hokein created this revision.
hokein added reviewers: alexfh, djasper.
hokein added a subscriber: cfe-commits.

The check doesn't mark the template argument as used when the template
argument is a template.

https://reviews.llvm.org/D22803

Files:
  clang-tidy/misc/UnusedUsingDeclsCheck.cpp
  test/clang-tidy/Inputs/unused-using-decls.h
  test/clang-tidy/misc-unused-using-decls.cpp

Index: test/clang-tidy/misc-unused-using-decls.cpp
===================================================================
--- test/clang-tidy/misc-unused-using-decls.cpp
+++ test/clang-tidy/misc-unused-using-decls.cpp
@@ -1,4 +1,5 @@
-// RUN: %check_clang_tidy %s misc-unused-using-decls %t -- -- -fno-delayed-template-parsing
+// RUN: %check_clang_tidy %s misc-unused-using-decls %t -- -- -fno-delayed-template-parsing -isystem %S/Inputs/
+
 
 // ----- Definitions -----
 template <typename T> class vector {};
@@ -54,6 +55,16 @@
 
 }  // namespace n
 
+#include "unused-using-decls.h"
+namespace ns {
+template <typename T>
+class AA {
+  T t;
+};
+template <typename T>
+T ff() { T t; return t; }
+} // namespace ns
+
 // ----- Using declarations -----
 // eol-comments aren't removed (yet)
 using n::A; // A
@@ -136,6 +147,9 @@
 using n::Color3;
 using n::Blue;
 
+using ns::AA;
+using ns::ff;
+
 // ----- Usages -----
 void f(B b);
 void g() {
@@ -151,4 +165,9 @@
   Color2 color2;
   int t1 = Color3::Yellow;
   int t2 = Blue;
+
+  MyClass a;
+  int t3 = 0;
+  a.func1<AA>(&t3);
+  a.func2<int, ff>(t3);
 }
Index: test/clang-tidy/Inputs/unused-using-decls.h
===================================================================
--- /dev/null
+++ test/clang-tidy/Inputs/unused-using-decls.h
@@ -0,0 +1,11 @@
+class MyClass {
+public:
+  template <template <typename> class S, typename T>
+  S<T> *func1(T *a) {
+    return new S<T>();
+  }
+  template <typename T, T (*S)()>
+  void func2(T a) {
+    S();
+  }
+};
Index: clang-tidy/misc/UnusedUsingDeclsCheck.cpp
===================================================================
--- clang-tidy/misc/UnusedUsingDeclsCheck.cpp
+++ clang-tidy/misc/UnusedUsingDeclsCheck.cpp
@@ -37,6 +37,9 @@
   Finder->addMatcher(declRefExpr().bind("used"), this);
   Finder->addMatcher(callExpr(callee(unresolvedLookupExpr().bind("used"))),
                      this);
+  Finder->addMatcher(
+      callExpr(hasDeclaration(functionDecl(isInstantiated()).bind("used"))),
+      this);
 }
 
 void UnusedUsingDeclsCheck::check(const MatchFinder::MatchResult &Result) {
@@ -71,16 +74,48 @@
       Contexts.push_back(Context);
     return;
   }
-
   // Mark using declarations as used by setting FoundDecls' value to zero. As
   // the AST is walked in order, usages are only marked after a the
   // corresponding using declaration has been found.
   // FIXME: This currently doesn't look at whether the type reference is
   // actually found with the help of the using declaration.
   if (const auto *Used = Result.Nodes.getNodeAs<NamedDecl>("used")) {
-    if (const auto *Specialization =
-            dyn_cast<ClassTemplateSpecializationDecl>(Used))
+    if (const auto *FD = dyn_cast<FunctionDecl>(Used)) {
+      // There is no straightforward way to match template arguments in a
+      // function call/class member call expression, so we iterate all template
+      // specializations of a function template to mark all template arguments
+      // as used.
+      //
+      // Find template argument that is provided for a template template
+      // parameter, e.g:
+      //
+      //   template<typename T> class A { T t; };
+      //   B.func<A>();
+      //
+      // Find template class A in B::func template argument.
+      if (const auto* TemplateArgs = FD->getTemplateSpecializationArgs()) {
+        for (size_t i = 0; i < TemplateArgs->size(); ++i) {
+          const auto& TemplateArg = TemplateArgs->get(i);
+          switch (TemplateArg.getKind()) {
+            case TemplateArgument::Template:
+              // Remove class template declaration.
+              removeFromFoundDecls(
+                  TemplateArg.getAsTemplate().getAsTemplateDecl());
+              break;
+            case TemplateArgument::Declaration:
+              // Remove function template declaration.
+              if (auto *FDT = dyn_cast<FunctionDecl>(TemplateArg.getAsDecl()))
+                removeFromFoundDecls(FDT->getPrimaryTemplate());
+              break;
+            default:
+              break;
+          }
+        }
+      }
+    } else if (const auto *Specialization =
+            dyn_cast<ClassTemplateSpecializationDecl>(Used)) {
       Used = Specialization->getSpecializedTemplate();
+    }
     removeFromFoundDecls(Used);
     return;
   }
@@ -109,6 +144,8 @@
 }
 
 void UnusedUsingDeclsCheck::removeFromFoundDecls(const Decl *D) {
+  if (!D)
+    return;
   // FIXME: Currently, we don't handle the using-decls being used in different
   // scopes (such as different namespaces, different functions). Instead of
   // giving an incorrect message, we mark all of them as used.
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