terraform/configs/configupgrade/upgrade_body.go

package configupgrade

import (
	"bytes"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"

	hcl1ast "github.com/hashicorp/hcl/hcl/ast"
	hcl1token "github.com/hashicorp/hcl/hcl/token"
	hcl2 "github.com/hashicorp/hcl2/hcl"
	hcl2syntax "github.com/hashicorp/hcl2/hcl/hclsyntax"
	"github.com/zclconf/go-cty/cty"

	"github.com/hashicorp/terraform/configs/configschema"
	"github.com/hashicorp/terraform/registry/regsrc"
	"github.com/hashicorp/terraform/terraform"
	"github.com/hashicorp/terraform/tfdiags"
)

// bodyContentRules is a mapping from item names (argument names and block type
// names) to a "rule" function defining what to do with an item of that type.
type bodyContentRules map[string]bodyItemRule

// bodyItemRule is just a function to write an upgraded representation of a
// particular given item to the given buffer. This is generic to handle various
// different mapping rules, though most values will be those constructed by
// other helper functions below.
type bodyItemRule func(buf *bytes.Buffer, blockAddr string, item *hcl1ast.ObjectItem) tfdiags.Diagnostics

func normalAttributeRule(filename string, wantTy cty.Type, an *analysis) bodyItemRule {
	exprRule := func(val interface{}) ([]byte, tfdiags.Diagnostics) {
		return upgradeExpr(val, filename, true, an)
	}
	return attributeRule(filename, wantTy, an, exprRule)
}

func noInterpAttributeRule(filename string, wantTy cty.Type, an *analysis) bodyItemRule {
	exprRule := func(val interface{}) ([]byte, tfdiags.Diagnostics) {
		return upgradeExpr(val, filename, false, an)
	}
	return attributeRule(filename, wantTy, an, exprRule)
}

func maybeBareKeywordAttributeRule(filename string, an *analysis, specials map[string]string) bodyItemRule {
	exprRule := func(val interface{}) ([]byte, tfdiags.Diagnostics) {
		// If the expression is a literal that would be valid as a naked keyword
		// then we'll turn it into one.
		if lit, isLit := val.(*hcl1ast.LiteralType); isLit {
			if lit.Token.Type == hcl1token.STRING {
				kw := lit.Token.Value().(string)
				if hcl2syntax.ValidIdentifier(kw) {

					// If we have a special mapping rule for this keyword,
					// we'll let that override what the user gave.
					if override := specials[kw]; override != "" {
						kw = override
					}

					return []byte(kw), nil
				}
			}
		}

		return upgradeExpr(val, filename, false, an)
	}
	return attributeRule(filename, cty.String, an, exprRule)
}

func maybeBareTraversalAttributeRule(filename string, an *analysis) bodyItemRule {
	exprRule := func(val interface{}) ([]byte, tfdiags.Diagnostics) {
		return upgradeTraversalExpr(val, filename, an)
	}
	return attributeRule(filename, cty.String, an, exprRule)
}

func dependsOnAttributeRule(filename string, an *analysis) bodyItemRule {
	return func(buf *bytes.Buffer, blockAddr string, item *hcl1ast.ObjectItem) tfdiags.Diagnostics {
		var diags tfdiags.Diagnostics
		val, ok := item.Val.(*hcl1ast.ListType)
		if !ok {
			diags = diags.Append(&hcl2.Diagnostic{
				Severity: hcl2.DiagError,
				Summary:  "Invalid depends_on argument",
				Detail:   `The "depends_on" argument must be a list of strings containing references to resources and modules.`,
				Subject:  hcl1PosRange(filename, item.Keys[0].Pos()).Ptr(),
			})
			return diags
		}

		var exprBuf bytes.Buffer
		multiline := len(val.List) > 1
		exprBuf.WriteByte('[')
		if multiline {
			exprBuf.WriteByte('\n')
		}
		for _, node := range val.List {
			lit, ok := node.(*hcl1ast.LiteralType)
			if (!ok) || lit.Token.Type != hcl1token.STRING {
				diags = diags.Append(&hcl2.Diagnostic{
					Severity: hcl2.DiagError,
					Summary:  "Invalid depends_on argument",
					Detail:   `The "depends_on" argument must be a list of strings containing references to resources and modules.`,
					Subject:  hcl1PosRange(filename, item.Keys[0].Pos()).Ptr(),
				})
				continue
			}
			refStr := lit.Token.Value().(string)
			if refStr == "" {
				continue
			}
			refParts := strings.Split(refStr, ".")
			var maxNames int
			switch refParts[0] {
			case "data", "module":
				maxNames = 3
			default: // resource references
				maxNames = 2
			}

