configupgrade: Analysis of input configuration

In order to properly migrate the contents of resource, data, provider and
provisioner blocks we will need the provider's schema in order to
understand what is expected, so we can resolve some ambiguities inherent
in the legacy HCL AST.

This includes an initial prototype of migrating the content of resource
blocks just to verify that the information is being gathered correctly.
As with the rest of the upgrade_native.go file, this will be reorganized
significantly once the basic end-to-end flow is established and we can
see how to organize this code better.

command/012_config_upgrade.go

@@ -145,7 +145,11 @@ command and dealing with them before running this command again.
 		c.Ui.Output(`-----------------------------------------------------------------------------`)
 	}
 
-	newSources, upgradeDiags := configupgrade.Upgrade(sources)
+	upgrader := &configupgrade.Upgrader{
+		Providers:    c.providerResolver(),
+		Provisioners: c.provisionerFactories(),
+	}
+	newSources, upgradeDiags := upgrader.Upgrade(sources)
 	diags = diags.Append(upgradeDiags)
 	if upgradeDiags.HasErrors() {
 		c.showDiagnostics(diags)

configs/configupgrade/analysis.go

@@ -0,0 +1,207 @@
+package configupgrade
+
+import (
+	"fmt"
+
+	hcl1 "github.com/hashicorp/hcl"
+	hcl1ast "github.com/hashicorp/hcl/hcl/ast"
+	hcl1parser "github.com/hashicorp/hcl/hcl/parser"
+
+	"github.com/hashicorp/terraform/addrs"
+	"github.com/hashicorp/terraform/config/configschema"
+	"github.com/hashicorp/terraform/moduledeps"
+	"github.com/hashicorp/terraform/plugin/discovery"
+	"github.com/hashicorp/terraform/terraform"
+)
+
+// analysis is a container for the various different information gathered
+// by ModuleSources.analyze.
+type analysis struct {
+	ProviderSchemas      map[string]*terraform.ProviderSchema
+	ProvisionerSchemas   map[string]*configschema.Block
+	ResourceProviderType map[addrs.Resource]string
+	ResourceHasCount     map[addrs.Resource]bool
+}
+
+// analyze processes the configuration files included inside the receiver
+// and returns an assortment of information required to make decisions during
+// a configuration upgrade.
+func (u *Upgrader) analyze(ms ModuleSources) (*analysis, error) {
+	ret := &analysis{
+		ProviderSchemas:      make(map[string]*terraform.ProviderSchema),
+		ProvisionerSchemas:   make(map[string]*configschema.Block),
+		ResourceProviderType: make(map[addrs.Resource]string),
+		ResourceHasCount:     make(map[addrs.Resource]bool),
+	}
+
+	m := &moduledeps.Module{
+		Providers: make(moduledeps.Providers),
+	}
+
+	// This is heavily based on terraform.ModuleTreeDependencies but
+	// differs in that it works directly with the HCL1 AST rather than
+	// the legacy config structs (and can thus outlive those) and that
+	// it only works on one module at a time, and so doesn't need to
+	// recurse into child calls.
+	for name, src := range ms {
+		if ext := fileExt(name); ext != ".tf" {
+			continue
+		}
+
+		f, err := hcl1parser.Parse(src)
+		if err != nil {
+			// If we encounter a syntax error then we'll just skip for now
+			// and assume that we'll catch this again when we do the upgrade.
+			// If not, we'll break the upgrade step of renaming .tf files to
+			// .tf.json if they seem to be JSON syntax.
+			continue
+		}
+
+		list, ok := f.Node.(*hcl1ast.ObjectList)
+		if !ok {
+			return nil, fmt.Errorf("error parsing: file doesn't contain a root object")
+		}
+
+		if providersList := list.Filter("provider"); len(providersList.Items) > 0 {
+			providerObjs := providersList.Children()
+			for _, providerObj := range providerObjs.Items {
+				if len(providerObj.Keys) != 1 {
+					return nil, fmt.Errorf("provider block has wrong number of labels")
+				}
+				name := providerObj.Keys[0].Token.Value().(string)
+
+				var listVal *hcl1ast.ObjectList
+				if ot, ok := providerObj.Val.(*hcl1ast.ObjectType); ok {
+					listVal = ot.List
+				} else {
+					return nil, fmt.Errorf("provider %q: must be a block", name)
+				}
+
+				var versionStr string
+				if a := listVal.Filter("version"); len(a.Items) > 0 {
+					err := hcl1.DecodeObject(&versionStr, a.Items[0].Val)
