Improve performance of AttachResourceConfigTransformer on big graphs

The current implementation of `AttachResourceConfigTransformer` has performance of `O(N^2)` to the number of vertices in the graph, and this leads to significant performance degradation on huge graphs.

The given implementation decreases the complexity to `O(N)` by performing direct lookup of a resource in the `ManagedResources` or `DataResources` depending on the object type.

Signed-off-by: Alex Ott <alexott@gmail.com>

internal/terraform/transform_attach_config_resource.go

@@ -6,6 +6,7 @@ package terraform
 import (
 	"log"
 
+	"github.com/hashicorp/terraform/internal/addrs"
 	"github.com/hashicorp/terraform/internal/configs"
 	"github.com/hashicorp/terraform/internal/dag"
 )
@@ -48,63 +49,25 @@ func (t *AttachResourceConfigTransformer) Transform(g *Graph) error {
 			log.Printf("[TRACE] AttachResourceConfigTransformer: %q (%T) has no configuration available", dag.VertexName(v), v)
 			continue
 		}
-
-		for _, r := range config.Module.ManagedResources {
-			rAddr := r.Addr()
-
-			if rAddr != addr.Resource {
-				// Not the same resource
-				continue
-			}
-
-			log.Printf("[TRACE] AttachResourceConfigTransformer: attaching to %q (%T) config from %s", dag.VertexName(v), v, r.DeclRange)
-			arn.AttachResourceConfig(r)
-
-			// attach the provider_meta info
-			if gnapmc, ok := v.(GraphNodeAttachProviderMetaConfigs); ok {
-				log.Printf("[TRACE] AttachResourceConfigTransformer: attaching provider meta configs to %s", dag.VertexName(v))
-				if config == nil {
-					log.Printf("[TRACE] AttachResourceConfigTransformer: no config set on the transformer for %s", dag.VertexName(v))
-					continue
-				}
-				if config.Module == nil {
-					log.Printf("[TRACE] AttachResourceConfigTransformer: no module in config for %s", dag.VertexName(v))
-					continue
-				}
-				if config.Module.ProviderMetas == nil {
-					log.Printf("[TRACE] AttachResourceConfigTransformer: no provider metas defined for %s", dag.VertexName(v))
-					continue
-				}
-				gnapmc.AttachProviderMetaConfigs(config.Module.ProviderMetas)
-			}
+		var m map[string]*configs.Resource
+		if addr.Resource.Mode == addrs.ManagedResourceMode {
+			m = config.Module.ManagedResources
+		} else if addr.Resource.Mode == addrs.DataResourceMode {
+			m = config.Module.DataResources
+		} else {
+			panic("unknown resource mode: " + addr.Resource.Mode.String())
 		}
-		for _, r := range config.Module.DataResources {
-			rAddr := r.Addr()
-
-			if rAddr != addr.Resource {
-				// Not the same resource
-				continue
-			}
-
+		coord := addr.Resource.String()
+		if r, ok := m[coord]; ok && r.Addr() == addr.Resource {
 			log.Printf("[TRACE] AttachResourceConfigTransformer: attaching to %q (%T) config from %#v", dag.VertexName(v), v, r.DeclRange)
 			arn.AttachResourceConfig(r)
-
-			// attach the provider_meta info
 			if gnapmc, ok := v.(GraphNodeAttachProviderMetaConfigs); ok {
 				log.Printf("[TRACE] AttachResourceConfigTransformer: attaching provider meta configs to %s", dag.VertexName(v))
-				if config == nil {
-					log.Printf("[TRACE] AttachResourceConfigTransformer: no config set on the transformer for %s", dag.VertexName(v))
-					continue
-				}
-				if config.Module == nil {
-					log.Printf("[TRACE] AttachResourceConfigTransformer: no module in config for %s", dag.VertexName(v))
-					continue
-				}
-				if config.Module.ProviderMetas == nil {
-					log.Printf("[TRACE] AttachResourceConfigTransformer: no provider metas defined for %s", dag.VertexName(v))
-					continue
+				if config.Module.ProviderMetas != nil {
+					gnapmc.AttachProviderMetaConfigs(config.Module.ProviderMetas)
+				} else {
+					log.Printf("[TRACE] AttachResourceConfigTransformer: no provider meta configs available to attach to %s", dag.VertexName(v))
 				}
-				gnapmc.AttachProviderMetaConfigs(config.Module.ProviderMetas)
 			}
 		}
 	}