			exprBuf.WriteString(refParts[0])
			for i, part := range refParts[1:] {
				if part == "*" {
					// We used to allow test_instance.foo.* as a reference
					// but now that's expressed instead as test_instance.foo,
					// referring to the tuple of instances. This also
					// always marks the end of the reference part of the
					// traversal, so anything after this would be resource
					// attributes that don't belong on depends_on.
					break
				}
				if i, err := strconv.Atoi(part); err == nil {
					fmt.Fprintf(&exprBuf, "[%d]", i)
					// An index always marks the end of the reference part.
					break
				}
				if (i + 1) >= maxNames {
					// We've reached the end of the reference part, so anything
					// after this would be invalid in 0.12.
					break
				}
				exprBuf.WriteByte('.')
				exprBuf.WriteString(part)
			}

			if multiline {
				exprBuf.WriteString(",\n")
			}
		}
		exprBuf.WriteByte(']')

		printAttribute(buf, item.Keys[0].Token.Value().(string), exprBuf.Bytes(), item.LineComment)

		return diags
	}
}

func attributeRule(filename string, wantTy cty.Type, an *analysis, exprRule func(val interface{}) ([]byte, tfdiags.Diagnostics)) bodyItemRule {
	return func(buf *bytes.Buffer, blockAddr string, item *hcl1ast.ObjectItem) tfdiags.Diagnostics {
		var diags tfdiags.Diagnostics

		name := item.Keys[0].Token.Value().(string)

		// 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(item.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.", blockAddr, name),
				Subject:  hcl1PosRange(filename, item.Keys[0].Pos()).Ptr(),
			})
			return diags
		}

		val := item.Val

		if typeIsSettableFromTupleCons(wantTy) && !typeIsSettableFromTupleCons(wantTy.ElementType()) {
			// In Terraform circa 0.10 it was required to wrap any expression
			// that produces a list in HCL list brackets to allow type analysis
			// to complete successfully, even though logically that ought to
			// have produced a list of lists.
			//
			// In Terraform 0.12 this construct _does_ produce a list of lists, so
			// we need to update expressions that look like older usage. We can't
			// do this exactly with static analysis, but we can make a best-effort
			// and produce a warning if type inference is impossible for a
			// particular expression. This should give good results for common
			// simple examples, like splat expressions.
			//
			// There are four possible cases here:
			// - The value isn't an HCL1 list expression at all, or is one that
			//   contains more than one item, in which case this special case
			//   does not apply.
			// - The inner expression after upgrading can be proven to return
			//   a sequence type, in which case we must definitely remove
			//   the wrapping brackets.
			// - The inner expression after upgrading can be proven to return
			//   a non-sequence type, in which case we fall through and treat
			//   the whole item like a normal expression.
			// - Static type analysis is impossible (it returns cty.DynamicPseudoType),
			//   in which case we will make no changes but emit a warning and
			//   a TODO comment for the user to decide whether a change needs
			//   to be made in practice.
			if list, ok := val.(*hcl1ast.ListType); ok {
				if len(list.List) == 1 {
					maybeAlsoList := list.List[0]
					if exprSrc, diags := upgradeExpr(maybeAlsoList, filename, true, an); !diags.HasErrors() {
						// Ideally we would set "self" here but we don't have
						// enough context to set it and in practice not setting
						// it only affects expressions inside provisioner and
						// connection blocks, and the list-wrapping thing isn't
						// common there.
						gotTy := an.InferExpressionType(exprSrc, nil)
						if typeIsSettableFromTupleCons(gotTy) {
							// Since this expression was already inside HCL list brackets,
							// the ultimate result would be a list of lists and so we
							// need to unwrap it by taking just the portion within
							// the brackets here.
							val = maybeAlsoList
						}
						if gotTy == cty.DynamicPseudoType {
							// User must decide.
							diags = diags.Append(&hcl2.Diagnostic{
								Severity: hcl2.DiagError,
								Summary:  "Possible legacy dynamic list usage",
								Detail:   "This list may be using the legacy redundant-list expression style from Terraform v0.10 and earlier. If the expression within these brackets returns a list itself, remove these brackets.",
								Subject:  hcl1PosRange(filename, list.Lbrack).Ptr(),
							})
							buf.WriteString(
								"# TF-UPGRADE-TODO: In Terraform v0.10 and earlier, it was sometimes necessary to\n" +
									"# force an interpolation expression to be interpreted as a list by wrapping it\n" +
									"# in an extra set of list brackets. That form was supported for compatibilty in\n" +
									"# v0.11, but is no longer supported in Terraform v0.12.\n" +
									"#\n" +
									"# If the expression in the following list itself returns a list, remove the\n" +
									"# brackets to avoid interpretation as a list of lists. If the expression\n" +
									"# returns a single list item then leave it as-is and remove this TODO comment.\n",
							)
						}
					}
				}
			}
		}

		valSrc, valDiags := exprRule(val)
		diags = diags.Append(valDiags)
		printAttribute(buf, item.Keys[0].Token.Value().(string), valSrc, item.LineComment)

		return diags
	}
}

func nestedBlockRule(filename string, nestedRules bodyContentRules, an *analysis, adhocComments *commentQueue) bodyItemRule {
	return func(buf *bytes.Buffer, blockAddr string, item *hcl1ast.ObjectItem) tfdiags.Diagnostics {
		// This simpler nestedBlockRule is for contexts where the special
		// "dynamic" block type is not accepted and so only HCL1 object
		// constructs can be accepted. Attempts to assign arbitrary HIL
		// expressions will be rejected as errors.