+					if err != nil {
+						return nil, fmt.Errorf("Error reading version for provider %q: %s", name, err)
+					}
+				}
+				var constraints discovery.Constraints
+				if versionStr != "" {
+					constraints, err = discovery.ConstraintStr(versionStr).Parse()
+					if err != nil {
+						return nil, fmt.Errorf("Error parsing version for provider %q: %s", name, err)
+					}
+				}
+
+				var alias string
+				if a := listVal.Filter("alias"); len(a.Items) > 0 {
+					err := hcl1.DecodeObject(&alias, a.Items[0].Val)
+					if err != nil {
+						return nil, fmt.Errorf("Error reading alias for provider %q: %s", name, err)
+					}
+				}
+
+				inst := moduledeps.ProviderInstance(name)
+				if alias != "" {
+					inst = moduledeps.ProviderInstance(name + "." + alias)
+				}
+				m.Providers[inst] = moduledeps.ProviderDependency{
+					Constraints: constraints,
+					Reason:      moduledeps.ProviderDependencyExplicit,
+				}
+			}
+		}
+
+		{
+			// For our purposes here we don't need to distinguish "resource"
+			// and "data" blocks -- provider references are the same for
+			// both of them -- so we'll just merge them together into a
+			// single list and iterate it.
+			resourceConfigsList := list.Filter("resource")
+			dataResourceConfigsList := list.Filter("data")
+			resourceConfigsList.Items = append(resourceConfigsList.Items, dataResourceConfigsList.Items...)
+
+			resourceObjs := resourceConfigsList.Children()
+			for _, resourceObj := range resourceObjs.Items {
+				if len(resourceObj.Keys) != 2 {
+					return nil, fmt.Errorf("resource or data block has wrong number of labels")
+				}
+				typeName := resourceObj.Keys[0].Token.Value().(string)
+				name := resourceObj.Keys[1].Token.Value().(string)
+				rAddr := addrs.Resource{
+					Mode: addrs.ManagedResourceMode, // not necessarily true, but good enough for our purposes here
+					Type: typeName,
+					Name: name,
+				}
+
+				var listVal *hcl1ast.ObjectList
+				if ot, ok := resourceObj.Val.(*hcl1ast.ObjectType); ok {
+					listVal = ot.List
+				} else {
+					return nil, fmt.Errorf("resource %q %q must be a block", typeName, name)
+				}
+
+				if o := listVal.Filter("count"); len(o.Items) > 0 {
+					ret.ResourceHasCount[rAddr] = true
+				}
+
+				var providerKey string
+				if o := listVal.Filter("provider"); len(o.Items) > 0 {
+					err := hcl1.DecodeObject(&providerKey, o.Items[0].Val)
+					if err != nil {
+						return nil, fmt.Errorf("Error reading provider for resource %q %q: %s", typeName, name, err)
+					}
+				}
+
+				if providerKey == "" {
+					providerKey = rAddr.DefaultProviderConfig().StringCompact()
+				}
+
+				inst := moduledeps.ProviderInstance(providerKey)
+				if _, exists := m.Providers[inst]; !exists {
+					m.Providers[inst] = moduledeps.ProviderDependency{
+						Reason: moduledeps.ProviderDependencyImplicit,
+					}
+				}
+				ret.ResourceProviderType[rAddr] = inst.Type()
+			}
+		}
+	}
+
+	providerFactories, err := u.Providers.ResolveProviders(m.PluginRequirements())
+	if err != nil {
+		return nil, fmt.Errorf("error resolving providers: %s", err)
+	}
+
+	for name, fn := range providerFactories {
+		provider, err := fn()
+		if err != nil {
+			return nil, fmt.Errorf("failed to load provider %q: %s", name, err)
+		}
+
+		// The current GetSchema interface is non-ideal. We're going to make
+		// this much simpler in the new interface, but we'll need to shim
+		// it for now.
+		resourceTypes := provider.Resources()
+		dataSources := provider.DataSources()
+		var resourceTypeNames, dataSourceNames []string
+		for _, t := range resourceTypes {
+			resourceTypeNames = append(resourceTypeNames, t.Name)
+		}
+		for _, t := range dataSources {
+			dataSourceNames = append(dataSourceNames, t.Name)
+		}
+		schema, err := provider.GetSchema(&terraform.ProviderSchemaRequest{
+			DataSources:   dataSourceNames,
+			ResourceTypes: resourceTypeNames,
+		})
+		if err != nil {
+			return nil, fmt.Errorf("failed to get schema from provider %q: %s", name, err)
+		}
+
+		ret.ProviderSchemas[name] = schema
+	}
+
+	// TODO: Also ProvisionerSchemas
+
+	return ret, nil
+}

