Add comments on partial GraphNodeProvider implementation

Signed-off-by: Christian Mesh <christianmesh1@gmail.com>

internal/tofu/node_provider.go

@@ -57,7 +57,7 @@ type NodeApplyableProvider struct {
 
 var (
 	_ GraphNodeExecutable = (*NodeApplyableProvider)(nil)
-	_ GraphNodeProvider   = (*NodeApplyableProvider)(nil)
+	_ GraphNodeProvider   = (*NodeApplyableProvider)(nil) // Partial, see NodeAbstractProvider
 )
 
 // GraphNodeProvider

internal/tofu/node_provider_abstract.go

@@ -18,7 +18,10 @@ import (
 type ConcreteProviderNodeFunc func(*NodeAbstractProvider) dag.Vertex
 
 // NodeAbstractProvider represents a provider that has no associated operations.
-// It registers all the common interfaces across operations for providers.
+// It registers all the common interfaces across operations for providers, except
+// for GraphNodeProvider as that depends on additional implementation details.
+// It does however implement what methods it can from GraphNodeProvider to reduce
+// duplication between concrete implementations.
 type NodeAbstractProvider struct {
 	Addr addrs.AbsProviderConfig
 
@@ -63,12 +66,12 @@ func (n *NodeAbstractProvider) References() []*addrs.Reference {
 	return ReferencesFromConfig(n.Config.Config, n.Schema)
 }
 
-// GraphNodeProvider
+// GraphNodeProvider (Partial Implementation)
 func (n *NodeAbstractProvider) ProviderAddr() addrs.AbsProviderConfig {
 	return n.Addr
 }
 
-// GraphNodeProvider
+// GraphNodeProvider (Partial Implementation)
 func (n *NodeAbstractProvider) ProviderConfig() *configs.Provider {
 	if n.Config == nil {
 		return nil

internal/tofu/node_provider_eval.go

@@ -24,7 +24,7 @@ type NodeEvalableProvider struct {
 }
 
 var _ GraphNodeExecutable = (*NodeEvalableProvider)(nil)
-var _ GraphNodeProvider = (*NodeEvalableProvider)(nil)
+var _ GraphNodeProvider = (*NodeEvalableProvider)(nil) // Partial, see NodeAbstractProvider
 
 // GraphNodeProvider
 func (n *NodeEvalableProvider) Instance(key addrs.InstanceKey) providers.Configured {

internal/tofu/transform_provider.go

@@ -54,7 +54,14 @@ type GraphNodeProvider interface {
 	GraphNodeModulePath
 	ProviderAddr() addrs.AbsProviderConfig
 	Name() string
+	// Retrieve the instance specified by the key.
+	// With the limited implementation of provider for_each, we only support
+	// keys after the AbsProviderConfig level and not at any of the modules it may live in
+	// This is a hard requirement that we have determined it is too hard to change,
+	// which is an extension of the "provider configurations may not live in modules with
+	// expansion" that we ensure within the configuration.
 	Instance(addrs.InstanceKey) providers.Configured
+	// Call close for all provider instances within this GraphNodeProvider
 	Close(ctx context.Context) error
 	// For test framework
 	MocksAndOverrides() (IsMocked bool, MockResources []*configs.MockResource, OverrideResources []*configs.OverrideResource)