		var diags tfdiags.Diagnostics
		declRange := hcl1PosRange(filename, item.Keys[0].Pos())
		blockType := item.Keys[0].Token.Value().(string)
		labels := make([]string, len(item.Keys)-1)
		for i, key := range item.Keys[1:] {
			labels[i] = key.Token.Value().(string)
		}

		var blockItems []*hcl1ast.ObjectType

		switch val := item.Val.(type) {

		case *hcl1ast.ObjectType:
			blockItems = []*hcl1ast.ObjectType{val}

		case *hcl1ast.ListType:
			for _, node := range val.List {
				switch listItem := node.(type) {
				case *hcl1ast.ObjectType:
					blockItems = append(blockItems, listItem)
				default:
					diags = diags.Append(&hcl2.Diagnostic{
						Severity: hcl2.DiagError,
						Summary:  "Invalid value for nested block",
						Detail:   fmt.Sprintf("In %s the name %q is a nested block type, so any value assigned to it must be an object.", blockAddr, blockType),
						Subject:  hcl1PosRange(filename, node.Pos()).Ptr(),
					})
				}
			}

		default:
			diags = diags.Append(&hcl2.Diagnostic{
				Severity: hcl2.DiagError,
				Summary:  "Invalid value for nested block",
				Detail:   fmt.Sprintf("In %s the name %q is a nested block type, so any value assigned to it must be an object.", blockAddr, blockType),
				Subject:  &declRange,
			})
			return diags
		}

		for _, blockItem := range blockItems {
			printBlockOpen(buf, blockType, labels, item.LineComment)
			bodyDiags := upgradeBlockBody(
				filename, fmt.Sprintf("%s.%s", blockAddr, blockType), buf,
				blockItem.List.Items, blockItem.Rbrace, nestedRules, adhocComments,
			)
			diags = diags.Append(bodyDiags)
			buf.WriteString("}\n")
		}

		return diags
	}
}

func nestedBlockRuleWithDynamic(filename string, nestedRules bodyContentRules, nestedSchema *configschema.NestedBlock, an *analysis, adhocComments *commentQueue) bodyItemRule {
	return func(buf *bytes.Buffer, blockAddr string, item *hcl1ast.ObjectItem) tfdiags.Diagnostics {
		// In Terraform v0.11 it was possible in some cases to trick Terraform
		// and providers into accepting HCL's attribute syntax and some HIL
		// expressions in places where blocks or sequences of blocks were
		// expected, since the information about the heritage of the values
		// was lost during decoding and interpolation.
		//
		// In order to avoid all of the weird rough edges that resulted from
		// those misinterpretations, Terraform v0.12 is stricter and requires
		// the use of block syntax for blocks in all cases. However, because
		// various abuses of attribute syntax _did_ work (with some caveats)
		// in v0.11 we will upgrade them as best we can to use proper block
		// syntax.
		//
		// There are a few different permutations supported by this code:
		//
		// - Assigning a single HCL1 "object" using attribute syntax. This is
		//   straightforward to migrate just by dropping the equals sign.
		//
		// - Assigning a HCL1 list of objects using attribute syntax. Each
		//   object in that list can be translated to a separate block.
		//
		// - Assigning a HCL1 list containing HIL expressions that evaluate
		//   to maps. This is a hard case because we can't know the internal
		//   structure of those maps during static analysis, and so we must
		//   generate a worst-case dynamic block structure for it.
		//
		// - Assigning a single HIL expression that evaluates to a list of
		//   maps. This is just like the previous case except additionally
		//   we cannot even predict the number of generated blocks, so we must
		//   generate a single "dynamic" block to iterate over the list at
		//   runtime.

		var diags tfdiags.Diagnostics
		blockType := item.Keys[0].Token.Value().(string)
		labels := make([]string, len(item.Keys)-1)
		for i, key := range item.Keys[1:] {
			labels[i] = key.Token.Value().(string)
		}

		var blockItems []hcl1ast.Node

		switch val := item.Val.(type) {

		case *hcl1ast.ObjectType:
			blockItems = append(blockItems, val)

		case *hcl1ast.ListType:
			for _, node := range val.List {
				switch listItem := node.(type) {
				case *hcl1ast.ObjectType:
					blockItems = append(blockItems, listItem)
				default:
					// We're going to cheat a bit here and construct a synthetic
					// HCL1 list just because that makes our logic
					// simpler below where we can just treat all non-objects
					// in the same way when producing "dynamic" blocks.
					synthList := &hcl1ast.ListType{
						List:   []hcl1ast.Node{listItem},
						Lbrack: listItem.Pos(),
						Rbrack: hcl1NodeEndPos(listItem),
					}
					blockItems = append(blockItems, synthList)
				}
			}