configs/configupgrade/upgrade.go

@@ -30,10 +30,16 @@ import (
 // warnings are also represented as "TF-UPGRADE-TODO:" comments in the
 // generated source files so that users can visit them all and decide what to
 // do with them.
-func Upgrade(input ModuleSources) (ModuleSources, tfdiags.Diagnostics) {
+func (u *Upgrader) Upgrade(input ModuleSources) (ModuleSources, tfdiags.Diagnostics) {
 	ret := make(ModuleSources)
 	var diags tfdiags.Diagnostics
 
+	an, err := u.analyze(input)
+	if err != nil {
+		diags = diags.Append(err)
+		return ret, diags
+	}
+
 	for name, src := range input {
 		ext := fileExt(name)
 		if ext == "" {
@@ -91,7 +97,7 @@ func Upgrade(input ModuleSources) (ModuleSources, tfdiags.Diagnostics) {
 		}
 
 		// TODO: Actually rewrite this .tf file.
-		result, fileDiags := upgradeNativeSyntaxFile(name, src)
+		result, fileDiags := u.upgradeNativeSyntaxFile(name, src, an)
 		diags = diags.Append(fileDiags)
 		if fileDiags.HasErrors() {
 			// Leave unchanged, then.

configs/configupgrade/upgrade_expr.go

@@ -17,7 +17,7 @@ import (
 	"github.com/hashicorp/terraform/tfdiags"
 )
 
-func upgradeExpr(val interface{}, filename string, interp bool) ([]byte, tfdiags.Diagnostics) {
+func upgradeExpr(val interface{}, filename string, interp bool, an *analysis) ([]byte, tfdiags.Diagnostics) {
 	var buf bytes.Buffer
 	var diags tfdiags.Diagnostics
 
@@ -47,7 +47,7 @@ func upgradeExpr(val interface{}, filename string, interp bool) ([]byte, tfdiags
 				})
 			}
 
-			interpSrc, interpDiags := upgradeExpr(hilNode, filename, interp)
+			interpSrc, interpDiags := upgradeExpr(hilNode, filename, interp, an)
 			buf.Write(interpSrc)
 			diags = diags.Append(interpDiags)
 
@@ -105,9 +105,9 @@ func upgradeExpr(val interface{}, filename string, interp bool) ([]byte, tfdiags
 
 		lhsExpr := tv.Exprs[0]
 		rhsExpr := tv.Exprs[1]
-		lhsSrc, exprDiags := upgradeExpr(lhsExpr, filename, true)
+		lhsSrc, exprDiags := upgradeExpr(lhsExpr, filename, true, an)
 		diags = diags.Append(exprDiags)
-		rhsSrc, exprDiags := upgradeExpr(rhsExpr, filename, true)
+		rhsSrc, exprDiags := upgradeExpr(rhsExpr, filename, true, an)
 		diags = diags.Append(exprDiags)
 
