Fix regression that allowed suppressing ERROR

There was a regression in #1890 that allowed ERROR events to be
suppressed. This was not intentional and we do not want to remove this
restriction. ERROR events indicate that the model is in an unusable
state because it violates a MUST in the spec or some other necessary
requirement to make it usable (like referring only to shapes that
exist).

New test cases have been added to guard against this regression in
the future.

Closes #2128

smithy-model/src/main/java/software/amazon/smithy/model/validation/suppressions/ModelBasedEventDecorator.java

@@ -151,6 +151,11 @@ private static ValidationEvent modifyEventSeverity(
             List<Suppression> suppressions,
             List<SeverityOverride> severityOverrides
     ) {
+        // ERROR and SUPPRESSED events cannot be suppressed.
+        if (!event.getSeverity().canSuppress()) {
+            return event;
+        }
+
         // Use a suppress trait if present.
         if (event.getShapeId().isPresent()) {
             ShapeId target = event.getShapeId().get();

smithy-model/src/test/java/software/amazon/smithy/model/knowledge/PropertyBindingIndexTest.java

@@ -15,20 +15,18 @@
 
 package software.amazon.smithy.model.knowledge;
 
-import static org.hamcrest.MatcherAssert.assertThat;
-import static org.hamcrest.Matchers.equalTo;
-import static org.hamcrest.Matchers.hasSize;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
+import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 import software.amazon.smithy.model.Model;
 import software.amazon.smithy.model.shapes.MemberShape;
 import software.amazon.smithy.model.shapes.OperationShape;
 import software.amazon.smithy.model.shapes.ShapeId;
-import software.amazon.smithy.model.validation.Severity;
 import software.amazon.smithy.model.validation.ValidatedResult;
+import software.amazon.smithy.model.validation.ValidatedResultException;
 
 public class PropertyBindingIndexTest {
 
@@ -71,8 +69,6 @@ public void testIndex() {
         assertTrue(index.doesMemberShapeRequireProperty(model.expectShape(
                 ShapeId.from("com.example#ChangeResourceOutput$id"), MemberShape.class)));
 
-        assertThat(vrmodel.getValidationEvents(Severity.SUPPRESSED), hasSize(1));
-        assertThat(vrmodel.getValidationEvents(Severity.SUPPRESSED).get(0).getId(),
-                   equalTo("ResourceOperationInputOutput"));
+        Assertions.assertThrows(ValidatedResultException.class, () -> vrmodel.unwrap());
     }
 }

smithy-model/src/test/resources/software/amazon/smithy/model/errorfiles/loader/suppression-metadata-cannot-suppress-errors.errors

@@ -0,0 +1 @@
+[ERROR] foo.baz#MyString: Trait `idempotent` | TraitTarget

smithy-model/src/test/resources/software/amazon/smithy/model/errorfiles/loader/suppression-metadata-cannot-suppress-errors.smithy

@@ -0,0 +1,13 @@
+$version: "2"
+
+metadata suppressions = [
+    {
+        namespace: "foo.baz"
+        id: "TraitTarget"
+    }
+]
+
+namespace foo.baz
+
+@idempotent // < this is invalid
+string MyString

smithy-model/src/test/resources/software/amazon/smithy/model/errorfiles/loader/suppression-trait-cannot-suppress-errors.errors

@@ -0,0 +1 @@
+[ERROR] foo.baz#MyString: Trait `idempotent` | TraitTarget

smithy-model/src/test/resources/software/amazon/smithy/model/errorfiles/loader/suppression-trait-cannot-suppress-errors.smithy

@@ -0,0 +1,7 @@
+$version: "2"
+
+namespace foo.baz
+
+@suppress(["TraitTarget"])
+@idempotent // < this is invalid
+string MyString

smithy-model/src/test/resources/software/amazon/smithy/model/knowledge/member-property-index.smithy

@@ -1,12 +1,5 @@
 $version: "2.0"
 
-metadata suppressions = [
-    {
-        id: "ResourceOperationInputOutput",
-        namespace: "com.example"
-    }
-]
-
 namespace com.example
 
 resource Resource1 {