Handle views in combo with Ace base templates

As views looks like a regular template, but doesn't need a base template, we have to look inside it.

Altough really not needed by this commit, reading the full file content into memory just to do a substring search is a waste.
So this commit implements a `ReaderContains` func that in most cases should be much faster than doing an `ioutil.ReadAll` and `bytes.Contains`:

```
benchmark                   old ns/op     new ns/op     delta
BenchmarkReaderContains     78452         20260         -74.18%

benchmark                   old allocs     new allocs     delta
BenchmarkReaderContains     46             20             -56.52%

benchmark                   old bytes     new bytes     delta
BenchmarkReaderContains     46496         1258          -97.29%
```

Fixes #999

3 files changed, 147 insertions, 4 deletions

diff --git a/helpers/general.go b/helpers/general.go
index 3e0a85fbc..baf957d75 100644
--- a/helpers/general.go
+++ b/helpers/general.go
@@ -112,6 +112,42 @@ func BytesToReader(in []byte) io.Reader {
 	return bytes.NewReader(in)
 }
 
+// ReaderContains reports whether subslice is within r.
+func ReaderContains(r io.Reader, subslice []byte) bool {
+
+	if len(subslice) == 0 {
+		return false
+	}
+
+	bufflen := len(subslice) * 4
+	halflen := bufflen / 2
+	buff := make([]byte, bufflen)
+	var err error
+	var n, i int
+
+	for {
+		i++
+		if i == 1 {
+			n, err = io.ReadAtLeast(r, buff[:halflen], halflen)
+		} else {
+			if i != 2 {
+				// shift left to catch overlapping matches
+				copy(buff[:], buff[halflen:])
+			}
+			n, err = io.ReadAtLeast(r, buff[halflen:], halflen)
+		}
+
+		if n > 0 && bytes.Contains(buff, subslice) {
+			return true
+		}
+
+		if err != nil {
+			break
+		}
+	}
+	return false
+}
+
 // ThemeSet checks whether a theme is in use or not.
 func ThemeSet() bool {
 	return viper.GetString("theme") != ""
diff --git a/helpers/general_test.go b/helpers/general_test.go
index b5706a445..496439db1 100644
--- a/helpers/general_test.go
+++ b/helpers/general_test.go
@@ -1,7 +1,9 @@
 package helpers
 
 import (
+	"bytes"
 	"github.com/stretchr/testify/assert"
+	"io/ioutil"
 	"reflect"
 	"strings"
 	"testing"
@@ -44,6 +46,101 @@ func TestStringToReader(t *testing.T) {
 	assert.Equal(t, asString, ReaderToString(asReader))
 }
 
+var containsTestText = (`На берегу пустынных волн
+Стоял он, дум великих полн,
+И вдаль глядел. Пред ним широко
+Река неслася; бедный чёлн
+По ней стремился одиноко.
+По мшистым, топким берегам
+Чернели избы здесь и там,
+Приют убогого чухонца;
+И лес, неведомый лучам
+В тумане спрятанного солнца,
+Кругом шумел.
+
+Τη γλώσσα μου έδωσαν ελληνική
+το σπίτι φτωχικό στις αμμουδιές του Ομήρου.
+Μονάχη έγνοια η γλώσσα μου στις αμμουδιές του Ομήρου.
+
+από το Άξιον Εστί
+του Οδυσσέα Ελύτη
+
+Sîne klâwen durh die wolken sint geslagen,
+er stîget ûf mit grôzer kraft,
+ich sih in grâwen tägelîch als er wil tagen,
+den tac, der im geselleschaft
+erwenden wil, dem werden man,
+den ich mit sorgen în verliez.
+ich bringe in hinnen, ob ich kan.
+sîn vil manegiu tugent michz leisten hiez.
+`)
+
+var containsBenchTestData = []struct {
+	v1     string
+	v2     []byte
+	expect bool
+}{
+	{"abc", []byte("a"), true},
+	{"abc", []byte("b"), true},
+	{"abcdefg", []byte("efg"), true},
+	{"abc", []byte("d"), false},
+	{containsTestText, []byte("стремился"), true},
+	{containsTestText, []byte(containsTestText[10:80]), true},
+	{containsTestText, []byte(containsTestText[100:110]), true},
+	{containsTestText, []byte(containsTestText[len(containsTestText)-100 : len(containsTestText)-10]), true},
+	{containsTestText, []byte(containsTestText[len(containsTestText)-20:]), true},
+	{containsTestText, []byte("notfound"), false},
+}
+
+// some corner cases
+var containsAdditionalTestData = []struct {
+	v1     string
+	v2     []byte
+	expect bool
+}{
+	{"", []byte("a"), false},
+	{"a", []byte(""), false},
+	{"", []byte(""), false},
+}
+
+func TestReaderContains(t *testing.T) {
+	for i, this := range append(containsBenchTestData, containsAdditionalTestData...) {
+		result := ReaderContains(StringToReader(this.v1), this.v2)
+		if result != this.expect {
+			t.Errorf("[%d] Got %t but expected %t", i, result, this.expect)
+		}
+	}
+}
+
+func BenchmarkReaderContains(b *testing.B) {
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		for i, this := range containsBenchTestData {
+			result := ReaderContains(StringToReader(this.v1), this.v2)
+			if result != this.expect {
+				b.Errorf("[%d] Got %t but expected %t", i, result, this.expect)
+			}
+		}
+	}
+}
+
+// kept to compare the above
+func _BenchmarkReaderContains(b *testing.B) {
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		for i, this := range containsBenchTestData {
+			bs, err := ioutil.ReadAll(StringToReader(this.v1))
+			if err != nil {
+				b.Fatalf("Failed %s", err)
+			}
+			result := bytes.Contains(bs, this.v2)
+			if result != this.expect {
+				b.Errorf("[%d] Got %t but expected %t", i, result, this.expect)
+			}
+		}
+	}
+}
+
 func TestFindAvailablePort(t *testing.T) {
 	addr, err := FindAvailablePort()
 	assert.Nil(t, err)
diff --git a/helpers/path.go b/helpers/path.go
index 91419e0c9..546f23d36 100644
--- a/helpers/path.go
+++ b/helpers/path.go
@@ -16,16 +16,15 @@ package helpers
 import (
 	"errors"
 	"fmt"
+	"github.com/spf13/afero"
+	jww "github.com/spf13/jwalterweatherman"
+	"github.com/spf13/viper"
 	"io"
 	"os"
 	"path/filepath"
 	"regexp"
 	"strings"
 	"unicode"
-
-	"github.com/spf13/afero"
-	jww "github.com/spf13/jwalterweatherman"
-	"github.com/spf13/viper"
 )
 
 // FilepathPathBridge is a bridge for common functionality in filepath vs path
@@ -153,6 +152,17 @@ func IsEmpty(path string, fs afero.Fs) (bool, error) {
 	return fi.Size() == 0, nil
 }
 
+// Check if a file contains a specified string.
+func FileContains(filename string, subslice []byte, fs afero.Fs) (bool, error) {
+	f, err := os.Open(filename)
+	if err != nil {
+		return false, err
+	}
+	defer f.Close()
+
+	return ReaderContains(f, subslice), nil
+}
+
 // Check if a file or directory exists.
 func Exists(path string, fs afero.Fs) (bool, error) {
 	_, err := fs.Stat(path)