Misc config loading fixes

The main motivation behind this is simplicity and correctnes, but the new small config library is also faster:

```
BenchmarkDefaultConfigProvider/Viper-16         	  252418	      4546 ns/op	    2720 B/op	      30 allocs/op
BenchmarkDefaultConfigProvider/Custom-16        	  450756	      2651 ns/op	    1008 B/op	       6 allocs/op
```

Fixes #8633
Fixes #8618
Fixes #8630
Updates #8591
Closes #6680
Closes #5192

19 files changed, 62 insertions, 54 deletions

diff --git a/tpl/cast/docshelper.go b/tpl/cast/docshelper.go
index 035db1740..a3cc26de5 100644
--- a/tpl/cast/docshelper.go
+++ b/tpl/cast/docshelper.go
@@ -15,18 +15,18 @@ package cast
 
 import (
 	"github.com/gohugoio/hugo/common/loggers"
+	"github.com/gohugoio/hugo/config"
 	"github.com/gohugoio/hugo/deps"
 	"github.com/gohugoio/hugo/docshelper"
 	"github.com/gohugoio/hugo/resources/page"
 	"github.com/gohugoio/hugo/tpl/internal"
-	"github.com/spf13/viper"
 )
 
 // This file provides documentation support and is randomly put into this package.
 func init() {
 	docsProvider := func() docshelper.DocProvider {
 		d := &deps.Deps{
-			Cfg:                 viper.New(),
+			Cfg:                 config.New(),
 			Log:                 loggers.NewErrorLogger(),
 			BuildStartListeners: &deps.Listeners{},
 			Site:                page.NewDummyHugoSite(newTestConfig()),
@@ -46,8 +46,8 @@ func init() {
 	docshelper.AddDocProviderFunc(docsProvider)
 }
 
-func newTestConfig() *viper.Viper {
-	v := viper.New()
+func newTestConfig() config.Provider {
+	v := config.New()
 	v.Set("contentDir", "content")
 	return v
 }
diff --git a/tpl/collections/collections_test.go b/tpl/collections/collections_test.go
index 1e0569751..3faf46930 100644
--- a/tpl/collections/collections_test.go
+++ b/tpl/collections/collections_test.go
@@ -32,7 +32,7 @@ import (
 	"github.com/gohugoio/hugo/hugofs"
 	"github.com/gohugoio/hugo/langs"
 	"github.com/spf13/afero"
-	"github.com/spf13/viper"
+	
 )
 
 type tstNoStringer struct{}
@@ -986,7 +986,7 @@ func newDeps(cfg config.Provider) *deps.Deps {
 }
 
 func newTestNs() *Namespace {
-	v := viper.New()
+	v := config.New()
 	v.Set("contentDir", "content")
 	return New(newDeps(v))
 }
diff --git a/tpl/data/init_test.go b/tpl/data/init_test.go
index fedce8e5c..9174d42a6 100644
--- a/tpl/data/init_test.go
+++ b/tpl/data/init_test.go
@@ -17,10 +17,10 @@ import (
 	"testing"
 
 	qt "github.com/frankban/quicktest"
+	"github.com/gohugoio/hugo/config"
 	"github.com/gohugoio/hugo/htesting/hqt"
 	"github.com/gohugoio/hugo/langs"
 	"github.com/gohugoio/hugo/tpl/internal"
-	"github.com/spf13/viper"
 )
 
 func TestInit(t *testing.T) {
@@ -28,7 +28,7 @@ func TestInit(t *testing.T) {
 	var found bool
 	var ns *internal.TemplateFuncsNamespace
 
-	v := viper.New()
+	v := config.New()
 	v.Set("contentDir", "content")
 	langs.LoadLanguageSettings(v, nil)
 
diff --git a/tpl/data/resources_test.go b/tpl/data/resources_test.go
index 18061c052..1bf6d769f 100644
--- a/tpl/data/resources_test.go
+++ b/tpl/data/resources_test.go
@@ -34,12 +34,12 @@ import (
 	"github.com/gohugoio/hugo/hugofs"
 	"github.com/gohugoio/hugo/langs"
 	"github.com/spf13/afero"
-	"github.com/spf13/viper"
+	
 )
 
 func TestScpGetLocal(t *testing.T) {
 	t.Parallel()
-	v := viper.New()
+	v := config.New()
 	fs := hugofs.NewMem(v)
 	ps := helpers.FilePathSeparator
 