 		// HIL's AST represents -foo as (0 - foo), so we'll recognize
@@ -133,18 +133,18 @@ func upgradeExpr(val interface{}, filename string, interp bool) ([]byte, tfdiags
 				buf.WriteString(", ")
 			}
 
-			exprSrc, exprDiags := upgradeExpr(arg, filename, true)
+			exprSrc, exprDiags := upgradeExpr(arg, filename, true, an)
 			diags = diags.Append(exprDiags)
 			buf.Write(exprSrc)
 		}
 		buf.WriteByte(')')
 
 	case *hilast.Conditional:
-		condSrc, exprDiags := upgradeExpr(tv.CondExpr, filename, true)
+		condSrc, exprDiags := upgradeExpr(tv.CondExpr, filename, true, an)
 		diags = diags.Append(exprDiags)
-		trueSrc, exprDiags := upgradeExpr(tv.TrueExpr, filename, true)
+		trueSrc, exprDiags := upgradeExpr(tv.TrueExpr, filename, true, an)
 		diags = diags.Append(exprDiags)
-		falseSrc, exprDiags := upgradeExpr(tv.FalseExpr, filename, true)
+		falseSrc, exprDiags := upgradeExpr(tv.FalseExpr, filename, true, an)
 		diags = diags.Append(exprDiags)
 
 		buf.Write(condSrc)
@@ -154,9 +154,9 @@ func upgradeExpr(val interface{}, filename string, interp bool) ([]byte, tfdiags
 		buf.Write(falseSrc)
 
 	case *hilast.Index:
-		targetSrc, exprDiags := upgradeExpr(tv.Target, filename, true)
+		targetSrc, exprDiags := upgradeExpr(tv.Target, filename, true, an)
 		diags = diags.Append(exprDiags)
-		keySrc, exprDiags := upgradeExpr(tv.Key, filename, true)
+		keySrc, exprDiags := upgradeExpr(tv.Key, filename, true, an)
 		diags = diags.Append(exprDiags)
 		buf.Write(targetSrc)
 		buf.WriteString("[")
@@ -176,7 +176,7 @@ func upgradeExpr(val interface{}, filename string, interp bool) ([]byte, tfdiags
 				// If there's only one expression and it isn't a literal string
 				// then we'll just output it naked, since wrapping a single
 				// expression in interpolation is no longer idiomatic.
-				interped, interpDiags := upgradeExpr(item, filename, true)
+				interped, interpDiags := upgradeExpr(item, filename, true, an)
 				diags = diags.Append(interpDiags)
 				buf.Write(interped)
 				break
@@ -192,7 +192,7 @@ func upgradeExpr(val interface{}, filename string, interp bool) ([]byte, tfdiags
 				}
 			}
 
-			interped, interpDiags := upgradeExpr(item, filename, true)
+			interped, interpDiags := upgradeExpr(item, filename, true, an)
 			diags = diags.Append(interpDiags)
 
 			buf.WriteString("${")

configs/configupgrade/upgrade_native.go

@@ -3,9 +3,12 @@ package configupgrade
 import (
 	"bytes"
 	"fmt"
+	"io"
 	"sort"
 	"strings"
 
+	"github.com/hashicorp/terraform/addrs"
+
 	version "github.com/hashicorp/go-version"
 
 	hcl1ast "github.com/hashicorp/hcl/hcl/ast"
@@ -24,7 +27,7 @@ type upgradeFileResult struct {
 	ProviderRequirements map[string]version.Constraints
 }
 
-func upgradeNativeSyntaxFile(filename string, src []byte) (upgradeFileResult, tfdiags.Diagnostics) {
+func (u *Upgrader) upgradeNativeSyntaxFile(filename string, src []byte, an *analysis) (upgradeFileResult, tfdiags.Diagnostics) {
 	var result upgradeFileResult
 	var diags tfdiags.Diagnostics
 
