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

[Vitaly Goldshteyn via cfe-commits]

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@@ -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:

Note that it is template specialization and not an overload.

Template specialization must have exactly the same signature.
See an example https://gcc.godbolt.org/z/cqTzG5Wsn

Note that nothing special is done to update both versions.
When template specialization is updated, the main template and all other template specializations are updated automatically.

I personally prefer to use overloads, but this test is necessary to be sure that we are not proposing non compiling changes.

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