terraform: expanded resources cannot genconfig (#33293)

This temporary measure prevents a panic further down the line when there is an unmatched expanded resource instance import target when running in config gen mode.

internal/terraform/context_plan2_test.go

@@ -4784,6 +4784,47 @@ import {
 	})
 }
 
+func TestContext2Plan_importResourceConfigGenExpandedResource(t *testing.T) {
+	m := testModuleInline(t, map[string]string{
+		"main.tf": `
+import {
+  to       = test_object.a[0]
+  id       = "123"
+}
+`,
+	})
+
+	p := simpleMockProvider()
+	ctx := testContext2(t, &ContextOpts{
+		Providers: map[addrs.Provider]providers.Factory{
+			addrs.NewDefaultProvider("test"): testProviderFuncFixed(p),
+		},
+	})
+	p.ReadResourceResponse = &providers.ReadResourceResponse{
+		NewState: cty.ObjectVal(map[string]cty.Value{
+			"test_string": cty.StringVal("foo"),
+		}),
+	}
+	p.ImportResourceStateResponse = &providers.ImportResourceStateResponse{
+		ImportedResources: []providers.ImportedResource{
+			{
+				TypeName: "test_object",
+				State: cty.ObjectVal(map[string]cty.Value{
+					"test_string": cty.StringVal("foo"),
+				}),
+			},
+		},
+	}
+
+	_, diags := ctx.Plan(m, states.NewState(), &PlanOpts{
+		Mode:               plans.NormalMode,
+		GenerateConfigPath: "generated.tf",
+	})
+	if !diags.HasErrors() {
+		t.Fatalf("expected plan to error, but it did not")
+	}
+}
+
 // config generation still succeeds even when planning fails
 func TestContext2Plan_importResourceConfigGenWithError(t *testing.T) {
 	addr := mustResourceInstanceAddr("test_object.a")

internal/terraform/transform_config.go

@@ -4,6 +4,7 @@
 package terraform
 
 import (
+	"fmt"
 	"log"
 
 	"github.com/hashicorp/terraform/internal/addrs"
@@ -170,6 +171,12 @@ func (t *ConfigTransformer) transformSingle(g *Graph, config *configs.Config, ge
 	// TODO: We could actually catch and process these kind of problems earlier,
 	//   this is something that could be done during the Validate process.
 	for _, i := range importTargets {
+		// The case in which an unmatched import block targets an expanded
+		// resource instance can error here. Others can error later.
+		if i.Addr.Resource.Key != addrs.NoKey {
+			return fmt.Errorf("Config generation for count and for_each resources not supported.\n\nYour configuration contains an import block with a \"to\" address of %s. This resource instance does not exist in configuration.\n\nIf you intended to target a resource that exists in configuration, please double-check the address. Otherwise, please remove this import block or re-run the plan without the -generate-config-out flag to ignore the import block.", i.Addr)
+		}
+
 		abstract := &NodeAbstractResource{
 			Addr:               i.Addr.ConfigResource(),
 			importTargets:      []*ImportTarget{i},