		default:
			blockItems = append(blockItems, item.Val)
		}

		for _, blockItem := range blockItems {
			switch ti := blockItem.(type) {
			case *hcl1ast.ObjectType:
				// If we have an object then we'll pass through its content
				// as a block directly. This is the most straightforward mapping
				// from the source input, since we know exactly which keys
				// are present.
				printBlockOpen(buf, blockType, labels, item.LineComment)
				bodyDiags := upgradeBlockBody(
					filename, fmt.Sprintf("%s.%s", blockAddr, blockType), buf,
					ti.List.Items, ti.Rbrace, nestedRules, adhocComments,
				)
				diags = diags.Append(bodyDiags)
				buf.WriteString("}\n")
			default:
				// For any other sort of value we can't predict what shape it
				// will have at runtime, so we must generate a very conservative
				// "dynamic" block that tries to assign everything from the
				// schema. The result of this is likely to be pretty ugly.
				printBlockOpen(buf, "dynamic", []string{blockType}, item.LineComment)
				eachSrc, eachDiags := upgradeExpr(blockItem, filename, true, an)
				diags = diags.Append(eachDiags)
				printAttribute(buf, "for_each", eachSrc, nil)
				if nestedSchema.Nesting == configschema.NestingMap {
					// This is a pretty odd situation since map-based blocks
					// didn't exist prior to Terraform v0.12, but we'll support
					// this anyway in case we decide to add support in a later
					// SDK release that is still somehow compatible with
					// Terraform v0.11.
					printAttribute(buf, "labels", []byte(fmt.Sprintf(`[%s.key]`, blockType)), nil)
				}
				printBlockOpen(buf, "content", nil, nil)
				buf.WriteString("# TF-UPGRADE-TODO: The automatic upgrade tool can't predict\n")
				buf.WriteString("# which keys might be set in maps assigned here, so it has\n")
				buf.WriteString("# produced a comprehensive set here. Consider simplifying\n")
				buf.WriteString("# this after confirming which keys can be set in practice.\n\n")
				printDynamicBlockBody(buf, blockType, &nestedSchema.Block)
				buf.WriteString("}\n")
				buf.WriteString("}\n")
				diags = diags.Append(&hcl2.Diagnostic{
					Severity: hcl2.DiagWarning,
					Summary:  "Approximate migration of invalid block type assignment",
					Detail:   fmt.Sprintf("In %s the name %q is a nested block type, but this configuration is exploiting some missing validation rules from Terraform v0.11 and prior to trick Terraform into creating blocks dynamically.\n\nThis has been upgraded to use the new Terraform v0.12 dynamic blocks feature, but since the upgrade tool cannot predict which map keys will be present a fully-comprehensive set has been generated.", blockAddr, blockType),
					Subject:  hcl1PosRange(filename, blockItem.Pos()).Ptr(),
				})
			}
		}

		return diags
	}
}

// schemaDefaultBodyRules constructs standard body content rules for the given
// schema. Each call is guaranteed to produce a distinct object so that
// callers can safely mutate the result in order to impose custom rules
// in addition to or instead of those created by default, for situations
// where schema-based and predefined items mix in a single body.
func schemaDefaultBodyRules(filename string, schema *configschema.Block, an *analysis, adhocComments *commentQueue) bodyContentRules {
	ret := make(bodyContentRules)
	if schema == nil {
		// Shouldn't happen in any real case, but often crops up in tests
		// where the mock schemas tend to be incomplete.
		return ret
	}

	for name, attrS := range schema.Attributes {
		ret[name] = normalAttributeRule(filename, attrS.Type, an)
	}
	for name, blockS := range schema.BlockTypes {
		nestedRules := schemaDefaultBodyRules(filename, &blockS.Block, an, adhocComments)
		ret[name] = nestedBlockRuleWithDynamic(filename, nestedRules, blockS, an, adhocComments)
	}

	return ret
}

// schemaNoInterpBodyRules constructs standard body content rules for the given
// schema. Each call is guaranteed to produce a distinct object so that
// callers can safely mutate the result in order to impose custom rules
// in addition to or instead of those created by default, for situations
// where schema-based and predefined items mix in a single body.
func schemaNoInterpBodyRules(filename string, schema *configschema.Block, an *analysis, adhocComments *commentQueue) bodyContentRules {
	ret := make(bodyContentRules)
	if schema == nil {
		// Shouldn't happen in any real case, but often crops up in tests
		// where the mock schemas tend to be incomplete.
		return ret
	}

	for name, attrS := range schema.Attributes {
		ret[name] = noInterpAttributeRule(filename, attrS.Type, an)
	}
	for name, blockS := range schema.BlockTypes {
		nestedRules := schemaDefaultBodyRules(filename, &blockS.Block, an, adhocComments)
		ret[name] = nestedBlockRule(filename, nestedRules, an, adhocComments)
	}