@@ -144,7 +144,7 @@ func TestScpGetRemoteParallel(t *testing.T) {
 	c.Assert(err, qt.IsNil)
 
 	for _, ignoreCache := range []bool{false} {
-		cfg := viper.New()
+		cfg := config.New()
 		cfg.Set("ignoreCache", ignoreCache)
 		cfg.Set("contentDir", "content")
 
@@ -223,7 +223,7 @@ func newDeps(cfg config.Provider) *deps.Deps {
 }
 
 func newTestNs() *Namespace {
-	v := viper.New()
+	v := config.New()
 	v.Set("contentDir", "content")
 	return New(newDeps(v))
 }
diff --git a/tpl/encoding/encoding.go b/tpl/encoding/encoding.go
index 09e2b94bc..ce25151a0 100644
--- a/tpl/encoding/encoding.go
+++ b/tpl/encoding/encoding.go
@@ -20,6 +20,7 @@ import (
 	"errors"
 	"html/template"
 
+	"github.com/gohugoio/hugo/common/maps"
 	"github.com/spf13/cast"
 )
 
@@ -71,7 +72,7 @@ func (ns *Namespace) Jsonify(args ...interface{}) (template.HTML, error) {
 	case 2:
 		var opts map[string]string
 
-		opts, err = cast.ToStringMapStringE(args[0])
+		opts, err = maps.ToStringMapStringE(args[0])
 		if err != nil {
 			break
 		}
diff --git a/tpl/hugo/init_test.go b/tpl/hugo/init_test.go
index c94a883fd..9b1b14be4 100644
--- a/tpl/hugo/init_test.go
+++ b/tpl/hugo/init_test.go
@@ -16,20 +16,21 @@ package hugo
 import (
 	"testing"
 
+	"github.com/gohugoio/hugo/config"
+
 	"github.com/gohugoio/hugo/htesting/hqt"
 
 	qt "github.com/frankban/quicktest"
 	"github.com/gohugoio/hugo/deps"
 	"github.com/gohugoio/hugo/resources/page"
 	"github.com/gohugoio/hugo/tpl/internal"
-	"github.com/spf13/viper"
 )
 
 func TestInit(t *testing.T) {
 	c := qt.New(t)
 	var found bool
 	var ns *internal.TemplateFuncsNamespace
-	v := viper.New()
+	v := config.New()
 	v.Set("contentDir", "content")
 	s := page.NewDummyHugoSite(v)
 
diff --git a/tpl/images/images_test.go b/tpl/images/images_test.go
index b1b1e1cfd..2a2b79478 100644
--- a/tpl/images/images_test.go
+++ b/tpl/images/images_test.go
@@ -22,11 +22,11 @@ import (
 	"testing"
 
 	qt "github.com/frankban/quicktest"
+	"github.com/gohugoio/hugo/config"
 	"github.com/gohugoio/hugo/deps"
 	"github.com/gohugoio/hugo/hugofs"
 	"github.com/spf13/afero"
 	"github.com/spf13/cast"
-	"github.com/spf13/viper"
 )
 
 type tstNoStringer struct{}
@@ -82,7 +82,7 @@ func TestNSConfig(t *testing.T) {
 	t.Parallel()
 	c := qt.New(t)
 
-	v := viper.New()
+	v := config.New()
 	v.Set("workingDir", "/a/b")
 
 	ns := New(&deps.Deps{Fs: hugofs.NewMem(v)})
diff --git a/tpl/os/os_test.go b/tpl/os/os_test.go
index 3adb6f8c2..bbc0d018c 100644
--- a/tpl/os/os_test.go
+++ b/tpl/os/os_test.go
@@ -17,11 +17,12 @@ import (
 	"path/filepath"
 	"testing"
 
+	"github.com/gohugoio/hugo/config"
+
 	qt "github.com/frankban/quicktest"
 	"github.com/gohugoio/hugo/deps"
 	"github.com/gohugoio/hugo/hugofs"
 	"github.com/spf13/afero"
-	"github.com/spf13/viper"
 )
 
 func TestReadFile(t *testing.T) {
@@ -30,7 +31,7 @@ func TestReadFile(t *testing.T) {
 
 	workingDir := "/home/hugo"
 
-	v := viper.New()
+	v := config.New()
 	v.Set("workingDir", workingDir)
 
 	// f := newTestFuncsterWithViper(v)
@@ -68,7 +69,7 @@ func TestFileExists(t *testing.T) {
 
 	workingDir := "/home/hugo"
 
