[clang-tools-extra] create new clang-tidy check to add namespaces to symbol references (PR #70621)

[via cfe-commits]

================
@@ -0,0 +1,220 @@
+// RUN: %check_clang_tidy %s readability-use-explicit-namespaces %t
+
+namespace foo {
+void doSomething() {}
+
+template <class T> void doTemplateThing(T &value) { value = value * 2; }
+
+struct StructTest {
+  int StructIntMember;
+};
+
+class ClassTest {
+public:
+  int ClassIntMember;
+  typedef int ClassTypeDefMember;
+};
+
+enum EnumTest {
+  EnumValueOne,
+  EnumValueTwo,
+  EnumValueThree,
+};
+
+template <class T> class TemplateClassTest {
+public:
+  T TemplatizedData;
+};
+
+typedef int TypeDefTest;
+typedef void (*event_callback)(ClassTest &value);
+
+} // namespace foo
+
+class OutsideNamespace : public foo::ClassTest {
+public:
+  ClassTypeDefMember UseTypeFromParentOk;
+};
+
+OutsideNamespace::ClassTypeDefMember UseTypeFromClassInheritedFromParentOk;
+
+foo::ClassTest AlreadyQualifiedOk() {
+  foo::doSomething();
+  foo::StructTest first;
+  foo::ClassTest second;
+  second.ClassIntMember = 55;
+  foo::EnumTest picked = foo::EnumValueThree;
+  foo::TemplateClassTest<foo::ClassTest> data;
+  foo::TemplateClassTest<
+      foo::TemplateClassTest<foo::TemplateClassTest<foo::ClassTest>>>
+      dataNested;
+  foo::StructTest many[8];
+  foo::TypeDefTest integer = 22;
+  foo::doTemplateThing(integer);
+  foo::doTemplateThing<foo::TypeDefTest>(integer);
+  struct foo::StructTest fooStruct;
+  auto lambdaReturn = []() -> foo::ClassTest { return foo::ClassTest(); };
+  auto lambdaTypes = [](foo::StructTest &start,
+                        foo::StructTest *end) -> foo::ClassTest {
+    return foo::ClassTest();
+  };
+
+  foo::ClassTest ConstructOnStack;
+  new foo::ClassTest;
+  foo::TemplateClassTest<foo::ClassTest> ConstructTemplateOnStack;
+  new foo::TemplateClassTest<foo::ClassTest>;
+  foo::ClassTest();
+  new foo::ClassTest();
+  foo::TemplateClassTest<foo::ClassTest>();
+  new foo::TemplateClassTest<foo::ClassTest>();
+  return foo::ClassTest();
+}
+
+namespace foo {
+ClassTest InsideNamespaceFooOk() {
+  doSomething();
+  StructTest first;
+  ClassTest second;
+  second.ClassIntMember = 55;
+  EnumTest picked = EnumValueThree;
+  TemplateClassTest<ClassTest> data;
+  TemplateClassTest<TemplateClassTest<TemplateClassTest<ClassTest>>> dataNested;
+  StructTest many[8];
+  TypeDefTest integer = 22;
+  doTemplateThing(integer);
+  doTemplateThing<TypeDefTest>(integer);
+  struct StructTest fooStruct;
+  auto lambdaReturn = []() -> ClassTest { return ClassTest(); };
+  auto lambdaTypes = [](StructTest &start, StructTest *end) -> ClassTest {
+    return ClassTest();
+  };
+
+  ClassTest ConstructOnStack;
+  new ClassTest;
+  TemplateClassTest<ClassTest> ConstructTemplateOnStack;
+  new TemplateClassTest<ClassTest>;
+  ClassTest();
+  new ClassTest();
+  TemplateClassTest<ClassTest>();
+  new TemplateClassTest<ClassTest>();
+  return ClassTest();
+}
+} // namespace foo
+
+using namespace foo;
+
+ClassTest FixAllMissingFoo()
+// CHECK-MESSAGES: :[[@LINE-1]]:1: warning: Missing namespace qualifiers
+// CHECK-FIXES:  foo::
+{
+  doSomething();
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: Missing namespace qualifiers foo::
+  // CHECK-FIXES:  foo::
+  StructTest first;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: Missing namespace qualifiers foo::
+  // CHECK-FIXES:  foo::
+  ClassTest second;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: Missing namespace qualifiers foo::
+  // CHECK-FIXES:  foo::
+  second.ClassIntMember = 55;
+  EnumTest picked = EnumValueThree;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: Missing namespace qualifiers foo::
----------------
daltairwalter wrote:

I am happy to make other changes, but I consider the diagnostics a critical part of this check because it is bringing together different types of information, and without the diagnostics, it is very difficult to determine what part of the decision the check got wrong.  There seem to be some strong feelings against diagnostics and this is why the check has not moved forward.

https://github.com/llvm/llvm-project/pull/70621