command/0.12checklist: Report invalid resource and provider alias names

Terraform 0.11 had incomplete validation of resource and provider alias
names, which worked only due to the strange way HIL parsed variable names.
Terraform 0.12 (based on HIL) requires valid identifiers, so we'll let
users know about this before they upgrade. It will be easier for users to
deal with this while still on Terraform 0.11 because it won't run into
parse errors trying to work with the invalid name.

command/012checklist.go

@@ -7,6 +7,8 @@ import (
 	"sort"
 	"strings"
 
+	hcl2syntax "github.com/hashicorp/hcl2/hcl/hclsyntax"
+	"github.com/hashicorp/terraform/config"
 	"github.com/hashicorp/terraform/config/module"
 )
 
@@ -115,7 +117,7 @@ func zeroTwelveChecklists(mod *module.Tree, into map[string][]string) bool {
 			// in the upstream repository.
 			childItems := zeroTwelveChecklistForModule(childMod)
 			if len(childItems) > 0 {
-				items = append(items, "Upgrade child module %q to a version that passes \"terraform 0.12checklist\".")
+				items = append(items, fmt.Sprintf("Upgrade child module %q to a version that passes \"terraform 0.12checklist\".", strings.Join(mod.Path(), ".")))
 			}
 			continue
 		}
@@ -135,6 +137,7 @@ func zeroTwelveChecklists(mod *module.Tree, into map[string][]string) bool {
 
 func zeroTwelveChecklistForModule(mod *module.Tree) []string {
 	var items []string
+	cfg := mod.Config()
 
 	// Strings added to items must be Markdown-formatted. They can be multi-line
 	// as long as all of the lines are valid to be nested inside a list item.
@@ -149,6 +152,37 @@ func zeroTwelveChecklistForModule(mod *module.Tree) []string {
 	// Each element of "items" will be rendered as a task list item using
 	// GitHub's task list extension.
 
+	for _, rc := range cfg.Resources {
+		var blockType string
+		switch rc.Mode {
+		case config.ManagedResourceMode:
+			blockType = "resource"
+		case config.DataResourceMode:
+			blockType = "data"
+		default: // should never happen, because any other type would be a configuration loading error
+			blockType = "???"
+		}
+		if !hcl2syntax.ValidIdentifier(rc.Name) {
+			items = append(items, fmt.Sprintf(
+				"`%s %q %q` has a name that is not a valid identifier.\n\n"+
+					"In Terraform 0.12, resource names must start with a letter. To fix this, rename the resource in the configuration and then use `terraform state mv` to mirror that name change in the state.",
+				blockType, rc.Type, rc.Name,
+			))
+		}
+	}
+	for _, pc := range cfg.ProviderConfigs {
+		if pc.Alias == "" {
+			continue
+		}
+		if !hcl2syntax.ValidIdentifier(pc.Alias) {
+			items = append(items, fmt.Sprintf(
+				"`provider %q` alias %q is not a valid identifier.\n\n"+
+					"In Terraform 0.12, provider aliases must start with a letter. To fix this, rename the provider alias and any references to it in the configuration and then run `terraform apply` to re-attach any existing resources to the new alias name.",
+				pc.Name, pc.Alias,
+			))
+		}
+	}
+
 	return items
 }