[clang-tools-extra] Allow unnecessary-value-param to match templated functions including lambdas with auto. (PR #97767)

[Vitaly Goldshteyn via cfe-commits]

================
@@ -0,0 +1,93 @@
+// RUN: %check_clang_tidy  -std=c++14-or-later %s performance-unnecessary-value-param %t
+
+struct ExpensiveToCopyType {
+  virtual ~ExpensiveToCopyType();
+};
+
+template <typename T> void templateWithNonTemplatizedParameter(const ExpensiveToCopyType S, T V) {
+  // CHECK-MESSAGES: [[@LINE-1]]:90: warning: the const qualified parameter 'S'
+  // CHECK-MESSAGES: [[@LINE-2]]:95: warning: the parameter 'V'
+  // CHECK-FIXES: template <typename T> void templateWithNonTemplatizedParameter(const ExpensiveToCopyType& S, const T& V) {
+}
+
+void instantiatedWithExpensiveValue() {
+  templateWithNonTemplatizedParameter(
+      ExpensiveToCopyType(), ExpensiveToCopyType());
+  templateWithNonTemplatizedParameter(ExpensiveToCopyType(), 5);
+}
+
+template <typename T> void templateWithNonTemplatizedParameterCheapTemplate(const ExpensiveToCopyType S, T V) {
+  // CHECK-MESSAGES: [[@LINE-1]]:103: warning: the const qualified parameter 'S'
+  // CHECK-FIXES: template <typename T> void templateWithNonTemplatizedParameterCheapTemplate(const ExpensiveToCopyType& S, T V) {
+}
+
+void instantiatedWithCheapValue() {
+  templateWithNonTemplatizedParameterCheapTemplate(ExpensiveToCopyType(), 5);
+}
+
+template <typename T> void nonInstantiatedTemplateWithConstValue(const T S) {}
+template <typename T> void nonInstantiatedTemplateWithNonConstValue(T S) {}
+
+template <typename T> void instantiatedTemplateSpecialization(T NoSpecS) {}
+template <>
+void instantiatedTemplateSpecialization<ExpensiveToCopyType>(
+    ExpensiveToCopyType SpecS) {
+  // CHECK-MESSAGES: [[@LINE-1]]:25: warning: the parameter 'SpecS'
+  // When updating a template specialization, we also update the main template.
----------------
goldvitaly wrote:

That is unfortunately correct.  I was aware that other TUs can be broken.

But it seems that other template instantiations are  not fixed in the same file as well.

Do you know how to skip template specialization, but not all other template functions?

https://github.com/llvm/llvm-project/pull/97767