go
+++ b/model.go
@@ -2,6 +2,7 @@ package kong
 
 import (
 	"fmt"
+	"os"
 	"reflect"
 	"strconv"
 	"strings"
@@ -282,11 +283,22 @@ func (v *Value) Apply(value reflect.Value) {
 	v.Set = true
 }
 
-// Reset this value to its default, either the zero value or the parsed result of its "default" tag.
+// Reset this value to its default, either the zero value or the parsed result of its envar,
+// or its "default" tag.
 //
 // Does not include resolvers.
 func (v *Value) Reset() error {
 	v.Target.Set(reflect.Zero(v.Target.Type()))
+	if v.Tag.Env != "" {
+		envar := os.Getenv(v.Tag.Env)
+		if envar != "" {
+			err := v.Parse(Scan(envar), v.Target)
+			if err != nil {
+				return fmt.Errorf("%s (from envar %s=%q)", err, v.Tag.Env, envar)
+			}
+			return nil
+		}
+	}
 	if v.Default != "" {
 		return v.Parse(Scan(v.Default), v.Target)
 	}
diff --git a/resolver.go b/resolver.go
index 5c89a18..9de21a5 100644
--- a/resolver.go
+++ b/resolver.go
@@ -4,7 +4,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"os"
 	"strings"
 )
 
@@ -61,16 +60,3 @@ func jsonDecodeValue(sep rune, value interface{}) (string, error) {
 	}
 	return "", fmt.Errorf("unsupported JSON value %v (of type %T)", value, value)
 }
-
-// Envars resolves flag values using the `env:"<name>"` tag. It ignores flags without this tag.
-//
-// This resolver is installed by default.
-func Envars() ResolverFunc {
-	return func(context *Context, parent *Path, flag *Flag) (string, error) {
-		if flag.Tag.Env == "" {
-			return "", nil
-		}
-		v, _ := os.LookupEnv(flag.Tag.Env)
-		return v, nil
-	}
-}
diff --git a/resolver_test.go b/resolver_test.go
index 501eae9..ad0cebe 100644
--- a/resolver_test.go
+++ b/resolver_test.go
@@ -61,31 +61,6 @@ func TestEnvarsFlagOverride(t *testing.T) {
 	require.Equal(t, "hello", cli.Flag)
 }
 
-func TestEnvarsOnlyPopulateUsedBranches(t *testing.T) {
-	// nolint
-	var cli struct {
-		UnvisitedArg struct {
-			UnvisitedArg string `arg`
-			Int          int    `env:"KONG_INT"`
-		} `arg`
-		UnvisitedCmd struct {
-			Int int `env:"KONG_INT"`
-		} `cmd`
-		Visited struct {
-			Int int `env:"KONG_INT"`
-		} `cmd`
-	}
-	parser, restoreEnv := newEnvParser(t, &cli, envMap{"KONG_INT": "512"})
-	defer restoreEnv()
-
-	_, err := parser.Parse([]string{"visited"})
-	require.NoError(t, err)
-
-	require.Equal(t, 512, cli.Visited.Int)
-	require.Equal(t, 0, cli.UnvisitedArg.Int)
-	require.Equal(t, 0, cli.UnvisitedCmd.Int)
-}
-
 func TestEnvarsTag(t *testing.T) {
 	var cli struct {
 		Slice []int `env:"KONG_NUMBERS"`