Fix HttpBindingsMissing skipping REST protocol services

The `HttpBindingsMissingValidator` had a top-level short-circuit that
returned early when no shape in the model carried `@http`. Services
with a protocol like `restJson1` that requires `@http` on all
operations would pass validation silently when no operations had the
trait yet.

Author: kstich

.changes/next-release/bugfix-9914eba50c5a25bdded5c4c8e6457d7a8375ea20.json

@@ -0,0 +1,7 @@
+{
+  "type": "bugfix",
+  "description": "Fixed a bug where HttpBindingMissing validation didn't fire if a service requiring `@http` traits had none at all.",
+  "pull_requests": [
+    "[#3122](https://github.com/smithy-lang/smithy/pull/3122)"
+  ]
+}

smithy-model/src/main/java/software/amazon/smithy/model/validation/validators/HttpBindingsMissingValidator.java

@@ -4,7 +4,6 @@
  */
 package software.amazon.smithy.model.validation.validators;
 
-import java.util.Collections;
 import java.util.List;
 import java.util.Set;
 import java.util.stream.Collectors;
@@ -29,10 +28,6 @@
 public final class HttpBindingsMissingValidator extends AbstractValidator {
     @Override
     public List<ValidationEvent> validate(Model model) {
-        if (!model.isTraitApplied(HttpTrait.class)) {
-            return Collections.emptyList();
-        }
-
         TopDownIndex topDownIndex = TopDownIndex.of(model);
         return model.shapes(ServiceShape.class)
                 .flatMap(shape -> validateService(topDownIndex, model, shape).stream())

smithy-model/src/test/resources/software/amazon/smithy/model/errorfiles/validators/http-bindings-missing-validator-no-bindings.errors

@@ -0,0 +1,2 @@
+[ERROR] ns.foo#MissingBindings1: The `ns.foo#restProtocol` protocol requires all operations in the `ns.foo#MyService` service define the `http` trait, but this operation is missing the `http` trait. | HttpBindingsMissing
+[ERROR] ns.foo#MissingBindings2: The `ns.foo#restProtocol` protocol requires all operations in the `ns.foo#MyService` service define the `http` trait, but this operation is missing the `http` trait. | HttpBindingsMissing

smithy-model/src/test/resources/software/amazon/smithy/model/errorfiles/validators/http-bindings-missing-validator-no-bindings.smithy

@@ -0,0 +1,41 @@
+$version: "2.0"
+
+namespace ns.foo
+
+@trait(selector: "service")
+@protocolDefinition(traits: [
+    smithy.api#cors
+    smithy.api#endpoint
+    smithy.api#hostLabel
+    smithy.api#http
+    smithy.api#httpError
+    smithy.api#httpHeader
+    smithy.api#httpLabel
+    smithy.api#httpPayload
+    smithy.api#httpPrefixHeaders
+    smithy.api#httpQuery
+    smithy.api#httpQueryParams
+    smithy.api#httpResponseCode
+    smithy.api#jsonName
+    smithy.api#timestampFormat
+])
+@documentation("A simple clone of AWS restJson1.")
+structure restProtocol {}
+
+@restProtocol
+service MyService {
+    version: "2017-01-17"
+    operations: [MissingBindings1, MissingBindings2]
+}
+
+@readonly
+operation MissingBindings1 {
+    input := {}
+    output := {}
+}
+
+@readonly
+operation MissingBindings2 {
+    input := {}
+    output := {}
+}

smithy-model/src/test/resources/software/amazon/smithy/model/errorfiles/validators/http-bindings-missing-validator.json

@@ -0,0 +1,48 @@
+$version: "2.0"
+
+namespace ns.foo
+
+@trait(selector: "service")
+@protocolDefinition(traits: [
+    smithy.api#cors
+    smithy.api#endpoint
+    smithy.api#hostLabel
+    smithy.api#http
+    smithy.api#httpError
+    smithy.api#httpHeader
+    smithy.api#httpLabel
+    smithy.api#httpPayload
+    smithy.api#httpPrefixHeaders
+    smithy.api#httpQuery
+    smithy.api#httpQueryParams
+    smithy.api#httpResponseCode
+    smithy.api#jsonName
+    smithy.api#timestampFormat
+])
+@documentation("A simple clone of AWS restJson1.")
+structure restProtocol {}
+
+@restProtocol
+service MyService {
+    version: "2017-01-17"
+    operations: [HasBindings, MissingBindings1, MissingBindings2]
+}
+
+@readonly
+@http(method: "GET", uri: "/A")
+operation HasBindings {
+    input := {}
+    output := {}
+}
+
+@readonly
+operation MissingBindings1 {
+    input := {}
+    output := {}
+}
+
+@readonly
+operation MissingBindings2 {
+    input := {}
+    output := {}
+}