config: "ResourceMode" concept for resources

Previously resources were assumed to always support the full set of
create, read, update and delete operations, and Terraform's resource
management lifecycle.

Data sources introduce a new kind of resource that only supports the
"read" operation. To support this, a new "Mode" field is added to
the Resource concept within the config layer, which can be set to
ManagedResourceMode (to indicate the only mode previously possible) or
DataResourceMode (to indicate that only "read" is supported).

To support both managed and data resources in the tests, the
stringification of resources in config_string.go is adjusted slightly
to use the Id() method rather than the unusual type[name] serialization
from before, causing a simple mechanical adjustment to the loader tests'
expected result strings.

config/config.go

@@ -67,9 +67,11 @@ type ProviderConfig struct {
 }
 
 // A resource represents a single Terraform resource in the configuration.
-// A Terraform resource is something that represents some component that
-// can be created and managed, and has some properties associated with it.
+// A Terraform resource is something that supports some or all of the
+// usual "create, read, update, delete" operations, depending on
+// the given Mode.
 type Resource struct {
+	Mode         ResourceMode // which operations the resource supports
 	Name         string
 	Type         string
 	RawCount     *RawConfig
@@ -85,6 +87,7 @@ type Resource struct {
 // interpolation.
 func (r *Resource) Copy() *Resource {
 	n := &Resource{
+		Mode:         r.Mode,
 		Name:         r.Name,
 		Type:         r.Type,
 		RawCount:     r.RawCount.Copy(),
@@ -210,7 +213,14 @@ func (r *Resource) Count() (int, error) {
 
 // A unique identifier for this resource.
 func (r *Resource) Id() string {
+	switch r.Mode {
+	case ManagedResourceMode:
 		return fmt.Sprintf("%s.%s", r.Type, r.Name)
+	case DataResourceMode:
+		return fmt.Sprintf("data.%s.%s", r.Type, r.Name)
+	default:
+		panic(fmt.Errorf("unknown resource mode %s", r.Mode))
+	}
 }
 
 // Validate does some basic semantic checking of the configuration.
@@ -804,13 +814,14 @@ func (c *ProviderConfig) mergerMerge(m merger) merger {
 }
 
 func (r *Resource) mergerName() string {
-	return fmt.Sprintf("%s.%s", r.Type, r.Name)
+	return r.Id()
 }
 
 func (r *Resource) mergerMerge(m merger) merger {
 	r2 := m.(*Resource)
 
 	result := *r
+	result.Mode = r2.Mode
 	result.Name = r2.Name
 	result.Type = r2.Type
 	result.RawConfig = result.RawConfig.merge(r2.RawConfig)

config/config_string.go

@@ -178,7 +178,7 @@ func resourcesStr(rs []*Resource) string {
 	ks := make([]string, 0, len(rs))
 	mapping := make(map[string]int)
 	for i, r := range rs {
-		k := fmt.Sprintf("%s[%s]", r.Type, r.Name)
+		k := r.Id()
 		ks = append(ks, k)
 		mapping[k] = i
 	}
@@ -190,9 +190,8 @@ func resourcesStr(rs []*Resource) string {
 	for _, i := range order {
 		r := rs[i]
 		result += fmt.Sprintf(
-			"%s[%s] (x%s)\n",
-			r.Type,
-			r.Name,
+			"%s (x%s)\n",
+			r.Id(),
 			r.RawCount.Value())
 
 		ks := make([]string, 0, len(r.RawConfig.Raw))

config/loader_hcl.go

@@ -566,6 +566,7 @@ func loadResourcesHcl(list *ast.ObjectList) ([]*Resource, error) {
 		}
 
 		result = append(result, &Resource{
+			Mode:         ManagedResourceMode,
 			Name:         k,
 			Type:         t,
 			RawCount:     countConfig,

config/loader_test.go

@@ -742,13 +742,13 @@ func TestLoad_jsonAttributes(t *testing.T) {
 }
 
 const jsonAttributeStr = `
-cloudstack_firewall[test] (x1)
+cloudstack_firewall.test (x1)
   ipaddress
   rule
 `
 
 const windowsHeredocResourcesStr = `
-aws_instance[test] (x1)
+aws_instance.test (x1)
   user_data
 `
 
