IdentifierHidden: add missing exception testcases and address nested named namespaces exception

Author: knewbury01

cpp/common/src/codingstandards/cpp/Scope.qll

@@ -295,3 +295,18 @@ predicate hasClassScope(Declaration decl) { exists(decl.getDeclaringType()) }
 
 /** Holds if `decl` has block scope. */
 predicate hasBlockScope(Declaration decl) { exists(BlockStmt b | b.getADeclaration() = decl) }
+
+/**
+ * identifiers in nested (named/nonglobal) namespaces are exceptions to hiding due to being able access via fully qualified ids
+ */
+predicate excludedViaNestedNamespaces(UserDeclaration v2, UserDeclaration v1) {
+  exists(Namespace inner, Namespace outer |
+    outer.getAChildNamespace+() = inner and
+    //outer is not global
+    not outer instanceof GlobalNamespace and
+    not outer.isAnonymous() and
+    not inner.isAnonymous() and
+    v2.getNamespace() = inner and
+    v1.getNamespace() = outer
+  )
+}

cpp/common/src/codingstandards/cpp/rules/identifierhidden/IdentifierHidden.qll

@@ -18,6 +18,7 @@ query predicate problems(UserDeclaration v2, string message, UserDeclaration v1,
   not v1 instanceof TemplateVariable and
   not v2 instanceof TemplateVariable and
   hidesStrict(v1, v2) and
+  not excludedViaNestedNamespaces(v2, v1) and
   varName = v1.getName() and
   message = "Declaration is hiding declaration $@."
 }

cpp/common/test/rules/identifierhidden/test.cpp

@@ -83,4 +83,23 @@ int a() {} // NON_COMPLIANT
 
 namespace b1 {
 typedef int a; // NON_COMPLIANT
-}
+}
+
+namespace ns_exception1_outer {
+int a1; // COMPLIANT - exception
+namespace ns_exception1_inner {
+void a1(); // COMPLIANT - exception
+}
+} // namespace ns_exception1_outer
+
+void f4() {
+  int a1, b;
+  auto lambda1 = [a1]() {
+    int b = 10; // COMPLIANT - exception - non captured variable b
+  };
+
+  auto lambda2 = [b]() {
+    int b = 10; // NON_COMPLIANT[FALSE_NEGATIVE] - not an exception - captured
+                // variable b
+  };
+}