-	v := viper.New()
+	v := config.New()
 	v.Set("workingDir", workingDir)
 
 	ns := New(&deps.Deps{Fs: hugofs.NewMem(v)})
@@ -103,7 +104,7 @@ func TestStat(t *testing.T) {
 	c := qt.New(t)
 	workingDir := "/home/hugo"
 
-	v := viper.New()
+	v := config.New()
 	v.Set("workingDir", workingDir)
 
 	ns := New(&deps.Deps{Fs: hugofs.NewMem(v)})
diff --git a/tpl/path/path_test.go b/tpl/path/path_test.go
index ce453b9a1..dc0761f2f 100644
--- a/tpl/path/path_test.go
+++ b/tpl/path/path_test.go
@@ -18,11 +18,11 @@ import (
 	"testing"
 
 	qt "github.com/frankban/quicktest"
+	"github.com/gohugoio/hugo/config"
 	"github.com/gohugoio/hugo/deps"
-	"github.com/spf13/viper"
 )
 
-var ns = New(&deps.Deps{Cfg: viper.New()})
+var ns = New(&deps.Deps{Cfg: config.New()})
 
 type tstNoStringer struct{}
 
diff --git a/tpl/resources/resources.go b/tpl/resources/resources.go
index da2b4ca3b..850def00e 100644
--- a/tpl/resources/resources.go
+++ b/tpl/resources/resources.go
@@ -282,7 +282,7 @@ func (ns *Namespace) ToCSS(args ...interface{}) (resource.Resource, error) {
 	}
 
 	if m != nil {
-		maps.ToLower(m)
+		maps.PrepareParams(m)
 		if t, found := m["transpiler"]; found {
 			switch t {
 			case transpilerDart, transpilerLibSass:
diff --git a/tpl/site/init_test.go b/tpl/site/init_test.go
index f4a7935ad..f4c2ecd5c 100644
--- a/tpl/site/init_test.go
+++ b/tpl/site/init_test.go
@@ -16,12 +16,13 @@ package site
 import (
 	"testing"
 
+	"github.com/gohugoio/hugo/config"
+
 	qt "github.com/frankban/quicktest"
 	"github.com/gohugoio/hugo/deps"
 	"github.com/gohugoio/hugo/htesting/hqt"
 	"github.com/gohugoio/hugo/resources/page"
 	"github.com/gohugoio/hugo/tpl/internal"
-	"github.com/spf13/viper"
 )
 
 func TestInit(t *testing.T) {
@@ -29,7 +30,7 @@ func TestInit(t *testing.T) {
 
 	var found bool
 	var ns *internal.TemplateFuncsNamespace
-	v := viper.New()
+	v := config.New()
 	v.Set("contentDir", "content")
 	s := page.NewDummyHugoSite(v)
 
diff --git a/tpl/strings/init_test.go b/tpl/strings/init_test.go
index b356896cf..dd15418c8 100644
--- a/tpl/strings/init_test.go
+++ b/tpl/strings/init_test.go
@@ -16,12 +16,13 @@ package strings
 import (
 	"testing"
 
+	"github.com/gohugoio/hugo/config"
+
 	"github.com/gohugoio/hugo/htesting/hqt"
 
 	qt "github.com/frankban/quicktest"
 	"github.com/gohugoio/hugo/deps"
 	"github.com/gohugoio/hugo/tpl/internal"
-	"github.com/spf13/viper"
 )
 
 func TestInit(t *testing.T) {
@@ -30,7 +31,7 @@ func TestInit(t *testing.T) {
 	var ns *internal.TemplateFuncsNamespace
 
 	for _, nsf := range internal.TemplateFuncsNamespaceRegistry {
-		ns = nsf(&deps.Deps{Cfg: viper.New()})
+		ns = nsf(&deps.Deps{Cfg: config.New()})
 		if ns.Name == name {
 			found = true
 			break
diff --git a/tpl/strings/strings_test.go b/tpl/strings/strings_test.go
index 6e14a408c..18c033793 100644
--- a/tpl/strings/strings_test.go
+++ b/tpl/strings/strings_test.go
@@ -17,14 +17,14 @@ import (
 	"html/template"
 	"testing"
 
+	"github.com/gohugoio/hugo/config"
 	"github.com/gohugoio/hugo/deps"
 
 	qt "github.com/frankban/quicktest"
 	"github.com/spf13/cast"
-	"github.com/spf13/viper"
 )
 
