make connection host Required

And provide the connection config for validation

terraform/eval_validate.go

@@ -218,6 +218,10 @@ var connectionBlockSupersetSchema = &configschema.Block{
 		// by the config loader and stored away in a separate field.
 
 		// Common attributes for both connection types
+		"host": {
+			Type:     cty.String,
+			Required: true,
+		},
 		"type": {
 			Type:     cty.String,
 			Optional: true,
@@ -230,10 +234,6 @@ var connectionBlockSupersetSchema = &configschema.Block{
 			Type:     cty.String,
 			Optional: true,
 		},
-		"host": {
-			Type:     cty.String,
-			Optional: true,
-		},
 		"port": {
 			Type:     cty.String,
 			Optional: true,

terraform/node_resource_validate.go

@@ -71,6 +71,7 @@ func (n *NodeValidatableResource) EvalTree() EvalNode {
 					Schema:           &provisionerSchema,
 					Config:           p,
 					ResourceHasCount: hasCount,
+					ConnConfig:       p.Connection,
 				},
 			)
 		}