	return ret
}

// justAttributesBodyRules constructs body content rules that just use the
// standard interpolated attribute mapping for every name already present
// in the given body object.
//
// This is a little weird vs. just processing directly the attributes, but
// has the advantage that the caller can then apply overrides to the result
// as necessary to deal with any known names that need special handling.
//
// Any attribute rules created by this function do not have a specific wanted
// value type specified, instead setting it to just cty.DynamicPseudoType.
func justAttributesBodyRules(filename string, body *hcl1ast.ObjectType, an *analysis) bodyContentRules {
	rules := make(bodyContentRules, len(body.List.Items))
	args := body.List.Items
	for _, arg := range args {
		name := arg.Keys[0].Token.Value().(string)
		rules[name] = normalAttributeRule(filename, cty.DynamicPseudoType, an)
	}
	return rules
}

func lifecycleBlockBodyRules(filename string, an *analysis) bodyContentRules {
	return bodyContentRules{
		"create_before_destroy": noInterpAttributeRule(filename, cty.Bool, an),
		"prevent_destroy":       noInterpAttributeRule(filename, cty.Bool, an),
		"ignore_changes": func(buf *bytes.Buffer, blockAddr string, item *hcl1ast.ObjectItem) tfdiags.Diagnostics {
			var diags tfdiags.Diagnostics
			val, ok := item.Val.(*hcl1ast.ListType)
			if !ok {
				diags = diags.Append(&hcl2.Diagnostic{
					Severity: hcl2.DiagError,
					Summary:  "Invalid ignore_changes argument",
					Detail:   `The "ignore_changes" argument must be a list of attribute expressions relative to this resource.`,
					Subject:  hcl1PosRange(filename, item.Keys[0].Pos()).Ptr(),
				})
				return diags
			}

			// As a special case, we'll map the single-element list ["*"] to
			// the new keyword "all".
			if len(val.List) == 1 {
				if lit, ok := val.List[0].(*hcl1ast.LiteralType); ok {
					if lit.Token.Value() == "*" {
						printAttribute(buf, item.Keys[0].Token.Value().(string), []byte("all"), item.LineComment)
						return diags
					}
				}
			}

			var exprBuf bytes.Buffer
			multiline := len(val.List) > 1
			exprBuf.WriteByte('[')
			if multiline {
				exprBuf.WriteByte('\n')
			}
			for _, node := range val.List {
				itemSrc, moreDiags := upgradeTraversalExpr(node, filename, an)
				diags = diags.Append(moreDiags)
				exprBuf.Write(itemSrc)
				if multiline {
					exprBuf.WriteString(",\n")
				}
			}
			exprBuf.WriteByte(']')

			printAttribute(buf, item.Keys[0].Token.Value().(string), exprBuf.Bytes(), item.LineComment)

			return diags
		},
	}
}

func provisionerBlockRule(filename string, resourceType string, an *analysis, adhocComments *commentQueue) bodyItemRule {
	// Unlike some other examples above, this is a rule for the entire
	// provisioner block, rather than just for its contents. Therefore it must
	// also produce the block header and body delimiters.
	return func(buf *bytes.Buffer, blockAddr string, item *hcl1ast.ObjectItem) tfdiags.Diagnostics {
		var diags tfdiags.Diagnostics
		body := item.Val.(*hcl1ast.ObjectType)
		declRange := hcl1PosRange(filename, item.Keys[0].Pos())

		if len(item.Keys) < 2 {
			diags = diags.Append(&hcl2.Diagnostic{
				Severity: hcl2.DiagError,
				Summary:  "Invalid provisioner block",
				Detail:   "A provisioner block must have one label: the provisioner type.",
				Subject:  &declRange,
			})
			return diags
		}

		typeName := item.Keys[1].Token.Value().(string)
		schema := an.ProvisionerSchemas[typeName]
		if schema == nil {
			// This message is assuming that if the user _is_ using a third-party
			// provisioner plugin they already know how to install it for normal
			// use and so we don't need to spell out those instructions in detail
			// here.
			diags = diags.Append(&hcl2.Diagnostic{
				Severity: hcl2.DiagError,
				Summary:  "Unknown provisioner type",
				Detail:   fmt.Sprintf("The provisioner type %q is not supported. If this is a third-party plugin, make sure its plugin executable is available in one of the usual plugin search paths.", typeName),
				Subject:  &declRange,
			})
			return diags
		}

		rules := schemaDefaultBodyRules(filename, schema, an, adhocComments)
		rules["when"] = maybeBareTraversalAttributeRule(filename, an)
		rules["on_failure"] = maybeBareTraversalAttributeRule(filename, an)
		rules["connection"] = connectionBlockRule(filename, resourceType, an, adhocComments)