@@ -63,18 +66,142 @@ func upgradeNativeSyntaxFile(filename string, src []byte) (upgradeFileResult, tf
 			diags = diags.Append(&hcl2.Diagnostic{
 				Severity: hcl2.DiagWarning,
 				Summary:  "Unsupported top-level attribute",
-				Detail:   fmt.Sprintf("Attribute %q is not expected here, so its expression was not migrated.", blockType),
+				Detail:   fmt.Sprintf("Attribute %q is not expected here, so its expression was not upgraded.", blockType),
 				Subject:  hcl1PosRange(filename, item.Keys[0].Pos()).Ptr(),
 			})
 			// Preserve the item as-is, using the hcl1printer package.
-			buf.WriteString("# TF-UPGRADE-TODO: Top-level attributes are not valid, so this was not automatically migrated.\n")
+			buf.WriteString("# TF-UPGRADE-TODO: Top-level attributes are not valid, so this was not automatically upgraded.\n")
 			hcl1printer.Fprint(&buf, item)
 			buf.WriteString("\n\n")
 			continue
 		}
+		declRange := hcl1PosRange(filename, item.Keys[0].Pos())
 
 		switch blockType {
 
+		case "resource":
+			if len(labels) != 2 {
+				// Should never happen for valid input.
+				diags = diags.Append(&hcl2.Diagnostic{
+					Severity: hcl2.DiagError,
+					Summary:  "Invalid resource block",
+					Detail:   "A resource block must have two labels: the resource type and name.",
+					Subject:  &declRange,
+				})
+				continue
+			}
+
+			rAddr := addrs.Resource{
+				Mode: addrs.ManagedResourceMode,
+				Type: labels[0],
+				Name: labels[1],
+			}
+
+			// We should always have a schema for each provider in our analysis
+			// object. If not, it's a bug in the analyzer.
+			providerType, ok := an.ResourceProviderType[rAddr]
+			if !ok {
+				panic(fmt.Sprintf("unknown provider type for %s", rAddr.String()))
+			}
+			providerSchema, ok := an.ProviderSchemas[providerType]
+			if !ok {
+				panic(fmt.Sprintf("missing schema for provider type %q", providerType))
+			}
+			schema, ok := providerSchema.ResourceTypes[rAddr.Type]
+			if !ok {
+				diags = diags.Append(&hcl2.Diagnostic{
+					Severity: hcl2.DiagError,
+					Summary:  "Unknown resource type",
+					Detail:   fmt.Sprintf("The resource type %q is not known to the currently-selected version of provider %q.", rAddr.Type, providerType),
+					Subject:  &declRange,
+				})
+				continue
+			}
+
+			printComments(&buf, item.LeadComment)
+			printBlockOpen(&buf, blockType, labels, item.LineComment)
+			args := body.List.Items
+			for i, arg := range args {
+				comments := adhocComments.TakeBefore(arg)
+				for _, group := range comments {
+					printComments(&buf, group)
+					buf.WriteByte('\n') // Extra separator after each group
+				}
+
+				printComments(&buf, arg.LeadComment)
+
+				name := arg.Keys[0].Token.Value().(string)
+				//labelKeys := arg.Keys[1:]
+
+				switch name {
+				// TODO: Special case for all of the "meta-arguments" allowed
+				// in a resource block, such as "count", "lifecycle",
+				// "provisioner", etc.
+
+				default:
+					// We'll consult the schema to see how we ought to interpret
+					// this item.
+
+					if _, isAttr := schema.Attributes[name]; isAttr {
+						// We'll tolerate a block with no labels here as a degenerate
+						// way to assign a map, but we can't migrate a block that has
+						// labels. In practice this should never happen because
+						// nested blocks in resource blocks did not accept labels
+						// prior to v0.12.
+						if len(arg.Keys) != 1 {
+							diags = diags.Append(&hcl2.Diagnostic{
+								Severity: hcl2.DiagError,
+								Summary:  "Block where attribute was expected",
+								Detail:   fmt.Sprintf("Within %s the name %q is an attribute name, not a block type.", rAddr.Type, name),
+								Subject:  hcl1PosRange(filename, arg.Keys[0].Pos()).Ptr(),
+							})
+							continue
+						}
+
+						valSrc, valDiags := upgradeExpr(arg.Val, filename, true, an)
+						diags = diags.Append(valDiags)
+						printAttribute(&buf, arg.Keys[0].Token.Value().(string), valSrc, arg.LineComment)
+					} else if _, isBlock := schema.BlockTypes[name]; isBlock {
+						// TODO: Also upgrade blocks.
