enable global schema cache

internal/plugin/grpc_provider.go

@@ -68,9 +68,9 @@ type GRPCProvider struct {
 	ctx context.Context
 
 	// schema stores the schema for this provider. This is used to properly
-	// serialize the state for requests.
-	mu      sync.Mutex
-	schemas providers.GetProviderSchemaResponse
+	// serialize the requests for schemas.
+	mu     sync.Mutex
+	schema providers.GetProviderSchemaResponse
 }
 
 func (p *GRPCProvider) GetProviderSchema() (resp providers.GetProviderSchemaResponse) {
@@ -85,8 +85,8 @@ func (p *GRPCProvider) GetProviderSchema() (resp providers.GetProviderSchemaResp
 		}
 	}
 
-	if p.schemas.Provider.Block != nil {
-		return p.schemas
+	if p.schema.Provider.Block != nil {
+		return p.schema
 	}
 
 	resp.ResourceTypes = make(map[string]providers.Schema)
@@ -135,18 +135,16 @@ func (p *GRPCProvider) GetProviderSchema() (resp providers.GetProviderSchemaResp
 
 	if protoResp.ServerCapabilities != nil {
 		resp.ServerCapabilities.PlanDestroy = protoResp.ServerCapabilities.PlanDestroy
+		resp.ServerCapabilities.GetProviderSchemaOptional = protoResp.ServerCapabilities.GetProviderSchemaOptional
 	}
 
-	// FIXME: Waiting for a provider capability to prevent caching
-	//        providers which always need GetProviderSchema called.
 	// set the global cache if we can
-	//if !p.Addr.IsZero() {
-	//    providers.SchemaCache.Set(p.Addr, resp)
-	//} else {
-	//    // otherwise store it in the local cache
-	//    p.schemas = resp
-	//}
-	p.schemas = resp
+	if !p.Addr.IsZero() && resp.ServerCapabilities.GetProviderSchemaOptional {
+		providers.SchemaCache.Set(p.Addr, resp)
+	} else {
+		// otherwise store it in the local cache
+		p.schema = resp
+	}
 
 	return resp
 }

internal/plugin6/grpc_provider.go

@@ -68,9 +68,9 @@ type GRPCProvider struct {
 	ctx context.Context
 
 	// schema stores the schema for this provider. This is used to properly
-	// serialize the state for requests.
-	mu      sync.Mutex
-	schemas providers.GetProviderSchemaResponse
+	// serialize the requests for schemas.
+	mu     sync.Mutex
+	schema providers.GetProviderSchemaResponse
 }
 
 func (p *GRPCProvider) GetProviderSchema() (resp providers.GetProviderSchemaResponse) {
@@ -85,8 +85,8 @@ func (p *GRPCProvider) GetProviderSchema() (resp providers.GetProviderSchemaResp
 		}
 	}
 
-	if p.schemas.Provider.Block != nil {
-		return p.schemas
+	if p.schema.Provider.Block != nil {
+		return p.schema
 	}
 
 	resp.ResourceTypes = make(map[string]providers.Schema)
@@ -135,18 +135,16 @@ func (p *GRPCProvider) GetProviderSchema() (resp providers.GetProviderSchemaResp
 
 	if protoResp.ServerCapabilities != nil {
 		resp.ServerCapabilities.PlanDestroy = protoResp.ServerCapabilities.PlanDestroy
+		resp.ServerCapabilities.GetProviderSchemaOptional = protoResp.ServerCapabilities.GetProviderSchemaOptional
 	}
 
-	// FIXME: Waiting for a provider capability to prevent caching
-	//        providers which always need GetProviderSchema called.
 	// set the global cache if we can
-	//if !p.Addr.IsZero() {
-	//    providers.SchemaCache.Set(p.Addr, resp)
-	//} else {
-	//    // otherwise store it in the local cache
-	//    p.schemas = resp
-	//}
-	p.schemas = resp
+	if !p.Addr.IsZero() && resp.ServerCapabilities.GetProviderSchemaOptional {
+		providers.SchemaCache.Set(p.Addr, resp)
+	} else {
+		// otherwise store it in the local cache
+		p.schema = resp
+	}
 
 	return resp
 }

internal/terraform/context_plugins.go

@@ -68,7 +68,10 @@ func (cp *contextPlugins) NewProvisionerInstance(typ string) (provisioners.Inter
 func (cp *contextPlugins) ProviderSchema(addr addrs.Provider) (providers.ProviderSchema, error) {
 	log.Printf("[TRACE] terraform.contextPlugins: Initializing provider %q to read its schema", addr)
 
-	// check the global schema cache first
+	// Check the global schema cache first.
+	// This cache is only written by the provider client, and transparently
+	// used by GetProviderSchema, but we check it here because at this point we
+	// may be able to avoid spinning up the provider instance at all.
 	schemas, ok := providers.SchemaCache.Get(addr)
 	if ok {
 		return schemas, nil