terraform/internal/addrs/partial_expanded.go

// Copyright (c) HashiCorp, Inc.
// SPDX-License-Identifier: BUSL-1.1

package addrs

import (
	"fmt"
	"strings"

	"github.com/hashicorp/hcl/v2"
	"github.com/zclconf/go-cty/cty"
	"github.com/zclconf/go-cty/cty/gocty"

	"github.com/hashicorp/terraform/internal/tfdiags"
)

// PartialExpandedModule represents a set of module instances which all share
// a common known parent module instance but the remaining call instance keys
// are not yet known.
type PartialExpandedModule struct {
	// expandedPrefix is the initial part of the module address whose expansion
	// is already complete and so has exact instance keys.
	expandedPrefix ModuleInstance

	// unexpandedSuffix is the remainder of the module address whose instance
	// keys are not known yet. This is a slight abuse of type [Module] because
	// it's representing a relative path from expandedPrefix rather than a
	// path from the root module as usual, so this value must never be exposed
	// in the public API of this package.
	//
	// This can be zero-length in PartialExpandedModule values used as part
	// of the internals of a PartialExpandedResource, but should never be
	// zero-length in a publicly-exposed PartialExpandedModule because that
	// would make this just a degenerate ModuleInstance.
	unexpandedSuffix Module
}

// ParsePartialExpandedModule parses a module address traversal and returns a
// PartialExpandedModule representing the known and unknown parts of the
// address.
//
// It returns the parsed PartialExpandedModule, the remaining traversal steps
// that were not consumed by this function, and any diagnostics that were
// generated during parsing.
func ParsePartialExpandedModule(traversal hcl.Traversal) (PartialExpandedModule, hcl.Traversal, tfdiags.Diagnostics) {
	var diags tfdiags.Diagnostics

	remain := traversal
	var partial PartialExpandedModule

	// We'll step through the traversal steps and build up the known prefix
	// of the module address. When we reach a call with an unknown index, we'll
	// switch to building up the unexpanded suffix.
	expanded := true

LOOP:
	for len(remain) > 0 {
		var next string
		switch tt := remain[0].(type) {
		case hcl.TraverseRoot:
			next = tt.Name
		case hcl.TraverseAttr:
			next = tt.Name
		default:
			diags = diags.Append(&hcl.Diagnostic{
				Severity: hcl.DiagError,
				Summary:  "Invalid address operator",
				Detail:   "Module address prefix must be followed by dot and then a name.",
				Subject:  remain[0].SourceRange().Ptr(),
			})
			break LOOP
		}

		if next != "module" {
			break
		}

		kwRange := remain[0].SourceRange()
		remain = remain[1:]
		if len(remain) == 0 {
			diags = diags.Append(&hcl.Diagnostic{
				Severity: hcl.DiagError,
				Summary:  "Invalid address operator",
				Detail:   "Prefix \"module.\" must be followed by a module name.",
				Subject:  &kwRange,
			})
			break
		}

		var moduleName string
		switch tt := remain[0].(type) {
		case hcl.TraverseAttr:
			moduleName = tt.Name
		default:
			diags = diags.Append(&hcl.Diagnostic{
				Severity: hcl.DiagError,
				Summary:  "Invalid address operator",
				Detail:   "Prefix \"module.\" must be followed by a module name.",
				Subject:  remain[0].SourceRange().Ptr(),
			})
			break LOOP
		}
		remain = remain[1:]

		if expanded {

			step := ModuleInstanceStep{
				Name: moduleName,
			}

			if len(remain) > 0 {
				if idx, ok := remain[0].(hcl.TraverseIndex); ok {
					remain = remain[1:]

					if !idx.Key.IsKnown() {
						// We'll switch to building up the unexpanded suffix
						// starting with this step.
						expanded = false
						partial.unexpandedSuffix = append(partial.unexpandedSuffix, moduleName)
						continue
					}