-var ns = New(&deps.Deps{Cfg: viper.New()})
+var ns = New(&deps.Deps{Cfg: config.New()})
 
 type tstNoStringer struct{}
 
diff --git a/tpl/tplimpl/template_funcs_test.go b/tpl/tplimpl/template_funcs_test.go
index 67e957924..6ddf13b76 100644
--- a/tpl/tplimpl/template_funcs_test.go
+++ b/tpl/tplimpl/template_funcs_test.go
@@ -37,13 +37,13 @@ import (
 	"github.com/gohugoio/hugo/tpl/internal"
 	"github.com/gohugoio/hugo/tpl/partials"
 	"github.com/spf13/afero"
-	"github.com/spf13/viper"
+	
 )
 
 var logger = loggers.NewErrorLogger()
 
 func newTestConfig() config.Provider {
-	v := viper.New()
+	v := config.New()
 	v.Set("contentDir", "content")
 	v.Set("dataDir", "data")
 	v.Set("i18nDir", "i18n")
@@ -206,7 +206,7 @@ func BenchmarkPartialCached(b *testing.B) {
 
 func doBenchmarkPartial(b *testing.B, f func(ns *partials.Namespace) error) {
 	c := qt.New(b)
-	config := newDepsConfig(viper.New())
+	config := newDepsConfig(config.New())
 	config.WithTemplate = func(templ tpl.TemplateManager) error {
 		err := templ.AddTemplate("partials/bench1", `{{ shuffle (seq 1 10) }}`)
 		if err != nil {
diff --git a/tpl/transform/remarshal_test.go b/tpl/transform/remarshal_test.go
index eb5f4253c..9f3e05e61 100644
--- a/tpl/transform/remarshal_test.go
+++ b/tpl/transform/remarshal_test.go
@@ -16,16 +16,16 @@ package transform
 import (
 	"testing"
 
+	"github.com/gohugoio/hugo/config"
 	"github.com/gohugoio/hugo/htesting"
 
 	qt "github.com/frankban/quicktest"
-	"github.com/spf13/viper"
 )
 
 func TestRemarshal(t *testing.T) {
 	t.Parallel()
 
-	v := viper.New()
+	v := config.New()
 	v.Set("contentDir", "content")
 	ns := New(newDeps(v))
 	c := qt.New(t)
@@ -112,7 +112,7 @@ title: Test Metadata
 func TestRemarshalComments(t *testing.T) {
 	t.Parallel()
 
-	v := viper.New()
+	v := config.New()
 	v.Set("contentDir", "content")
 	ns := New(newDeps(v))
 
@@ -158,7 +158,7 @@ func TestTestRemarshalError(t *testing.T) {
 	t.Parallel()
 	c := qt.New(t)
 
-	v := viper.New()
+	v := config.New()
 	v.Set("contentDir", "content")
 	ns := New(newDeps(v))
 
@@ -172,7 +172,7 @@ func TestTestRemarshalError(t *testing.T) {
 func TestTestRemarshalMapInput(t *testing.T) {
 	t.Parallel()
 	c := qt.New(t)
-	v := viper.New()
+	v := config.New()
 	v.Set("contentDir", "content")
 	ns := New(newDeps(v))
 
diff --git a/tpl/transform/transform_test.go b/tpl/transform/transform_test.go
index b98d82d27..1dbf97f98 100644
--- a/tpl/transform/transform_test.go
+++ b/tpl/transform/transform_test.go
@@ -26,7 +26,7 @@ import (
 	"github.com/gohugoio/hugo/helpers"
 	"github.com/gohugoio/hugo/hugofs"
 	"github.com/gohugoio/hugo/langs"
-	"github.com/spf13/viper"
+	
 )
 
 type tstNoStringer struct{}
@@ -35,7 +35,7 @@ func TestEmojify(t *testing.T) {
 	t.Parallel()
 	c := qt.New(t)
 
-	v := viper.New()
+	v := config.New()
 	ns := New(newDeps(v))
 
 	for _, test := range []struct {
@@ -64,7 +64,7 @@ func TestHighlight(t *testing.T) {
 	t.Parallel()
 	c := qt.New(t)
 
-	v := viper.New()
+	v := config.New()
 	v.Set("contentDir", "content")
 	ns := New(newDeps(v))
 
@@ -96,7 +96,7 @@ func TestHTMLEscape(t *testing.T) {
 	t.Parallel()
 	c := qt.New(t)
 
-	v := viper.New()
+	v := config.New()
 	v.Set("contentDir", "content")
 	ns := New(newDeps(v))
 
