Merge #11011

11011: Add PCL as a target language for pulumi convert r=Zaid-Ajaj a=Zaid-Ajaj

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# Description

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Every time I need to debug `pulumi convert` I have to hack YAML program-gen and make it output the intermediate PCL program text to stdout and work from there. Here, I've added PCL as a proper target language for `pulumi convert` (without needing to parse the program text and generate `pcl.Program` from it) 

I tried a simpler approach:
```go
projectGenerator = func(directory string, project workspace.Project, p *pcl.Program) error {
	programText := fmt.Sprintf("%v", p)
	outputFile := path.Join(directory, "main.pp")
	err := ioutil.WriteFile(outputFile, []byte(programText), 0600)
	if err != nil {
		return fmt.Errorf("could not write output program: %w", err)
	}
	return nil
}
```
but the default formatter for `pcl.Program` writes out invalid PCL (including non-formatted type metadata) so I went with this approach instead 

## Checklist

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- [ ] I have added tests that prove my fix is effective or that my feature works
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User-facing changes require a CHANGELOG entry.
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- [x] I have run `make changelog` and committed the `changelog/pending/<file>` documenting my change
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- [ ] Yes, there are changes in this PR that warrants bumping the Pulumi Service API version
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Co-authored-by: Zaid Ajaj <zaid.naom@gmail.com>

pkg/cmd/pulumi/convert.go

@@ -16,7 +16,9 @@ package main
 
 import (
 	"fmt"
+	"io/ioutil"
 	"os"
+	"path"
 
 	"github.com/spf13/cobra"
 
@@ -79,6 +81,44 @@ func newConvertCmd() *cobra.Command {
 	return cmd
 }
 
+// runConvert converts a Pulumi program from YAML into PCL without generating a full pcl.Program
+func runConvertPcl(cwd string, outDir string) result.Result {
+	host, err := newPluginHost()
+	if err != nil {
+		return result.FromError(fmt.Errorf("could not create plugin host: %w", err))
+	}
+	defer contract.IgnoreClose(host)
+	loader := schema.NewPluginLoader(host)
+	_, template, diags, err := yamlgen.LoadTemplate(cwd)
+	if err != nil {
+		return result.FromError(err)
+	}
+
+	if diags.HasErrors() {
+		return result.FromError(diags)
+	}
+
+	programText, diags, err := yamlgen.ConvertTemplateIL(template, loader)
+	if err != nil {
+		return result.FromError(err)
+	}
+
+	if outDir != "." {
+		err := os.MkdirAll(outDir, 0755)
+		if err != nil {
+			return result.FromError(fmt.Errorf("could not create output directory: %w", err))
+		}
+	}
+
+	outputFile := path.Join(outDir, "main.pp")
+	err = ioutil.WriteFile(outputFile, []byte(programText), 0600)
+	if err != nil {
+		return result.FromError(fmt.Errorf("could not write output program: %w", err))
+	}
+
+	return nil
+}
+
 func runConvert(cwd string, language string, outDir string, generateOnly bool) result.Result {
 	var projectGenerator projectGeneratorFunc
 	switch language {
@@ -94,6 +134,15 @@ func runConvert(cwd string, language string, outDir string, generateOnly bool) r
 		projectGenerator = javagen.GenerateProject
 	case "yaml": // nolint: goconst
 		projectGenerator = yamlgen.GenerateProject
+	case "pulumi", "pcl":
+		if cmdutil.IsTruthy(os.Getenv("PULUMI_DEV")) {
+			// since we don't need Eject to get the full program,
+			// we can just convert the YAML directly to PCL
+			return runConvertPcl(cwd, outDir)
+		}
+
+		fallthrough
+
 	default:
 		return result.Errorf("cannot generate programs for %q language", language)
 	}