					switch idx.Key.Type() {
					case cty.String:
						step.InstanceKey = StringKey(idx.Key.AsString())
					case cty.Number:
						var idxInt int
						err := gocty.FromCtyValue(idx.Key, &idxInt)
						if err == nil {
							step.InstanceKey = IntKey(idxInt)
						} else {
							diags = diags.Append(&hcl.Diagnostic{
								Severity: hcl.DiagError,
								Summary:  "Invalid address operator",
								Detail:   fmt.Sprintf("Invalid module index: %s.", err),
								Subject:  idx.SourceRange().Ptr(),
							})
						}
					default:
						// Should never happen, because no other types are allowed in traversal indices.
						diags = diags.Append(&hcl.Diagnostic{
							Severity: hcl.DiagError,
							Summary:  "Invalid address operator",
							Detail:   "Invalid module key: must be either a string or an integer.",
							Subject:  idx.SourceRange().Ptr(),
						})
					}
				}
			}

			partial.expandedPrefix = append(partial.expandedPrefix, step)
			continue
		}

		// Otherwise, we'll process this as an unexpanded suffix.
		partial.unexpandedSuffix = append(partial.unexpandedSuffix, moduleName)

		if len(remain) > 0 {
			if _, ok := remain[0].(hcl.TraverseIndex); ok {
				// Then we have a module instance key. We're now parsing the
				// unexpanded suffix of the module address, so we'll just
				// ignore it.
				remain = remain[1:]
			}
		}
	}

	var retRemain hcl.Traversal
	if len(remain) > 0 {
		retRemain = make(hcl.Traversal, len(remain))
		copy(retRemain, remain)
		// The first element here might be either a TraverseRoot or a
		// TraverseAttr, depending on whether we had a module address on the
		// front. To make life easier for callers, we'll normalize to always
		// start with a TraverseRoot.
		if tt, ok := retRemain[0].(hcl.TraverseAttr); ok {
			retRemain[0] = hcl.TraverseRoot{
				Name:     tt.Name,
				SrcRange: tt.SrcRange,
			}
		}
	}

	return partial, retRemain, diags
}

func (m ModuleInstance) UnexpandedChild(call ModuleCall) PartialExpandedModule {
	return PartialExpandedModule{
		expandedPrefix:   m,
		unexpandedSuffix: Module{call.Name},
	}
}

// PartialModule reverses the process of UnknownModuleInstance by converting a
// ModuleInstance back into a PartialExpandedModule.
func (m ModuleInstance) PartialModule() PartialExpandedModule {
	pem := PartialExpandedModule{}
	for _, step := range m {
		if step.InstanceKey == WildcardKey {
			pem.unexpandedSuffix = append(pem.unexpandedSuffix, step.Name)
			continue
		}
		pem.expandedPrefix = append(pem.expandedPrefix, step)
	}
	return pem
}

// UnknownModuleInstance expands the receiver to a full ModuleInstance by
// replacing the unknown instance keys with a wildcard value.
func (pem PartialExpandedModule) UnknownModuleInstance() ModuleInstance {
	base := pem.expandedPrefix
	for _, call := range pem.unexpandedSuffix {
		base = append(base, ModuleInstanceStep{
			Name:        call,
			InstanceKey: WildcardKey,
		})
	}
	return base
}

// LevelsKnown returns the number of module path segments of the address that
// have known instance keys.
//
// This might be useful, for example, for preferring a more-specifically-known
// address over a less-specifically-known one when selecting a placeholder
// value to use to represent an object beneath an unexpanded module address.
func (pem PartialExpandedModule) LevelsKnown() int {
	return len(pem.expandedPrefix)
}

// MatchesInstance returns true if and only if the given module instance
// belongs to the recieving partially-expanded module address pattern.
func (pem PartialExpandedModule) MatchesInstance(inst ModuleInstance) bool {
	// Total length must always match.
	if len(inst) != (len(pem.expandedPrefix) + len(pem.unexpandedSuffix)) {
		return false
	}

	// The known prefix must match exactly.
	givenExpandedPrefix := inst[:len(pem.expandedPrefix)]
	if !givenExpandedPrefix.Equal(pem.expandedPrefix) {
		return false
	}