@@ -126,7 +126,7 @@ func TestHTMLUnescape(t *testing.T) {
 	t.Parallel()
 	c := qt.New(t)
 
-	v := viper.New()
+	v := config.New()
 	v.Set("contentDir", "content")
 	ns := New(newDeps(v))
 
@@ -156,7 +156,7 @@ func TestMarkdownify(t *testing.T) {
 	t.Parallel()
 	c := qt.New(t)
 
-	v := viper.New()
+	v := config.New()
 	v.Set("contentDir", "content")
 	ns := New(newDeps(v))
 
@@ -185,7 +185,7 @@ func TestMarkdownify(t *testing.T) {
 func TestMarkdownifyBlocksOfText(t *testing.T) {
 	t.Parallel()
 	c := qt.New(t)
-	v := viper.New()
+	v := config.New()
 	v.Set("contentDir", "content")
 	ns := New(newDeps(v))
 
@@ -211,7 +211,7 @@ func TestPlainify(t *testing.T) {
 	t.Parallel()
 	c := qt.New(t)
 
-	v := viper.New()
+	v := config.New()
 	ns := New(newDeps(v))
 
 	for _, test := range []struct {
diff --git a/tpl/transform/unmarshal_test.go b/tpl/transform/unmarshal_test.go
index ec81c316a..85e3610d1 100644
--- a/tpl/transform/unmarshal_test.go
+++ b/tpl/transform/unmarshal_test.go
@@ -19,13 +19,14 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/gohugoio/hugo/config"
+
 	"github.com/gohugoio/hugo/common/hugio"
 	"github.com/gohugoio/hugo/resources/resource"
 
 	"github.com/gohugoio/hugo/media"
 
 	qt "github.com/frankban/quicktest"
-	"github.com/spf13/viper"
 )
 
 const (
@@ -79,7 +80,7 @@ func (t testContentResource) Key() string {
 }
 
 func TestUnmarshal(t *testing.T) {
-	v := viper.New()
+	v := config.New()
 	ns := New(newDeps(v))
 	c := qt.New(t)
 
@@ -173,7 +174,7 @@ a;b;c`, mime: media.CSVType}, map[string]interface{}{"DElimiter": ";", "Comment"
 }
 
 func BenchmarkUnmarshalString(b *testing.B) {
-	v := viper.New()
+	v := config.New()
 	ns := New(newDeps(v))
 
 	const numJsons = 100
@@ -196,7 +197,7 @@ func BenchmarkUnmarshalString(b *testing.B) {
 }
 
 func BenchmarkUnmarshalResource(b *testing.B) {
-	v := viper.New()
+	v := config.New()
 	ns := New(newDeps(v))
 
 	const numJsons = 100
diff --git a/tpl/urls/init_test.go b/tpl/urls/init_test.go
index f88aaf398..27b21144a 100644
--- a/tpl/urls/init_test.go
+++ b/tpl/urls/init_test.go
@@ -16,11 +16,12 @@ package urls
 import (
 	"testing"
 
+	"github.com/gohugoio/hugo/config"
+
 	qt "github.com/frankban/quicktest"
 	"github.com/gohugoio/hugo/deps"
 	"github.com/gohugoio/hugo/htesting/hqt"
 	"github.com/gohugoio/hugo/tpl/internal"
-	"github.com/spf13/viper"
 )
 
 func TestInit(t *testing.T) {
@@ -29,7 +30,7 @@ func TestInit(t *testing.T) {
 	var ns *internal.TemplateFuncsNamespace
 
 	for _, nsf := range internal.TemplateFuncsNamespaceRegistry {
-		ns = nsf(&deps.Deps{Cfg: viper.New()})
+		ns = nsf(&deps.Deps{Cfg: config.New()})
 		if ns.Name == name {
 			found = true
 			break
diff --git a/tpl/urls/urls_test.go b/tpl/urls/urls_test.go
index 9c005d2df..23068c243 100644
--- a/tpl/urls/urls_test.go
+++ b/tpl/urls/urls_test.go
@@ -17,14 +17,15 @@ import (
 	"net/url"
 	"testing"
 
+	"github.com/gohugoio/hugo/config"
+
 	"github.com/gohugoio/hugo/htesting/hqt"
 
 	qt "github.com/frankban/quicktest"
 	"github.com/gohugoio/hugo/deps"
-	"github.com/spf13/viper"
 )
 
-var ns = New(&deps.Deps{Cfg: viper.New()})
+var ns = New(&deps.Deps{Cfg: config.New()})
 
 type tstNoStringer struct{}