feat(templater): provides a simple tool to process templates

You can provide a go template (text/template) or a hcl2 template with a
JSON representation of your configuration and this tool will print the
generated "file" on stdout.

Makefile

@@ -0,0 +1,36 @@
+LINT_ARGS ?= ./...
+DESTDIR ?= "/usr/local"
+
+bin:
+	GOOS=linux go build -o bin/templater-linux main.go
+	upx bin/templater-linux
+
+install:
+	cp bin/templater-linux $(DESTDIR)/bin/templater
+
+uninstall:
+	rm $(DESTDIR)/bin/templater
+
+
+test: tidy
+	go clean -testcache
+	go test -mod=vendor -v ./...
+
+lint:
+	golangci-lint run -e '.*/pkg/mod' -e ".*/go/src" --enable-all --disable lll $(LINT_ARGS)
+
+tidy:
+	go mod tidy
+
+vendor: tidy
+	go mod vendor
+
+clean:
+	rm -rf ./bin
+	go clean -i -x -r -modcache
+
+watch:
+	modd
+
+
+.PHONY: clean generate vendor lint watch tidy bin/templater

main.go

@@ -0,0 +1,95 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"encoding/json"
+	"text/template"
+	//"github.com/hashicorp/hcl2/gohcl"
+	"github.com/hashicorp/hcl/v2"
+	"github.com/hashicorp/hcl/v2/hclsyntax"
+	//"github.com/zclconf/go-cty/cty"
+	//"github.com/zclconf/go-cty/cty/gocty"
+	ctyjson "github.com/zclconf/go-cty/cty/json"
+)
+
+func checkErr(e error) {
+	if e != nil {
+		panic(e)
+	}
+}
+
+func processGoTemplate(file string, config []byte) {
+
+	// The JSON configuration
+	var confData map[string]interface{}
+	err := json.Unmarshal(config, &confData)
+	checkErr(err)
+
+	// Read the template
+	data, err := os.ReadFile(file)
+	checkErr(err)
+
+
+	tpl, err := template.New("conf").Parse(string(data))
+	checkErr(err)
+
+	checkErr(tpl.Execute(os.Stdout,config))
+
+}
+
+func processHCLTemplate(file string, config []byte) {
+
+	fct, err:= os.ReadFile(file)
+	checkErr(err)
+
+	expr, diags := hclsyntax.ParseTemplate(fct, file, hcl.Pos{Line:1, Column: 1})
+	if diags.HasErrors() {
+		panic(diags.Error())
+	}
+
+	ctyType, err := ctyjson.ImpliedType(config)
+	checkErr(err)
+	varsVal, err := ctyjson.Unmarshal(config,ctyType)
+	checkErr(err)
+
+	ctx := &hcl.EvalContext{
+		Variables: varsVal.AsValueMap(),
+	}
+
+	for n := range ctx.Variables {
+		if !hclsyntax.ValidIdentifier(n) {
+			panic(fmt.Errorf("invalid template variable name %q: must start with a letter, followed by zero or more letters, digits, and underscores", n))
+		}
+	}
+
+	for _, traversal := range expr.Variables() {
+		root := traversal.RootName()
+		if _, ok := ctx.Variables[root]; !ok {
+			panic(fmt.Errorf("vars map does not contain key %q, referenced at %s", root, traversal[0].SourceRange()))
+		}
+	}
+
+	val, diags := expr.Value(ctx)
+	if diags.HasErrors() {
+		panic(diags.Error())
+	}
+
+	fmt.Printf("%s",val.AsString())
+}
+
+func main() {
+	// The template to process
+	templateType := os.Args[1]
+	templateFile := os.Args[2]
+	config := []byte(os.Args[3])
+
+
+	if templateType == "go" {
+		processGoTemplate(templateFile, config)
+	} else if templateType == "hcl" {
+		processHCLTemplate(templateFile, config)
+	} else {
+		panic(fmt.Errorf("Unsupported template type"))
+	}
+}