	// The known suffix must match the call names, even though we don't yet
	// know the specific instance keys.
	givenExpandedSuffix := inst[len(pem.expandedPrefix):]
	for i := range pem.unexpandedSuffix {
		if pem.unexpandedSuffix[i] != givenExpandedSuffix[i].Name {
			return false
		}
	}

	// If we passed all the filters above then it's a match.
	return true
}

// MatchesPartial returns true if and only if the receiver represents the same
// static module as the other given module and the receiver's known instance
// keys are a prefix of the other module's.
func (pem PartialExpandedModule) MatchesPartial(other PartialExpandedModule) bool {
	// The two addresses must represent the same static module, regardless
	// of the instance keys of those modules.
	if !pem.Module().Equal(other.Module()) {
		return false
	}

	if len(pem.expandedPrefix) > len(other.expandedPrefix) {
		return false
	}

	thisPrefix := pem.expandedPrefix
	otherPrefix := other.expandedPrefix[:len(pem.expandedPrefix)]
	return thisPrefix.Equal(otherPrefix)
}

// Module returns the unexpanded module address that this pattern originated
// from.
func (pem PartialExpandedModule) Module() Module {
	ret := pem.expandedPrefix.Module()
	return append(ret, pem.unexpandedSuffix...)
}

// KnownPrefix returns the longest possible ModuleInstance address made of
// known segments of this partially-expanded module instance address.
func (pem PartialExpandedModule) KnownPrefix() ModuleInstance {
	if len(pem.expandedPrefix) == 0 {
		return nil
	}

	// Although we can't enforce it with the Go compiler, our convention is
	// that we never mutate address values outside of this package and so
	// we'll expose our pem.expandedPrefix buffer directly here and trust that
	// the caller will play nice with it. However, we do force the unused
	// capacity to zero so that the caller can safely construct child addresses,
	// which would append new steps to the end.
	return pem.expandedPrefix[:len(pem.expandedPrefix):len(pem.expandedPrefix)]
}

// FirstUnexpandedCall returns the address of the first step in the module
// path whose instance keys are not yet known, discarding any subsequent
// calls beneath it.
func (pem PartialExpandedModule) FirstUnexpandedCall() AbsModuleCall {
	// NOTE: This assumes that there's always at least one element in
	// unexpandedSuffix because it should only be used with the public-facing
	// version of PartialExpandedModule where that contract always holds. It's
	// not safe to use this for the PartialExpandedModule value hidden in the
	// internals of PartialExpandedResource.
	return AbsModuleCall{
		Module: pem.KnownPrefix(),
		Call: ModuleCall{
			Name: pem.unexpandedSuffix[0],
		},
	}
}

// UnexpandedSuffix returns the local addresses of all of the calls whose
// instances are not yet expanded, in the module tree traversal order.
//
// Method KnownPrefix concatenated with UnexpandedSuffix (assuming that were
// actually possible) represents the whole module path that the
// PartialExpandedModule encapsulates.
func (pem PartialExpandedModule) UnexpandedSuffix() []ModuleCall {
	if len(pem.unexpandedSuffix) == 0 {
		// Should never happen for any publicly-visible value of this type,
		// because we should always have at least one unexpanded call,
		// but we'll allow it anyway since we have a reasonable return value
		// for that case.
		return nil
	}

	// A []ModuleCall is the only representation of a non-rooted chain of
	// module calls that we're allowed to export in our public API, and so
	// we'll transform our not-quite-allowed unrooted "Module" value in that
	// form externally.
	ret := make([]ModuleCall, len(pem.unexpandedSuffix))
	for i, name := range pem.unexpandedSuffix {
		ret[i].Name = name
	}
	return ret
}

// Child returns the address of a child of the receiver that belongs to the
// given module call.
func (pem PartialExpandedModule) Child(call ModuleCall) PartialExpandedModule {
	return PartialExpandedModule{
		expandedPrefix:   pem.expandedPrefix,
		unexpandedSuffix: append(pem.unexpandedSuffix, call.Name),
	}
}

// Resource returns the address of a resource within the receiver.
func (pem PartialExpandedModule) Resource(resource Resource) PartialExpandedResource {
	return PartialExpandedResource{
		module:   pem,
		resource: resource,
	}
}