		printComments(buf, item.LeadComment)
		printBlockOpen(buf, "provisioner", []string{typeName}, item.LineComment)
		bodyDiags := upgradeBlockBody(filename, fmt.Sprintf("%s.provisioner[%q]", blockAddr, typeName), buf, body.List.Items, body.Rbrace, rules, adhocComments)
		diags = diags.Append(bodyDiags)
		buf.WriteString("}\n")

		return diags
	}
}

func connectionBlockRule(filename string, resourceType string, an *analysis, adhocComments *commentQueue) bodyItemRule {
	// Unlike some other examples above, this is a rule for the entire
	// connection block, rather than just for its contents. Therefore it must
	// also produce the block header and body delimiters.
	return func(buf *bytes.Buffer, blockAddr string, item *hcl1ast.ObjectItem) tfdiags.Diagnostics {
		var diags tfdiags.Diagnostics
		body := item.Val.(*hcl1ast.ObjectType)

		// TODO: For the few resource types that were setting ConnInfo in
		// state after create/update in prior versions, generate the additional
		// explicit connection settings that are now required if and only if
		// there's at least one provisioner block.
		// For now, we just pass this through as-is.

		schema := terraform.ConnectionBlockSupersetSchema()
		rules := schemaDefaultBodyRules(filename, schema, an, adhocComments)
		rules["type"] = noInterpAttributeRule(filename, cty.String, an) // type is processed early in the config loader, so cannot interpolate

		printComments(buf, item.LeadComment)
		printBlockOpen(buf, "connection", nil, item.LineComment)

		// Terraform 0.12 no longer supports "magical" configuration of defaults
		// in the connection block from logic in the provider because explicit
		// is better than implicit, but for backward-compatibility we'll populate
		// an existing connection block with any settings that would've been
		// previously set automatically for a set of instance types we know
		// had this behavior in versions prior to the v0.12 release.
		if defaults := resourceTypeAutomaticConnectionExprs[resourceType]; len(defaults) > 0 {
			names := make([]string, 0, len(defaults))
			for name := range defaults {
				names = append(names, name)
			}
			sort.Strings(names)
			for _, name := range names {
				exprSrc := defaults[name]
				if existing := body.List.Filter(name); len(existing.Items) > 0 {
					continue // Existing explicit value, so no need for a default
				}
				printAttribute(buf, name, []byte(exprSrc), nil)
			}
		}

		bodyDiags := upgradeBlockBody(filename, fmt.Sprintf("%s.connection", blockAddr), buf, body.List.Items, body.Rbrace, rules, adhocComments)
		diags = diags.Append(bodyDiags)
		buf.WriteString("}\n")

		return diags
	}
}

func moduleSourceRule(filename string, an *analysis) bodyItemRule {
	return func(buf *bytes.Buffer, blockAddr string, item *hcl1ast.ObjectItem) tfdiags.Diagnostics {
		var diags tfdiags.Diagnostics
		val, ok := item.Val.(*hcl1ast.LiteralType)
		if !ok {
			diags = diags.Append(&hcl2.Diagnostic{
				Severity: hcl2.DiagError,
				Summary:  "Invalid source argument",
				Detail:   `The "source" argument must be a single string containing the module source.`,
				Subject:  hcl1PosRange(filename, item.Keys[0].Pos()).Ptr(),
			})
			return diags
		}
		if val.Token.Type != hcl1token.STRING {
			diags = diags.Append(&hcl2.Diagnostic{
				Severity: hcl2.DiagError,
				Summary:  "Invalid source argument",
				Detail:   `The "source" argument must be a single string containing the module source.`,
				Subject:  hcl1PosRange(filename, item.Keys[0].Pos()).Ptr(),
			})
			return diags
		}

		litVal := val.Token.Value().(string)

		if isMaybeRelativeLocalPath(litVal, an.ModuleDir) {
			diags = diags.Append(&hcl2.Diagnostic{
				Severity: hcl2.DiagWarning,
				Summary:  "Possible relative module source",
				Detail:   "Terraform cannot determine the given module source, but it appears to be a relative path",
				Subject:  hcl1PosRange(filename, item.Keys[0].Pos()).Ptr(),
			})
			buf.WriteString(
				"# TF-UPGRADE-TODO: In Terraform v0.11 and earlier, it was possible to\n" +
					"# reference a relative module source without a preceding ./, but it is no\n" +
					"# longer supported in Terraform v0.12.\n" +
					"#\n" +
					"# If the below module source is indeed a relative local path, add ./ to the\n" +
					"# start of the source string. If that is not the case, then leave it as-is\n" +
					"# and remove this TODO comment.\n",
			)
		}
		newVal, exprDiags := upgradeExpr(val, filename, false, an)
		diags = diags.Append(exprDiags)
		buf.WriteString("source = " + string(newVal) + "\n")
		return diags
	}
}