+						// In particular we need to handle the tricky case where
+						// a user attempts to treat a block type name like it's
+						// an attribute, by producing a "dynamic" block.
+						hcl1printer.Fprint(&buf, arg)
+						buf.WriteByte('\n')
+					} else {
+						if arg.Assign.IsValid() {
+							diags = diags.Append(&hcl2.Diagnostic{
+								Severity: hcl2.DiagError,
+								Summary:  "Unrecognized attribute name",
+								Detail:   fmt.Sprintf("Resource type %s does not expect an attribute named %q.", rAddr.Type, name),
+								Subject:  hcl1PosRange(filename, arg.Keys[0].Pos()).Ptr(),
+							})
+						} else {
+							diags = diags.Append(&hcl2.Diagnostic{
+								Severity: hcl2.DiagError,
+								Summary:  "Unrecognized block type",
+								Detail:   fmt.Sprintf("Resource type %s does not expect blocks of type %q.", rAddr.Type, name),
+								Subject:  hcl1PosRange(filename, arg.Keys[0].Pos()).Ptr(),
+							})
+						}
+						continue
+					}
+				}
+
+				// If we have another item and it's more than one line away
+				// from the current one then we'll print an extra blank line
+				// to retain that separation.
+				if (i + 1) < len(args) {
+					next := args[i+1]
+					thisPos := arg.Pos()
+					nextPos := next.Pos()
+					if nextPos.Line-thisPos.Line > 1 {
+						buf.WriteByte('\n')
+					}
+				}
+			}
+			buf.WriteString("}\n\n")
+
 		case "variable":
 			printComments(&buf, item.LeadComment)
 			printBlockOpen(&buf, blockType, labels, item.LineComment)
@@ -85,11 +212,11 @@ func upgradeNativeSyntaxFile(filename string, src []byte) (upgradeFileResult, tf
 					diags = diags.Append(&hcl2.Diagnostic{
 						Severity: hcl2.DiagWarning,
 						Summary:  "Invalid nested block",
-						Detail:   fmt.Sprintf("Blocks of type %q are not expected here, so this was not automatically migrated.", arg.Keys[0].Token.Value().(string)),
+						Detail:   fmt.Sprintf("Blocks of type %q are not expected here, so this was not automatically upgraded.", arg.Keys[0].Token.Value().(string)),
 						Subject:  hcl1PosRange(filename, arg.Keys[0].Pos()).Ptr(),
 					})
 					// Preserve the item as-is, using the hcl1printer package.
-					buf.WriteString("\n# TF-UPGRADE-TODO: Blocks are not expected here, so this was not automatically migrated.\n")
+					buf.WriteString("\n# TF-UPGRADE-TODO: Blocks are not expected here, so this was not automatically upgraded.\n")
 					hcl1printer.Fprint(&buf, arg)
 					buf.WriteString("\n\n")
 					continue
@@ -133,7 +260,7 @@ func upgradeNativeSyntaxFile(filename string, src []byte) (upgradeFileResult, tf
 					// into the default case and migrate it as a normal expression.
 					fallthrough
 				default:
-					valSrc, valDiags := upgradeExpr(arg.Val, filename, false)
+					valSrc, valDiags := upgradeExpr(arg.Val, filename, false, an)
 					diags = diags.Append(valDiags)
 					printAttribute(&buf, arg.Keys[0].Token.Value().(string), valSrc, arg.LineComment)
 				}
@@ -162,11 +289,11 @@ func upgradeNativeSyntaxFile(filename string, src []byte) (upgradeFileResult, tf
 					diags = diags.Append(&hcl2.Diagnostic{
 						Severity: hcl2.DiagWarning,
 						Summary:  "Invalid nested block",
-						Detail:   fmt.Sprintf("Blocks of type %q are not expected here, so this was not automatically migrated.", arg.Keys[0].Token.Value().(string)),
+						Detail:   fmt.Sprintf("Blocks of type %q are not expected here, so this was not automatically upgraded.", arg.Keys[0].Token.Value().(string)),
 						Subject:  hcl1PosRange(filename, arg.Keys[0].Pos()).Ptr(),
 					})
 					// Preserve the item as-is, using the hcl1printer package.
-					buf.WriteString("\n# TF-UPGRADE-TODO: Blocks are not expected here, so this was not automatically migrated.\n")
+					buf.WriteString("\n# TF-UPGRADE-TODO: Blocks are not expected here, so this was not automatically upgraded.\n")
 					hcl1printer.Fprint(&buf, arg)
 					buf.WriteString("\n\n")
 					continue
@@ -186,7 +313,7 @@ func upgradeNativeSyntaxFile(filename string, src []byte) (upgradeFileResult, tf
 					interp = true
 				}
 