// Action returns the address of an action within the receiver.
func (pem PartialExpandedModule) Action(action Action) PartialExpandedAction {
	return PartialExpandedAction{
		module: pem,
		action: action,
	}
}

// String returns a string representation of the pattern where the known
// prefix uses the normal module instance address syntax and the unknown
// suffix steps use a similar syntax but with "[*]" as a placeholder to
// represent instance keys that aren't yet known.
func (pem PartialExpandedModule) String() string {
	var buf strings.Builder
	if len(pem.expandedPrefix) != 0 {
		buf.WriteString(pem.expandedPrefix.String())
	}
	for i, callName := range pem.unexpandedSuffix {
		if i > 0 || len(pem.expandedPrefix) != 0 {
			buf.WriteByte('.')
		}
		buf.WriteString("module.")
		buf.WriteString(callName)
		buf.WriteString("[*]")
	}
	return buf.String()
}

func (pem PartialExpandedModule) UniqueKey() UniqueKey {
	return partialExpandedModuleKey(pem.String())
}

type partialExpandedModuleKey string

var _ UniqueKey = partialExpandedModuleKey("")

func (partialExpandedModuleKey) uniqueKeySigil() {}

// PartialExpandedResource represents a set of resource instances which all share
// a common known parent module instance but the remaining call instance keys
// are not yet known and the resource's own instance keys are not yet known.
//
// A PartialExpandedResource with a fully-known module instance address is
// semantically interchangable with an [AbsResource], which is useful when we
// need to represent an assortment of variously-unknown resource instance
// addresses, but [AbsResource] is preferable in situations where the module
// instance address is _always_ known and it's only the resource instance
// key that is not represented.
type PartialExpandedResource struct {
	// module is the partially-expanded module instance address that this
	// resource belongs to.
	//
	// This value can actually represent a fully-expanded module if its
	// unexpandedSuffix field is zero-length, in which case it's only the
	// resource itself that's unexpanded, which would make this equivalent
	// to an AbsResource.
	//
	// We mustn't directly expose this value in the public API because
	// external callers must never see a PartialExpandedModule that is
	// actually fully-expanded; that should be a ModuleInstance instead.
	module   PartialExpandedModule
	resource Resource
}

// ParsePartialExpandedResource parses a resource address traversal and returns
// a PartialExpandedResource representing the known and unknown parts of the
// address.
func ParsePartialExpandedResource(traversal hcl.Traversal) (PartialExpandedResource, hcl.Traversal, tfdiags.Diagnostics) {
	var diags tfdiags.Diagnostics

	pem, remain, diags := ParsePartialExpandedModule(traversal)
	if len(remain) == 0 {
		diags = diags.Append(&hcl.Diagnostic{
			Severity: hcl.DiagError,
			Summary:  "Invalid address",
			Detail:   "Resource address must be a module address followed by a resource address.",
			Subject:  traversal.SourceRange().Ptr(),
		})
		return PartialExpandedResource{}, nil, diags
	}

	// We know that remain[0] is a hcl.TraverseRoot object as the
	// ParsePartialExpandedModule function always returns a hcl.TraverseRoot
	// object as the first element in the remain slice.

	mode := ManagedResourceMode
	if remain.RootName() == "data" {
		mode = DataResourceMode
		remain = remain[1:]
	} else if remain.RootName() == "resource" {
		// Starting a resource address with "resource" is optional, so we'll
		// just ignore it if it's present.
		remain = remain[1:]
	}

	if len(remain) < 2 {
		diags = diags.Append(&hcl.Diagnostic{
			Severity: hcl.DiagError,
			Summary:  "Invalid address",
			Detail:   "Resource specification must include a resource type and name.",
			Subject:  remain.SourceRange().Ptr(),
		})
		return PartialExpandedResource{}, nil, diags
	}

