[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:

I have found a partial fix for this issue (and created fixup commit).

The changes are:
1. No fixes are proposed for explicit specializations.
2. Fixes are still proposed for the main template in case warning is issued during instantiation of the main template. I couldn't find the way to find that any instantiation is available. And in case they are defined in another translation unit, there is no way to do it.


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