-				valSrc, valDiags := upgradeExpr(arg.Val, filename, interp)
+				valSrc, valDiags := upgradeExpr(arg.Val, filename, interp, an)
 				diags = diags.Append(valDiags)
 				printAttribute(&buf, arg.Keys[0].Token.Value().(string), valSrc, arg.LineComment)
 
@@ -215,11 +342,11 @@ func upgradeNativeSyntaxFile(filename string, src []byte) (upgradeFileResult, tf
 					diags = diags.Append(&hcl2.Diagnostic{
 						Severity: hcl2.DiagWarning,
 						Summary:  "Invalid nested block",
-						Detail:   fmt.Sprintf("Blocks of type %q are not expected here, so this was not automatically migrated.", arg.Keys[0].Token.Value().(string)),
+						Detail:   fmt.Sprintf("Blocks of type %q are not expected here, so this was not automatically upgraded.", arg.Keys[0].Token.Value().(string)),
 						Subject:  hcl1PosRange(filename, arg.Keys[0].Pos()).Ptr(),
 					})
 					// Preserve the item as-is, using the hcl1printer package.
-					buf.WriteString("\n# TF-UPGRADE-TODO: Blocks are not expected here, so this was not automatically migrated.\n")
+					buf.WriteString("\n# TF-UPGRADE-TODO: Blocks are not expected here, so this was not automatically upgraded.\n")
 					hcl1printer.Fprint(&buf, arg)
 					buf.WriteString("\n\n")
 					continue
@@ -235,7 +362,7 @@ func upgradeNativeSyntaxFile(filename string, src []byte) (upgradeFileResult, tf
 
 				name := arg.Keys[0].Token.Value().(string)
 				expr := arg.Val
-				exprSrc, exprDiags := upgradeExpr(expr, filename, true)
+				exprSrc, exprDiags := upgradeExpr(expr, filename, true, an)
 				diags = diags.Append(exprDiags)
 				printAttribute(&buf, name, exprSrc, arg.LineComment)
 
@@ -259,12 +386,12 @@ func upgradeNativeSyntaxFile(filename string, src []byte) (upgradeFileResult, tf
 			diags = diags.Append(&hcl2.Diagnostic{
 				Severity: hcl2.DiagWarning,
 				Summary:  "Unsupported root block type",
-				Detail:   fmt.Sprintf("The block type %q is not expected here, so its content was not migrated.", blockType),
+				Detail:   fmt.Sprintf("The block type %q is not expected here, so its content was not upgraded.", blockType),
 				Subject:  hcl1PosRange(filename, item.Keys[0].Pos()).Ptr(),
 			})
 