	var typeName, name string
	switch tt := remain[0].(type) {
	case hcl.TraverseRoot:
		typeName = tt.Name
	case hcl.TraverseAttr:
		typeName = tt.Name
	default:
		switch mode {
		case ManagedResourceMode:
			diags = diags.Append(&hcl.Diagnostic{
				Severity: hcl.DiagError,
				Summary:  "Invalid address",
				Detail:   "A resource type name is required.",
				Subject:  remain[0].SourceRange().Ptr(),
			})
		case DataResourceMode:
			diags = diags.Append(&hcl.Diagnostic{
				Severity: hcl.DiagError,
				Summary:  "Invalid address",
				Detail:   "A data source name is required.",
				Subject:  remain[0].SourceRange().Ptr(),
			})
		default:
			panic("unknown mode")
		}
		return PartialExpandedResource{}, nil, diags
	}

	switch tt := remain[1].(type) {
	case hcl.TraverseAttr:
		name = tt.Name
	default:
		diags = diags.Append(&hcl.Diagnostic{
			Severity: hcl.DiagError,
			Summary:  "Invalid address",
			Detail:   "A resource name is required.",
			Subject:  remain[1].SourceRange().Ptr(),
		})
		return PartialExpandedResource{}, nil, diags
	}

	remain = remain[2:]
	if len(remain) > 0 {
		if _, ok := remain[0].(hcl.TraverseIndex); ok {
			// Then we have a resource instance key. Since, we're building a
			// PartialExpandedResource, we'll just ignore it.
			remain = remain[1:]
		}
	}

	return PartialExpandedResource{
		module: pem,
		resource: Resource{
			Mode: mode,
			Type: typeName,
			Name: name,
		},
	}, remain, diags
}

// UnexpandedResource returns the address of a child resource expressed as a
// [PartialExpandedResource].
//
// The result always has a fully-qualified module instance address and is
// therefore semantically equivalent to an [AbsResource], so this variannt
// should be used only in contexts where we might also be storing resources
// belonging to not-fully-expanded modules and need to use the same static
// address type for all of them.
func (m ModuleInstance) UnexpandedResource(resource Resource) PartialExpandedResource {
	return PartialExpandedResource{
		module: PartialExpandedModule{
			expandedPrefix: m,
		},
		resource: resource,
	}
}

// UnexpandedResource returns the receiver reinterpreted as a
// [PartialExpandedResource], which is an alternative form we use in situations
// where we might also need to mix in resources belonging to not-yet-fully-known
// module instance addresses.
func (r AbsResource) UnexpandedResource() PartialExpandedResource {
	return PartialExpandedResource{
		module: PartialExpandedModule{
			expandedPrefix: r.Module,
		},
		resource: r.Resource,
	}
}

// PartialResource reverses UnknownResourceInstance by converting the
// AbsResourceInstance back into a PartialExpandedResource.
func (r AbsResourceInstance) PartialResource() PartialExpandedResource {
	return PartialExpandedResource{
		module:   r.Module.PartialModule(),
		resource: r.Resource.Resource,
	}
}

// UnknownResourceInstance returns an [AbsResourceInstance] that represents the
// same resource as the receiver but with all instance keys replaced with a
// wildcard value.
func (per PartialExpandedResource) UnknownResourceInstance() AbsResourceInstance {
	return AbsResourceInstance{
		Module:   per.module.UnknownModuleInstance(),
		Resource: per.resource.Instance(WildcardKey),
	}
}

// MatchesInstance returns true if and only if the given resource instance
// belongs to the recieving partially-expanded resource address pattern.
func (per PartialExpandedResource) MatchesInstance(inst AbsResourceInstance) bool {
	if !per.module.MatchesInstance(inst.Module) {
		return false
	}
	return inst.Resource.Resource.Equal(per.resource)
}

// MatchesResource returns true if and only if the given resource belongs to
// the recieving partially-expanded resource address pattern.
func (per PartialExpandedResource) MatchesResource(inst AbsResource) bool {
	if !per.module.MatchesInstance(inst.Module) {
		return false
	}
	return inst.Resource.Equal(per.resource)
}

// MatchesPartial returns true if the underlying partial module address matches
// the given partial module address and the resource type and name match the
// receiver's resource type and name.
func (per PartialExpandedResource) MatchesPartial(other PartialExpandedResource) bool {
	if !per.module.MatchesPartial(other.module) {
		return false
	}
	return per.resource.Equal(other.resource)
}

