Generate dummy Query for shared query test files

Shared query test files were not excluding elements outside the source
archive because they did not implement the `..SharedQuery` mechanism.
This commit adjusts the `Query` class to provide a dummy query for this
purpose, and updates the generator to create an instance of that
abstract class for each shared query.

Author: lcartey

cpp/common/src/codingstandards/cpp/exclusions/RuleMetadata.qll

@@ -5,7 +5,9 @@ private import codingstandards.cpp.guideline_recategorizations.GuidelineRecatego
 
 newtype TQuery =
   TQueryCPP(CPPRuleMetadata::TCPPQuery t) or
-  TQueryC(CRuleMetadata::TCQuery t)
+  TQueryC(CRuleMetadata::TCQuery t) or
+  /* A dummy query for testing purposes */
+  TQueryTestDummy()
 
 private predicate isMisraRuleCategory(string category) {
   category = ["disapplied", "advisory", "required", "mandatory"]
@@ -47,18 +49,27 @@ class EffectiveCategory extends TEffectiveCategory {
 
 class Query extends TQuery {
   string getQueryId() {
-    CPPRuleMetadata::isQueryMetadata(this, result, _, _) or
+    CPPRuleMetadata::isQueryMetadata(this, result, _, _)
+    or
     CRuleMetadata::isQueryMetadata(this, result, _, _)
+    or
+    this = TQueryTestDummy() and result = "cpp/test/dummy"
   }
 
   string getRuleId() {
-    CPPRuleMetadata::isQueryMetadata(this, _, result, _) or
+    CPPRuleMetadata::isQueryMetadata(this, _, result, _)
+    or
     CRuleMetadata::isQueryMetadata(this, _, result, _)
+    or
+    this = TQueryTestDummy() and result = "cpp-test-dummy"
   }
 
   string getCategory() {
-    CPPRuleMetadata::isQueryMetadata(this, _, _, result) or
+    CPPRuleMetadata::isQueryMetadata(this, _, _, result)
+    or
     CRuleMetadata::isQueryMetadata(this, _, _, result)
+    or
+    this = TQueryTestDummy() and result = "required"
   }
 
   EffectiveCategory getEffectiveCategory() {
@@ -72,3 +83,8 @@ class Query extends TQuery {
 
   string toString() { result = getQueryId() }
 }
+
+/** A `Query` used for shared query test cases. */
+class TestQuery extends Query {
+  TestQuery() { this = TQueryTestDummy() }
+}

scripts/generate_rules/generate_package_files.py

@@ -181,6 +181,8 @@ def write_shared_implementation(package_name, rule_id, query, language_name, ql_
                 .replace("/", ".")
                 + "\n"
             )
+            f.write("\n");
+            f.write("class TestFileQuery extends " + str(query["shared_implementation_short_name"]) + "SharedQuery, TestQuery { }\n")
 
         # Create an empty test file, if one doesn't already exist
         shared_impl_test_dir.joinpath(