// Prior to Terraform 0.12 providers were able to supply default connection
// settings that would partially populate the "connection" block with
// automatically-selected values.
//
// In practice, this feature was often confusing in that the provider would not
// have enough information to select a suitable host address or protocol from
// multiple possible options and so would just make an arbitrary decision.
//
// With our principle of "explicit is better than implicit", as of Terraform 0.12
// we now require all connection settings to be configured explicitly by the
// user so that it's clear and explicit in the configuration which protocol and
// IP address are being selected. To avoid generating errors immediately after
// upgrade, though, we'll make a best effort to populate something functionally
// equivalent to what the provider would've done automatically for any resource
// types we know about in this table.
//
// The leaf values in this data structure are raw expressions to be inserted,
// and so they must use valid expression syntax as understood by Terraform 0.12.
// They should generally be expressions using only constant values or expressions
// in terms of attributes accessed via the special "self" object. These should
// mimic as closely as possible the logic that the provider itself used to
// implement.
//
// NOTE: Because provider releases are independent from Terraform Core releases,
// there could potentially be new 0.11-compatible provider releases that
// introduce new uses of default connection info that this map doesn't know
// about. The upgrade tool will not handle these, and so we will advise
// provider developers that this mechanism is not to be used for any new
// resource types, even in 0.11 mode.
var resourceTypeAutomaticConnectionExprs = map[string]map[string]string{
	"aws_instance": map[string]string{
		"type": `"ssh"`,
		"host": `coalesce(self.public_ip, self.private_ip)`,
	},
	"aws_spot_instance_request": map[string]string{
		"type":     `"ssh"`,
		"host":     `coalesce(self.public_ip, self.private_ip)`,
		"user":     `self.username != "" ? self.username : null`,
		"password": `self.password != "" ? self.password : null`,
	},
	"azure_instance": map[string]string{
		"type": `"ssh" # TF-UPGRADE-TODO: If this is a windows instance without an SSH server, change to "winrm"`,
		"host": `coalesce(self.vip_address, self.ip_address)`,
	},
	"azurerm_virtual_machine": map[string]string{
		"type": `"ssh" # TF-UPGRADE-TODO: If this is a windows instance without an SSH server, change to "winrm"`,
		// The azurerm_virtual_machine resource type does not expose a remote
		// access IP address directly, instead requring the user to separately
		// fetch the network interface.
		// (If we can add a "default_ssh_ip" or similar attribute to this
		// resource type before its first 0.12-compatible release then we should
		// update this to use that instead, for simplicity's sake.)
		"host": `"" # TF-UPGRADE-TODO: Set this to the IP address of the machine's primary network interface`,
	},
	"brightbox_server": map[string]string{
		"type": `"ssh"`,
		"host": `coalesce(self.public_hostname, self.ipv6_hostname, self.fqdn)`,
	},
	"cloudscale_server": map[string]string{
		"type": `"ssh"`,
		// The logic for selecting this is pretty complicated for this resource
		// type, and the result is not exposed as an isolated attribute, so
		// the conversion here is a little messy. We include newlines in this
		// one so that the auto-formatter can indent it nicely for readability.
		// NOTE: In v1.0.1 of this provider (the latest at the time of this
		// writing) it has an possible bug where it selects _public_ IPv4
		// addresses but _private_ IPv6 addresses. That behavior is followed
		// here to maximize compatibility with existing configurations.
		"host": `coalesce( # TF-UPGRADE-TODO: Simplify this to reference a specific desired IP address, if possible.
			concat(
				flatten([
					for i in self.network_interface : [
						for a in i.addresses : a.address
						if a.version == 4
					]
					if i.type == "public"
				]),
				flatten([
					for i in self.network_interface : [
						for a in i.addresses : a.address
						if a.version == 6
					]
					if i.type == "private"
				]),
			)...
		)`,
	},
	"cloudstack_instance": map[string]string{
		"type": `"ssh"`,
		"host": `self.ip_address`,
	},
	"digitalocean_droplet": map[string]string{
		"type": `"ssh"`,
		"host": `self.ipv4_address`,
	},
	"flexibleengine_compute_bms_server_v2": map[string]string{
		"type": `"ssh"`,
		"host": `coalesce(self.access_ip_v4, self.access_ip_v6)`,
	},
	"flexibleengine_compute_instance_v2": map[string]string{
		"type": `"ssh"`,
		"host": `coalesce(self.access_ip_v4, self.access_ip_v6)`,
	},
	"google_compute_instance": map[string]string{
		"type": `"ssh"`,
		// The logic for selecting this is pretty complicated for this resource
		// type, and the result is not exposed as an isolated attribute, so
		// the conversion here is a little messy. We include newlines in this
		// one so that the auto-formatter can indent it nicely for readability.
		// (If we can add a "default_ssh_ip" or similar attribute to this
		// resource type before its first 0.12-compatible release then we should
		// update this to use that instead, for simplicity's sake.)
		"host": `coalesce( # TF-UPGRADE-TODO: Simplify this to reference a specific desired IP address, if possible.
			concat(
				# Prefer any available NAT IP address
				flatten([
					for ni in self.network_interface : [
						for ac in ni.access_config : ac.nat_ip
					]
				]),

