feat: add template function for reading files from the pack templates…

… directory

When distributing a pack, it is common to wish to ship larger config files as part of a pack in separate files. This allows for better readability, as well as ensuring users can fallback on syntax highlighting from their editors when working on those files.

docs/writing-packs.md

@@ -180,7 +180,7 @@ The `datacenters` value shows slightly more complex Go Template, which allows fo
 
 #### Template Functions
 
-To supplement the standard Go Template set of template functions, the (masterminds/sprig)[https://github.com/Masterminds/sprig] library is used. This adds helpers for various use cases such as string manipulation, cryptographics, and data conversion (for instance to and from JSON).
+To supplement the standard Go Template set of template functions, the [masterminds/sprig](https://github.com/Masterminds/sprig) library is used. This adds helpers for various use cases such as string manipulation, cryptographics, and data conversion (for instance to and from JSON).
 
 Custom Nomad-specific and debugging functions are also provided:
 
@@ -189,7 +189,8 @@ Custom Nomad-specific and debugging functions are also provided:
 - `nomadNamespace` takes a single string parameter of a namespace ID which will be read via `/v1/namespace/:namespace`.
 - `spewDump` dumps the entirety of the passed object as a string. The output includes the content types and values. This uses the `spew.SDump` function.
 - `spewPrintf` dumps the supplied arguments into a string according to the supplied format. This utilises the `spew.Printf` function.
-- `fileContents` takes an argument to a file of the local host, reads its contents and provides this as a string.
+- `fileContents` takes an argument to a file on the local host relative to the directory `nomad-pack` is invoked in, reads its contents and provides the output as a string.
+- `packFileContents` takes an argument to a file on the local host relative to the pack's `templates` directory, reads its contents and provides the output as a string.
 
 A custom function within a template is called like any other:
 
@@ -249,7 +250,7 @@ dependency "demo_dep" {
 }
 ```
 
-The dependency name label *must* match the `name` property of the dependant pack, as specified in its `metadata.hcl`.
+The dependency name label _must_ match the `name` property of the dependant pack, as specified in its `metadata.hcl`.
 
 This would allow templates of "simple_service" to use "demo_dep"'s helper templates in the following way:
 
@@ -283,7 +284,7 @@ If you wish to share your packs, please consider adding them to the
 If you don't want to host a pack registry in version control, you can work locally
 using the filesystem method.
 
-## Step Six: Deploy your Custom Pack!
+## Step Six: Deploy your Custom Pack
 
 Add your custom repository using the `nomad-pack registry add` command.
 

internal/pkg/manager/manager.go

@@ -118,6 +118,7 @@ func (pm *PackManager) ProcessTemplates(renderAux bool, format bool, ignoreMissi
 
 	r := new(renderer.Renderer)
 	r.Client = pm.client
+	r.PackPath = pm.cfg.Path
 	pm.renderer = r
 
 	// should auxiliary files be rendered as well?

internal/pkg/renderer/funcs.go

@@ -6,6 +6,7 @@ package renderer
 import (
 	"fmt"
 	"os"
+	"path/filepath"
 	"strings"
 	"text/template"
 
@@ -51,6 +52,13 @@ func funcMap(r *Renderer) template.FuncMap {
 		f["nomadRegions"] = nomadRegions(r.Client)
 	}
 
+	if r != nil && r.PackPath != "" {
+		f["packFileContents"] = func(file string) (string, error) {
+			file = filepath.Join(r.PackPath, "templates", file)
+			return fileContents(file)
+		}
+	}
+
 	// Add additional custom functions.
 	f["fileContents"] = fileContents
 	f["toStringList"] = toStringList

internal/pkg/renderer/renderer.go

@@ -27,6 +27,9 @@ type Renderer struct {
 	// set to true error will be used, otherwise zero is used.
 	Strict bool
 
+	// Config is the configuration used when running Nomad Pack
+	PackPath string
+
 	// Client is the Nomad API client used when running the Nomad template
 	// functions. It can potentially be nil, therefore care should be taken
 	// when accessing it.