@@ -759,17 +759,17 @@ aws
 `
 
 const heredocResourcesStr = `
-aws_iam_policy[policy] (x1)
+aws_iam_policy.policy (x1)
   description
   name
   path
   policy
-aws_instance[heredocwithnumbers] (x1)
+aws_instance.heredocwithnumbers (x1)
   ami
   provisioners
     local-exec
       command
-aws_instance[test] (x1)
+aws_instance.test (x1)
   ami
   provisioners
     remote-exec
@@ -777,7 +777,7 @@ aws_instance[test] (x1)
 `
 
 const escapedquotesResourcesStr = `
-aws_instance[quotes] (x1)
+aws_instance.quotes (x1)
   ami
   vars
     user: var.ami
@@ -800,7 +800,7 @@ do
 `
 
 const basicResourcesStr = `
-aws_instance[db] (x1)
+aws_instance.db (x1)
   VPC
   security_groups
   provisioners
@@ -811,7 +811,7 @@ aws_instance[db] (x1)
     aws_instance.web
   vars
     resource: aws_security_group.firewall.*.id
-aws_instance[web] (x1)
+aws_instance.web (x1)
   ami
   network_interface
   security_groups
@@ -822,7 +822,7 @@ aws_instance[web] (x1)
   vars
     resource: aws_security_group.firewall.foo
     user: var.foo
-aws_security_group[firewall] (x5)
+aws_security_group.firewall (x5)
 `
 
 const basicVariablesStr = `
@@ -854,18 +854,18 @@ do
 `
 
 const dirBasicResourcesStr = `
-aws_instance[db] (x1)
+aws_instance.db (x1)
   security_groups
   vars
     resource: aws_security_group.firewall.*.id
-aws_instance[web] (x1)
+aws_instance.web (x1)
   ami
   network_interface
   security_groups
   vars
     resource: aws_security_group.firewall.foo
     user: var.foo
-aws_security_group[firewall] (x5)
+aws_security_group.firewall (x5)
 `
 
 const dirBasicVariablesStr = `
@@ -891,10 +891,10 @@ do
 `
 
 const dirOverrideResourcesStr = `
-aws_instance[db] (x1)
+aws_instance.db (x1)
   ami
   security_groups
-aws_instance[web] (x1)
+aws_instance.web (x1)
   ami
   foo
   network_interface
@@ -902,7 +902,7 @@ aws_instance[web] (x1)
   vars
     resource: aws_security_group.firewall.foo
     user: var.foo
-aws_security_group[firewall] (x5)
+aws_security_group.firewall (x5)
 `
 
 const dirOverrideVariablesStr = `
@@ -918,8 +918,8 @@ aws
 `
 
 const importResourcesStr = `
-aws_security_group[db] (x1)
-aws_security_group[web] (x1)
+aws_security_group.db (x1)
+aws_security_group.web (x1)
 `
 
 const importVariablesStr = `
@@ -938,7 +938,7 @@ bar
 `
 
 const provisionerResourcesStr = `
-aws_instance[web] (x1)
+aws_instance.web (x1)
   ami
   security_groups
   provisioners
@@ -950,7 +950,7 @@ aws_instance[web] (x1)
 `
 
 const connectionResourcesStr = `
-aws_instance[web] (x1)
+aws_instance.web (x1)
   ami
   security_groups
   provisioners
@@ -976,17 +976,17 @@ foo (required)
 `
 
 const createBeforeDestroyResourcesStr = `
-aws_instance[bar] (x1)
+aws_instance.bar (x1)
   ami
-aws_instance[web] (x1)
+aws_instance.web (x1)
   ami
 `
 
 const ignoreChangesResourcesStr = `
-aws_instance[bar] (x1)
+aws_instance.bar (x1)
   ami
-aws_instance[baz] (x1)
+aws_instance.baz (x1)
   ami
-aws_instance[web] (x1)
+aws_instance.web (x1)
   ami
 `

config/resource_mode.go

@@ -0,0 +1,9 @@
+package config
+
+//go:generate stringer -type=ResourceMode -output=resource_mode_string.go resource_mode.go
+type ResourceMode int
+
+const (
+	ManagedResourceMode ResourceMode = iota
+	DataResourceMode
+)

config/resource_mode_string.go

@@ -0,0 +1,16 @@
+// Code generated by "stringer -type=ResourceMode -output=resource_mode_string.go resource_mode.go"; DO NOT EDIT
+
+package config
+
+import "fmt"
+
+const _ResourceMode_name = "ManagedResourceModeDataResourceMode"
+
+var _ResourceMode_index = [...]uint8{0, 19, 35}
+
+func (i ResourceMode) String() string {
+	if i < 0 || i >= ResourceMode(len(_ResourceMode_index)-1) {
+		return fmt.Sprintf("ResourceMode(%d)", i)
+	}
+	return _ResourceMode_name[_ResourceMode_index[i]:_ResourceMode_index[i+1]]
+}