				# Otherwise, use the first available LAN IP address
				[
					for ni in self.network_interface : ni.network_ip
				],
			)...
		)`,
	},
	"hcloud_server": map[string]string{
		"type": `"ssh"`,
		"host": `self.ipv4_address`,
	},
	"huaweicloud_compute_instance_v2": map[string]string{
		"type": `"ssh"`,
		"host": `coalesce(self.access_ip_v4, self.access_ip_v6)`,
	},
	"linode_instance": map[string]string{
		"type": `"ssh"`,
		"host": `self.ipv4[0]`,
	},
	"oneandone_baremetal_server": map[string]string{
		"type":        `ssh`,
		"host":        `self.ips[0].ip`,
		"password":    `self.password != "" ? self.password : null`,
		"private_key": `self.ssh_key_path != "" ? file(self.ssh_key_path) : null`,
	},
	"oneandone_server": map[string]string{
		"type":        `ssh`,
		"host":        `self.ips[0].ip`,
		"password":    `self.password != "" ? self.password : null`,
		"private_key": `self.ssh_key_path != "" ? file(self.ssh_key_path) : null`,
	},
	"openstack_compute_instance_v2": map[string]string{
		"type": `"ssh"`,
		"host": `coalesce(self.access_ip_v4, self.access_ip_v6)`,
	},
	"opentelekomcloud_compute_bms_server_v2": map[string]string{
		"type": `"ssh"`,
		"host": `coalesce(self.access_ip_v4, self.access_ip_v6)`,
	},
	"opentelekomcloud_compute_instance_v2": map[string]string{
		"type": `"ssh"`,
		"host": `coalesce(self.access_ip_v4, self.access_ip_v6)`,
	},
	"packet_device": map[string]string{
		"type": `"ssh"`,
		"host": `self.access_public_ipv4`,
	},
	"profitbricks_server": map[string]string{
		"type": `"ssh"`,
		"host": `coalesce(self.primary_nic.ips...)`,
		// The value for this isn't exported anywhere on the object, so we'll
		// need to have the user fix it up manually.
		"password": `"" # TF-UPGRADE-TODO: set this to a suitable value, such as the boot image password`,
	},
	"scaleway_server": map[string]string{
		"type": `"ssh"`,
		"host": `self.public_ip`,
	},
	"telefonicaopencloud_compute_bms_server_v2": map[string]string{
		"type": `"ssh"`,
		"host": `coalesce(self.access_ip_v4, self.access_ip_v6)`,
	},
	"telefonicaopencloud_compute_instance_v2": map[string]string{
		"type": `"ssh"`,
		"host": `coalesce(self.access_ip_v4, self.access_ip_v6)`,
	},
	"triton_machine": map[string]string{
		"type": `"ssh"`,
		"host": `self.primaryip`, // convention would call for this to be named "primary_ip", but "primaryip" is the name this resource type uses
	},
	"vsphere_virtual_machine": map[string]string{
		"type": `"ssh"`,
		"host": `self.default_ip_address`,
	},
	"yandex_compute_instance": map[string]string{
		"type": `"ssh"`,
		// The logic for selecting this is pretty complicated for this resource
		// type, and the result is not exposed as an isolated attribute, so
		// the conversion here is a little messy. We include newlines in this
		// one so that the auto-formatter can indent it nicely for readability.
		"host": `coalesce( # TF-UPGRADE-TODO: Simplify this to reference a specific desired IP address, if possible.
			concat(
				# Prefer any available NAT IP address
				for i in self.network_interface: [
					i.nat_ip_address
				],

				# Otherwise, use the first available internal IP address
				for i in self.network_interface: [
					i.ip_address
				],
			)...
		)`,
	},
}

// copied directly from internal/initwd/getter.go
var localSourcePrefixes = []string{
	"./",
	"../",
	".\\",
	"..\\",
}

// isMaybeRelativeLocalPath tries to catch situations where a module source is
// an improperly-referenced relative path, such as "module" instead of
// "./module". This is a simple check that could return a false positive in the
// unlikely-yet-plausible case that a module source is for eg. a github
// repository that also looks exactly like an existing relative path. This
// should only be used to return a warning.
func isMaybeRelativeLocalPath(addr, dir string) bool {
	for _, prefix := range localSourcePrefixes {
		if strings.HasPrefix(addr, prefix) {
			// it is _definitely_ a relative path
			return false
		}
	}

	_, err := regsrc.ParseModuleSource(addr)
	if err == nil {
		// it is a registry source
		return false
	}

	possibleRelPath := filepath.Join(dir, addr)
	_, err = os.Stat(possibleRelPath)
	if err == nil {
		// If there is no error, something exists at what would be the relative
		// path, if the module source started with ./
		return true
	}

	return false
}