tpl: Add template function namespaces

This commit moves almost all of the template functions into separate
packages under tpl/ and adds a namespace framework.  All changes should
be backward compatible for end users, as all existing function names in
the template funcMap are left intact.

Seq and DoArithmatic have been moved out of the helpers package and into
template namespaces.

Most of the tests involved have been refactored, and many new tests have
been written.  There's still work to do, but this is a big improvement.

I got a little overzealous and added some new functions along the way:

- strings.Contains
- strings.ContainsAny
- strings.HasSuffix
- strings.TrimPrefix
- strings.TrimSuffix

Documentation is forthcoming.

Fixes #3042

2 files changed, 166 insertions, 0 deletions

diff --git a/tpl/os/os.go b/tpl/os/os.go
new file mode 100644
index 000000000..91d6e14f6
--- /dev/null
+++ b/tpl/os/os.go
@@ -0,0 +1,101 @@
+// Copyright 2017 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package os
+
+import (
+	"errors"
+	"fmt"
+	_os "os"
+
+	"github.com/spf13/afero"
+	"github.com/spf13/cast"
+	"github.com/spf13/hugo/deps"
+)
+
+// New returns a new instance of the os-namespaced template functions.
+func New(deps *deps.Deps) *Namespace {
+	return &Namespace{
+		deps: deps,
+	}
+}
+
+// Namespace provides template functions for the "os" namespace.
+type Namespace struct {
+	deps *deps.Deps
+}
+
+// Namespace returns a pointer to the current namespace instance.
+func (ns *Namespace) Namespace() *Namespace { return ns }
+
+// Getenv retrieves the value of the environment variable named by the key.
+// It returns the value, which will be empty if the variable is not present.
+func (ns *Namespace) Getenv(key interface{}) (string, error) {
+	skey, err := cast.ToStringE(key)
+	if err != nil {
+		return "", nil
+	}
+
+	return _os.Getenv(skey), nil
+}
+
+// readFile reads the file named by filename relative to the given basepath
+// and returns the contents as a string.
+// There is a upper size limit set at 1 megabytes.
+func readFile(fs *afero.BasePathFs, filename string) (string, error) {
+	if filename == "" {
+		return "", errors.New("readFile needs a filename")
+	}
+
+	if info, err := fs.Stat(filename); err == nil {
+		if info.Size() > 1000000 {
+			return "", fmt.Errorf("File %q is too big", filename)
+		}
+	} else {
+		return "", err
+	}
+	b, err := afero.ReadFile(fs, filename)
+
+	if err != nil {
+		return "", err
+	}
+
+	return string(b), nil
+}
+
+// ReadFilereads the file named by filename relative to the configured
+// WorkingDir.  It returns the contents as a string.  There is a upper size
+// limit set at 1 megabytes.
+func (ns *Namespace) ReadFile(i interface{}) (string, error) {
+	s, err := cast.ToStringE(i)
+	if err != nil {
+		return "", err
+	}
+
+	return readFile(ns.deps.Fs.WorkingDir, s)
+}
+
+// ReadDir lists the directory contents relative to the configured WorkingDir.
+func (ns *Namespace) ReadDir(i interface{}) ([]_os.FileInfo, error) {
+	path, err := cast.ToStringE(i)
+	if err != nil {
+		return nil, err
+	}
+
+	list, err := afero.ReadDir(ns.deps.Fs.WorkingDir, path)
+	if err != nil {
+		return nil, fmt.Errorf("Failed to read Directory %s with error message %s", path, err)
+	}
+
+	return list, nil
+}
diff --git a/tpl/os/os_test.go b/tpl/os/os_test.go
new file mode 100644
index 000000000..166df5e51
--- /dev/null
+++ b/tpl/os/os_test.go
@@ -0,0 +1,65 @@
+// Copyright 2017 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package os
+
+import (
+	"fmt"
+	"path/filepath"
+	"testing"
+
+	"github.com/spf13/afero"
+	"github.com/spf13/hugo/deps"
+	"github.com/spf13/hugo/hugofs"
+	"github.com/spf13/viper"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestReadFile(t *testing.T) {
+	t.Parallel()
+
+	workingDir := "/home/hugo"
+
+	v := viper.New()
+	v.Set("workingDir", workingDir)
+
+	// f := newTestFuncsterWithViper(v)
+	ns := New(&deps.Deps{Fs: hugofs.NewMem(v)})
+
+	afero.WriteFile(ns.deps.Fs.Source, filepath.Join(workingDir, "/f/f1.txt"), []byte("f1-content"), 0755)
+	afero.WriteFile(ns.deps.Fs.Source, filepath.Join("/home", "f2.txt"), []byte("f2-content"), 0755)
+
+	for i, test := range []struct {
+		filename string
+		expect   interface{}
+	}{
+		{filepath.FromSlash("/f/f1.txt"), "f1-content"},
+		{filepath.FromSlash("f/f1.txt"), "f1-content"},
+		{filepath.FromSlash("../f2.txt"), false},
+		{"", false},
+		{"b", false},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test)
+
+		result, err := ns.ReadFile(test.filename)
+
+		if b, ok := test.expect.(bool); ok && !b {
+			require.Error(t, err, errMsg)
+			continue
+		}
+
+		require.NoError(t, err, errMsg)
+		assert.Equal(t, test.expect, result, errMsg)
+	}
+}