Use Standard Go Template Syntax

[aFlyBird0]

Why

If we render config.yaml before encoding it into struct, users will be able to write more complex, richer configuration files(like values.yaml of helm)

And there are many matured FuncMaps of go template, such as sprig.

e.g. with sprig, it is easy to read env from config.yaml:

githubToken: [[ env "GITHUB_TOKEN"]]

(env is a built-in template function of sprig)

Conflicts && Solutions

However, the current devstream syntax is not the standard go template (nothing to do with the difference between {{ and [[, this is just delims)

Conflicts are mainly focused on variable references and output references.

Here is the current syntax of dtm defined:

[[ githubToken ]] # variable references
${{ trello.default.outputs.boardId }} # output references

For variable references , dtm is missing a . compared to the standard go template:

[[ .githubToken ]] # standard

The output references are a bit more complex, with two solutions:

1. make outputs a built-in top-level object, similar to .Values of helm, and then refer to it with variable syntax.

# .Outputs.<tool name>.<instanceID>.<key1>.<key2>.
[[ .Outputs.trello.default.boardId ]] 

2. use outputs as a custom function.

# outputs "<tool name>.<instanceID>" "<key1>.<key2>"
[[ outputs "trello.default" "boardId" ]]

The following is a demo code with outputs as a function.

import (
	"fmt"
	"testing"

	"github.com/Masterminds/sprig/v3"
)

// mock all outputs from all plugins
var outputs = map[string]interface{}{
	"jenkins.default": map[string]interface{}{
		"key1": "value1",
	},
}

// retrieve plugin.key from outputs
var outputsFunc = func(plugin, key string) (string, error) {
	outputsOfThisPlugin, ok := outputs[plugin]
	if !ok {
		return "", fmt.Errorf("outputs of  %s not found", plugin)
	}

	outsputsMap, ok := outputsOfThisPlugin.(map[string]interface{})
	if !ok {
		return "", fmt.Errorf("outputs of  %s is not a map", plugin)
	}

	value, ok := outsputsMap[key].(string)
	if !ok {
		return "", fmt.Errorf("outputs of  %s not found in plugin.instance %s", key, plugin)
	}

	return value, nil

}

// go template function
var outputsFuncMap = map[string]any{
	"outputs": outputsFunc,
}

func TestSprigEnv(t *testing.T) {
	tpl := `
token: [[ env "GITHUB_TOKEN" | trunc 9]]
outputExample: [[ outputs "jenkins.default" "key1" ]]
`

	s, err := Render("test", tpl, nil, sprig.FuncMap(), outputsFuncMap)
	if err != nil {
		t.Fatalf("Error rendering template: %s", err)
	}
	fmt.Println(s)
}

[daniel-hutao]

githubToken: [[ env GITHUB_TOKEN ]] looks good to me.