// AbsResource returns the single [AbsResource] that this address represents
// if this pattern is specific enough to match only a single resource, or
// the zero value of AbsResource if not.
//
// The second return value is true if and only if the returned address is valid.
func (per PartialExpandedResource) AbsResource() (AbsResource, bool) {
	if len(per.module.unexpandedSuffix) != 0 {
		return AbsResource{}, false
	}

	return AbsResource{
		Module:   per.module.expandedPrefix,
		Resource: per.resource,
	}, true
}

// ConfigResource returns the unexpanded resource address that this
// partially-expanded resource address originates from.
func (per PartialExpandedResource) ConfigResource() ConfigResource {
	return ConfigResource{
		Module:   per.module.Module(),
		Resource: per.resource,
	}
}

// Resource returns just the leaf resource address that this partially-expanded
// resource address uses, discarding the containing module instance information
// altogether.
func (per PartialExpandedResource) Resource() Resource {
	return per.resource
}

// KnownModuleInstancePrefix returns the longest possible ModuleInstance address
// made of known segments of the module instances that this set of resource
// instances all belong to.
//
// If the whole module instance address is known and only the resource
// instances are not then this returns the full prefix, which will be the same
// as the module from a successful return value from
// [PartialExpandedResource.AbsResource].
func (per PartialExpandedResource) KnownModuleInstancePrefix() ModuleInstance {
	return per.module.KnownPrefix()
}

// ModuleInstance returns the fully-qualified [ModuleInstance] that this
// partial-expanded resource belongs to, but only if its module instance
// address is fully known.
//
// The second return value is false if the module instance address is not
// fully expanded, in which case the first return value is invalid. Use
// [PartialExpandedResource.PartialExpandedModule] instead in that case.
func (per PartialExpandedResource) ModuleInstance() (ModuleInstance, bool) {
	if len(per.module.unexpandedSuffix) != 0 {
		return nil, false
	}
	return per.module.expandedPrefix, true
}

// PartialExpandedModule returns a [PartialExpandedModule] address describing
// the partially-unknown module instance address that the resource belongs to,
// but only if the module instance address is not fully known.
//
// The second return value is false if the module instance address is actually
// fully expanded, in which case the first return value is invalid. Use
// [PartialExpandedResource.ModuleInstance] instead in that case.
func (per PartialExpandedResource) PartialExpandedModule() (PartialExpandedModule, bool) {
	if len(per.module.unexpandedSuffix) == 0 {
		return PartialExpandedModule{}, false
	}
	return per.module, true
}

// IsTargetedBy returns true if and only if the given targetable address might
// target the resource instances that could exist if the receiver were fully
// expanded.
func (per PartialExpandedResource) IsTargetedBy(addr Targetable) bool {

	compareModule := func(module Module) bool {
		// We'll step through each step in the module address and compare it
		// to the known prefix and unexpanded suffix of the receiver. If we
		// find a mismatch then we know the receiver can't be targeted by this
		// address.
		for ix, step := range module {
			if ix >= len(per.module.expandedPrefix) {
				ix = ix - len(per.module.expandedPrefix)
				if ix >= len(per.module.unexpandedSuffix) {
					// Then the target address has more steps than the receiver
					// and so can't possibly target it.
					return false
				}
				if step != per.module.unexpandedSuffix[ix] {
					// Then the target address has a different step at this
					// position than the receiver does, so it can't target it.
					return false
				}
			} else {
				if step != per.module.expandedPrefix[ix].Name {
					// Then the target address has a different step at this
					// position than the receiver does, so it can't target it.
					return false
				}
			}
		}

