Add template_dir function to HCL

Signed-off-by: Jeremiah Snapp <jeremiah@chef.io>

hcl2template/function/templatedir.go

@@ -0,0 +1,18 @@
+package function
+
+import (
+	"github.com/zclconf/go-cty/cty"
+	"github.com/zclconf/go-cty/cty/function"
+)
+
+// MakeTemplateDirFunc constructs a function that returns the directory
+// in which the configuration file is located.
+func MakeTemplateDirFunc(baseDir string) function.Function {
+	return function.New(&function.Spec{
+		Params: []function.Parameter{},
+		Type:   function.StaticReturnType(cty.String),
+		Impl: func(args []cty.Value, retType cty.Type) (cty.Value, error) {
+			return cty.StringVal(baseDir), nil
+		},
+	})
+}

hcl2template/functions.go

@@ -94,6 +94,7 @@ func Functions(basedir string) map[string]function.Function {
 		"split":           stdlib.SplitFunc,
 		"strrev":          stdlib.ReverseFunc,
 		"substr":          stdlib.SubstrFunc,
+		"template_dir":    pkrfunction.MakeTemplateDirFunc(basedir),
 		"timestamp":       pkrfunction.TimestampFunc,
 		"timeadd":         stdlib.TimeAddFunc,
 		"title":           stdlib.TitleFunc,

website/data/docs-navigation.js

@@ -113,6 +113,7 @@ export default [
               'fileset',
               'pathexpand',
               'pwd',
+              'template_dir',
             ],
           },
           {

website/pages/docs/from-1.5/functions/file/template_dir.mdx

@@ -0,0 +1,21 @@
+---
+layout: docs
+page_title: template_dir - Functions - Configuration Language
+sidebar_title: template_dir
+description: The template_dir function returns the directory in which the configuration file is located.
+---
+
+# `template_dir` Function
+
+`template_dir` returns the directory in which the configuration file is located.
+
+```hcl
+template_dir()
+```
+
+## Examples
+
+```shell-session
+> template_dir()
+packer
+```