 			// Preserve the block as-is, using the hcl1printer package.
-			buf.WriteString("# TF-UPGRADE-TODO: Block type was not recognized, so this block and its contents were not automatically migrated.\n")
+			buf.WriteString("# TF-UPGRADE-TODO: Block type was not recognized, so this block and its contents were not automatically upgraded.\n")
 			hcl1printer.Fprint(&buf, item)
 			buf.WriteString("\n\n")
 			continue
@@ -414,13 +541,13 @@ func (q *commentQueue) TakeBefore(node hcl1ast.Node) []*hcl1ast.CommentGroup {
 
 func hcl1ErrSubjectRange(filename string, err error) *hcl2.Range {
 	if pe, isPos := err.(*hcl1parser.PosError); isPos {
-		return hcl1PosRange(filename, pe.Pos)
+		return hcl1PosRange(filename, pe.Pos).Ptr()
 	}
 	return nil
 }
 
-func hcl1PosRange(filename string, pos hcl1token.Pos) *hcl2.Range {
-	return &hcl2.Range{
+func hcl1PosRange(filename string, pos hcl1token.Pos) hcl2.Range {
+	return hcl2.Range{
 		Filename: filename,
 		Start: hcl2.Pos{
 			Line:   pos.Line,
@@ -434,3 +561,9 @@ func hcl1PosRange(filename string, pos hcl1token.Pos) *hcl2.Range {
 		},
 	}
 }
+
+func passthruBlockTodo(w io.Writer, node hcl1ast.Node, msg string) {
+	fmt.Fprintf(w, "\n# TF-UPGRADE-TODO: %s\n", msg)
+	hcl1printer.Fprint(w, node)
+	w.Write([]byte{'\n', '\n'})
+}

configs/configupgrade/upgrade_test.go

@@ -8,6 +8,9 @@ import (
 	"os/exec"
 	"path/filepath"
 	"testing"
+
+	testprovider "github.com/hashicorp/terraform/builtin/providers/test"
+	"github.com/hashicorp/terraform/terraform"
 )
 
 func TestUpgradeValid(t *testing.T) {
@@ -28,6 +31,9 @@ func TestUpgradeValid(t *testing.T) {
 		t.Run(entry.Name(), func(t *testing.T) {
 			inputDir := filepath.Join(fixtureDir, entry.Name(), "input")
 			wantDir := filepath.Join(fixtureDir, entry.Name(), "want")
+			u := &Upgrader{
+				Providers: terraform.ResourceProviderResolverFixed(testProviders),
+			}
 
 			inputSrc, err := LoadModule(inputDir)
 			if err != nil {
@@ -38,7 +44,7 @@ func TestUpgradeValid(t *testing.T) {
 				t.Fatal(err)
 			}
 
-			gotSrc, diags := Upgrade(inputSrc)
+			gotSrc, diags := u.Upgrade(inputSrc)
 			if diags.HasErrors() {
 				t.Error(diags.Err())
 			}
@@ -83,7 +89,10 @@ func TestUpgradeRenameJSON(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	gotSrc, diags := Upgrade(inputSrc)
+	u := &Upgrader{
+		Providers: terraform.ResourceProviderResolverFixed(testProviders),
+	}
+	gotSrc, diags := u.Upgrade(inputSrc)
 	if diags.HasErrors() {
 		t.Error(diags.Err())
 	}
@@ -166,3 +175,9 @@ func diffSourceFilesFallback(got, want []byte) []byte {
 	buf.WriteString("\n")
 	return buf.Bytes()
 }
+
+var testProviders = map[string]terraform.ResourceProviderFactory{
+	"test": terraform.ResourceProviderFactory(func() (terraform.ResourceProvider, error) {
+		return testprovider.Provider(), nil
+	}),
+}

configs/configupgrade/upgrader.go

@@ -0,0 +1,12 @@
+package configupgrade
+
+import (
+	"github.com/hashicorp/terraform/terraform"
+)
+
+// Upgrader is the main type in this package, containing all of the
+// dependencies that are needed to perform upgrades.
+type Upgrader struct {
+	Providers    terraform.ResourceProviderResolver
+	Provisioners map[string]terraform.ResourceProvisionerFactory
+}