		// If we make it here then the target address is a prefix of the
		// receivers module address, so it could potentially target the
		// receiver.
		return true
	}

	compareModuleInstance := func(inst ModuleInstance) bool {
		// We'll step through each step in the module address and compare it
		// to the known prefix and unexpanded suffix of the receiver. If we
		// find a mismatch then we know the receiver can't be targeted by this
		// address.
		for ix, step := range inst {
			if ix >= len(per.module.expandedPrefix) {
				ix = ix - len(per.module.expandedPrefix)
				if ix >= len(per.module.unexpandedSuffix) {
					// Then the target address has more steps than the receiver
					// and so can't possibly target it.
					return false
				}
				if step.Name != per.module.unexpandedSuffix[ix] {
					// Then the target address has a different step at this
					// position than the receiver does, so it can't target it.
					return false
				}
			} else {
				if step.Name != per.module.expandedPrefix[ix].Name || (step.InstanceKey != NoKey && step.InstanceKey != per.module.expandedPrefix[ix].InstanceKey) {
					// Then the target address has a different step at this
					// position than the receiver does, so it can't target it.
					return false
				}
			}
		}

		// If we make it here then the target address is a prefix of the
		// receivers module address, so it could potentially target the
		// receiver.
		return true
	}

	switch addr.AddrType() {
	case ConfigResourceAddrType:
		addr := addr.(ConfigResource)
		if !compareModule(addr.Module) {
			return false
		}
		return addr.Resource.Equal(per.resource)
	case AbsResourceAddrType:
		addr := addr.(AbsResource)
		if !compareModuleInstance(addr.Module) {
			return false
		}
		return addr.Resource.Equal(per.resource)
	case AbsResourceInstanceAddrType:
		addr := addr.(AbsResourceInstance)
		if !compareModuleInstance(addr.Module) {
			return false
		}
		return addr.Resource.Resource.Equal(per.resource)
	case ModuleAddrType:
		return compareModule(addr.(Module))
	case ModuleInstanceAddrType:
		return compareModuleInstance(addr.(ModuleInstance))
	}

	return false
}

// String returns a string representation of the pattern which uses the special
// placeholder "[*]" to represent positions where instance keys are not yet
// known.
func (per PartialExpandedResource) String() string {
	moduleAddr := per.module.String()
	if len(moduleAddr) != 0 {
		return moduleAddr + "." + per.resource.String() + "[*]"
	}
	return per.resource.String() + "[*]"
}

func (per PartialExpandedResource) UniqueKey() UniqueKey {
	// If this address is equivalent to an AbsResource address then we'll
	// return its instance key here so that function Equivalent will consider
	// the two as equivalent.
	if ar, ok := per.AbsResource(); ok {
		return ar.UniqueKey()
	}
	// For not-fully-expanded module paths we'll use a distinct address type
	// since there is no other address type equivalent to those.
	return partialExpandedResourceKey(per.String())
}

type partialExpandedResourceKey string

var _ UniqueKey = partialExpandedModuleKey("")

func (partialExpandedResourceKey) uniqueKeySigil() {}

// InPartialExpandedModule is a generic type used for all address types that
// represent objects that exist inside module instances but do not have any
// expansion capability of their own beyond just the containing module
// expansion.
//
// Although not enforced by the type system, this type should be used only for
// address types T that are combined with a ModuleInstance value in a type
// whose name starts with "Abs". For example, [LocalValue] is a reasonable T
// because [AbsLocalValue] represents a local value inside a particular module
// instance. InPartialExpandedModule[LocalValue] is therefore like an
// [AbsLocalValue] whose module path isn't fully known yet.
//
// This type is here primarily just to have implementations of [UniqueKeyer]
// so we can store partially-evaluated objects from unexpanded modules in
// collections for later reference downstream.
type InPartialExpandedModule[T interface {
	UniqueKeyer
	fmt.Stringer
}] struct {
	Module PartialExpandedModule
	Local  T
}

// ObjectInPartialExpandedModule is a constructor for [InPartialExpandedModule]
// that's here primarily just to benefit from function type parameter inference
// to avoid manually writing out type T when constructing such a value.
func ObjectInPartialExpandedModule[T interface {
	UniqueKeyer
	fmt.Stringer
}](module PartialExpandedModule, local T) InPartialExpandedModule[T] {
	return InPartialExpandedModule[T]{
		Module: module,
		Local:  local,
	}
}

var _ UniqueKeyer = InPartialExpandedModule[LocalValue]{}

// ModuleLevelsKnown returns the number of module path segments of the address
// that have known instance keys.
//
// This might be useful, for example, for preferring a more-specifically-known
// address over a less-specifically-known one when selecting a placeholder
// value to use to represent an object beneath an unexpanded module address.
func (in InPartialExpandedModule[T]) ModuleLevelsKnown() int {
	return in.Module.LevelsKnown()
}

