feat: add logging w/ DEMUX_LOG env variable

.gitignore

@@ -1 +1 @@
-terraform-demux
+/terraform-demux

cmd/terraform-demux/main.go

@@ -1,17 +1,30 @@
 package main
 
 import (
+	"io/ioutil"
 	"log"
 	"os"
 
 	"github.com/etsy/terraform-demux/internal/wrapper"
 )
 
+var (
+	Version = "v0.0.1+dev"
+)
+
 func main() {
+	if os.Getenv("DEMUX_LOG") == "" {
+		log.SetOutput(ioutil.Discard)
+	}
+
+	log.Printf("terraform-demux version %s", Version)
+
 	exitCode, err := wrapper.RunTerraform(os.Args[1:])
 
 	if err != nil {
-		log.Fatal(err)
+		log.SetOutput(os.Stderr)
+
+		log.Fatal("error: ", err)
 	}
 
 	os.Exit(exitCode)

internal/releaseapi/client.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	"log"
 	"net/http"
 	"os"
 	"path/filepath"
@@ -89,6 +90,8 @@ func (c *Client) ListReleases(ctx context.Context) (ListReleasesResponse, error)
 	if err != nil {
 		return releases, err
 	} else if isFresh {
+		log.Printf("using cached release list")
+
 		return releases, nil
 	}
 
@@ -102,6 +105,8 @@ func (c *Client) ListReleases(ctx context.Context) (ListReleasesResponse, error)
 		req.Header.Set(`If-None-Match`, releases.ETag)
 	}
 
+	log.Printf("downloading release index from Hashicorp")
+
 	resp, err := c.httpclient.Do(req)
 
 	if err != nil {
@@ -233,11 +238,15 @@ func (c *Client) downloadBuild(b Build) (string, error) {
 	path := cachedExecutablePath(c.cacheDir, b)
 
 	if _, err := os.Stat(path); err == nil {
+		log.Printf("found cached Terraform executable at %s", path)
+
 		return path, nil
 	} else if !os.IsNotExist(err) {
-		return "", errors.Wrap(err, "could not stat terraform executable")
+		return "", errors.Wrap(err, "could not stat Terraform executable")
 	}
 
+	log.Printf("dowloading release archive from %s", b.URL)
+
 	zip, zipCleanupFunc, err := c.downloadZip(b.URL)
 
 	defer zipCleanupFunc()

internal/wrapper/wrapper.go

@@ -3,6 +3,7 @@ package wrapper
 import (
 	"context"
 	"fmt"
+	"log"
 	"net/http"
 	"os"
 	"os/exec"
@@ -80,9 +81,13 @@ func getTerraformVersionConstraints(directory string) ([]version.Constraints, er
 	currentDirectory := directory
 
 	for {
+		log.Printf("inspecting terraform module in %s", currentDirectory)
+
 		module, diags := tfconfig.LoadModule(currentDirectory)
 
-		if !diags.HasErrors() && len(module.RequiredCore) > 0 {
+		if diags.HasErrors() {
+			log.Printf("encountered error parsing configuration: %v", diags.Err())
+		} else if len(module.RequiredCore) > 0 {
 			var allConstraints []version.Constraints
 
 			for _, constraintString := range module.RequiredCore {
@@ -95,12 +100,16 @@ func getTerraformVersionConstraints(directory string) ([]version.Constraints, er
 				allConstraints = append(allConstraints, constraints)
 			}
 
+			log.Printf("found constraints: %v", allConstraints)
+
 			return allConstraints, nil
 		}
 
 		parentDirectory := filepath.Dir(currentDirectory)
 
 		if parentDirectory == currentDirectory {
+			log.Printf("no constraints found")
+
 			return nil, nil
 		}