// String returns a string representation of the pattern which uses the special
// placeholder "[*]" to represent positions where module instance keys are not
// yet known.
func (in InPartialExpandedModule[T]) String() string {
	moduleAddr := in.Module.String()
	if len(moduleAddr) != 0 {
		return moduleAddr + "." + in.Local.String()
	}
	return in.Local.String()
}

func (in InPartialExpandedModule[T]) UniqueKey() UniqueKey {
	return inPartialExpandedModuleUniqueKey{
		moduleKey: in.Module.UniqueKey(),
		localKey:  in.Local.UniqueKey(),
	}
}

type inPartialExpandedModuleUniqueKey struct {
	moduleKey UniqueKey
	localKey  UniqueKey
}

func (inPartialExpandedModuleUniqueKey) uniqueKeySigil() {}

// PartialExpandedAction represents a partially-expanded action address.
// See PartialExpandedResource for more information.
type PartialExpandedAction struct {
	module PartialExpandedModule
	action Action
}

func (per PartialExpandedAction) AbsAction() (AbsAction, bool) {
	if len(per.module.unexpandedSuffix) != 0 {
		return AbsAction{}, false
	}

	return AbsAction{
		Module: per.module.expandedPrefix,
		Action: per.action,
	}, true
}

// ConfigAction returns the unexpanded action address that this
// partially-expanded action address originates from.
func (per PartialExpandedAction) ConfigAction() ConfigAction {
	return ConfigAction{
		Module: per.module.Module(),
		Action: per.action,
	}
}

func (per PartialExpandedAction) ModuleInstance() (ModuleInstance, bool) {
	if len(per.module.unexpandedSuffix) != 0 {
		return nil, false
	}
	return per.module.expandedPrefix, true
}

func (m ModuleInstance) UnexpandedAction(action Action) PartialExpandedAction {
	return PartialExpandedAction{
		module: PartialExpandedModule{
			expandedPrefix: m,
		},
		action: action,
	}
}

func (a *AbsAction) UnexpandedAction(action Action) PartialExpandedAction {
	return PartialExpandedAction{
		module: PartialExpandedModule{
			expandedPrefix: a.Module,
		},
		action: action,
	}
}

func (pea PartialExpandedAction) String() string {
	moduleAddr := pea.module.String()
	if len(moduleAddr) != 0 {
		return moduleAddr + "." + pea.action.String() + "[*]"
	}
	return pea.action.String() + "[*]"
}

func (pea PartialExpandedAction) Equal(other PartialExpandedAction) bool {
	return pea.module.MatchesPartial(other.module.expandedPrefix.PartialModule()) && pea.action.Equal(other.action)
}

func (pea PartialExpandedAction) UniqueKey() UniqueKey {
	// If this address is equivalent to an AbsAction address then we'll
	// return its instance key here so that function Equivalent will consider
	// the two as equivalent.
	if ar, ok := pea.AbsAction(); ok {
		return ar.UniqueKey()
	}
	// For not-fully-expanded module paths we'll use a distinct address type
	// since there is no other address type equivalent to those.
	return partialExpandedActionKey(pea.String())
}

type partialExpandedActionKey string

func (partialExpandedActionKey) uniqueKeySigil() {}

// PartialExpandedModule returns a [PartialExpandedModule] address describing
// the partially-unknown module instance address that the action belongs to,
// but only if the module instance address is not fully known.
//
// The second return value is false if the module instance address is actually
// fully expanded, in which case the first return value is invalid. Use
// [PartialExpandedAction.ModuleInstance] instead in that case.
func (per PartialExpandedAction) PartialExpandedModule() (PartialExpandedModule, bool) {
	if len(per.module.unexpandedSuffix) == 0 {
		return PartialExpandedModule{}, false
	}
	return per.module, true
}